tag:theconversation.com,2011:/au/topics/evolution-115/articlesEvolution – The Conversation2024-03-27T12:37:29Ztag:theconversation.com,2011:article/2232682024-03-27T12:37:29Z2024-03-27T12:37:29ZHorses lived in the Americas for millions of years – new research helps paleontologists understand the fossils we’ve found and those that are missing from the record<figure><img src="https://images.theconversation.com/files/574775/original/file-20240211-26-t88v8r.jpg?ixlib=rb-1.1.0&rect=63%2C121%2C4179%2C2650&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">People have collected fossil horses throughout North America for centuries.</span> <span class="attribution"><span class="source">Florida Museum/Mary Warrick</span></span></figcaption></figure><p>Many people assume that horses first came to the Americas when Spanish explorers brought them here about 500 years ago. In fact, recent research has <a href="https://theconversation.com/archaeology-and-genomics-together-with-indigenous-knowledge-revise-the-human-horse-story-in-the-american-west-202222">confirmed a European origin</a> for horses associated with humans in the American Southwest and Great Plains.</p>
<p>But those weren’t the first horses in North America. The family Equidae, which includes domesticated varieties of horses and donkeys along with zebras and their kin, is actually native to the Americas. The <a href="https://doi.org/10.1126/science.1105458">fossil record reveals</a> horse origins here more than 50 million years ago, as well as their extinction throughout the Americas during the last Ice Age about 10,000 years ago.</p>
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<a href="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="family tree showing horse evolution diversifying over time" src="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=741&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=741&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=741&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=932&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=932&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=932&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Phylogeny, geographic distribution, diet and body sizes of the family Equidae over the past 55 million years.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1126/science.1105458">From 'Fossil horses–evidence for evolution.' Science. MacFadden, 2005. Reprinted with permission from AAAS.</a></span>
</figcaption>
</figure>
<p>We are <a href="https://scholar.google.com/citations?user=xhm6ez4AAAAJ&hl=en&oi=ao">paleontologists</a> <a href="https://scholar.google.com/citations?user=oZ8oBigAAAAJ&hl=en&oi=ao">who focus our research</a> on various types of fossils, including ancient horses. <a href="https://doi.org/10.1017/pab.2023.35">Our most recent work</a> used computer statistics to analyze gaps in the fossil record to infer more about which horse species really did and didn’t live in one ancient habitat in Florida.</p>
<h2>Horses evolved as ecosystems changed</h2>
<p>People have collected fossil horses throughout North America for centuries. Because horse fossils are abundant and widespread across the continent, scientists often point to the <a href="https://www.cambridge.org/us/universitypress/subjects/earth-and-environmental-science/palaeontology-and-life-history/fossil-horses-systematics-paleobiology-and-evolution-family-equidae?format=PB">long span of the horse family</a> as evidence of long-term evolutionary change.</p>
<p>Paleontologists like us, who study extinct mammals, almost never find complete skeletons. Instead, we focus on durable fossil teeth, which help us understand ancient diets, and fossil limbs, which help clarify how these animals moved.</p>
<p>Horses are eating machines. In the wild today, they primarily feed on grasses that don’t provide much nutrition, and thus they need to consume large quantities to survive. The large teeth of modern horses and their ancestors are adapted primarily for grazing on gritty grasses. They replaced smaller teeth of more primitive horses adapted to <a href="https://doi.org/10.1016/S0031-0182(01)00359-5">browsing on soft leafy vegetation</a>.</p>
<p>We know what horses ate millions of years ago by studying distinctive microscopic scratches, pits and other wear patterns on their teeth that were created <a href="https://doi.org/10.1016/j.palaeo.2015.11.004">as the ancient horses chewed plant foods</a>. And analyses of carbon preserved in fossil teeth show that <a href="https://doi.org/10.1016/0031-0182(94)90099-X">coexisting horse species ate different plants</a>; some browsed on leaves from bushes and trees, some grazed on grasses, and yet others were mixed feeders.</p>
<p>The change in tooth shape tracks the change in dominant vegetation types in North America, from tropical forests that then gave way to the <a href="https://doi.org/10.1146/annurev-earth-040809-152402">great expansion of open prairie grasslands</a>. As the climate and flora changed over millions of years, horses shifted from being largely forest-dwelling browsers to largely open-country grazers. Their teeth and feeding patterns adapted to the environment.</p>
<p>Another adaptation is visible on horses’ feet. Modern horses have one hoofed toe on each foot. Many extinct fossil horses – the ancient ancestors of today’s horses – had three toes per foot. The single toe on each elongated foot is good for rapid and sustained running to evade predators and for long-distance seasonal migrations. The more ancient three-toed feet provided <a href="https://doi.org/10.1038/308179a0">stability on unstable or wet ground</a>. The adaptation from three toes to one was likely in response to changing habitats.</p>
<p>But even as the environment changed, one distinct species didn’t completely replace another overnight. The fossil record in North America documents periods millions of years ago when multiple horse species coexisted on the ancient landscapes. Species were of different sizes and had teeth equipped for munching different plants, so they weren’t competing directly for the same foods. Different habitats within these ancient ecosystems likely had some species more adapted to forests and others more adapted to grasslands.</p>
<h2>Understanding Florida’s fossil record</h2>
<p>Paleontologists have been collecting horse fossils in Florida for over 125 years. The Florida Museum of Natural History at the University of Florida, where we work, has more than 70,000 fossil horse specimens from more than a thousand locations across the state.</p>
<p>One of our more <a href="https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/sites/montbrook/">prolific fossil sites, Montbrook</a>, provides a glimpse of a 5.8 million-year-old ancient stream bed. It preserved more than 30 extinct mammals, including rhinos, elephants and carnivores, as well as hundreds of bones and teeth of fossil horses.</p>
<p>Although six horse species are known elsewhere in Florida, we have only found four so far at Montbrook. This smaller number of horse species perplexed us, <a href="https://doi.org/10.1017/pab.2023.35">so we decided to investigate</a>. Did the two “missing” horse species truly not live at Montbrook, or have scientists simply not discovered their fossil remains yet?</p>
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<a href="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Representative fossil horse teeth of Florida" src="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=784&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=784&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=784&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=985&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=985&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=985&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Each of the six fossil horse species (A-F) found in Florida have distinct teeth. Scale bar = 1 centimeter.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1017/pab.2023.35">Killingsworth & MacFadden, Paleobiology, 2024</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>We designed a theoretical model that compares Montbrook, with only four horse species, to other fossil sites in Florida that contain all six. Using a statistical technique that scientists call “<a href="https://www.lancaster.ac.uk/stor-i-student-sites/jack-trainer/bootstrapping-in-statistics/">bootstrapping</a>,” our computer essentially simulated continued fossil collecting over time. We generated 1,000 theoretical fossil collection events based on the fossil species counts from the sites where all six are present, to predict the probability of collecting the species that are currently missing at Montbrook.</p>
<p>Results from our simulation show that the two missing horse species at Montbrook were absent for different reasons. One of the horses is likely to be truly absent; the other may still be discovered with further excavation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="About a dozen people focused on digging in soil a few feet below the surface of surrounding landscape." src="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Excavations are ongoing at the Montbrook fossil site in Florida.</span>
<span class="attribution"><span class="source">Florida Museum/Jeff Gage</span></span>
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<h2>Probing ‘gaps’ in the fossil record</h2>
<p>Knowing a species is absent is just as important as knowing when one is present at a fossil site. Absences may be indicators of underlying ecological and biological drivers changing population dynamics. Coupled with other types of analyses, researchers can apply this kind of predictive modeling across many fossil species and ancient landscapes.</p>
<p>Ever since <a href="https://www.britannica.com/biography/Charles-Darwin/Evolution-by-natural-selection-the-London-years-1836-42">Charles Darwin proposed his theory of evolution</a>, scientists have known that the fossil record is incomplete, resulting in gaps in our knowledge of the ancient past and evolutionary change. Paleontologists are challenged to explain these gaps, including which species were or were not present at particular fossil sites.</p>
<p>Gaps can result from certain materials, such as teeth and shells, which are often more durable than porous bone, fossilizing better than others. Likewise, different chemical conditions during fossilization, and even the amount of time spent collecting fossils at a particular site, <a href="https://doi.org/10.1016/j.earscirev.2023.104537">can contribute to the lack of knowledge</a>.</p>
<p>Fortunately, fossil horse teeth preserve quite well and are commonly found. As new discoveries are made, such as those from our ongoing excavations in Florida, they’ll help clarify and narrow gaps in the fossil record.</p><img src="https://counter.theconversation.com/content/223268/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bruce J. MacFadden receives funding from the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Stephanie Killingsworth does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Horse fossils are abundant and widespread across North America. Scientists often use their long history to illustrate how species evolve in response to a changing environment.Stephanie Killingsworth, Ph.D. Student in Geological Sciences, University of FloridaBruce J. MacFadden, Distinguished Professor and Director of Thompson Earth Systems Institute (TESI), University of FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1950562024-03-26T12:50:05Z2024-03-26T12:50:05ZWhy did modern humans replace the Neanderthals? The key might lie in our social structures<figure><img src="https://images.theconversation.com/files/502800/original/file-20230101-16-hk5jco.jpg?ixlib=rb-1.1.0&rect=12%2C16%2C2705%2C1674&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rock art showing a hunter-gatherer ritual dance; Kondoa, Tanzania</span> <span class="attribution"><span class="source">Nick Longrich</span></span></figcaption></figure><p>Why did humans take over the world while our closest relatives, the <a href="https://www.nhm.ac.uk/discover/who-were-the-neanderthals.html#:%7E:text=The%20best%2Dknown%20Neanderthals%20lived,is%20around%20130%2C000%20years%20old.">Neanderthals</a>, became extinct? It’s possible we were just smarter, but there’s surprisingly little evidence that’s true.</p>
<p>Neanderthals had <a href="https://www.nature.com/articles/s41467-021-24290-7">big brains</a>, language and <a href="https://www.science.org/doi/full/10.1126/sciadv.aba3831">sophisticated tools</a>. They made <a href="https://www.science.org/doi/10.1126/science.aap7778">art</a> and <a href="https://www.pnas.org/doi/10.1073/pnas.0914088107">jewellery</a>. They were smart, suggesting a curious possibility. Maybe the crucial differences weren’t at the individual level, but in our societies.</p>
<p>Two hundred and fifty thousand years ago, Europe and western Asia were <a href="https://theconversation.com/war-in-the-time-of-neanderthals-how-our-species-battled-for-supremacy-for-over-100-000-years-148205">Neanderthal lands</a>. <em>Homo sapiens</em> inhabited <a href="https://www.science.org/doi/full/10.1126/science.aao6266">southern Africa</a>. Estimates vary but perhaps <a href="https://www.science.org/doi/10.1126/science.1199113">100,000 years ago</a>, modern humans migrated out of Africa. </p>
<p><a href="https://www.pnas.org/doi/full/10.1073/pnas.2022466118">Forty thousand</a> years ago Neanderthals disappeared from Asia and Europe, replaced by humans. Their slow, inevitable <a href="https://www.pnas.org/doi/10.1073/pnas.0903446106">replacement</a> suggests humans had some advantage, but not what it was.</p>
<p>Anthropologists once saw Neanderthals as <a href="https://doi.org/10.1002/evan.21918">dull-witted brutes</a>. But recent archaeological finds show they rivalled us in intelligence. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502739/original/file-20221230-14-cx4yog.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Neanderthal hand axes, Aisne, France.</span>
<span class="attribution"><span class="source">Metropolitan Museum of art</span></span>
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<p>Neanderthals <a href="https://theconversation.com/how-a-handful-of-prehistoric-geniuses-launched-humanitys-technological-revolution-171511">mastered fire before we did</a>. They were deadly hunters, taking big game like <a href="https://doi.org/10.1016/j.quaint.2011.11.019">mammoths</a> and <a href="https://doi.org/10.1002/1099-1212(200009/10)10:5%3C379::AID-OA558%3E3.0.CO;2-4">woolly rhinos</a>, and small animals like <a href="https://link.springer.com/chapter/10.1007/978-1-4419-8219-3_10">rabbits and birds</a>. </p>
<p>They gathered <a href="https://doi.org/10.1016/j.jhevol.2018.02.009">plants</a>, <a href="https://www.pnas.org/doi/abs/10.1073/pnas.1016868108">seeds</a> and <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024026">shellfish</a>. Hunting and foraging all those species demanded deep understanding of nature. </p>
<p>Neanderthals also had a sense of beauty, making beads and <a href="https://www.theguardian.com/science/2021/aug/02/tinted-cave-stalagmites-are-neanderthal-art-say-archaeologists">cave paintings</a>. They were spiritual people, <a href="https://doi.org/10.15184/aqy.2019.207">burying their dead with flowers</a>. </p>
<p><a href="https://www.newscientist.com/article/2090183-neanderthals-built-mystery-underground-circles-175000-years-ago/">Stone circles</a> found inside caves may be Neanderthal shrines. Like modern hunter-gatherers, Neanderthal lives were probably steeped in superstition and magic; their skies full of gods, the caves inhabited by ancestor-spirits.</p>
<p>Then there’s the fact <em>Homo sapiens</em> and Neanderthals <a href="https://doi.org/10.1371/journal.pgen.1006340">had children together</a>. We weren’t that different. But we met Neanderthals many times, over many millennia, always with the same result. They disappeared. We remained.</p>
<h2>The hunter-gatherer society</h2>
<p>It may be that the key differences were less at the individual level than at the societal level. It’s impossible to understand humans in isolation, any more than you can understand a honeybee without considering its colony. We prize our individuality, but our survival is tied to larger social groups, like a bee’s fate depends on the colony’s survival. </p>
<figure class="align-center ">
<img alt="Cave dwellers gathered around a campfire" src="https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/501921/original/file-20221219-24-ujgcq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Neanderthals lived in smaller groups.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/cave-dwellers-gathered-around-campfire-208334998">Esteban De Armas/Shutterstock</a></span>
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<p>Modern hunter-gatherers provide our best guess at how early humans and Neanderthals lived. People like the Namibia’s <a href="https://www.amazon.com/Harmless-People-Elizabeth-Marshall-Thomas/dp/067972446X/ref=sr_1_1?crid=UARD13U3IN5L&keywords=harmless+people&qid=1671374437&s=books&sprefix=harmless+people%2Cstripbooks%2C77&sr=1-1">Khoisan</a> and Tanzania’s <a href="https://www.amazon.com/Hadza-Hunter-Gatherers-Tanzania-Origins-Behavior/dp/0520253426">Hadzabe</a> gather families into <a href="https://www.cambridge.org/core/journals/africa/article/abs/kung-bushman-bands/A2D674BE115E1A10399BD4CE7EFA1EC9">wandering bands of ten to 60 people</a>. The bands combine into a loosely organised tribe of a thousand people or more.</p>
<p>These tribes lack hierachical structures, but they’re linked by shared language and religion, marriages, kinships and friendships. Neanderthal societies may have been similar but with one crucial difference: smaller social groups. </p>
<h2>Tight-knit tribes</h2>
<p>What points to this is evidence that Neanderthals had <a href="https://phys.org/news/2020-06-genetic-diversity-neanderthals-principal-extinction.html">lower genetic diversity</a>.</p>
<p>In small populations, genes are easily lost. If one person in ten carries a gene for curly hair, then in a ten-person band, one death could remove the gene from the population. In a band of fifty, five people would carry the gene – multiple backup copies. So over time, small groups tend to lose genetic variation, ending up with fewer genes.</p>
<p>In 2022, DNA was recovered from <a href="https://www.nature.com/articles/s41586-022-05283-y">bones and teeth</a> of 11 Neanderthals found in a cave in the Altai Mountains of Siberia. Several individuals were related, including a father and a daughter – they were from a single band. And they showed low genetic diversity.</p>
<p>Because we inherit two sets of chromosomes – one from our mother, one from our father – we carry two copies of each gene. Often, we have two different versions of a gene. You might get a gene for blue eyes from your mother, and one for brown eyes from your father. </p>
<p>But the Altai Neanderthals often had one version of each gene. As the study reports, that low diversity suggests they lived in small bands – probably averaging just 20 people.</p>
<p>It’s possible Neanderthal anatomy favoured small groups. Being robust and muscular, Neanderthals were heavier than us. So each Neanderthal needed more food, meaning the <a href="https://www.nature.com/articles/s41467-021-24290-7">land could support</a> fewer Neanderthals than <em>Homo sapiens</em>. </p>
<p>And Neanderthals may have mainly <a href="https://www.pnas.org/doi/10.1073/pnas.2109315119">eaten meat</a>. Meat-eaters would get fewer calories from the land than people who ate meat and plants, again leading to smaller populations.</p>
<h2>Group size matters</h2>
<p>If humans lived in bigger groups than Neanderthals it could have given us advantages.</p>
<p>Neanderthals, strong and skilled with <a href="https://www.theatlantic.com/science/archive/2019/01/neanderthal-spears-threw-pretty-well/581218/">spears</a> were likely good fighters. Lightly built humans probably countered by <a href="https://www.nature.com/articles/s41559-019-0990-3#:%7E:text=The%20multiple%20findings%2C%20such%20as,is%20more%20than%2020%2C000%20years">using bows</a> to attack at range. </p>
<p>But even if Neanderthals and humans were equally dangerous in battle, if humans also had a numeric advantage they could bring more fighters and absorb more losses.</p>
<p>Big societies have other, subtler advantages. Larger bands have more brains. More brains to solve problems, remember lore about animals and plants, and techniques for crafting tools and sewing clothing. Just as big groups have higher genetic diversity, they’ll have higher diversity of ideas.</p>
<p>And more people means more connections. Network connections increase exponentially with network size, following <a href="https://en.wikipedia.org/wiki/Metcalfe%27s_law">Metcalfe’s Law</a>. A 20-person band has 190 possible connections between members, while 60 people have 1770 possible connections. </p>
<p>Information flows through these connections: news about people and movements of animals; toolmaking techniques; and words, songs and myths. Plus the group’s behaviour becomes increasingly complex.</p>
<p>Consider ants. Individually, ants aren’t smart. But interactions between millions of ants lets colonies make elaborate nests, forage for food and kill animals many times an ant’s size. Likewise, human groups do things no one person can – design buildings and cars, write elaborate computer programmes, fight wars, run companies and countries. </p>
<p>Humans aren’t unique in having big brains (whales and elephants have these) or in having huge social groups (zebras and wildebeest form huge herds). But we’re unique in combining them. </p>
<p>To <a href="https://allpoetry.com/No-man-is-an-island">paraphrase poet John Dunne</a>, no man – and no Neanderthal – is an island. We’re all part of something larger. And throughout history, humans formed larger and larger social groups: bands, tribes, cities, nation states, international alliances. </p>
<p>It may be then that an ability to build large social structures gave <em>Homo sapiens</em> the edge, against nature, and other hominin species.</p><img src="https://counter.theconversation.com/content/195056/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas R. Longrich does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Neanderthals and humans may have been equally smart and skilled, but some evidence points to humans living in larger groups.Nicholas R. Longrich, Senior Lecturer in Paleontology and Evolutionary Biology, Life Sciences at the University of Bath, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2236462024-03-14T03:55:30Z2024-03-14T03:55:30ZWhy is the male body the scientific default when the female body drives the reproductive success of our species?<figure><img src="https://images.theconversation.com/files/581526/original/file-20240313-20-9ueone.jpg?ixlib=rb-1.1.0&rect=6%2C0%2C2038%2C1536&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Eve – Lucas Cranach the Elder (c.1510)</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cranach_Adam_and_Eve_(detail)_3.jpg">Public domain, via Wikimedia Commons</a></span></figcaption></figure><p>American essayist Cat Bohannon loves a bit of pop culture to contextualise her ideas. <a href="https://www.penguin.com.au/books/eve-9781529151244">Eve: How the Female Body Drove 200 Million Years of Human Evolution</a> – her ambitious, funny, intelligent history of female evolution – is threaded with it. </p>
<p>The book opens with a futuristic scene from <a href="https://www.imdb.com/title/tt1446714/">Prometheus</a>, the 2012 prequel to <a href="https://www.imdb.com/title/tt0078748/">Alien</a>. Archaeologist Elizabeth Shaw is in an AI surgery pod, seeking a life-saving caesarean (she has been impregnated with an alien squid) when an affectless voice gives her an error message: “This medpod is calibrated for male patients only.” </p>
<p>Crash-test dummies, heart-attack symptoms, anti-depressant dosages, air-conditioning systems in large office buildings: we are all pretty aware by now that these are “calibrated for male bodies only”. Alien Prometheus is set in 2093; one can only hope the scientific technology of the late 21st-century turns out to have, at least, a “female-registering” option.</p>
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<p><em>Eve: How the Female Body Drove 200 Million Years of Human Evolution – Cat Bohannon (Hutchinson Heinemann)</em> </p>
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<p>While women’s hormonal cycles have made us messy in the arena of “clean science” – not good controls, not good at being controlled for – Bohannon reminds us that an understanding of the female body cannot be retrofitted to an understanding of the male body. Women are not just men with extra fleshy bits and confounding hormones. </p>
<p>Bohannon also reminds us those “fleshy bits” have a function beyond providing a curvaceous silhouette. </p>
<p>Female adipose tissue, 600 million years old, stored around our butts and thighs, is necessary to the development of babies’ brains. It is so necessary that girls begin storing it in childhood and when women liposuction it out of their lower bodies it returns in unexpected places: the armpits, for example. Bohannon points out that the possible repercussions of liposuction on the brain health of future offspring has not yet been studied.</p>
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Read more:
<a href="https://theconversation.com/women-have-heart-attacks-too-but-their-symptoms-are-often-dismissed-as-something-else-76083">Women have heart attacks too, but their symptoms are often dismissed as something else</a>
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<h2>Reproductive success</h2>
<p>The salient question here is: why is the male body the scientific default when it is the female body that crucially drives the evolution and reproductive success of our species? Eve is both a rectification of this immense blind spot and, in Bohannon’s own words, “a user’s manual for the female mammal”. </p>
<p>Yet how to collapse 200 million years of evolutionary history into 500 pages (let alone 1500 words)? </p>
<p>Bohannon does this by organising her book into a series of “Eves” from whom we inherited our current biological functions, creating an often diverging, often interlocking chronology. There is the Eve of milk, “the real Madonna”; placental Eve, “an HR Giger fever-dream meat factory” (Bohannon has fun with language); Donna, Eve of the uterus; and Pergi, the tree-dwelling Eve of perception. </p>
<p>This structure allows Bohannon to move from microbiology to paleoanthropology, evolutionary biology to gynaecology, anatomy to social history. I learnt much about my own body in her sprawling, illuminating discussions, but also about animal reproductive biology in general — from monotremal cloacas (platypuses and echidnas have them) to squamation hemipenises (snakes and lizards) and “notoriously foldy” anti-rape duck vaginas designed to circumvent corkscrew penises. </p>
<p>It was some small relief to learn the fairly straightforward design of the human penis is testament to a “not-particularly rapey” human evolutionary history. </p>
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<a href="https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581824/original/file-20240314-18-pjj64q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">‘Notoriously foldy.’</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Detailed_white_duck.jpg">Image: Roger Heslop, via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Bohannon writes with tender care of her “Eves”. She manages to both penetrate and animate deep time for the reader, a textual equivalent perhaps of Walking with Dinosaurs. She describes the Jurassic insect-eater <a href="https://museum.wales/blog/1895/Meet-Morgie/">Morgie</a> (my favourite), one of the earliest known mammals, skittering over the feet of dinosaurs to get home to her burrow, where she sweats milk through mammary patches to feed her hidden brood. Morgie comes vividly alive in her small precarious existence: “funny, warm, heart-fluttering Eve”, Bohannon writes. </p>
<p>For a female with a uterus, who has twice given birth and twice breastfed, Bohannon’s book demystified many of the mysterious goings-on of my reproductive system. I had no idea, for instance, that lactation was such an intensive co-production between mother and baby. </p>
<p>I knew it enabled a baby’s gut to be colonised with good maternal bacteria, and I knew the basic mechanics of the let-down reflex. But I didn’t know that the composition of the milk itself is informed by a baby’s needs. These needs, codified in a baby’s saliva, are registered by the mother’s body, which then customises its milk accordingly, so it is full of the particular bacteria- or virus-fighting agents required.</p>
<p>This recriprocity is also apparent in the biological wonder that is the placenta. Built out of both endometrial and embryonic tissue, the placenta is “one of the only organs in the animal world made out of two separate organisms”. </p>
<p>Did you know this? I certainly didn’t. </p>
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<a href="https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581827/original/file-20240314-30-yukxv4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">‘Morgie’ – Morganucodon, one of the earliest known mammals.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Morganucodon.jpg">FunkMonk (Michael B.H.), via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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Read more:
<a href="https://theconversation.com/a-raunchy-new-big-history-tells-the-story-of-sex-but-raises-some-unanswered-questions-213538">A raunchy new 'Big History' tells the story of sex, but raises some unanswered questions</a>
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<h2>Life: a user’s manual</h2>
<p>In this sense, Eve really is a user’s manual. At the risk of sounding “miracle of life” about it, Bohannon’s book puts wonder into the commonplace by explaining not only how our reproductive systems work, but how they came to be.</p>
<p>Women’s bodies are not just about babies, of course. Bohannon charts new political territory, tracing her anatomical discoveries through to their social outcomes. Truisms of human and social evolution are turned on their heads and gynaecology gets its rightful place in the story. </p>
<p>Milk again: the population growth that enabled humans to become the ferocious planet-hogs we are today might be down to the humble wet-nurse of ancient civilisations. The prevalence of wet-nursing meant the natural contraceptive properties of breastfeeding were not in play for many women. This meant women had much shorter spaces between pregnancies and had more babies. Wet-nurses, those under-sung footnotes in history, might well have catalysed the growth of modern cities.</p>
<p>Bipedalism? It might just be that we stood up on two feet not so we could better carry spears, but so we had free arms to carry babies while hunting and still cart as much food home with us as possible.</p>
<p>Tool-making? The seminal moment here may not have been a Kubrick-style raising of a femur bone to crunch down on a challenger’s head, or beat an animal to death for dinner (fossil remains show we really didn’t eat a particularly intensive paleo diet). Instead, it might have been a woman, baby on back, chewing a sapling to a neat point to hunt “<a href="https://www.nationalgeographic.com/animals/mammals/facts/bushbabies">bush-babies</a>” asleep in tree hollows. </p>
<p>Bohannon makes a good argument that it was women, not men, who most needed tools to hunt. Our biologically stronger male counterparts often needed only the heft of their bodies to bring down an animal. Women were inventors, she says, because, being smaller, being weaker, they had more need.</p>
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<a href="https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581555/original/file-20240313-18-z1f8bf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Cave painting depicting a woman giving birth, Serra da Capivara national park, Brazil.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Serra_da_Capivara_-_Painting_8.JPG">Vitor 1234, via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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Read more:
<a href="https://theconversation.com/friday-essay-matrilineal-societies-exist-around-the-world-its-time-to-look-beyond-the-patriarchy-200825">Friday essay: matrilineal societies exist around the world – it's time to look beyond the patriarchy</a>
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<h2>Womb triumphalism</h2>
<p>Our most important invention, though – and this is the overarching thesis of Bohannan’s book – is gynaecology. “What got us here,” she writes, “is not tool triumphalism but womb triumphalism.” </p>
<p>Considering how hard it is for the human female body to get pregnant, stay pregnant, deliver a baby (without us or it dying), and then look after it through its protracted childhood, it is a miracle that humans populate – and over-populate — the planet in the way we have come to. Gynaecology, Bohannon writes, </p>
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<p>is absolutely essential for our species’ evolutionary fitness. Without it, it’s doubtful we would have made it this far […] The arrival of midwifery is one of those moments when we can truly say, “Here is when we become human” […] No other mammals on the planet have been observed regularly helping one another give birth.</p>
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<p>With gynaecology comes contraception, reproductive choice and birth-spacing. Knowledge about the properties of herbs and plants, about labour, about delivering a breech or posterior baby, or really <em>any</em> baby (they are all life and death situations) – all of these combine to enable the flourishing of humans, in spite of our large heads, narrow pelvises, complex gestation and birthing trajectories. </p>
<p>“Women had their hands on the actual machinery of evolution,” Bohannon writes. And while she notes that “[m]odern female coalitions are scattered, vulnerable, brittle”, her book celebrates the ancient collaboration between women and the spirit of cooperation over competition that got us here. </p>
<p>Bohannon repositions this as profound in its significance for the human race. A failure to fully apprehend the different workings of male and female bodies and not provide for these differences – or to provide comprehensively for one sex, and neglect the other – doesn’t just mean there will be no caesarean option in a future surgery-pod. </p>
<p>It means limiting human possibility and opportunity. It represents a failure to grasp the whole human story and its potential.</p>
<p>Bohannon ends her book with a practical feminist statement about the importance – and boon to society – of educating women, feeding them properly (not last), and putting financial means in their hands. </p>
<p>Smart humans of the future – who might want to flourish without destroying the means of their flourishing – will require women with adipose fat to feed the brains of their suckling babies, with reproductive choices to plan and space those babies, and with life choices which enable them to contribute their full potential to the world. </p>
<img src="https://counter.theconversation.com/content/223646/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Edwina Preston has received funding from Creative Victoria and the Australia Council for the Arts. She works for the Australian Education Union</span></em></p>The story of human evolution is inextricable from the story of gynaecology.Edwina Preston, PhD Candidate, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2255962024-03-13T15:03:15Z2024-03-13T15:03:15ZIt’s a myth that male animals are usually larger than females – new study<p>Males are bigger than females, right? Generally, this is true of humans – imagine the extremes of Dwayne “The Rock” Johnson and singer Kylie Minogue. It is also true of other familiar mammals including pets, such as cats and dogs, and livestock such as sheep and cows.</p>
<p>But <a href="https://www.nature.com/articles/s41467-024-45739-5">a new study</a> by US scientist Kaia Tombak and colleagues found that, in many mammal species, males are not larger than females. In fact, in a comparison of 429 species in the wild, 50% of species including rodents and some bats – which make up <a href="https://news.mongabay.com/2022/04/of-rats-and-bats-hundreds-of-mammal-species-still-unidentified-study-says/">a large proportion</a> of all mammal species – showed no difference in body size between the sexes. Male-biased size dimorphism (where males are larger than females) was found in only 28% of mammal species.</p>
<p>So, why do a lot of people have a misconception that males are normally larger than females? </p>
<p><a href="https://www.nature.com/scitable/students-page/160/">Anisogamy</a> is the term used to describe the difference in sex cells – small, numerous, sperm, compared to relatively large eggs. Males can produce sperm throughout most of their lifespan, whereas females are born with a finite number of eggs. Therefore, females (or rather, their eggs), are a scare resource for which males compete for access. Generally, in species where females are a limited resource that males need to fight over, males are larger than females.</p>
<p>In terms of evolution, most males have been shaped to be larger, bolder, heavier, more adorned and have more weaponry than females. This is due to males fighting to acquire females – a larger stag with bigger antlers would do much better in a fight, <a href="https://www.discoverwildlife.com/animal-%20facts/mammals/understand-the-british-deer-rut">known as a rut</a>, than a small stag with tiny antlers. So, bigger usually wins.</p>
<p>This includes species such as lions and baboons, where size is an advantage when competing physically for mates. Male northern elephant seals, who fight for access to harems of females, show the largest male-biased size dimorphism, being over 3.2 times heavier than females. These are the animals that tend to attract research</p>
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<h2>The strange world of fish</h2>
<p>But, what happens in species where males don’t fight for access to females? Generally, females are larger than males. This is because larger females usually produce more offspring. Indeed, Tombak’s study noted that larger female rabbits usually have multiple litters each mating season. Being a larger female is much more advantageous in terms of reproductive success. But more so when offspring do not need extended parental care and when gestation periods are short.</p>
<p>The most extreme sexual size dimorphism is found outside of mammals. Cichlid fish (<em>Lamprologus callipterus</em>) males are up to 60 times larger than females. The males protect empty snail shells for the females to breed in. <a href="https://link.springer.com/article/10.1007/s12038-010-0030-6">Larger females</a> can produce more offspring but they need larger shells and therefore a larger male to defend those shells.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/hmlXKgVaDl8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>In mammals, the largest female-biased size dimorphism is found in peninsular tube-nosed bats, where females are 1.4 times the size of males. However, more dimorphism in body size is seen in fish, reptiles and insects. For example, the female orb-weaving spider (<em>Nephila plumipes</em>) has a much larger body size than the male, reaching up to ten times his size. Size dimorphism also shows a correlation with cannibalism, where larger females are more likely to eat their male partner.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Large spider and small one in a web" src="https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581306/original/file-20240312-22-e1nldo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A female golden orb weaving spider and the smaller male.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-photograph-female-golden-orb-weaving-1692871246">Cassandra Madsen/Shutterstock</a></span>
</figcaption>
</figure>
<p>Anglerfish that typically live at the bottom of oceans, are an example of extreme sexual dimorphism in body size. While the females look like typical fish, the males are tiny, basic organisms. In order to survive, the male needs to fuse with a female, tapping into her nutrients to produce enough sperm to fertilise her. Female deep-sea anglerfish (<em>Ceratias
holboelli</em>) are <a href="https://www.livescience.com/49330-animal-sex-anglerfish.html">60 times longer</a> and half a million times heavier than males.</p>
<p>But, the most extreme sexual size dimorphism is found in rhizocephala, types of barnacle where the male looks like a larvae. Once a male finds a mate, he <a href="https://www.wired.com/2015/07/absurd-creature-of-the-week-rhizocephalan/">inserts himself into the females</a>, transforming into nothing more than a mass of cells.</p>
<h2>What about mammals?</h2>
<p>So, why isn’t sexual size dimorphism seen in more mammals? Mammals tend to have fewer offspring than other species such as fish or spiders. They only have a few offspring at a time, and often have long gestation periods or extended periods of parental care. In addition, the majority of mammals are monogamous, so there is less need for males to fight over females. That’s why species such as lemurs, golden moles, horses, zebra and tenrecs, usually have similar sized males and females.</p>
<p>It is thought that biases in the scientific literature may have led to the misconception that males are normally bigger as research historically focused on <a href="https://wwf.panda.org/discover/our_focus/wildlife_practice/flagship_keystone_indicator_definition/">species considered “charismatic”</a>, such as primates and carnivores, that attract funding. These are some of the few mammalian species where males compete for mates, and so gain an evolutionary advantage if they are larger. </p>
<p>There was also a bias of <a href="https://www.nationalgeographic.co.uk/science-and-technology/2019/10/once-most-famous-scientists-were-men-thats-changing">male scientists</a> conducting research. And, although a study in 1977 <a href="https://www.journals.uchicago.edu/doi/epdf/10.1086/283223">by a female scientist</a> found that species with little sexual size dimorphism were frequent in mammals, the research was drowned out by studies on charismatic species with a bias towards large males. Perhaps if there had been more female scientists at the time, we might have had a different preconception about body size in the animal kingdom.</p><img src="https://counter.theconversation.com/content/225596/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Louise Gentle works for Nottingham Trent University. </span></em></p>Does size matter? In the animal kingdom, yes.Louise Gentle, Principal Lecturer in Wildlife Conservation, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2243852024-02-28T16:00:10Z2024-02-28T16:00:10ZLosing their tails provided our ape ancestors with an evolutionary advantage – but we’re still paying the price<figure><img src="https://images.theconversation.com/files/578565/original/file-20240228-27-5jpovx.jpg?ixlib=rb-1.1.0&rect=41%2C5%2C3417%2C2504&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Unlike humans, many animals still have tails.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/monkey-zoo-game-asking-food-46190563">vblinov/Shutterstock</a></span></figcaption></figure><p>Put the word “evolution” into Google images and the results are largely variations on one theme: Ralph Zallinger’s illustration, <a href="https://theconversation.com/evolution-that-famous-march-of-progress-image-is-just-wrong-132536">March of Progress</a>. Running left to right, we see a chimp-like knuckle walker gradually becoming taller and standing erect. </p>
<p>Implicit in such images – and the title of the picture – are biases in common views of evolution: that we are some sort of peak, the perfected product of the process. We imagine we are indeed the fittest survivors, the very best we can be. But seen that way, there’s a paradox. If we are so amazing, how come so many of us suffer from developmental or genetic diseases? </p>
<p>A new study, <a href="https://www.nature.com/articles/s41586-024-07095-8">published in Nature</a>, provides an explanation for our error-prone early development by looking at the genetic changes that enabled our ancestors to lose their tails.</p>
<p>Current estimates suggest that about half of all fertilised eggs never even make it to be <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001671">recognised pregnancies</a> and that for every child born about <a href="https://www.biorxiv.org/content/10.1101/372193v1.full">two never made it to term</a>. In fish and amphibians, such <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001671">early death is unheard of</a>. Of those of us lucky enough to be born, <a href="https://www.nature.com/articles/s41431-019-0508-0">a little under 10%</a> will suffer one of the many thousand “rare” genetic diseases, such as haemophilia. The not so rare diseases, such as sickle cell disease and cystic fibrosis, affect yet more of us. </p>
<p>Surely this wouldn’t be the case in an evolutionary successful species? Where is the progress? </p>
<p>There are multiple possible solutions to this problem. One is that, compared to other species, we have an unusually high mutation rate. There’s a relatively high likelihood that in your DNA there will be a change that wasn’t inherited by either your mother or father. You were probably born with between ten and 100 such new changes to your DNA. For most other species that number is under one – often far under one. </p>
<h2>The genetics of tails</h2>
<p>There are other solutions too. One of the more obvious differences between us and many primate relatives is that we don’t have a tail. The loss of the tail happened <a href="https://onlinelibrary.wiley.com/doi/epdf/10.1002/jez.b.21029">around 25 million years ago</a> (for comparison our common ancestor with chimps was about 6 million years ago). We still have the coccyx as an evolutionary hangover from this tail-bearing ancestry. </p>
<p>Tail loss occurred in our ape ancestors at the same time as the evolution of a more erect back and, in turn, a tendency to use only two of the four limbs to support the body. While we can speculate on why these evolutionary changes may be coupled, that doesn’t address the problem of how (rather than why) tail-loss evolved: what were the underlying genetic changes?</p>
<p>The recent study looked at just that question. It identified an intriguing genetic mechanism. Many genes combine to enable the development of the tail in mammals. The team identified that primates without a tail had one additional “jumping gene” – sequences of DNA that can transfer to new areas of a genome – in a one such tail-determining gene, <em>TBXT</em>.</p>
<p>Much more of our DNA is the remains of such jumping genes than is sequence specifying proteins (the classical function of genes), so the gain of a jumping gene is nothing special. </p>
<h2>Evolutionary cost</h2>
<p>What was unusual was the effect that this new addition had. The team also identified that the same primates also had an older but similar jumping gene just a little bit of a distance away in the DNA also embedded within the TBXT gene. </p>
<p>The effect of these two in close proximity was to alter the processing of the resulting TBXT messenger RNA (molecules created from DNA that contain instructions for how to make proteins). The two jumping genes can stick to each other in the RNA, causing the block of RNA between them to be excluded from the RNA that gets coded into protein, resulting in a shorter protein.</p>
<p>To see the effect of this unusual exclusion, the team genetically mimicked this situation in mice by making a version of the mouse <em>Tbxt</em> gene that was also missing the excluded section. And indeed, the more of the form of the RNA with the section of the gene excluded, the more likely that the mouse would be born without a tail.</p>
<p>We have then a strong candidate for a mutational change that underpins the evolution of being tailless. </p>
<p>But the team noticed something else odd. If you make a mouse with only the form of the <em>Tbxt</em> gene with the section excluded, they can develop a condition that closely resembles the human condition spina bifida (when the spine and spinal cord fail to develop properly in the womb, causing a gap in the spine). Mutations in human <em>TBXT</em> had previously been <a href="https://academic.oup.com/hmg/article/5/5/669/2568755">implicated in this condition</a>. Other mice had other defects in the spine and spinal cord.</p>
<p>The team suggest that just as the coccyx is an evolutionary hangover of the evolution of being tailless that we all have, so too spina bifida may be a rare hangover resulting from the disruption to the gene that underpins our lack of a tail. </p>
<p>Being tailless, they suggest, was a large advantage, and so an increase in incidences of spina bifida was still worth it. This may be the case for many genetic and development diseases – they are an occasional byproduct of some mutation that on balance helped us. Recent work, for example, finds that the genetic variants that help us fight pneumonia also predispose us to <a href="https://www.sciencedirect.com/science/article/pii/S0002929723000526?via%3Dihub">Crohn’s disease</a> . </p>
<p>This goes to show how misleading the march of progress really can be. Evolution can only deal with the variation that is present at any time. And, as this latest study shows, many changes also come with costs. Not so much a march as a drunken stumbling.</p><img src="https://counter.theconversation.com/content/224385/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laurence D. Hurst receives funding from European Research Council to examine the relationships between evolution and medicine. He is also an author of a book on the same subject and is on the scientific advisory board of ExpressionEdits. </span></em></p>Many evolutionary changes also come with costs.Laurence D. Hurst, Professor of Evolutionary Genetics at The Milner Centre for Evolution, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2225992024-02-26T05:03:51Z2024-02-26T05:03:51ZSecrets in the canopy: scientists discover 8 striking new bee species in the Pacific<figure><img src="https://images.theconversation.com/files/577494/original/file-20240222-16-pcdtt5.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C2000&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">James Dorey Photography</span></span></figcaption></figure><p>After a decade searching for new species of bees in forests of the Pacific Islands, all we had to do was look up. </p>
<p>We soon found <a href="https://www.frontiersin.org/articles/10.3389/fevo.2024.1339446/full">eight new species</a> of masked bees in the forest canopy: six in Fiji, one in French Polynesia and another in Micronesia. Now we expect to find many more. </p>
<p>Forest-dwelling bees evolved for thousands of years alongside native plants, and play unique and important roles in nature. Studying these species can help us better understand bee evolution, diversity and conservation.</p>
<p>Almost <a href="https://www.nature.com/articles/s41597-023-02626-w">21,000 bee species are known to science</a>. Many more remain undiscovered. But it’s a race against time, as the twin challenges of habitat loss and climate change threaten bee survival. We need to identify and protect bee species before they disappear forever.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A group of research students using stepping stones to cross a creek in the rainforest while carrying sampling nets on short poles" src="https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577774/original/file-20240225-24-qvx9ve.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Searching for bees in the rainforest on Vanua Levu, formerly known as Sandalwood Island, the second largest island of Fiji.</span>
<span class="attribution"><span class="source">James Dorey Photography</span></span>
</figcaption>
</figure>
<h2>Introducing the new masked bees</h2>
<p><a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12947">Pollinators abound in forests</a>. But scientific research has tended to focus on bees living closer to the ground.</p>
<p>We believe this sampling bias is replicated across much of the world. For example, another related Oceanic masked bee, <em>Pharohylaeus lactiferus</em> (a cloaked bee), was recently found in the canopy <a href="https://theconversation.com/phantom-of-the-forest-after-100-years-in-hiding-i-rediscovered-the-rare-cloaked-bee-in-australia-156026">after 100 years in hiding</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Closeup of one of the new masked bees showing the yellow markings on its face" src="https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577776/original/file-20240225-30-ni8m63.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This masked bee was collected from a canopy-flowering mistletoe near Mount Nadarivatu on Viti Levu, Fiji.</span>
<span class="attribution"><span class="source">James Dorey Photography</span></span>
</figcaption>
</figure>
<p>Our <a href="https://doi.org/10.11646/zootaxa.4674.1.1">first decade of bee sampling</a> in Fiji turned up only one bee from the genus <em>Hylaeus</em>. This bee probably belonged in the canopy so we were very lucky to catch it near the ground. Targeted attempts over the next few years, using our standard short insect nets, failed to find any more. </p>
<p>But this changed when we turned our attention to searching the forest canopy. </p>
<p>Sampling in the canopy is physically challenging. Strength and skill are required to sweep a long, heavy net and pole through the treetops. It’s quite a workout. We limit our efforts to the edges of forests, where branches won’t tangle the whole contraption.</p>
<p>By lifting our gaze in this way, we discovered eight new bee species, all in the genus <em>Hylaeus</em>. They are mostly black with stunning yellow or white highlights, especially on their faces – hence the name, masked bees. </p>
<p>They appear to rely exclusively on the forest canopy. This behaviour is striking and has rarely been identified in bees before (perhaps because few scientists have been looking for bees up there). </p>
<p>Because the new species live in forests and native tree tops, they’re likely to be vulnerable to land clearing, cyclones and climate change. </p>
<p>More work is needed to uncover the secrets hidden in these dense tropical treetops. It may require engineering solutions such as canopy cranes and drones, as well as skilful tree-climbing using ropes, pulleys and harnesses.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/move-over-honeybees-aussie-native-bees-steal-the-show-with-unique-social-and-foraging-behaviours-200536">Move over, honeybees: Aussie native bees steal the show with unique social and foraging behaviours</a>
</strong>
</em>
</p>
<hr>
<h2>Michener’s missing links</h2>
<p>The journey of bees across the Pacific region is a tale of great dispersals and isolation.</p>
<p>Almost 60 years ago, world-renowned bee expert <a href="https://catalogue.nla.gov.au/catalog/787658">Charles Michener described</a> what was probably the most isolated masked bee around, <em>Hylaeus tuamotuensis</em>. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Searching for bees on Fiji’s highest peak, Mount Tomanivi, here two researchers are picking a path through dense undergrowth while carrying nets on short poles" src="https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577779/original/file-20240225-16-iay0de.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fiji’s highest peak, Mount Tomanivi, is home to unique bee species.</span>
<span class="attribution"><span class="source">James Dorey Photography</span></span>
</figcaption>
</figure>
<p>The specimen was found in French Polynesia. At the time, Michener said that was “entirely unexpected”, because the nearest relatives were, as the bee flies, 4,000km north in Hawaii, 5,000km southwest in New Zealand, and 6,000km west in Australia. </p>
<p>So how did it get there and where did it come from?</p>
<p>Our research helps to answer these questions. We found eight new <em>Hylaeus</em> species including one from French Polynesia. Using genetic analysis and other methods, we found strong links between these species and <em>H. tuamotuensis</em>. </p>
<p>So Michener’s bee was probably an ancient immigrant from Fiji, 3,000km away. A journey of that magnitude is no mean feat for bees smaller than a grain of rice.</p>
<p>Of course, there are <a href="https://geoscienceletters.springeropen.com/articles/10.1186/s40562-016-0041-8">more than 1,700 islands in the Pacific</a>, which can serve as stepping stones for bees on their long journeys. </p>
<p>We don’t yet know how many new <em>Hylaeus</em> species might exist in the South Pacific, or the routes they took to get to their island homes. But we suspect there are many more to be found.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/phantom-of-the-forest-after-100-years-in-hiding-i-rediscovered-the-rare-cloaked-bee-in-australia-156026">Phantom of the forest: after 100 years in hiding, I rediscovered the rare cloaked bee in Australia</a>
</strong>
</em>
</p>
<hr>
<h2>Our Pacific emissaries</h2>
<p>The early origins of Fijian bees – both <a href="https://doi.org/10.1080/03721426.2020.1740957">ground-dwelling <em>Homalictus</em></a> and <a href="https://doi.org/10.1016/j.ympev.2012.10.018">forest-loving <em>Hylaeus</em></a> – can be traced to the ancient past when Australia and New Guinea were part of one land mass, known as Sahul. The ancestors of both groups then undertook epic oceanic journeys to travel from Sahul to the furthest reaches of the Pacific, where they diversified. But the <em>Hylaeus</em> travelled furthest, by thousands of kilometres.</p>
<p>These little emissaries have similarly brought together researchers across the region. We resolved difficulties sampling and gathering knowledge by working with people across the Pacific, including Fiji, French Polynesia, and Hawaii. It shows what can be accomplished with international collaboration. </p>
<p>Together we are making great strides towards understanding our shared bee biodiversity. Such collaborations are our best chance of discovering and conserving species while we can.</p>
<p><em>We would like to thank Ben Parslow and Karl Magnacca for their contribution to this article. We would further like to thank our collaborators and their home institutions, the Hawiian Department of Land and Natural Resources, Muséum national d’Histoire naturelle, University of the South Pacific, the South Australian Museum and Adelaide University.</em></p><img src="https://counter.theconversation.com/content/222599/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James B. Dorey has received funding for this work from The Playford Trust as a PhD and Honours scholarship recipient, Flinders University through the AJ and IM Naylon PhD Scholarship, and the Australian Government through the New Colombo Plan . He is affiliated with both Flinders University and the University of Wollongong.</span></em></p><p class="fine-print"><em><span>Amy-Marie Gilpin is affiliated with the School of Science and Hawkesbury Institute for the Environment, Western Sydney University. Funding to publish this work was in part provided by Western Sydney University. Amy-Marie is also a member of the IUCN Wild Bee Specialist Group Oceania. </span></em></p><p class="fine-print"><em><span>Olivia Davies does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>By lifting their gaze to the treetops rather than poking around on the ground, researchers discovered eight new species of masked bees.James B. Dorey, Lecturer in Biological Sciences, University of WollongongAmy-Marie Gilpin, Lecturer in Invertebrate Ecology, Western Sydney UniversityOlivia Davies, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2202832024-02-22T13:42:50Z2024-02-22T13:42:50ZBacteria can develop resistance to drugs they haven’t encountered before − scientists figured this out decades ago in a classic experiment<figure><img src="https://images.theconversation.com/files/575458/original/file-20240213-24-7w1h4o.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2048%2C1480&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bacteria are evolutionarily primed to outpace drug developers.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/nihgov/28881401596/in/photolist-U4kMcq-c57xDd-L19JtW-c9uWe5-dYBMYW-a5tw3L-2joPCWz-2jfgs7P-9VPmA4-fuUV2g-fvxv6D-ot5Jyg-fvacBd-vughy5-7NapMs-7N7qSL-yrSV6f-7N5dpc-Mj3KFR-7Na6i5-ysPK3x-7Na5Wq-ftHb6n-ftXtfs-ftH7Vt-7Na6P5-tCCMPo-xvLN1S-ybiGai-yqtCoy-982F9z-ftHaAP-7N3qKg-7N674D-fvxufn-fvMDps-x2Btgv-ftHapZ-7Na6sy-7NaoHs-fuUUt8-fuUQjz-fvxptp-fuUXN2-7U2mNs-7N66b2-fvaabC-xtGans">National Institute of Allergy and Infectious Diseases, National Institutes of Health/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Do bacteria mutate randomly, or do they mutate for a purpose? Researchers have been <a href="https://doi.org/10.1017/S0022172400017125">puzzling over this conundrum for over a century</a>.</p>
<p>In 1943, microbiologist Salvador Luria and physicist turned biologist Max Delbrück <a href="https://doi.org/10.1080/09332480.2010.10739800">invented an experiment</a> to argue that bacteria mutated aimlessly. Using their test, other scientists showed that bacteria could acquire resistance to antibiotics they hadn’t encountered before.</p>
<p>The <a href="https://doi.org/10.1080/09332480.2010.10739800">Luria–Delbrück experiment</a> has had a significant effect on science. The findings helped Luria and Delbruck win the <a href="https://www.nobelprize.org/prizes/medicine/1969/summary/">Nobel Prize in physiology or medicine in 1969</a>, and students today learn this experiment in <a href="https://doi.org/10.1128/jmbe.00161-23">biology classrooms</a>. I have been studying this experiment in my work as a biostatistician for <a href="https://doi.org/10.1016/S0025-5564(99)00045-0">over 20 years</a>.</p>
<hr>
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<p>Decades later, this experiment offers lessons still relevant today, because it implies that bacteria can develop resistance to antibiotics that haven’t been developed yet.</p>
<h2>Slot machines and a eureka moment</h2>
<p>Imagine a test tube containing bacteria living in nutrient broth. The broth is cloudy due to the high concentration of bacteria within it. Adding a virus that infects bacteria, <a href="https://theconversation.com/viruses-are-both-the-villains-and-heroes-of-life-as-we-know-it-169131">also known as a phage</a>, into the tube kills most of the bacteria and makes the broth clear.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of bacteriophage structure." src="https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1014&fit=crop&dpr=1 600w, https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1014&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1014&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1274&fit=crop&dpr=1 754w, https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1274&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/426550/original/file-20211014-27-n6jugx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1274&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bacteriophages are viruses that specifically infect bacteria.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/flat-illustration-of-bacteriophage-royalty-free-illustration/1285360925">Kristina Dukart/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>However, keeping the test tube under conditions favorable for bacterial growth will turn the broth cloudy again over time. This indicates that the bacteria developed resistance against the phages and were able to proliferate.</p>
<p>What role did the phages play in this change?</p>
<p>Some scientists thought the phages incited the bacteria to mutate for survival. Others suggested that bacteria routinely mutate randomly, and the development of phage-resistant variants was simply <a href="https://doi.org/10.1128/jb.28.6.619-639.1934">a lucky outcome</a>. Luria and Delbrück had been working together for months to solve this conundrum, but none of their experiments had been successful. </p>
<p>On the night of Jan. 16, 1943, Luria got a hint about how to crack the mystery while watching a colleague hit the jackpot at a slot machine. The next morning, he hurried to his lab.</p>
<p>Luria’s experiment consisted of a few tubes and dishes. Each tube contained nutrient broth that would help the bacteria <em>E. coli</em> multiply, while each dish contained material coated with phages. A few bacteria were placed into each tube and given two opportunities to generate phage-resistant variants. They could either mutate in the tubes in the absence of phages, or they could mutate in the dishes in the presence of phages.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of six test tubes and and six petri dishes, a few of the dishes containing red dots" src="https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=277&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=277&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=277&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=348&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=348&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575442/original/file-20240213-28-9m0ay7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=348&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This diagram of the Luria-Delbrück experiment depicts colonies of phage-resistant variants of <em>E. coli</em> (red) developing in petri dishes.</span>
<span class="attribution"><span class="source">Qi Zheng</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The next day, Luria transferred the bacteria in each tube into a dish filled with phages. The day after that, he counted the number of resistant bacterial colonies in each dish. </p>
<p>If bacteria develop resistance against phages by interacting with them, none of the bacteria in the tubes should have mutations. On the other hand, only a few of the bacteria – say, 1 out of 10 million bacteria – should spawn resistant variants when they are transferred into a dish containing phages. Each phage-resistant variant would grow into a colony, but the remaining bacteria would die from infection.</p>
<p>If bacteria develop resistance independently of interacting with phages, some of the bacteria in the tubes will have mutations. This is because each time a bacterium divides in a tube, it has a small probability of spawning a resistant variant. If the starting generation of bacteria is the first to mutate, at least half of the bacteria will be resistant in later generations. If a bacterium in the second generation is the first to mutate, at least an eighth of the bacteria will be resistant in later generations.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Four tree diagrams of green and red circles, with subsequent branches from red dots turning red" src="https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=340&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=340&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=340&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=427&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=427&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575444/original/file-20240213-30-vbeqfp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=427&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mutations that confer resistance against phages (red) early on will spawn a large number of phage-resistant variants, while mutations that occur later on will spawn only a few resistant variants.</span>
<span class="attribution"><span class="source">Qi Zheng</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Like small-prize cash-outs in slot machines, late-generation mutations occur more often but give fewer resistant variants. Like jackpots, early-generation mutations occur rarely but give large numbers of variants. Early-generation mutations are rare because early on there are only a small number of bacteria available to mutate.</p>
<p>For example, in a 20-generation experiment, a mutation occurring at the 10th generation of bacteria would give 1,024 phage-resistant variants. A mutation occurring at the 17th generation would give only four phage-resistant variants. </p>
<p>The number of resistant colonies in Luria’s experiments showed a similar pattern to that of slot machine cash-outs. Most dishes contained no or small numbers of mutant colonies, but several contained a large number of mutant colonies that Luria considered jackpots. This meant that the bacteria developed resistant variants before they interacted with the phages in the dishes.</p>
<h2>An experiment’s legacy</h2>
<p>Luria sent a note to Delbrück after his experiment was completed, asking him to check his work. The two scientists then worked together to write <a href="https://doi.org/10.1093/genetics/28.6.491">a classic paper</a> describing the experimental protocol and a theoretical framework to measure bacterial mutation rates.</p>
<p>Other scientists conducted similar experiments by replacing phages <a href="https://doi.org/10.1073/pnas.31.1.16">with penicillin</a> and with <a href="https://doi.org/10.1128/am.20.5.810-814.1970">tuberculosis drugs</a>. Similarly, they found that bacteria did not need to encounter an antibiotic to acquire resistance to it.</p>
<p>Bacteria have relied on random mutations to cope with harsh, constantly changing environments <a href="https://theconversation.com/antibiotic-resistance-is-not-new-it-existed-long-before-people-used-drugs-to-kill-bacteria-115836">for millions of years</a>. Their incessant, random mutations will lead them to inevitably develop variants that are resistant to the antibiotics of the future. </p>
<p>Drug resistance is a reality of life we will have to accept and continue to fight against.</p><img src="https://counter.theconversation.com/content/220283/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Qi Zheng does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Nobel Prize-winning Luria−Delbrück experiment showed that random mutations in bacteria can allow them to develop resistance by chance.Qi Zheng, Professor of Biostatistics, Texas A&M UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2227432024-02-21T19:12:19Z2024-02-21T19:12:19ZHard to kill: here’s why eucalypts are survival experts<figure><img src="https://images.theconversation.com/files/576420/original/file-20240219-24-nbwq6k.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2094%2C1551&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://flickr.com/photos/88123769@N02/8065560838">Bernard Spragg/Flickr</a></span></figcaption></figure><p>They can recover from fire. Grow back from a bare stump. Shrug aside bark loss that would kill a lesser tree. Endure drought and floods. </p>
<p>Eucalypts are not interested in dying. They’re survivors. The world’s 800-plus species are almost all found in Australia, a continent with old, degraded soils and frequent fires and droughts. </p>
<p>In the fossil record, they first appear about 34 million years ago. As the Australian continent dried out, eucalypts <a href="https://www.science.org.au/curious/earth-environment/story-our-eucalypts">gradually emerged</a> as the dominant trees in all but the most arid and tropical areas. </p>
<p>But what is it about eucalypts that makes them survivors? It’s a combination. Leathery leaves. Fire-resistant bark. Dormant buds under bark, waiting for fire. Mallee roots (lignotubers) at ground level to let them regrow. Roots which put out special chemicals to unlock scarce nutrients. And gumnuts which use fire to germinate and get a head-start on any rivals. </p>
<p>In a difficult place to survive, they thrive. Here’s how they do it. </p>
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Read more:
<a href="https://theconversation.com/new-research-reveals-how-forests-reduce-their-own-bushfire-risk-if-theyre-left-alone-201868">New research reveals how forests reduce their own bushfire risk, if they're left alone</a>
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</em>
</p>
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<h2>Leaves</h2>
<p>Many gum species have leaves which hang vertically. These adaptations are about water. Water in Australia is often scarce, and it makes sense for trees to hold onto it when they have it. Vertical leaves means less direct sun, which means less evaporation. Their dry, leathery leaves also keep the water inside. It also improves their tolerance to bushfire. </p>
<h2>Bark</h2>
<p>Stringybark, ironbark, candlebark – the bark of eucalypts is used to identify them. But it’s also one of their great adaptations. The bark is often an excellent insulator against hot, dry summers as well as a <a href="https://www.australiangeographic.com.au/topics/science-environment/2021/11/eucalyptus-and-the-ancient-kingdom-of-fire/">protective barrier</a> against fire. </p>
<p>Stringy bark is so fibrous that despite singeing and looking black on the surface, it <a href="https://www.theage.com.au/interactive/2023/tree-flammability/index.html">often doesn’t burn</a>, meaning buds beneath it are protected from damage.</p>
<h2>Buds</h2>
<p>Underneath the bark of a normal-looking eucalypt lie <a href="https://www.treenet.org/wp-content/uploads/2017/06/2010-fire-trees-and-climate-change-g.-m.-moore.pdf">thousands of dormant buds</a>. These invisible “epicormic” buds are a remarkable adaptation, letting the tree rapidly regrow after bushfires, severe insect and animal grazing, storms, droughts or floods. </p>
<p>You can spot epicormic shoots sprouting up and down the trunks of gum trees after a fire, making them look like “toothbrush trees”. </p>
<figure class="align-center ">
<img alt="Eucalyptus Epicormic Buds" src="https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576427/original/file-20240219-16-2svnqh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Epicormic Shoots emerge from Eucalyptus buds hidden under the bark after a bush fire.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/usforestservice/49836705293">Forest Service/Flickr</a></span>
</figcaption>
</figure>
<p>Epicormic shoots <a href="https://www.tandfonline.com/doi/abs/10.1080/03071375.2015.1066559">can grow</a> 27cm in a single day, or up to 6 metres in a year. When epicormic buds touch soil, they can sometimes develop as roots. This allows fallen trees or even large branches to re-establish and anchor after storms and floods. </p>
<p>You can sometimes see hundreds of woody spines on the trunks of old dead trees. These are a pointy reminder of how many undeveloped epicormic buds lurk under the bark.</p>
<h2>Mallee roots (lignotubers)</h2>
<p>As remarkable as epicormic buds are, they’re not the recovery mechanism of last resort. That job falls to the bulge at the bottom of many eucalypt trunks, which we often call “mallee roots”. </p>
<p>These are <a href="https://www.tandfonline.com/doi/abs/10.1080/03071375.2015.1066559">lignotubers</a>, remarkable adaptations possessed by most eucalypts. </p>
<figure class="align-left ">
<img alt="Base of Eucalyptus Tree" src="https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576423/original/file-20240219-30-66bvoo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lignotubers growing at the base of eucalyptus tree.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/eucalyptus-gum-tree-colorful-small-trunk-765407536">Anitham Raju Yaragorla/ShutterStock</a></span>
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</figure>
<p>To appreciate the complexity and biological beauty of a lignotuber, imagine the trunk of a eucalypt with all its epicormic buds scrunched into a ball at the base of the trunk. The buds have direct access to a large root system able to supply water, nutrients and carbohydrates. </p>
<p>This is a gum tree’s emergency reboot option. Even when the tree above is falling apart, the lignotuber can rapidly regrow the tree at a rate of 6 metres or more in a year. </p>
<h2>Roots</h2>
<p>The roots of species such as river red gums drive deep into the soil along water courses, searching for subterranean water supplies as a backup in case the river dries up. </p>
<p>For other species, the solution to limited water is to send roots far and wide, often many times further than the tree’s height. In many species, the lignotuber and roots are buried under an insulating layer of soil. This acts as protection against fire. </p>
<p>That’s not all. Many eucalypt species produce “exudates” from their roots – chemicals which leach into the soil and free any locked-up nutrients in poor soils. </p>
<p>Still other exudates seep out to help feed mycorrhizal fungi in the soil. The gum trees do this as part of a wonderful symbiosis, allowing both tree and fungus to thrive. The gum gives sugar, the fungi give water and nutrients. </p>
<p>This underground exchange <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/root-exudate">greatly improves soil quality</a> and lets other species grow in difficult conditions. </p>
<h2>Gumnuts</h2>
<p>Gumnuts – woody fruits of eucalypts – are familiar to many of us from May Gibbs’ famous Snugglepot and Cuddlepie stories. </p>
<p>These capsules protect the tiny seeds inside from desiccation and fire. After a fire, eucalyptus fruit may be damaged or dry out. This frees the fine seeds, which sprinkle over the soil like pepper over dinner. </p>
<p>Some eucalypts rely not on lignotubers or epicormic buds but on the seeds <a href="https://www.washingtonpost.com/world/asia_pacific/australians-love-a-home-among-gum-trees-but-can-eucalyptus-forests-recover-from-the-fires/2020/01/17/413d25fa-36b7-11ea-a1ff-c48c1d59a4a1_story.html">contained and protected</a> in those woody gumnuts. The seeds fall to the ground and germinate when conditions are right renewing the forest. </p>
<h2>Survivors – but not immortal</h2>
<p>In the years ahead, we’ll see natural disasters occurring more often and with greater ferocity as the climate changes. And in the aftermath, we will also see the spectacular and rapid responses of eucalypts – one of the world’s great families of survivors. </p>
<p>But we will also see dead forests. Gum trees do perish, despite their abilities to regenerate. Some species such as mountain ash are <a href="https://theconversation.com/its-not-just-victorias-iconic-mountain-ash-trees-at-risk-its-every-species-in-their-community-214582">not coping</a> with pressures such as logging and climate change, while thin-barked snow gums are <a href="https://pursuit.unimelb.edu.au/articles/recurring-fires-are-threatening-the-iconic-snow-gum">struggling to cope</a> with new fire regimes. Every living thing has limits. </p>
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<strong>
Read more:
<a href="https://theconversation.com/yes-the-australian-bush-is-recovering-from-bushfires-but-it-may-never-be-the-same-131390">Yes, the Australian bush is recovering from bushfires – but it may never be the same</a>
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<img src="https://counter.theconversation.com/content/222743/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gregory Moore does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From sacrificial bark to fire-germinating gumnuts to stealthy buds the eucalyptus has evolved an arsenal of protective measures.Gregory Moore, Senior Research Associate, School of Ecosystem and Forest Sciences, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2225332024-02-14T16:55:57Z2024-02-14T16:55:57ZMen become less fertile with age, but the same isn’t true for all animals – new study<figure><img src="https://images.theconversation.com/files/573049/original/file-20240202-27-wscv4y.jpg?ixlib=rb-1.1.0&rect=0%2C34%2C5833%2C3938&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/colorful-balloons-spermatozoid-shape-on-blue-1100465771">olliulli/Shutterstock</a></span></figcaption></figure><p>We take it for granted that humans find it <a href="https://www.tandfonline.com/doi/full/10.3109/09513590.2010.501889">more difficult to conceive</a> as they grow older. But <a href="https://www.nature.com/articles/s41467-024-44768-4">our recent study</a>, which analysed data from 157 animal species, found that male reproductive ageing seems to be a lot less common in other male animals. </p>
<p>With fertility in men <a href="https://www.bmj.com/content/305/6854/609">declining worldwide</a>, understanding ageing of sperm in other animals could give new insights into our own fertility. </p>
<p>Human fertility declines with age because sperm and eggs of older people are <a href="https://academic.oup.com/humupd/article/11/3/261/759255">more deteriorated</a> or fewer in number than those of young people. Reproducing at an older age not only affects your fertility, but can also <a href="https://www.nature.com/articles/nrurol.2013.18">reduce the fertility</a>, survival rate and physical and cognitive performance of the children you conceive.</p>
<h2>Humans versus other animals</h2>
<p>Humans <a href="https://link.springer.com/article/10.1007/s00239-019-09896-2">live considerably longer</a> than we did just a century ago. This <a href="https://www.pnas.org/doi/full/10.1073/pnas.0909606106">recent, rapid extension</a> in our longevity might be one reason why humans reproductively age at faster rates than other animals. Our reproductive ageing rate hasn’t slowed down yet to match our longer lifespans. </p>
<p>Animals might also face greater evolutionary pressure to maximise their reproductive potential at all ages, because most animals reproduce throughout their lives. But this isn’t the case for humans. We rarely <a href="https://academic.oup.com/humrep/article/29/6/1304/625687">reproduce</a> in our late life. </p>
<p>Additionally, we have <a href="https://academic.oup.com/humrep/article/37/4/629/6515525">fewer offspring</a> compared to our ancestors. This makes it harder for natural selection to select genes that improve human reproduction due to less variation in the population’s fecundity. </p>
<h2>Females versus males</h2>
<p>Males and females in many species age reproductively at different rates. </p>
<p>For instance, in red wolves, male reproductive success declines with age but it <a href="https://link.springer.com/article/10.1007/s00265-016-2241-9">does not</a> for females. Yet female killifish show stronger decline in fertility with age <a href="https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2656.13382">than males</a>. Despite the fact human females live longer than males, they tend to become infertile <a href="https://www.science.org/doi/abs/10.1126/science.3755843">earlier than men</a>, and go through menopause. </p>
<p>In some species, including humans, where females help raise their grand-offspring (such as humans and whales), females live <a href="https://www.sciencedirect.com/science/article/pii/S0960982218316828?via%3Dihub">much beyond the age</a> of reproduction. An <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsos.191972">evolutionary explanation</a> for this is that older females can better pass on their genes by helping their relatives survive and rear young than by reproducing themselves.</p>
<p>There are some hypotheses that try to explain these <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/acel.13542">sex-specific differences</a> in reproductive ageing. </p>
<p>Sperm are continuously produced in males, but eggs in many species, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8769179/">including humans</a>, are produced early in the life of females. This might lead eggs to <a href="https://academic.oup.com/humupd/article/6/6/532/616993">accumulate more damage</a> due to being stored for longer durations inside older females than sperm are stored in old males. </p>
<p>Another hypothesis suggests that males might age faster because sperm DNA <a href="https://elifesciences.org/articles/80008">accumulate more</a> mutations than egg DNA. Sperm have poorer DNA repair machinery than eggs, causing males to <a href="https://www.nature.com/articles/s41586-023-05752-y">pass on more mutations</a> to the next generation than females with advancing age, a pattern observed across vertebrate animals.</p>
<p>Sexes also face different environmental pressures. For instance, in many mammals, males, <a href="https://theconversation.com/of-mice-and-matriarchs-the-female-led-societies-of-the-animal-kingdom-186875">but not females</a>, disperse away from the family group when they mature. This sort of environmental pressure leads to differences in the strategies males and females use to pass on their genes, which can create differences in <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/acel.13542">rates of reproductive ageing</a> between the sexes. </p>
<figure class="align-center ">
<img alt="Humpback whale mother with her calf" src="https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573052/original/file-20240202-19-valjo5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Female whales live long after their reproductive window.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/humpback-whale-mother-calf-on-tonga-1907017690">Tomas Kotouc/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Patterns of reproductive ageing in animals</h2>
<p>In our study, we showed that reproductive ageing rates in males <a href="https://www.nature.com/articles/s41467-024-44768-4">vary vastly</a> across the animal kingdom. We found invertebrates such as crustacea and insects have some of the slowest rates of reproductive ageing, compared to lab rodents who had some of the fastest rates.
Generally though, male animals showed few signs of age-related declines in their ejaculate traits (such as sperm quality and quantity). </p>
<p>We also found that different ejaculate traits, such as sperm viability, number, motility or velocity, aged at different rates.</p>
<p>In species that grow throughout their lives, such as some fish and crustacea, old animals have a lower mortality risk and larger gonads than young males. This can cause old males <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2021.2146">in such species</a> to age at slower rates, with older males producing larger ejaculates than younger males.</p>
<p>In animals such as lab rodents, who have some genetic lines selected for accelerated ageing, reproductive ageing was universal across ejaculate traits. Lab rodents are generally kept in highly controlled environments where ageing is easier to detect – due to fewer confounding effects that could mask ageing. This suggests that a lot of the variation in male reproductive ageing between different species could be due to their environment. </p>
<p>We also discovered that closely related species showed similar rates of decline in ejaculates with age, suggested that ageing is also shaped by an animal’s evolutionary history. </p>
<p>Some of the patterns we mention above also reflected methodological differences between studies. For example, when studies kept male animals as virgins, old males can <a href="https://www.pnas.org/doi/full/10.1073/pnas.2009053117">accumulate more sperm</a> than young males, leading to old males producing larger ejaculates. </p>
<p>Additionally, studies that only sampled young to middle-aged males showed an increase in sperm quality and quantity with age, compared to studies that sampled middle-aged to old males, suggesting that fertility peaks around middle age in male animals generally.</p>
<h2>Reproductive ageing</h2>
<p>Reproductive ageing occurs because as individuals grow older, their sperm and eggs <a href="https://www.nature.com/articles/nrurol.2013.18">accumulate damage</a>. Organisms have evolved to reproduce earlier in life rather than when old, which leads to a <a href="https://academic.oup.com/genetics/article/156/3/927/6051413">weaker ability of natural selection</a> to weed out bad genes that are expressed in old but not young organisms, in turn promoting ageing.</p>
<p>There are however, opposing forces that determine whether old individuals will leave more copies of their genes to successive lineages compared to young animals, and reproductive ageing is only one process determining this. </p>
<p><a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.201100157">An alternative hypothesis</a> is that parents who conceive at an older age would have more gene variants for longer lifespans which could benefit their offspring. This could lead to longer lived offspring from older conceiving parents. However evidence for this hypothesis is still limited. </p>
<p>While most scientists accept that at least some reproductive traits decline with age, biologists are still uncovering what the exact mechanisms and evolutionary reasons for these declines are. But by looking at other species to investigate the drivers of reproductive ageing, we can understand and perhaps even seek to alleviate our own reproductive decline with age.</p><img src="https://counter.theconversation.com/content/222533/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Krish Sanghvi receives funding from Society for the study of evolution (Rosemary grant award).</span></em></p><p class="fine-print"><em><span>Irem Sepil receives funding from the Royal Society, BBSRC and Wellcome Trust. </span></em></p><p class="fine-print"><em><span>Regina Vega-Trejo receives funding from Biotechnology and Biological Sciences Research Council.</span></em></p>Understanding how the ageing of sperm works in other animals is more important than ever as human male fertility is in decline.Krish Sanghvi, PhD student at the department of Biology, University of Oxford, University of OxfordIrem Sepil, Lecturer in Evolutionary Biology, University of OxfordRegina Vega-Trejo, Postdoctoral Research Assistant in Evolutionary Biology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2234612024-02-14T01:12:59Z2024-02-14T01:12:59ZA secret war between cane toads and parasitic lungworms is raging across Australia<p>When the first cane toads were brought from South America to Queensland in 1935, many of the parasites that troubled them were left behind. But deep inside the lungs of at least one of those pioneer toads lurked small nematode lungworms.</p>
<p>Almost a century later, the toads are evolving and spreading across the Australian continent. In <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2023.2403">new research</a> published in Proceedings of the Royal Society B, we show that the lungworms too are evolving: for reasons we do not yet understand, worms taken from the toad invasion front in Western Australia are better at infecting toads than their Queensland cousins.</p>
<h2>An eternal arms race</h2>
<p>Nematode lungworms are tiny threadlike creatures that live in the lining of a toad’s lung, suck its blood, and release their eggs through the host’s digestive tract. The larva that hatch in the toad’s droppings lie in wait for a new host to pass by, then penetrate through its skin and migrate through the amphibian’s body to find the lungs and settle into a comfortable life, and begin the cycle anew.</p>
<p>Parasites and their hosts are locked into an eternal arms race. Any characteristic that makes a parasite better at finding a new host, setting up an infection, and defeating the host’s attempts to destroy it, will be favoured by natural selection. </p>
<p>Over generations, parasites get better and better at infecting their hosts. But at the same time, any new trick that enables a host to detect, avoid or repel the parasites is favoured as well. </p>
<p>So it’s a case of parasites evolving to infect, and hosts evolving to defeat that new tactic. Mostly, parasites win because they have so many offspring and each generation is very short. As a result, they can evolve new tricks faster than the host can evolve to fight them. </p>
<h2>The march of the toads</h2>
<p>The co-evolution between hosts and parasites is most in sync among the ones in the same location, because they encounter each other most regularly. A parasite is usually better able to <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2007.01028.x">infect hosts from the local population</a> it encounters regularly than those from a distant population.</p>
<p>But when hosts invade new territory, it can play havoc with the evolutionary matching between local hosts and parasites. </p>
<p>Since cane toads were released into the fields around Cairns in 1935, the toxic amphibians have hopped some 2,500 kilometres westwards and are currently on the doorstep of Broome. And they have <a href="https://www.nature.com/articles/439803a">changed dramatically</a> along the way. </p>
<p>The Queensland toads are homebodies and spend their lives in a small area, often reusing the same shelter night after night. As a result, their populations can build up to high densities. </p>
<p>For a lungworm larva, having lots of toads in a small area, reusing and sharing shelter sites, makes it simple to find a new host. But at the invasion front (currently in Western Australia), <a href="https://www.publish.csiro.au/wr/WR08021">toads are highly mobile</a>, moving over a kilometre per night when conditions permit, and rarely spending two nights in the same place. </p>
<p>At the forefront of the invasion, toads are few and far between. A lungworm larva at the invasion front, waiting in the soil for a toad to pass by, will have <a href="https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/09-0530.1">few opportunities</a> to encounter and infect a new host. </p>
<h2>Lungworms from the invasion front</h2>
<p>When hosts are rare, we expect the parasite will evolve to get better at infecting the ones it does encounter, because it is unlikely to get a second chance.</p>
<p>To understand how this co-evolution is playing out between cane toads and their lungworms, we did some experiments pairing hosts and parasites from different locations in Australia. What would happen when toad and lungworm strains that had been separated by 90 years of invasion were reintroduced to each other?</p>
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<em>
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Read more:
<a href="https://theconversation.com/is-toadzilla-a-sign-of-enormous-cane-toads-to-come-its-possible-toads-grow-as-large-as-their-environment-allows-195929">Is 'Toadzilla' a sign of enormous cane toads to come? It's possible – toads grow as large as their environment allows</a>
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<p>To study this we collected toads from different locations, bred them in captivity and reared the offspring in the lab under common conditions. We then exposed them to 50 lungworm larvae from a different area of the range, waited four months for infections to develop, then killed the toads and counted how many adult worms had successfully established in their lungs.</p>
<p>As expected, worms from the invasion front were best at infecting toads, not just their local ones. Behind the invasion front, in intermediate and old populations we found that hosts were able to fight their local parasites better than those from distant populations. </p>
<p>While we saw dramatic differences in infection outcomes, we have yet to determine what biochemical mechanisms caused the differences and how changes in genetic variation of host and parasite populations might have shaped them. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/in-the-evolutionary-arms-race-between-cane-toads-and-lungworms-skin-secretions-play-a-surprising-role-163821">In the evolutionary arms race between cane toads and lungworms, skin secretions play a surprising role</a>
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<img src="https://counter.theconversation.com/content/223461/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lee A Rollins receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Rick Shine receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Greg Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Cane toads are evolving as they spread across Australia. Parasitic lungworms are becoming more infectious to keep up.Greg Brown, Postdoctoral researcher, Macquarie UniversityLee A Rollins, Scientia Associate Professor, UNSW SydneyRick Shine, Professor in Evolutionary Biology, Macquarie UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2227672024-02-06T16:34:20Z2024-02-06T16:34:20ZWe’ve found out how earless moths use sound to defend themselves against bats – and it could give engineers new ideas<figure><img src="https://images.theconversation.com/files/573732/original/file-20240206-20-zrb59g.jpg?ixlib=rb-1.1.0&rect=26%2C40%2C4466%2C2950&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ermine moths are deaf, but have an intricate wing structure that protects them from bats by producing warning clicks when they fly.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/detailed-closeup-on-white-speckled-yponomeuta-2169581991">HWall/Shutterstock</a></span></figcaption></figure><p>An acoustic battle between <a href="https://www.annualreviews.org/doi/10.1146/annurev-ento-121510-133537">bats and their insect prey</a> has been raging in the night skies for over 65 million years. Many different techniques are used, and <a href="https://www.pnas.org/doi/10.1073/pnas.2313549121">our new study</a> reveals the fascinating strategy of the small, deaf ermine moth, which has evolved a tiny wing structure that produces warning sounds. We hope this insight could inspire engineers to create new technology.</p>
<p>Bats count on their secret weapon, <a href="https://www.bats.org.uk/about-bats/flight-food-and-echolocation">echolocation</a>, to find and catch their flying prey, and in response, nocturnal insects have evolved interesting defences. Many silk moths, for instance, rely on a kind of <a href="https://doi.org/10.1073/pnas.2014531117">sound-absorbing stealth cloak</a> that makes them “disappear” from bat sonar. Some large moth species have <a href="https://doi.org/10.1016/j.cub.2021.08.038">evolved reflective decoys</a> that draw bat attacks away from their body and towards the tips of their wings.</p>
<p>The next level of defence is <a href="https://www.annualreviews.org/doi/10.1146/annurev-ento-121510-133537">ears</a> that allow insects, including many moths, to pick up bat echolocation calls and fly out of harm’s way. They can also use their sensory awareness of location to blast an attacking bat with ultrasonic sounds that deter or confuse their biosonar. </p>
<p>However, scientists have long been puzzled about the many earless moths that cannot detect their predators and are too small for decoys. How do they protect themselves? </p>
<p>We recently discovered that <a href="https://research-information.bris.ac.uk/ws/portalfiles/portal/185355664/tymbals.pdf">even earless moths</a>, such as <a href="https://butterfly-conservation.org/moths/white-ermine">ermine moths</a> (<em>Yponomeuta</em>), use acoustic signals as a defence against bat attacks. These moths have a tiny structure in their hind wings which creates a powerful ultrasonic signal that jams the echolocating sonar of bats.</p>
<p>Because these moths don’t have hearing organs, they are not aware of their unique defence mechanism, and nor can they control it. Instead, the sound production mechanism is coupled to the flapping of their wings.</p>
<h2>Protective wing beats</h2>
<p>When we studied the ermine moth’s wing under a microscope, it became clear that one part of the wing stands out from the rest. While most of it is covered by small hairs and scales, one patch of wing is clear and located adjacent to a corrugated structure of ridges and valleys. In our new study, we found this structure produces sound perfectly tuned to confuse bats. </p>
<figure class="align-center ">
<img alt="Pipistrelle bat flying on wooden ceiling of house in darkness" src="https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573422/original/file-20240205-21-ssex63.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Bats such as this pipistrelle use echolocation to hunt.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pipistrelle-bat-pipistrellus-flying-on-wooden-1018158514">Rudmer Zwerver/Shutterstock</a></span>
</figcaption>
</figure>
<p><a href="https://dosits.org/science/sound/what-is-sound/">Sound is a pressure wave</a> that travels through a fluid or solid and requires a displacement of this medium, usually a vibration, to produce noise. Large vibrating surfaces over cavities are <a href="https://cmtext.indiana.edu/acoustics/chapter1_resonance.php">good for amplifying sound</a> – a good example is a tymbal drum, which has a taught skin stretched over a cavity. As the drum skin is struck by a drumstick, the skin vibrates at its natural frequencies and transmits these vibrations into the surrounding air as sound.</p>
<p>In ermine moths, the clear patch in the hind wing serves as the drum skin, while the corrugated structure of valleys and ridges act as drumsticks. During flight, the moth’s wing makes the ridges snap one after the other in a sequence. Each snap makes the clear patch, known as an <a href="https://research-information.bris.ac.uk/en/publications/a-bioinspired-mechanical-model-of-the-ultrasonic-clicks-produced-">aeroelastic tymbal</a>, vibrate and amplifies the sound volume.</p>
<p>Recordings we made of ermine moths found their wings make clicking noises during flight, which we could detect using a bat detector that converts ultrasound into sound audible to humans.</p>
<p>Using 3D X-ray and a sophisticated microscope technique called <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961134/#:%7E:text=The%20primary%20functions%20of%20a,3D%20reconstructions%20of%20imaged%20samples.">confocal microscopy</a>, our study’s lead author, Hernaldo Mendoza Nava, mapped out the intricate properties of the materials that make these moths’ aeroelastic tymbals. We then used computer simulations to test our hypothesis that the deformations of the corrugations stimulate the wing’s membrane in a way that produces sound. These simulations produced a sound that matched our recordings of the moths’ clicks in frequency, structure, amplitude and direction.</p>
<p>Some eared moths can make similar warning sounds, but none of them (so far) have been shown to do this with an aeroelastic tymbal. </p>
<p>To our team of biologists and engineers, these wing structures are fascinating because they rely on a mechanism that we teach our engineering students to avoid. “Snap through” is an example of a <a href="https://www.egr.msu.edu/classes/me471/thompson/handout/class07_2005S_Buckling.pdf">buckling instability</a> – when a structure loses stability when loaded, and suddenly snaps into a different state.</p>
<p>In a buckling instability, the material doesn’t break but the structure usually loses stiffness and can even collapse. This can have catastrophic consequences for any structure that carries load, such as buildings, bridges and aeroplanes.</p>
<h2>Inspired by nature</h2>
<p>Historically, structures were made to be rigid enough to withstand external forces. Over the last decade, researchers and engineers have started to question this default position, and have begun to use buckling instabilities to create structures with new capabilities. </p>
<p>One example is engineers designing <a href="https://www.nature.com/collections/aabiaicgej#:%7E:text=Traditionally%2C%20structures%20were%20constructed%20to,and%20maintain%20its%20desired%20form.">morphing structures</a> <a href="https://www.cambridge.org/core/journals/aeronautical-journal/article/abs/morphing-skins/912AB6CFD2C2075099CC5D362D8BCB60">for future aircraft wings</a> that autonomously adapt their shape to perform better when the environment changes. The aeroelastic tymbal of ermine moths embodies this concept and demonstrates how nature can be an inspiration for new technology.</p>
<p>Our hope is that these deaf moths’ aeroelastic tymbals will encourage new developments in engineering domains such as acoustic structural monitoring, where structures give off sound when overloaded. This is often used to check the safety of infrastructure. It could also lead to innovations in <a href="https://en.wikipedia.org/wiki/Soft_robotics">soft robotics</a>, where the robots are made of fluids and gels instead of metal and plastics.</p><img src="https://counter.theconversation.com/content/222767/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marc Holderied receives funding from the Biotechnology and Biological Sciences Research Council (grant no. BB/N009991/1) and the Engineering and Physical Sciences Research Council (grant no. EP/T002654/1). We thank Diamond Light Source for access
to beamline I13 (proposal MT17616) and to Dr. Shashi Marathe and Kaz Wanelik for their assistance at the facility. We thank Daniel Robert for access to and support with Laser Doppler vibrometry.</span></em></p><p class="fine-print"><em><span>Alberto Pirrera has received funding for this research from the Engineering and Physical Sciences Research Council (grant no. EP/M013170/1).</span></em></p><p class="fine-print"><em><span>Rainer Groh has received funding from the Royal Academy of Engineering (grant no. RF/201718/17178) for this research. Hernaldo Mendoza Nava, a PhD student who worked on this project for his thesis, was funded by the Science and Technology National Council (CONACYT-Mexico, CVU/studentship no. 530777/472285) and the Engineering and Physical Sciences Research Council through the EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science (grant no. EP/L0160208/1).</span></em></p>The ermine moth’s wing structures are fascinating because they rely on a mechanism we teach our engineering students to avoidMarc Holderied, Professor in Sensory Biology, University of BristolAlberto Pirrera, Professor of Nonlinear Structural Mechanics, University of BristolRainer Groh, Senior Lecturer in Digital Engineering of Structures, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2226322024-02-06T06:13:31Z2024-02-06T06:13:31ZNewly identified prehistoric pterosaur will help us understand evolution of flying reptiles<figure><img src="https://images.theconversation.com/files/573093/original/file-20240202-19-jahq7z.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C2246%2C1232&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of the new pterosaur species, Cheoptera </span> <span class="attribution"><span class="source">Mark Witton/Natural History Museum</span>, <span class="license">Author provided</span></span></figcaption></figure><p>When dinosaurs roamed the land, the skies above their heads were filled with a variety of soaring reptiles, which swept through the air on <a href="https://www.scientificamerican.com/article/pterosaurs-were-monsters-of-the-mesozoic-skies/">slender, membranous wings</a>. These animals, pterosaurs, were not dinosaurs but their <a href="https://www.nhm.ac.uk/discover/watch-a-pterosaur-fly.html">evolutionary cousins</a>. </p>
<p><a href="https://www.tandfonline.com/doi/full/10.1080/02724634.2023.2298741">We’ve just announced</a> the discovery of a new species of pterosaur nearly 15 years after a fossil was found on the Isle of Skye. It is one of the most complete pterosaur fossils to be found in the UK since palaeontologist <a href="https://www.nhm.ac.uk/discover/mary-anning-unsung-hero.html">Mary Anning</a> unearthed <a href="https://www.geolsoc.org.uk/Library-and-Information-Services/Collection-Highlights/Mary-Anning-and-the-Geological-Society/pterosaurs-coprolites-and-sepia/dimorphodon-macronyx">the first</a> from the Dorset coast in 1828. </p>
<p>Pterosaurs were the first backboned animals to achieve powered flight (<a href="https://www.sciencedirect.com/science/article/pii/S0960982216314610">insects got there</a> first). Pterosaur fossils are known worldwide but their remains are rare in comparison to those of their land and water-based relatives. This is due to the <a href="https://theconversation.com/pterosaurs-should-%20have-been-too-big-to-fly-so-how-did-they-manage-it-60892">fragile nature of their skeletons</a>, which are composed of thin-walled, hollow bones.</p>
<p>Pterosaur fossils are often incomplete, <a href="https://www.amnh.org/exhibitions/pterosaurs-flight-in-the-age-of-dinosaurs/why-are-pterosaur-fossils-rare">crushed and distorted</a>. A sparse pterosaur record has been harvested from the Jurassic period (200-145 million years ago) and <a href="https://www.nhm.ac.uk/discover/the-cretaceous-period.html#:%7E:text=When%20was%20the%20Cretaceous%20Period,Cenozoic%20Era%2C%20our%20current%20era.">Cretaceous period</a> (145-66 million years ago) rocks of the UK since Anning’s discoveries. </p>
<p>But most of these are limited to a few isolated bones <a href="https://www.southampton.ac.uk/oes/news/2013/03/20_new_pterosaur_from_isle_of_wight.page">such as <em>Vectidraco</em></a>, a toothless pterosaur whose fossilised remains were found on the Isle of Wight in 2008 by five-year-old Daisy Morris. </p>
<p>This is where <a href="https://www.scottishtours.co.uk/scotland/isle-of-skye/">the Isle of Skye</a> comes in. Although Skye is most famous for the ancient volcanic landscapes of the <a href="https://www.isleofskye.com/skye-guide/skye-places/the-cuillin">Cuillin Hills</a> mountain range, there are <a href="https://www.isleofskye.com/skye-guide/history/jurassic-skye#:%7E:text=The%20Isle%20of%20Skye%20holds,mainly%20contained%20in%20local%20knowledge.">Jurassic-aged rocks</a> around the margins of the island. </p>
<p>Over the past 50 years teams of geologists and palaeontologists have been gradually uncovering <a href="https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/diverse-vertebrate-assemblage-of-the-kilmaluag-formation-bathonian-middle-jurassic-of-skye-scotland/B8DD4D46839FA83FA2E57437BDEBF2B8">more of Skye’s ancient</a> past. This work has accelerated thanks to the new imaging techniques, mainly CT scanning, which <a href="https://www.theguardian.com/science/2016/mar/30/getting-under-a-fossils-skin-how-ct-scans-have-changed-palaeontology-dinosaur-lizard">make it easier</a> to study these fossils. </p>
<p>Our new pterosaur was found in 2006 by a team of researchers including Paul Barrett in a loose boulder lying on the beach at <a href="https://canmore.org.uk/site/138335/cladach-a-ghlinne">Cladach a’Glinne</a>, on the edge of a remote bay overshadowed by the Cuillins. </p>
<p>At first sight, the new skeleton was an underwhelming smear of thin, broken, black bone set in a hard, dark-grey mudstone. But, even then, these thin bones suggested that the find would turn out to be interesting.</p>
<p>It took <a href="https://www.nhm.ac.uk/our-science/departments-and-staff/staff-directory/lu-allington-jones.html">Lu Allington-Jones</a>, one of the Natural History Museum’s fossil technicians, nearly two years to prepare our discovery for study. The rocks from Skye are extremely hard, and the fossil bones are delicate. </p>
<p>Although Lu’s work allowed us to study some of the bones, others remained encased in rock as they were too dainty to remove or expose further.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573095/original/file-20240202-21-y3x46f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Skeleton of the new pterosaur <em>Ceoptera evansae</em> from the Isle of Skye.</span>
<span class="attribution"><span class="source">The Trustees of the Natural History Museum</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Once this work was complete, the specimen lay dormant in the museum’s collections for about nine years. But then we decided to examine the fossil using the <a href="https://www.bristol.ac.uk/earthsciences/research/palaeobiology/facilities/xtm-facility/">university’s CT scanner</a>. </p>
<p>Using this equipment, similar to that used in a hospital for diagnosing broken bones, with many months of careful imaging we were able to reveal almost the entire animal in three dimensions. </p>
<p>After comparing it with other pterosaur fossils from around the world, we realised that we were dealing with something new and we called it <em>Ceoptera evansae</em> (from the Gaelic name for Skye, Eilean a’ Cheò, Isle of Mist, and honouring <a href="https://profiles.ucl.ac.uk/9226-susan-evans">Professor Susan Evans</a> who has worked extensively in the area). </p>
<p>This pterosaur species is important because of the quality of preservation and its age. It is one of only a <a href="https://epub.ub.uni-muenchen.de/12007/1/zitteliana_2008_b28_05.pdf">handful of pterosaur skeletons</a> from the <a href="https://www.nationalgeographic.com/science/article/jurassic">Middle Jurassic period</a>, approximately 167 million years ago. </p>
<p>At this time pterosaurs were undergoing colossal anatomical changes from early small-bodied, long-tailed pterosaurs such as <em><a href="https://www.britannica.com/animal/Dimorphodon">Dimorphodon</a></em> (roughly the size of a raven) to later pterosaurs like <em><a href="https://www.britannica.com/animal/Pteranodon">Pteranodon</a></em> which had a wingspan similar to that of a small airplane. </p>
<p>The lack of good pterosaur specimens from this time interval has hindered scientists’ attempts to understand how pterosaurs evolved from these earlier forms to those that dominated the skies later in Earth’s history. <em>Ceoptera</em> helps to fill this a gap. </p>
<p>For 15 years scientists have studied <a href="https://www.smithsonianmag.com/science-%20nature/darwinopterus-a-transitional-pterosaur-55145586/">transitional pterosaurs</a> that show a mix of features seen in the
earlier, tailed forms and their later, giant relatives. <em>Ceoptera</em> is one of these transitional forms (called a <a href="https://www.smithsonianmag.com/science-nature/darwinopterus-a-transitional-pterosaur-55145586/">Darwinopteran</a>), one of the first members of this group known from Europe, and is the second-oldest darwinopteran worldwide. </p>
<p>This makes <em>Ceoptera</em> crucial in understanding the pace of pterosaur evolution, and it has pushed back the appearance of more advanced pterosaurs to the Early Jurassic period, about 10 million years earlier than previously thought. It brings us one step closer to understanding where and when the more advanced pterosaurs evolved. </p>
<p><em>Ceoptera</em>‘s discovery shows how palaeontologists are making new discoveries all the time, even in places like the UK - one of the most heavily surveyed places worldwide. It also shows how new technology can is helping to unearth the mysteries of Earth’s ancient past. </p>
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<img alt="" src="https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536131/original/file-20230706-17-460x2d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Paul Barrett is affiliated with The Linnean Society (Trustee).</span></em></p><p class="fine-print"><em><span>Elizabeth Martin-Silverstone does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Isle of Skye has a rich palaeontological heritage, so perhaps it’s no surprise scientists made an important discovery there.Elizabeth Martin-Silverstone, Research Assistant in Palaeontology, University of BristolPaul Barrett, Individual Merit Researcher, Natural History MuseumLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2212182024-01-25T20:46:04Z2024-01-25T20:46:04ZThe first flowers evolved before bees – so how did they become so dazzling?<figure><img src="https://images.theconversation.com/files/571111/original/file-20240124-17-j4irzv.jpg?ixlib=rb-1.1.0&rect=60%2C25%2C5596%2C3802&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/red-pink-and-yellow-flowering-plants-v-3NQ3pmWkY">Nature Uninterrupted Photography/Unsplash</a></span></figcaption></figure><p>Colourful flowers, and the insects and birds that fly among their dazzling displays, are a joy of nature. But how did early relationships between flower colour and animal pollinators emerge?</p>
<p>In a study published in <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2023.2018">Proceedings of the Royal Society</a>, we have unravelled this mystery by analysing the visual environments in which the ancestors of today’s bees foraged from flowers.</p>
<p>We measured and analysed the light reflected from today’s flowers, as well as the rocks, soil, sticks, bark and leaves that form their natural backgrounds.</p>
<p>From this data we built computer simulations that recreate the ancient visual environment when the first flowers emerged.</p>
<h2>Insect colour vision came before flowers</h2>
<p>Today, bees are prolific pollinators of flowering plants, including <a href="https://theconversation.com/our-bee-eye-camera-helps-us-support-bees-grow-food-and-protect-the-environment-110022">food crops</a>. Bees use <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2010.2412">colour vision</a> based on ultraviolet, blue and green sensitive photoreceptors (light-sensing cells) to detect and discriminate the most rewarding flowers. In comparison, most humans perceive colour using blue, green and red sensitive photoreceptors.</p>
<p>When the first flowers evolved during the Mesozoic era, between 252 million and 66 million years ago, the ancestors of bees had to orientate themselves, maintain stable flight, avoid collisions, and find food among natural backgrounds. We suspect their visual systems may have been influenced by evolution to efficiently operate in that environment.</p>
<p>By the time the first flowering plants appeared, bees’ ancestors had already evolved colour vision – and we know it <a href="https://link.springer.com/article/10.1007/BF01142181">has stuck around throughout the evolutionary history of bees</a>.</p>
<p>So, while bees weren’t initially around, their ancestors were. Flower colours likely evolved the vivid colours we see today to suit this ancient visual system. At the same time, the first bees emerged as the most efficient pollinators. </p>
<h2>What colour were flower backgrounds on the ancient Earth?</h2>
<p>Australia is an ideal place to collect data on natural background materials that early insects would have seen, as it is a <a href="https://www.publish.csiro.au/bt/BT00023">geologically ancient continent</a>.</p>
<p>We collected background samples from across Australia and measured their reflective properties using a tool called a <a href="https://en.wikipedia.org/wiki/Spectrophotometry">spectrophotometer</a>.</p>
<p>We used this data to create a database of materials that would have been present in the visual environment of flying insects more than 100 million years ago – when the first flowers appeared.</p>
<h2>Flower colour evolved in response to bee colour vision</h2>
<p>For our collection of natural backgrounds, insect and bird pollinated flowers, we calculated <a href="https://www.sciencedirect.com/science/article/pii/S2215016120300479">marker points</a> – rapid changes in the intensity of light reflected from a surface, within a small wavelength band.</p>
<p>These marker points identify the key visual features of coloured surfaces, and we can use them for statistical testing of the evolutionary process. </p>
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Read more:
<a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">Explainer: what is the electromagnetic spectrum?</a>
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<p>We then wrote computer simulations to generate possible flower backgrounds. By analysing their marker points, we tested the visibility of today’s flowers against the simulated backgrounds.</p>
<p>Interestingly, we showed that the distribution of marker points on petals from plants pollinated by bees clearly indicates these flowers are “salient” – that is, they stand out as stronger signals from natural backgrounds.</p>
<p>This finding matches with previous studies suggesting that in the <a href="https://link.springer.com/article/10.1007/BF00188925">Northern Hemisphere</a> and <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2012.0827">Australia</a>, flowering plants evolved colour signals to facilitate colour perception by bees.</p>
<p>The very first flowers were likely a <a href="https://theconversation.com/flies-like-yellow-bees-like-blue-how-flower-colours-cater-to-the-taste-of-pollinating-insects-167111">dull greenish-yellow colour and initially pollinated by flies</a>. However, as the first bees – with their tuned vision systems – started pollinating flowers, the flowers likely evolved new colours to match the bees’ visual capabilities.</p>
<p>The process of natural selection seems to have driven flower colours to stand out from their backgrounds in the eyes of pollinators.</p>
<h2>Birds were involved, too</h2>
<p>Birds became established as flower visitors <a href="https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17822">millions of years after insect pollination evolved</a>. Bird vision uses <a href="https://www.journals.uchicago.edu/doi/abs/10.1086/510141">four types of colour photoreceptors</a>, and they can see long-wavelength red colours that bees cannot easily process against natural backgrounds.</p>
<p>Our analysis confirmed that bird-pollinated flowers evolved marker points towards <a href="https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.12135">longer wavelengths than bee-pollinated flowers</a>. Our new discovery also showed that these flowers systematically differ from natural backgrounds.</p>
<p>As Earth’s climate changes, it is important to consider what might happen to ecosystems and our food production systems <a href="https://www.publish.csiro.au/RS/RS23003">in a world without bees</a>. It is vital that we understand how pollination and plant reproduction may be altered.</p>
<p>Our research shows that bees are a major driver of floral evolution. Unless we protect these insects and their habitat, we will lose fundamental and beautiful aspects of life we all enjoy and need.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/bees-can-do-so-much-more-than-you-think-from-dancing-to-being-little-art-critics-204039">Bees can do so much more than you think – from dancing to being little art critics</a>
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<img src="https://counter.theconversation.com/content/221218/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adrian Dyer receives funding from the Alexander von Humboldt Foundation, the Air Force Office of Scientific Research and the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Alan Dorin receives or has received funding and/or support from the Australian Research Council, Microsoft, National Geographic Society, AgriFutures Australia, Costa Group, Australian Blueberry Grower's Association, Sunny Ridge Berries.</span></em></p><p class="fine-print"><em><span>Mani Shrestha worked under the German Federal Ministry of Education (BMBF) funded project, Professor Anke Jentsch, Disturbance Ecology Lab, University of Bayreuth, Germany and also wok in the Department of Life Science, National Taiwan University, Taipei, Taiwan </span></em></p><p class="fine-print"><em><span>Jair Garcia does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Flowers tend to stand out against a natural background. A new study shows this contrast evolved in a key relationship with their most famous pollinators – bees.Adrian Dyer, Associate Professor, Department of Physiology, Monash UniversityAlan Dorin, Associate Professor, Faculty of Information Technology, Monash UniversityJair Garcia, Researcher and analyst, Monash UniversityMani Shrestha, Senior Researcher and International Fellow, Disturbance Ecology, University of Bayreuth, Germany, Bayreuth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2195772024-01-14T19:05:59Z2024-01-14T19:05:59ZDo they see what we see? Bees and wasps join humans in being tricked by illusions of quantity<figure><img src="https://images.theconversation.com/files/565690/original/file-20231214-18-xu49z8.jpg?ixlib=rb-1.1.0&rect=404%2C0%2C2068%2C1213&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Scarlett Howard</span></span></figcaption></figure><p>If you’ve ever been tricked by a visual illusion, you know the feeling of disconnect between what your eyes perceive and what is actually there. Visual illusions occur due to errors in our perception, causing us to misperceive certain characteristics of objects or scenes.</p>
<p>As it turns out, many non-human animals also experience these effects, including illusions of item size, brightness, colour, shape, orientation, motion or quantity. We study these illusions and the differences between animals as it can tell us how visual systems evolved.</p>
<p>Our latest study, published in <a href="https://www.cell.com/iscience/fulltext/S2589-0042(23)02774-8">iScience</a>, shows that European honeybees and European wasps see illusions of quantity in a similar way to humans.</p>
<figure class="align-center ">
<img alt="Muller-Lyer illusion; Vertical-horizontal illusion; Ponzo illusion; Illusory contour; Delboeuf illusion; Ebbinghaus illusion" src="https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568540/original/file-20240110-21-nn3vhp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Examples of different visual illusions where the eye is tricked to perceive incorrect proportions of objects.</span>
<span class="attribution"><span class="source">Scarlett Howard</span></span>
</figcaption>
</figure>
<h2>An illusion perceived by several species</h2>
<p>The study of visual illusions provides interesting windows into how brains operate. Visual illusions are perceptual errors, which likely enable us to process complex natural information efficiently.</p>
<p>The Solitaire illusion causes a misperception of quantity based on the configuration of dots in an image. Those who perceive the illusion will overestimate the quantity of dots when they are clustered together and/or underestimate the number of dots when unclustered.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two images containing a cross shape made up of yellow and blue dots" src="https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=313&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=313&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=313&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=393&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=393&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565938/original/file-20231215-20-ftnpzs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=393&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An example of the Solitaire illusion. The yellow elements generally appear more numerous on the right than the left, despite both images having an identical quantity of yellow and blue elements.</span>
<span class="attribution"><span class="source">Scarlett Howard</span></span>
</figcaption>
</figure>
<p>We know the Solitaire illusion is perceived by <a href="https://psycnet.apa.org/record/2014-33482-001">humans, capuchin monkeys</a>, <a href="https://psycnet.apa.org/record/2017-55920-001">guppies</a> and <a href="https://www.biorxiv.org/content/10.1101/2023.08.22.554303v1.abstract">bumblebees</a>. <a href="https://psycnet.apa.org/record/2014-33482-001">Chimpanzees, rhesus monkeys</a> and <a href="https://www.mdpi.com/2076-2615/10/12/2304">domestic dogs</a> do not appear to perceive the illusion. Interestingly, in humans age appears to impact the perception of the Solitaire illusion – younger children are less susceptible than <a href="https://www.sciencedirect.com/science/article/pii/S0022096515002258">older children</a>.</p>
<p>A possible evolutionary reason humans and other species may experience this misperception of quantities is it may allow us to process and compare large numbers of items more efficiently and quickly.</p>
<p>For quantities greater than about five, fast decisions may be more important than absolute accuracy, which would require manual, sequential counting.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/one-then-some-how-to-count-like-a-bee-138815">One, then some: how to count like a bee</a>
</strong>
</em>
</p>
<hr>
<h2>Testing honeybees</h2>
<p>Some insects, including bees and wasps, are very “motivated” to participate in behavioural experiments. European honeybees and wasps are central-place foragers: they will return to the location of a high-quality food source.</p>
<p>We provided freely flying bees and wasps with a reward of sugar water for participating in experiments. This allows us to train and test individually colour-marked insects throughout a day, with them returning by their own choice.</p>
<p>We have used this method to show honeybees can perform a variety of numerical tasks such as <a href="https://theconversation.com/bees-join-an-elite-group-of-species-that-understands-the-concept-of-zero-as-a-number-97316">understanding the concept of zero</a>, <a href="https://theconversation.com/bees-can-learn-higher-numbers-than-we-thought-if-we-train-them-the-right-way-124887">discriminating between quantities</a>, <a href="https://theconversation.com/can-bees-do-maths-yes-new-research-shows-they-can-add-and-subtract-108074">performing simple addition and subtraction</a>, <a href="https://theconversation.com/we-taught-bees-a-simple-number-language-and-they-got-it-117816">matching symbols with quantities</a>, and <a href="https://theconversation.com/honeybees-join-humans-as-the-only-known-animals-that-can-tell-the-difference-between-odd-and-even-numbers-181040">categorising quantities as odd or even</a>.</p>
<p>Honeybees are also known to perceive some <a href="https://theconversation.com/which-square-is-bigger-honeybees-see-visual-illusions-like-humans-do-87673">spatial</a>, movement and colour illusions. These past skills make them an ideal candidate to study and see if they are fooled by illusions of quantity.</p>
<p>Wasps are far less tested than honeybees for their behaviour and cognition, but recent <a href="https://theconversation.com/many-people-hate-wasps-but-theyre-smarter-than-you-might-think-and-ecologically-important-212706">studies</a> show they are also capable of advanced learning. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A grey circular screen displaying stimuli to insects" src="https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=706&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=706&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=706&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=888&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=888&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565683/original/file-20231214-29-eewqnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=888&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The circular rotating screen used to present stimuli to insects during training and testing. Insects were trained one at a time and rewarded with a sugar water drop for landing on the correct stimulus option during training.</span>
<span class="attribution"><span class="source">Scarlett Howard</span></span>
</figcaption>
</figure>
<h2>Bees, wasps and the Solitaire illusion</h2>
<p>We tested the European honeybee (<em>Apis mellifera</em>) and the European wasp (<em>Vespula vulgaris</em>) using an identical method for both species.</p>
<p>We presented each insect with images containing blue and yellow dots. For 70 trials, the insects were trained with a sugar reward to visit an image with a higher quantity of yellow dots versus blue.</p>
<p>We then presented them with the Solitaire illusion – one image with the yellow dots clustered in the middle and the blue dots unclustered, versus one image of the opposite. </p>
<p>The images actually contained an identical number of blue and yellow dots. So, if the insects perceived the illusion, they would choose the option with the yellow dots clustered in the centre, revealing an overestimation of the quantity of yellow dots.</p>
<p>We found both honeybees and wasps perceived the illusion in a similar way to humans, capuchin monkeys and guppies.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A wasp sits on a platform in front of an image of yellow and blue dots. A honeybee is approaching to land" src="https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565942/original/file-20231215-15-307y5z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A bee and wasp in front of one of the training images.</span>
<span class="attribution"><span class="source">Scarlett Howard</span></span>
</figcaption>
</figure>
<h2>Is there an evolutionary clue here?</h2>
<p>We now know the perception of the Solitaire illusion occurs across a range of species including humans, non-human primates, fish and insects. There are also primates and other mammals that appear not to perceive the illusion.</p>
<p>This could suggest two potential evolutionary pathways of experiencing the illusion. </p>
<p>One is <em>convergent</em> evolution, where different species separately developed the ability to perceive this illusion due to the requirements of their environment.</p>
<p>The other pathway is that the perception occurred through <em>conserved</em> evolution, where a common ancestor perceived the illusion, and subsequently some species either retained or lost the illusion perception.</p>
<p>One important consideration is that while the Solitaire illusion is considered an illusion of quantity, it could also be perceived as an illusion of colour area, size, line length, or perimeter. More research will be needed to determine whether the illusion induces the misperception of quantity or other cues that correlate with quantity.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/which-square-is-bigger-honeybees-see-visual-illusions-like-humans-do-87673">Which square is bigger? Honeybees see visual illusions like humans do</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/219577/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Scarlett Howard receives funding from the Australian Research Council, Monash University, Australian Academy of Sciences, and the Hermon Slade Foundation. She is affiliated with Triple R.</span></em></p><p class="fine-print"><em><span>Adrian Dyer receives funding from the Alexander von Humboldt Foundation, the Air Force Office of Scientific Research and the Australian Research Council.</span></em></p>Being susceptible to visual illusions is part and parcel of life not just for humans, but many other species – including bees.Scarlett Howard, Lecturer, School of Biological Sciences, Monash UniversityAdrian Dyer, Associate Professor, Department of Physiology, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2135382023-12-31T20:27:02Z2023-12-31T20:27:02ZA raunchy new ‘Big History’ tells the story of sex, but raises some unanswered questions<figure><img src="https://images.theconversation.com/files/565406/original/file-20231213-21-483trl.jpg?ixlib=rb-1.1.0&rect=0%2C11%2C7976%2C3976&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/sperm-egg-cell-on-microscope-scientific-1053858512">Maxx-Studio/Shutterstock</a></span></figcaption></figure><p>David Baker’s <a href="https://www.blackincbooks.com.au/books/sex">Sex: Two Billion Years of Procreation and Recreation</a> condenses the story of the evolution of (predominantly) reproductive sex into 300 pages. That is quite a feat. </p>
<p>The book is one of the latest additions to the popular “<a href="https://www.goodreads.com/shelf/show/big-history">Big History</a>” genre. First defined by Macquarie University historian <a href="https://www.jstor.org/stable/20078501?seq=1">David Christian</a> in the early 1990s, the idea of Big History is that the temporal scale on which history should be studied is “the whole of time”. Its ambition is no less than to survey history from the Big Bang to the present, taking an interdisciplinary approach to its scholarship. </p>
<p>Baker is a science writer with a PhD in Big History and one of the writers behind the <a href="https://www.mq.edu.au/bighistory/threshold-nine/issue-eleven/behind-big-history-crash-course-series-2">Big History Crash Course</a> on YouTube. In his introduction to Sex, he declares “this is the first book that seeks to weave together the grand narrative of sex in its entirety”. </p>
<hr>
<p><em>Sex: Two Billion Years of Procreation and Recreation – David Christian (Black Inc.)</em></p>
<hr>
<p>The book is divided into three sections. The first – titled Evolutionary Foreplay – covers the period from 13.8 billion to 66 million years ago. Baker races through the 10 billion years following the Big Bang, when “the cosmos was devoid of life”. </p>
<p>He summarises the formation of Earth and its atmosphere, the origins of living organisms 3.8 billion years ago, the emergence of DNA, and the cloning (asexual reproduction) of “microscopic blobs living on the edge of underwater volcanoes”. </p>
<p>We are taken from the earliest forms of sexual reproduction between two single-celled organisms to the differentiation of cells, and on to the evolution of specialised reproductive cells, the gametes. This development was followed by the rapid appearance of diverse animal species, from fish and amphibians to reptiles, insects, dinosaurs, birds and mammals. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=918&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=918&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=918&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1154&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1154&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565398/original/file-20231213-19-9rpgqu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1154&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption"></span>
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<p>In the second section, Primate Climax – which covers the period from 66 million to 315,000 years ago – we learn about the development of external genitals and the birth of “the age of the orgasm”, as well as primate sexual behaviour and social organisation. </p>
<p>The final section, Cultural Afterglow, which extends from 315,000 years ago to the present, traces the history of Homo sapiens from hunter-gatherers, to the first agrarian societies, and on to the present day. </p>
<p>The word length of each section is inversely proportional to the time scale being described – a reflection of our relative knowledge about sexual behaviour, but also its evolving complexity over time.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/sex-and-the-single-gene-new-research-shows-a-genetic-master-switch-determines-sex-in-most-animals-203055">Sex and the single gene: new research shows a genetic ‘master switch’ determines sex in most animals</a>
</strong>
</em>
</p>
<hr>
<h2>Evolution</h2>
<p>Baker’s prose is animated and deliberately raunchy, making what would be a dense read light and entertaining. But to weave his “grand narrative of sex” he also anthropomorphises reproduction of even the earliest living organisms. </p>
<p>For example, explaining theory behind the first, possibly accidental, mixing of genes two billion years ago, Baker describes “Snowball Earth” – a period when the average global temperature was minus 50 degrees Celsius. His argument is that asexual reproduction at this time of catastrophic climatic conditions was causing overpopulation and that sexual reproduction would slow population growth. </p>
<p>This sounds counter-intuitive, but sexual reproduction takes time, much longer than simply cloning oneself. Two separate, unrelated organisms need to find each other and then exchange DNA. And it seems that the very first time this happened was what Baker describes as “cannibal sex”: one cell ingesting another due to starvation and accidentally mixing DNA. Baker thus writes:</p>
<blockquote>
<p>To put it slightly more crudely, 2 billion years ago our ancestors felt so much pressure from the environment that they needed to fuck in order to survive. </p>
</blockquote>
<p>A few pages later, he writes “furthermore, sex bequeathed upon those hardy, horny eukaryotes the potential for rapid evolution into increasingly complex species”. </p>
<p>Throughout his descriptions of sexual and reproductive behaviour of pre-primate species, Baker attributes very human characteristics to living organisms that simply don’t make sense. While this can be amusing, I also found it slightly irritating. The long bow being drawn between “sexual” behaviour involving the first exchange of DNA by single-celled organisms and the first modern humans is long indeed. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566199/original/file-20231218-19-kx7tvl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hardy and horny? Euglena, a genus of single-celled flagellate Eukaryotes.</span>
<span class="attribution"><span class="source">Rattiya Thongdumhyu/Shutterstock</span></span>
</figcaption>
</figure>
<p>Baker provides an interesting summary of the diversity among our primate ancestors. He notes differences in anatomy and genital size, and considers variations in practices such as masturbation and sexual partnering, including polygamy, monogamy, promiscuity, homosexual and bisexual behaviour. </p>
<p>He delves into the issues of pleasure, romantic love and parenting, and related forms of social organisation, such as patriarchy and matriarchy. And he considers variations, such as patrilocality (where males remain in their families and females move out to live with the male parent of their offspring) and its reverse, matrilocality. </p>
<p>Baker also points out that a pleasure response to copulation can be seen in fish and reptiles, similar to the sensations experienced after eating, but that the orgasm emerges with placental mammals. </p>
<p>It is, however, the evolution of human culture that radically changes everything. Baker condenses a few hundred thousand years of the history of human sexuality into 150 pages. He covers diversity (including intersex characteristics and gender and sexual diversity) and considers the ways in which societies have controlled sexuality and sexual behaviour through legal and other sanctions. </p>
<p>Central to these cultural practices is the control of female sexuality, which emerged with the development of agriculture and the need to retain land ownership and safeguard inheritance down patriarchal lines.</p>
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Read more:
<a href="https://theconversation.com/guide-to-the-classics-darwins-the-descent-of-man-150-years-on-sex-race-and-our-lowly-ape-ancestry-155305">Guide to the classics: Darwin's The Descent of Man 150 years on — sex, race and our 'lowly' ape ancestry</a>
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</em>
</p>
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<h2>The future of sex</h2>
<p>In the book’s final chapter, The Future of Sex, Baker shares his belief that “Nurture has ceased to impede the sexual impulses of Nature”, leading to a state where “loneliness is at an all-time high and personal happiness is at its lowest ebb”. </p>
<p>This is a sweeping statement. How did we measure loneliness and personal happiness in, say, Ancient Egypt? Do experiences of loneliness and personal happiness vary around the globe? Do they mean different things in different cultures? </p>
<p>Informing some of Baker’s thinking are statistics about the number of Millennials “projected to never get married in their lifetimes” and the decline in rates of casual sex. But it is not clear if they are only from studies in Western countries or how representative they are at a global level. </p>
<p>Baker concludes the book with four categories of future forecasts. His “projected future” is based on current observation. Here he predicts a rise in singledom and a state where promiscuity and sexlessness both exist and birth rates decline. </p>
<p>His “probable future” anticipates a “cultural rejection of relationships as the key to happiness”. It would involve more hook-ups and the growing replacement of human-to-human sex with sex dolls and bots. Alternatively, Baker suggests humanity might swing back towards traditional monogamous couplings, or a revival of polygyny, or a “promiscuity overdrive”. </p>
<p>In a “possible future”, he considers how internet technology might lead to virtual, AI-driven partnered sex. Finally, in a “preposterous future”, he suggests that sex could cease to be important to living organisms at all.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566207/original/file-20231218-29-1fao4w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Could sex dolls and bots be the future of sex?</span>
<span class="attribution"><span class="source">Fossiant/Shutterstock</span></span>
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</figure>
<p>While Baker’s deliberations are interesting and worth pondering, it is difficult to accept his claim that “the liberalisation of attitudes towards sex has released human sexuality from the grip of culture”. Indeed, the statement is something of an oxymoron, since “liberalising attitudes” are themselves a cultural phenomenon. </p>
<p>The “grip of culture” is still ever-present in the policing of female sexual behaviour, which continues to the present day the world over. So does the epidemic of sexual violence against women. </p>
<p>The other aspect of Baker’s book that I wonder about is its “knowability”. How many of the “facts” presented are really known? How much is be conjecture? While there is an impressive list of references at the end of the book, Baker admits that many of the beliefs he shares about the evolution of sex are not certain.</p>
<p>This speaks, in part, to the tensions that exist between “Big History” and “Deep History”. Big History presents itself as an answer to an existential question – why are we here? But, as some critics have <a href="https://aeon.co/essays/we-should-be-wary-about-what-big-history-overlooks-in-its-myth">argued</a>, humans do not “easily fit into a Big History framework”.</p>
<p>Baker concludes with a statement about what he wanted to achieve in writing this book. He hopes that “some aspects of sex have become slightly less baffling for the reader” and wishes his readers the “sensation of feeling truly loved” – a kind sentiment, but slightly at odds with what has come before. </p>
<p>From my perspective, the world has a long way to go to achieve human rights for all in the areas of sexuality and gender. If Baker’s book helps this endeavour by getting us to think about human sexuality more deeply, then it will prove worthwhile.</p><img src="https://counter.theconversation.com/content/213538/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Melissa Kang has received research funding from government grant schemes (including the NHMRC and ARC). She is the co-author of books and book chapters about adolescent sexuality and adolescent health. </span></em></p>The evolution of sexual behaviour is a long and complicated tale. Taking a long view involves a degree of speculation.Melissa Kang, Associate Professor in the Specialty of General Practice, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2188102023-12-21T19:08:14Z2023-12-21T19:08:14ZWhat octopus DNA tells us about Antarctic ice sheet collapse<figure><img src="https://images.theconversation.com/files/563522/original/file-20231205-29-pymbyu.jpg?ixlib=rb-1.1.0&rect=17%2C26%2C5973%2C3961&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>If we want to understand the future, it’s often useful to look at the past. And even more useful if you use octopus DNA to peer into worlds long gone. </p>
<p>About 125,000 years ago, the Earth was in its last warm period between ice ages. Global average temperatures during this interglacial period were about 0.5–1.5°C warmer than pre-industrial levels. </p>
<p>This has strong parallels with our time. For a <a href="https://www.bbc.com/news/science-environment-66857354">third of 2023</a>, the Earth’s temperature has been 1.5°C warmer than the pre-industrial era, driven by climate change. </p>
<p>For <a href="https://www.nature.com/articles/271321a0">almost 50 years</a> physical scientists have sought the answer to whether or not the vast West Antarctic Ice Sheet collapsed the last time global temperatures were this high. Rather than relying only on geological sampling, we turned to the DNA of a small Antarctic octopus for clues to the deep past. </p>
<p>The DNA had an answer. Our <a href="https://science.org/doi/10.1126/science.ade0664">new research</a> shows yes, it most likely collapsed. </p>
<p>The West Antarctic Ice Sheet is <a href="https://www.science.org/doi/10.1126/science.aaz5487">very susceptible to warming</a>. If it melts, it has enough water to raise global sea levels by 3.3 to 5 metres.</p>
<h2>Of octopuses and giant ice sheets</h2>
<p>Sediment records and other ice cores show us that the ice sheet retreated at some point during the last ~1 million years in the late Pleistocene, but the exact timing and extent of any collapse remain ambiguous.</p>
<p>To get a more precise answer, we looked to cephalopod genetics. </p>
<p>Every organism’s DNA is a history book, and we now have the technology to read it. We can use DNA to look back in time and pinpoint when different populations of animals were interbreeding. </p>
<p>Turquet’s octopus (<em>Pareledone turqueti</em>) is fairly small, weighing up to 600 grams. They live on the seafloor all around Antarctica, but individuals don’t move far from home. Antarctica is so vast that populations in different regions cannot usually interbreed. </p>
<p>Deep under West Antarctica lies gaps in the rocks. At present, these are filled by the ice sheet, making the Weddell, Amundsen and Ross seas separate from each other. </p>
<p>If the ice melted, seaways would open up and connect these isolated basins. Octopuses could directly migrate into these regions and the evidence of their breeding would be laid down in DNA. </p>
<p>But if the ice sheet didn’t melt, we would only see evidence of breeding between octopus populations along the circumference of the continent.</p>
<p>We compared DNA patterns in Turquet octopus genomes all around Antarctica to see if there were direct and unique connections between octopus populations in the Weddell, Amundsen and Ross seas. We used statistical models to figure out if these connections could be explained by their present day connections around the Antarctic coastline.</p>
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Read more:
<a href="https://theconversation.com/we-can-still-prevent-the-collapse-of-the-west-antarctic-ice-sheet-if-we-act-fast-to-keep-future-warming-in-check-215878">We can still prevent the collapse of the West Antarctic ice sheet – if we act fast to keep future warming in check</a>
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<p>The story was clear in the DNA: yes, there had been direct connections between these three octopus populations. Their connections could not be statistically explained by interbreeding around the present day Antarctic coastline. These populations could only come into contact through seaways now blocked by the West Antarctic Ice Sheet. </p>
<p>Even more interesting, we first found direct connections between the three populations during the mid-Pliocene, 3 million to 3.6 million years ago when temperatures were 2–3°C hotter and sea levels 25m higher than today. This supports <a href="https://www.nature.com/articles/nature07867">existing geological evidence</a> that the West Antarctic Ice Sheet collapsed during that era. </p>
<p>The most recent DNA signatures of direct connections between the octopuses of these three seas was during the last interglacial period around 125,000 years ago. That suggests the ice sheet collapsed when the global average temperature was around 1.5°C hotter than pre-industrial levels.</p>
<p>Our work provides the first empirical evidence the West Antarctic Ice Sheet could begin to collapse if we exceed the Paris Agreement goal of limiting warming to 1.5°C or even 2°C. </p>
<h2>This discovery took effort across disciplines and countries</h2>
<p>To use animal DNA as a proxy for changes in the ice sheet, we had to work across disciplines and countries. Bringing together physical scientists and biologists gave rise to new ways to answer long standing questions of vital importance to all of us. </p>
<p>We also turned to museum collections for samples. Some dated back three decades – well before the genetic sequencing and analytical techniques we used were available. This demonstrates the vital importance of careful sample preservation, linked with metadata, with specimens protected for future access.</p>
<p>Interdisciplinary science is hard. It requires time, effort, and an open mind to appreciate new terminologies, scales and approaches. Journal editors and scientists can be reluctant to review such papers, as some aspects of the research will necessarily be outside the area of their expertise. But we hope our results show the value of this approach. </p>
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<figcaption><span class="caption">The Antarctic seafloor is covered in marine life. Many of their ancestors also lived through climate changes in the past.</span></figcaption>
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<h2>What’s next?</h2>
<p>We hope to continue using DNA as a proxy to explore other parts of Antarctica with poorly understood climate histories. </p>
<p>There is a <a href="https://onlinelibrary.wiley.com/doi/10.1111/gcb.16356">wealth of information</a> on Antarctica’s recent and distant past also hidden in other types of biological data in moss beds and peat profiles, vertebrate animal colonies and living terrestrial and marine invertebrates. To date, very few of these biological archives have been brought into our understanding of Antarctica’s past climates. </p>
<p>As the world heats up at an unprecedented rate, we need to use these types of approaches to understand what else is likely to happen down on the ice. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/increasing-melting-of-west-antarctic-ice-shelves-may-be-unavoidable-new-research-216030">Increasing melting of West Antarctic ice shelves may be unavoidable – new research</a>
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<img src="https://counter.theconversation.com/content/218810/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sally Lau receives funding from the Australian Research Council (ARC). </span></em></p><p class="fine-print"><em><span>Jan Strugnell receives funding from the Australian Research Council (ARC), the Fisheries Research and Development Corporation (FRDC), the Department of Agriculture Water and the Environment through the National Environmental Science Program (NESP) and the Queensland Government through the Queensland Citizen Science Grants.</span></em></p><p class="fine-print"><em><span>Nerida Wilson receives funding from the Australian Research Council (ARC), Interact for Change and the Morris Animal Foundation (Wild Genomes).</span></em></p>Did the enormous West Antarctic Ice Sheet collapse the last time global temperatures were 1.5°C above preindustrial levels? The answer lay in the DNA of an octopus.Sally Lau, Postdoctoral Research Fellow, James Cook UniversityJan Strugnell, Professor Marine Biology and Aquaculture, James Cook UniversityNerida Wilson, Adjunct Senior Research Fellow, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2194352023-12-20T16:05:40Z2023-12-20T16:05:40ZCould dinosaurs be the reason humans can’t live for 200 years?<figure><img src="https://images.theconversation.com/files/565275/original/file-20231212-17-7baa92.jpg?ixlib=rb-1.1.0&rect=0%2C23%2C4000%2C2640&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/human-hand-compare-real-dinosaur-footprint-1205774944">Rattana/Shutterstock</a></span></figcaption></figure><p>All human beings age. It is part of our biology and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4010874/">limits our lifespan</a> to slightly over 120 years.</p>
<p>Not all animals <a href="https://www.sciencedirect.com/science/article/pii/S0925443917302193">experience ageing</a> during their lives. Some animals’ bodies do not gradually degenerate as they get older the way our bodies do.</p>
<p>But for humans once they reach about age 30 their <a href="https://www.smithsonianmag.com/smart-news/your-probability-of-dying-doubles-every-eight-years-180948228/">chance of dying</a> <a href="https://arxiv.org/PS_cache/q-bio/pdf/0411/0411019v3.pdf">doubles roughly</a> every eight years. So even if you are fortunate enough to become a centenarian, your chance of dying each year will be high. </p>
<p>This high mortality reflects numerous other health problems, such as <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2804956/#R4">loss of muscle mass</a> and general frailty, <a href="https://www.thieme-connect.de/products/ejournals/abstract/10.1055/s-0035-1555115">cognitive decline</a>, loss of vision and hearing and many other degenerative changes that characterise the <a href="https://www.ncbi.nlm.nih.gov/books/NBK10041/#:%7E:text=Aging%20is%20the%20time%2Drelated,disease%20(which%20affect%20individuals).">human ageing process</a>. </p>
<p>And the reason humans age so markedly may be due to the fact our ancestors evolved during the <a href="https://www.embopress.org/doi/full/10.15252/embr.202051617">time of the dinosaurs</a>.</p>
<p>Compared to other mammals, humans have a long life. We have the longest lifespan of all land-based mammals, and of all mammals <a href="https://news.liverpool.ac.uk/2015/01/06/scientists-sequence-genome-longest-lived-mammal/">only whales probably</a> outlive us. I say “probably” because you need to keep animals in captivity to do a detailed study on lifespan, which for whales is virtually impossible due to their size and longevity. </p>
<p>We know that species of whales and dolphins <a href="https://www.pnas.org/doi/10.1073/pnas.1903844116">exhibit menopause</a>, and all mammals show some form of reproductive decline with age. In fact, all studied mammals show physiological ageing and increased mortality with age, even if some species – like mice and voles – age much faster than others – such as humans, whales, and elephants. </p>
<p>But many species of reptiles, amphibians and fish do not show signs of ageing. <a href="https://genomics.senescence.info/species/nonaging.php">Examples include</a> turtles and tortoises, salamanders and rockfishes. </p>
<p>One study of 77 species of reptiles and amphibians published in Science in 2022 showed that age-related increases in mortality <a href="https://www.science.org/doi/10.1126/science.abm0151">are not seen</a> in many species of reptiles and amphibians. It is as if these animals do not age at all. Some of these animals, such as turtles, probably live longer than humans.</p>
<p>Perhaps if we study these apparently non-ageing species for long enough they will show signs of ageing. But good luck studying animals such as the <a href="https://www.science.org/doi/10.1126/science.aaf1703">Greenland shark</a>, which has been estimated to live nearly 400 years. </p>
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<p>For now we can at least say that among reptiles, amphibians and fish, some species not only live longer than the longest living mammals, but they age substantially slower. Besides, some of these non-ageing species grow throughout their lives, which means that older females <a href="https://www.sciencedirect.com/science/article/pii/S0531556500002424">lay more eggs</a>, again in stark contrast to what happens in mammals. </p>
<p>These animals die mainly from being eaten by predators and diseases. Indeed, most animals in the wild do not die of old age and, until the 20th century, of course, most people died of infectious diseases.</p>
<p>Some reptiles, amphibians and fish are also known for their <a href="https://www.mdpi.com/2221-3759/9/3/36">ability to regenerate</a> tissue. </p>
<h2>Pressure on mammals</h2>
<p>Amphibians evolved from fish about 370 million years ago, and about 50 million years later reptiles evolved from amphibians. <a href="https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Introductory_Biology_(CK-12)/12%3A_Vertebrates/12.07%3A_Vertebrate_Evolution">Mammals then evolved</a> from reptiles about 250-300 million years ago. </p>
<p>We are all products of evolution, which we see in relics such as <a href="https://www.biorxiv.org/content/10.1101/2021.09.14.460388v1">our tailbone</a>. Our evolutionary history can have a profound influence in modern times. For example, humans maintain evolutionary traits from when our ancestors roamed the savannah that are no longer fit for the modern world, from <a href="https://theconversation.com/the-science-of-sugar-why-were-hardwired-to-love-it-and-what-eating-too-much-does-to-your-brain-podcast-175272">craving sugar</a> to <a href="https://theconversation.com/how-morbid-curiosity-can-lead-people-to-conspiracy-theories-214532">behaviour</a> that leads to prejudices. </p>
<p>About 200 million years ago, massive volcanic eruptions <a href="https://www.britannica.com/science/end-Triassic-extinction">wiped out 76%</a> of marine and land species. Afterwards, the dinosaurs became the dominant predators in the land. To survive and avoid being hunted to extinction by dinosaurs, mammals became small, nocturnal and short-lived. </p>
<p>Our ancestors of this time were not like us at all. They were more like <a href="https://www.livescience.com/60888-rat-creatures-were-earliest-eutherian-mammal-ancestors.html">voles and mice</a>, small animals going out in the dark to catch insects. Under the pressure from the dinosaurs, ancestral mammals had to reproduce rapidly, just like mice and rats do now. And just like mice, rats and voles, our ancestors had short lifespans. </p>
<p>For 100 million years, during the time of the dinosaurs, mammals were at or near the bottom of the food chain. Mammals were more often prey than predators. During this time there was no reason for mammals to keep processes and genes related to long life, such as DNA repair and tissue regeneration systems. </p>
<p>My <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/bies.202300098">longevity bottleneck hypothesis</a> proposes that repair and regeneration systems were lost, mutated or inactivated by the evolution of early mammals. This imposed biological constraints that shape how mammals age to this day. </p>
<p>After the dinosaurs disappeared when an asteroid hit the Earth <a href="https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html">66 million years</a> ago, mammals conquered the world. An astonishing diversity of species evolved with a variety of lifespans. Some species, like humans, evolved a long lifespan, but they may have done it under constraints, remnants from the time of the dinosaurs.</p>
<h2>Why dinosaurs made a difference</h2>
<figure class="align-center ">
<img alt="Lizard rests on the ground" src="https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=362&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=362&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=362&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=455&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=455&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564332/original/file-20231207-15-xjtuw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=455&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Tuatara lives for over a hundred years.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/tuatara-310936394">BeautifulBlossoms/Shutterstock</a></span>
</figcaption>
</figure>
<p>We can take a guess by looking at species that did not undergo the same evolutionary pressures as early mammals. For example, the tuatara, a reptile endemic to New Zealand, may look like a lizard but it diverged from snakes and lizards about 250 million years ago. It is sometimes referred to as a “living fossil”, due to its slow evolution. </p>
<p>Tuataras are thought to live for more than 100 years and age much slower than human beings, as a <a href="https://www.science.org/doi/10.1126/science.abm0151">2022 DNA analysis study showed</a>. Perhaps they have kept their anti-ageing genes, unlike even the longest lived mammals. </p>
<p>Our lifespan may be limited because of our evolutionary history.</p><img src="https://counter.theconversation.com/content/219435/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joao Pedro de Magalhaes receives funding from the Wellcome Trust, Longevity Impetus Grants, LongeCity, and the Biotechnology and Biological Sciences Research Council.</span></em></p>Our mammal ancestors evolved to compete with dinosaurs but may have lost something in the process.Joao Pedro de Magalhaes, Chair of Molecular Biogerontology, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2199612023-12-20T00:06:41Z2023-12-20T00:06:41Z19-million-year-old fossil jaw bone hints the biggest whales first evolved somewhere unexpected<figure><img src="https://images.theconversation.com/files/566527/original/file-20231219-15-u7qnu9.jpg?ixlib=rb-1.1.0&rect=68%2C0%2C1773%2C1279&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The baleen whale fossil at Museums Victoria Research Institute.</span> <span class="attribution"><span class="source">Eugene Hyland, Museums Victoria</span></span></figcaption></figure><p>Baleen whales are the titans of the ocean, the largest animals to have ever lived. The record holder is the blue whale (<em>Balaenoptera musculus</em>), which can reach <a href="https://www.worldwildlife.org/stories/meet-the-biggest-animal-in-the-world">lengths of up to 30 metres</a>. That’s longer than a basketball court.</p>
<p>However, throughout their evolutionary history, most baleen whales <a href="https://www.science.org/content/article/why-whales-grew-such-monster-sizes">were relatively much smaller</a>, around five metres in length. While still big compared to most animals, for a baleen whale that’s quite small.</p>
<p>However, new fossil discoveries from the Southern Hemisphere are beginning to disrupt this story. The latest is an unassuming fossil from the banks of the Murray River in South Australia.</p>
<p>Roughly 19 million years old, this fossil is the tip of the lower jaws (or “chin”) of a baleen whale estimated to be around nine metres in length, which makes it the new record holder from its time. This find has been published today in the journal <a href="https://doi.org/10.1098/rspb.2023.2177">Proceedings of the Royal Society B: Biological Sciences</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of a whale with a piece of yellow bone superimposed on its lower jaw" src="https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566189/original/file-20231218-23-ajfj29.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The roughly 19-million-year-old fossil ‘chin’ bone superimposed on a Murray River whale illustration.</span>
<span class="attribution"><span class="source">Art by Ruairidh Duncan</span></span>
</figcaption>
</figure>
<h2>What are baleen whales?</h2>
<p>Most mammals have teeth in their mouth. Baleen whales are a strange exception. While <a href="https://theconversation.com/ancient-whales-had-more-bite-than-todays-gentle-giants-82907">their ancestors had teeth</a>, today’s baleen whales instead have baleen – a large rack of fine, hair-like keratin used to filter out small krill from the water.</p>
<p>This structure enabled baleen whales to feed efficiently on <a href="https://www.scientificamerican.com/article/why-are-blue-whales-so-gigantic/">enormous shoals of tiny zooplankton</a> in productive parts of the ocean, which facilitated the evolution of larger and larger body sizes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of a large dark humpback whale with its mouth open, showing off what looks like a solid filter at the top of its mouth" src="https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=325&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=325&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=325&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=408&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=408&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566194/original/file-20231218-21-bvvl3z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=408&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The bristle-like baleen, as shown on a humpback whale.</span>
<span class="attribution"><span class="source">Art by Ruairidh Duncan</span></span>
</figcaption>
</figure>
<h2>The ‘missing years’ of whale evolution</h2>
<p>Various groups of <a href="https://www.telegraph.co.uk/news/2023/08/02/whale-heaviest-animal-ever-lived-perucetus-colossus/">toothed whales</a> terrorised the ocean for millions of years, including some that were the <a href="https://theconversation.com/ancient-ancestors-of-modern-baleen-whales-were-toothy-not-so-gentle-giants-96338">ancestors of the toothless baleen whales</a>. Yet at some time between 23 and 18 million years ago these ancient “toothed baleen whales” went extinct.</p>
<p>We aren’t exactly sure when, as fossil whales from this episode in Earth’s history <a href="https://museumsvictoria.com.au/media-releases/mystery-of-whale-fossil-dark-age-solved-in-new-palaeontology-research/">are exceedingly rare</a>. What we do know is immediately after this gap in the whale fossil record, only the relatively small, toothless ancestors of baleen whales remained. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dark silhouette of a whale next to a smaller figure of a whale and even smaller human figure" src="https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566198/original/file-20231218-25-dshb8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The newly described extinct Murray River whale (9 metres) next to a fin whale (26 metres) and a human diver (2 metres).</span>
<span class="attribution"><span class="source">Art by Ruairidh Duncan, graphic by Rob French</span></span>
</figcaption>
</figure>
<p>Scientists previously thought baleen whales kept to relatively small proportions until the ice ages (which began from about 3–2.5 million years ago). But the majority of research on trends in the evolutionary history of whales is based on the reasonably well-explored fossil record from the Northern Hemisphere – a notable bias that likely shaped these theories.</p>
<p>Crucially, new fossil finds from the Southern Hemisphere are starting to show us that at least down south, whales got bigger much earlier than previous theories suggest.</p>
<h2>An unexpected find</h2>
<p>More than 100 years ago, palaeontologist Francis Cudmore found the very tips of a large pair of fossil whale jaws eroding out of the banks of the Murray River in South Australia. These 19-million-year-old fossils made their way to Museums Victoria and remained unrecognised in the collection until they were rediscovered in a drawer by one of the authors, Erich Fitzgerald.</p>
<p>Using equations derived from measurements of modern-day baleen whales, we predicted the whale this fossilised “chin” came from was approximately nine metres long. The previous record holder from this early period of whale evolution was only six metres long.</p>
<p>Together with <a href="https://www.nationalgeographic.co.uk/animals/2019/05/fossil-of-85-foot-blue-whale-is-largest-ever-discovered">other fossils</a> from Peru in South America, this suggests larger baleen whales may have emerged much earlier in their evolutionary history and the large body size of whales evolved gradually over many more millions of years than previous research suggested.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artist's reconstruction of the extinct whale, showing where the fossil is located, and a map of Australia showing the location it was found" src="https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566195/original/file-20231218-30-l3q7vz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The fossilised baleen whale ‘chin’ was found along the banks of the Murray River in South Australia.</span>
<span class="attribution"><span class="source">Art by Ruairidh Duncan, photo by Eugene Hyland</span></span>
</figcaption>
</figure>
<h2>The Southern Hemisphere as the cradle of gigantic whale evolution</h2>
<p>The large whale fossils from Australasia and South America seem to suggest that for most of the evolutionary history of baleen whales, whenever a large baleen whale shows up in the fossil record, it is in the Southern Hemisphere.</p>
<p>Strikingly, this pattern persists despite the fact the Southern Hemisphere contains less than 20% of the known fossil record of baleen whales. While this is an unexpectedly strong signal from our research, it doesn’t come as a complete surprise when we consider living baleen whales.</p>
<p>Today, the temperate seas of the Southern Hemisphere are connected by the chilly Southern Ocean, which surrounds Antarctica and is <a href="https://niwa.co.nz/productivity-of-the-southern-ocean-antarctica">extremely productive</a>, supporting the greatest biomass of marine megafauna on Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph, showing that baleen whales in the Southern Hemisphere were larger than Northern Hemisphere whales throughout most of the last 23 million years" src="https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566197/original/file-20231218-19-6xezc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fossils from the Southern Hemisphere, including the Murray River whale fossil, are demonstrating that whales may have evolved large body sizes first in the Southern Hemisphere.</span>
<span class="attribution"><span class="source">Art by Ruairidh Duncan</span></span>
</figcaption>
</figure>
<p>Around the time baleen whales started evolving from big to gigantic, the strength of the Antarctic Circumpolar Current was intensifying, eventually leading to the present day powerhouse Southern Ocean. </p>
<p>Today, baleen whales are ecosystem engineers, their huge bodies consuming tremendous amounts of energy. <a href="https://oceanservice.noaa.gov/facts/whale-fall.html">Upon death</a>, these whales provide an abundance of nutrients to deep-sea ecosystems.</p>
<p>As we learn more about the evolutionary history of whales, such as when and where their large size evolved, we can begin to understand just how ancient their role in the ocean ecosystem may have been and how it could shift in tune with global climate change.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-true-origins-of-the-worlds-smallest-and-weirdest-whale-208279">The true origins of the world's smallest and weirdest whale</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/219961/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Patrick Rule currently receives funding from an Engineering and Physical Sciences Research Council UKRI Fellowship, and previously received funding from an Australian Research Council Discovery Project.</span></em></p><p class="fine-print"><em><span>Erich Fitzgerald received funding from an Australian Research Council Linkage Project that supported part of this research.</span></em></p>A newly described fossil from South Australia is making waves in our understanding of where and when whales evolved titanic body sizes.James Patrick Rule, Research Affiliate, Monash UniversityErich Fitzgerald, Senior Curator, Vertebrate Palaeontology, Museums Victoria Research InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2196692023-12-13T19:01:44Z2023-12-13T19:01:44ZHuman intelligence: how cognitive circuitry, rather than brain size, drove its evolution<figure><img src="https://images.theconversation.com/files/565513/original/file-20231213-20-grbqn0.png?ixlib=rb-1.1.0&rect=25%2C33%2C2779%2C1837&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">wikipedia/Foley</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It’s one of the great paradoxes of evolution. Humans have demonstrated that having <a href="https://theconversation.com/why-do-humans-have-such-large-brains-our-study-suggests-ecology-was-the-driving-force-96873">large brains</a> are key to our evolutionary success, and yet such brains are extremely rare in other animals. Most get by on tiny brains, and don’t seem to miss the extra brain cells (neurons). </p>
<p>Why? The answer that most biologists have settled on is that large brains are costly in terms of the energy they require to run. And, given the way natural selection works, the benefits <a href="https://pubmed.ncbi.nlm.nih.gov/9234964/">simply don’t exceed the costs</a>. </p>
<p>But is it just a matter of size? Does the way our brains are laid out also affect their costs? A new study, <a href="http://www.science.org/doi/10.1126/sciadv.adi7632">published in Science Advances</a>, has produced some intriguing answers. </p>
<p>All our organs have running costs, but <a href="https://www.jstor.org/stable/2744104">some are cheap and others expensive</a>. Bones, for example, are relatively cheap. Although they make up around 15% of your weight, they only use 5% of your metabolism. Brains are at the other end of the spectrum, and at about 2% of typical human body weight, running them uses around 20% of our metabolism. And this without doing any conscious thinking – it even happens when we’re asleep.</p>
<p>For most animals, the benefits of serious thinking are simply not worth it. But for some reason – the greatest puzzle in human evolution, perhaps – humans found ways to overcome the costs of having a larger brain and reap the benefits.</p>
<p>All this is fairly well known, but there is a more tantalising question. Certainly humans have to bear the greater costs of our brains because they are so large, but are there different costs because of the special nature of our cognition? Does thinking, speaking, being self-conscious or doing sums cost more than typical day-to-day animal activities?</p>
<p>It’s not an easy question to answer, but the team behind the new study, led by Valentin Riedl of the Technical University of Munich, Germany, have risen to the challenge. </p>
<p>The authors had a number of known points to start with. The basic design and structure of neurons is much the same across the brain – and across species. The neuronal density is also the same for humans and other primates, so these are unlikely to be the driver of intelligence. If they were, some animals with large brains such as orcas and elephants would likely be smarter than humans.</p>
<figure class="align-center ">
<img alt="Elephant and woman in village Surin Thailand." src="https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565485/original/file-20231213-19-jr94u6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Elephants have larger brains than humans.</span>
<span class="attribution"><span class="source">venusvi/Shutterstock</span></span>
</figcaption>
</figure>
<p>They also knew that across human evolution, the neocortex – the largest part of the outermost layer of the brain, known as cerebral cortex – has expanded at a greater rate than other parts. This region, which involves the prefrontal cortex, is responsible for tasks involving attention, thought, planning, perception and episodic memory – all needed for higher cognitive function.</p>
<p>These two observations led them to investigate whether there are different costs of signalling across different regions of the brain.</p>
<p>The team scanned the brains of 30 people using a technique that could simultaneously measure glucose metabolism (a measure of energy consumption) and the level of signalling across the cortex. They could then look at the correlation between these two elements and see whether different parts of the brain used different levels of energy – and if so how. </p>
<h2>Surprising findings</h2>
<p>Neurobiologists will surely ponder and explore the fine details of the results, but from an evolutionary point of view, they are thought-provoking. What they found is that the difference in energy consumption between different areas of the brain is big. Not all bits of the brain are equal, energetically speaking.</p>
<p>Not only that, but the parts of the human brain that have expanded most had higher costs than expected. The neocortex in fact demanded around 67% more energy than sensorimotor networks per gram of tissue. </p>
<p>This means that during the course of human evolution, not only did the metabolic costs of our brains go up as they became larger, but they did so at an accelerating rate as the neocortex expanded faster than the rest of the brain. </p>
<p>Why should that be the case? A neuron is a neuron, after all. The neocortex relates directly to higher cognitive function. </p>
<p>The signals sent across this area are mediated through brain chemicals such as serotonin, dopamine and noradrenaline (neuromodulators), which create circuits in the brain to help maintain a general level of excitement (in a neurological sense of the word meaning being awake, not having fun). These circuits, which regulate some brain areas more than others, control and modify the ability of neurons across the brain to communicate with each other.</p>
<p>In other words, they keep the brain active for memory storage and thinking – a generally higher level of cognitive activity. Not surprisingly, perhaps, the higher level of activity involved in our advanced cognition comes at a higher energetic cost.</p>
<p>Ultimately then, it seems the human brain evolved to such advanced levels of cognition not just because we have large brains, nor even just because certain areas of our brain grew disproportionately big, but because – at a cost – the connectivity improved.</p>
<p>Many animals with large brains, such as elephants and orcas, are highly intelligent. But it seems it is possible to have a large brain without developing the “right” circuitry for human-level cognition.</p>
<p>The results help us understand why larger brains are so rare. A larger brain can enable more complex cognition to evolve. It is not just a matter of scaling up brains and energy at the same rate though, but taking on additional costs.</p>
<p>This doesn’t really answer the ultimate question – how did humans manage to break through the brain-energy ceiling? As so often in evolution, the answer must lie in ecology, the ultimate source of energy. To grow and maintain a large brain – whatever social, cultural, technological or other things it is used for – <a href="https://royalsocietypublishing.org/doi/10.1098/rstb.1991.0111">requires a dependable and high quality diet</a>.</p>
<p>To learn more, we need to explore the last million years, the period when our ancestors’ brains really expanded, to investigate this interface between energy expenditure and cognition.</p><img src="https://counter.theconversation.com/content/219669/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The human brain uses up 20% of the energy we consume.Robert Foley, Emeritus Professor of Human Evolution, University of CambridgeMarta Mirazon Lahr, Professor of Human Evolutionary Biology & Director of the Duckworth Collection, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2185682023-12-13T12:41:22Z2023-12-13T12:41:22ZSocial isolation and loneliness linked to poor health – our study could help explain why<figure><img src="https://images.theconversation.com/files/563987/original/file-20231206-30728-3itee.jpg?ixlib=rb-1.1.0&rect=57%2C74%2C5452%2C3593&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/sad-smiley-drawn-by-hand-on-2107775873">ERIK Miheyeu/Shutterstock</a></span></figcaption></figure><p>Numerous studies have shown that social isolation and loneliness are associated with an <a href="https://protect-eu.mimecast.com/s/lJnICBN5VhvJA8ztzCXXn">increased risk of early death</a>, on a scale comparable to other known risk factors such as smoking and obesity. This year, the US surgeon general declared social isolation and loneliness to be a <a href="https://www.hhs.gov/sites/default/files/surgeon-general-social-connection-advisory.pdf">significant public health concern</a>.</p>
<p>But scientists are still trying to untangle the physical processes behind the relationship. Our team’s <a href="https://www.sciencedirect.com/science/article/pii/S0889159123003562">recent study</a> showed that social isolation and loneliness seem to be associated with higher levels of inflammation, which goes hand in hand with many health problems.</p>
<p>Researchers have argued that a desire for social connection –- and, conversely, an aversion to social disconnection –- is <a href="https://www.sciencedirect.com/science/article/abs/pii/S0092656606000055">part of our evolutionary heritage</a>. As a species, humans are not particularly big, strong or fast, but we are highly social, and our ancestors’ chances of survival and reproductive success would have relied on the principle of safety in numbers. Being cut off from the social group represents a threat to your safety. </p>
<p>The immune system is one of several processes in the body that come into play under this scenario. A lone individual without the protection of a social group would be at greater risk of injury, and it therefore makes sense that the immune system would respond by preparing itself to battle off infection. This inflammatory response protects you in the short term. However, it is not ideal for your body to be in this stressed state for a prolonged period, and it could <a href="https://www.nature.com/articles/s41591-019-0675-0">exert a toll on your physical health over time</a>. </p>
<p>In <a href="https://www.sciencedirect.com/science/article/pii/S0889159123003562">our study published in November 2023</a> in the journal Brain, Behavior, and Immunity, we investigated the associations of social isolation and loneliness with markers of inflammation. Social isolation and loneliness are not the same thing. The former is an objective measure of your social connections, and the latter an emotion that can be experienced even when surrounded by other people. Both can have implications for mental and physical health.</p>
<p>In this study, we used data from three studies. Each of them had data on social isolation, loneliness and inflammation. Two of these studies followed participants from early childhood through to adulthood. This enabled us not only to test whether shortcomings in early social relationships foreshadowed increased inflammation later in life, but also to check whether any effects we found in one sample could be replicated in another sample.</p>
<p>We looked at three different markers of inflammation. Two of these, a protein made in the liver called <a href="https://www.mayoclinic.org/tests-procedures/c-reactive-protein-test/about/pac-20385228">C-Reactive Protein</a> (CRP) and a type of protein involved in immune regulation called <a href="https://www.sciencedirect.com/topics/neuroscience/interleukin-6">Interleukin-6</a> (IL-6) have been used extensively in medical research. The third, a protein called <a href="https://pubmed.ncbi.nlm.nih.gov/34925360/">Soluble Urokinase Plasminogen Activator Receptor (suPAR)</a>, is a recently identified biomarker that research suggests is useful as an indicator of chronic (as opposed to acute) inflammation.</p>
<p>Our findings indicated that social isolation in childhood was correlated with all three markers of inflammation in adulthood, both at the ages of 18 and 45. When we controlled for factors such as smoking and body mass index – which could be alternative explanations for these associations – we found that social isolation remained specifically associated with elevated suPAR. </p>
<figure class="align-center ">
<img alt="Man sitting alone in park under a tree" src="https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564212/original/file-20231207-23-am6op0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Loneliness also seems to be associated with ill health.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/man-sitting-alone-on-park-bench-1669176061">Vladiri/Shutterstock</a></span>
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</figure>
<p>This finding was replicated in both of the longitudinal studies. We also found that living alone was associated with elevated inflammation (particularly suPAR) among patients in a clinical sample.</p>
<p>Loneliness was also associated with inflammation, although the pattern was less consistent. There was a correlation between loneliness and elevated suPAR in mid-life. But, in early adulthood (age 18), loneliness was associated with lower CRP. The latter, somewhat counter-intuitive finding, is harder to interpret, but it may reflect the fact that lonelier 18 year-olds are less likely to be socialising and <a href="https://pubmed.ncbi.nlm.nih.gov/34821551/#:%7E:text=Infectious%20diseases%2C%20particularly%20those%20caused,carry%20out%20large%20contact%20surveys.">coming into contact with pathogens</a>.</p>
<h2>Towards a more connected future</h2>
<p>Our findings highlight*<em>suggest</em>* that social isolation experienced in childhood can foreshadow health issues decades later. Social connection is not just rewarding in its own right – there is now an abundance of research showing that social health goes hand-in-hand with <a href="https://pubmed.ncbi.nlm.nih.gov/29684289/">mental</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/23530191/">physical</a> health. We often talk about social isolation as something mostly experienced by older adults. But, as our study shows, it is a problem for people of all ages. </p>
<p>Studying the way our social world intertwines with our biological world can help us unravel the complex web of factors that shapes long-term health.</p>
<p>This body of research shows us how important it is to think about how we can intervene to spare lonely and isolated young people from negative long-term health outcomes. To address this issue, we need to think about what it means to be “socially connected” in a world in which everyone is, seemingly, always connected to each other through digital media. Modern technology has the potential to be <a href="https://theconversation.com/does-social-media-make-us-more-or-less-lonely-depends-on-how-you-use-it-128468">a force for both good and bad</a> when it comes to social health, and we must think carefully about what role it has to play in tackling isolation and loneliness in society.</p><img src="https://counter.theconversation.com/content/218568/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Inflammation could be the missing puzzle piece.Timothy Matthews, Lecturer in Psychology, University of GreenwichLine Jee Hartmann Rasmussen, Senior researcher of Psychology and Neuroscience, Duke UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2161482023-12-11T13:12:05Z2023-12-11T13:12:05ZWhy do people have wisdom teeth?<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do people have wisdom teeth? – Jack J., age 17, Dedham, Massachusetts</strong></p>
</blockquote>
<hr>
<p>Wisdom teeth are the third set of molars located at the very back of the mouth. They look just like the first and second molars, but can sometimes be a little smaller. </p>
<p>They are commonly called wisdom teeth because they are the last of the 32 permanent teeth to appear, emerging <a href="https://doi.org/10.1159/000151214">between 17 and 25 years of age</a>, when you are older and wiser.</p>
<p>You might know that <a href="https://doi.org/10.7717/peerj.10367">not everyone grows</a> all four wisdom teeth. You might also know many people get them pulled. So it’s fair to wonder – why do humans even have them? </p>
<p><a href="https://scholar.google.com/citations?hl=en&user=0lZq0kYAAAAJ">We</a> <a href="https://scholar.google.com/citations?hl=en&user=GYMrNdIAAAAJ">study</a> teeth and can tell you the answer has a lot to do with the distant past – and a bit about the present day, too. </p>
<h2>More powerful jaws</h2>
<p>Just like you have many features in common with the people you’re related to, humans share features with their extended family – the primates. <a href="https://doi.org/10.3389/fdmed.2023.1158482">Monkeys, gorillas and chimpanzees</a> all have wisdom teeth. </p>
<p>A few million years ago, early human ancestors had larger jaws and teeth than humans do today. For example, a species called <em>Australopithecus afarensis</em>, <a href="https://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis">nicknamed Lucy’s species</a> after a <a href="https://www.nature.com/scitable/knowledge/library/lucy-a-marvelous-specimen-135716086/">famous fossil specimen called Lucy</a>, lived roughly 3 million to 4 million years ago. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A fossilized jaw showing powerful molars and some broken and missing front teeth." src="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A fossilized jaw from the extinct human ancestor, <em>Australopithecus afarensis</em>, also known as Lucy’s species.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Australopithecus_afarensis_jaw_-_Fossils_in_the_Arppeanum_-_DSC05509.JPG">Daderot/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The jaw and teeth of an <em>Australopithecus afarensis</em> individual were quite a bit <a href="https://doi.org/10.1002/ajpa.21183">larger and thicker</a> than your own. They had three <a href="https://doi.org/10.1007/s12052-010-0249-6">big molar teeth with thick enamel</a>. The fossil skulls of some of these very early humans also show evidence of <a href="https://doi.org/10.1002/ajpa.21183">powerful chewing muscles</a>.</p>
<h2>Changes in diet</h2>
<p>Scientists think more robust jaws and teeth were needed because the foods early human ancestors ate, like raw meat and <a href="https://doi.org/10.1016/j.jhevol.2017.10.013">plants</a>, were much more difficult to chew than food is today. Researchers look at things like <a href="https://doi.org/10.1038/sj.bdj.2014.353">marks and microscopic wear patterns</a> <a href="https://theconversation.com/tooth-be-told-millions-of-years-of-evolutionary-history-mark-those-molars-71428">on fossilized teeth</a> to figure out <a href="https://press.princeton.edu/books/hardcover/9780691160535/evolutions-bite">what extinct ancestors may have eaten</a>. </p>
<p>Today’s food is much softer than it was in the past due to many factors, including <a href="https://doi.org/10.1111/joim.13011">agriculture</a>, <a href="https://doi.org/10.1007/s12110-009-9075-3">cooking</a> and <a href="https://doi.org/10.1038/nplants.2016.194">food storage</a>. Softer, easier-to-chew food means teeth have a less challenging job. As a result, modern human jaws have evolved to be <a href="https://doi.org/10.1038/s41559-019-0865-7">smaller and faces to be flatter</a> than our extinct ancestors’ were, because our meals don’t require the same big, sharp teeth that theirs did. </p>
<p>Given these changes, which took place very slowly over millions of years, the third molars – wisdom teeth – might not be as important now as they once were.</p>
<h2>Missing wisdom teeth</h2>
<p>About <a href="https://www.ncbi.nlm.nih.gov/books/NBK572295/">25% of people today are missing at least</a> one wisdom tooth completely, meaning it never formed at all. While people occasionally don’t grow other teeth, it’s <a href="https://pubmed.ncbi.nlm.nih.gov/34292692/">much more common for wisdom teeth</a>. </p>
<p>Scientists are not sure why this is the case, but it <a href="https://doi.org/10.1007/s11914-022-00761-8">may have to do with the genes</a> <a href="https://doi.org/10.3390/genes9050255">you inherit from your parents</a>. Some scientists have argued that the <a href="https://doi.org/10.1093/ejo/cjad057">lack of wisdom teeth is an advantage</a> for modern, smaller-jawed humans. It’s certainly easier to fit fewer teeth into a smaller jaw.</p>
<p>Sometimes, due to lack of space, wisdom teeth can get stuck inside the jawbone and never fully come up – or they only partially emerge. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A radiograph showing a back molar growing sideways into its neighbor." src="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An impacted wisdom tooth will never come up properly.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Impacted_Wisdom_Tooth_aka_Lower_Right_Third_Molar_48_RVG_IOPA_Xray.jpg">Nizil Shah/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>A so-called impacted wisdom tooth happens <a href="https://pubmed.ncbi.nlm.nih.gov/2205795/">more often in the lower jaw</a> than in the upper jaw. In cases where wisdom teeth are only partially up, people can sometimes experience pain, tooth decay or gum inflammation, which is why they have them pulled by a dentist.</p>
<p>But wisdom teeth don’t usually need to be removed if they are fully erupted in the mouth, positioned correctly and healthy.</p>
<p>Dentists can examine your mouth to see if your wisdom teeth are present, or look at X-ray pictures of your jaw if these last molars haven’t yet emerged and you suspect they may be impacted.</p>
<p>Dentists can also advise you if any treatment – or removal – is recommended for your wisdom teeth. In the meantime, <a href="https://www.mouthhealthy.org/all-topics-a-z/brushing-your-teeth">brushing</a> at least twice a day and <a href="https://www.mouthhealthy.org/all-topics-a-z/flossing">flossing</a> daily will help keep all your teeth healthy. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/216148/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ariadne Letra receives funding from the National Institute for Dental and Craniofacial Research.</span></em></p><p class="fine-print"><em><span>Seth M. Weinberg receives funding from the National Institutes of Health. </span></em></p>Two dental experts explain that these furthest-back molars may be a not-so-necessary leftover from early human evolution.Ariadne Letra, Professor of Dental Medicine, University of PittsburghSeth M. Weinberg, Professor of Oral and Craniofacial Sciences and Human Genetics, University of PittsburghLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2172862023-11-29T23:11:39Z2023-11-29T23:11:39ZNew unified theory shows how past landscapes drove the evolution of Earth’s rich diversity of life<p>Earth’s surface is the living skin of our planet – it connects the physical, chemical and biological systems.</p>
<p>Over geological time, this surface evolves. Rivers fragment the landscape into an environmentally diverse range of habitats. These rivers also transfer sediments from the mountains to the continental plains and ultimately the oceans. </p>
<p>The idea that landscapes have influenced the trajectory of life on our planet has a long history, dating back to the early 19th century scientific narratives of German polymath <a href="https://learningfromlandscapes.com/2019/06/11/humboldt-the-invention-of-nature/">Alexander von Humboldt</a>. While we’ve learnt more since then, many aspects of biodiversity evolution remain enigmatic. For example, it’s still unclear why there is a 100-million-year gap between the explosion of marine life and the development of plants on continents.</p>
<p>In research <a href="https://www.nature.com/articles/s41586-023-06777-z">published in Nature</a> today, we propose a new theory that relates the evolution of biodiversity over the past 540 million years to sediment “pulses” controlled by past landscapes.</p>
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<h2>10 years of computational time</h2>
<p>Our simulations are based on an open-source code released as part of a <a href="https://theconversation.com/scientists-just-revealed-the-most-detailed-geological-model-of-earths-past-100-million-years-200898">Science paper</a> published earlier this year.</p>
<p>To drive the evolution of the landscape through space and time in our computer model, we used a series of reconstructions for what the climate and tectonics were like in the past.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two colourful computer simulated Earth globes side by side" src="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=291&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=291&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=291&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=365&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=365&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=365&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These two globes from our simulation show landscapes 200 million years ago (just before the Pangea supercontinent broke up, left) and 15 million years ago (right), after the formation of the Andes, Alps and Himalayas.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>We then compared the results of our global simulations with reconstructions of marine and continental biodiversity over the past 540 million years.</p>
<p>To perform our computer simulations, we took advantage of Australia’s <a href="https://nci.org.au/">National Computational Infrastructure</a> running on several hundreds of processors. The combined simulations presented in our study are equivalent to ten years of computational time.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-the-earths-last-supercontinent-broke-apart-to-form-the-world-we-have-today-131632">How the Earth's last supercontinent broke apart to form the world we have today</a>
</strong>
</em>
</p>
<hr>
<h2>Marine life and river sediment were closely linked</h2>
<p>In our model, we discovered that the more sediment rivers carried into the oceans, the more the sea life diversified (a positive correlation). You can see this tracked by the red line in the chart below. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=222&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=222&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=222&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=279&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=279&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=279&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Reconstructed sediment fluxes to the oceans (red line) versus diversity of marine animals (black line, adapted from C. Bentley using Sepkoski’s compendium) from the Cambrian through to the Neogene.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>As the continents weather, rivers don’t just carry sediment into the oceans, they also bring a large quantity of nutrients. These nutrients, such as carbon, nitrogen and phosphorus, are essential to the <a href="https://www.britannica.com/science/biogeochemical-cycle">biological cycles</a> that move vital elements through all living things.</p>
<p>This is why we think rivers delivering more or less nutrients to the ocean – on a geological timescale of millions of years – is related to the diversification of marine life.</p>
<p>Perhaps even more surprisingly, we found that episodes of mass extinctions in the oceans happened shortly after significant decreases in sedimentary flow. This suggests that a lack or deficiency of nutrients can destabilise biodiversity and make it vulnerable to catastrophic events (like asteroid impacts or volcanic eruptions).</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-a-mass-extinction-and-are-we-in-one-now-122535">What is a 'mass extinction' and are we in one now?</a>
</strong>
</em>
</p>
<hr>
<h2>Landscapes also drove the diversity of plants</h2>
<p>On the continents, we designed a variable that integrates sediment cover and landscape ruggedness to describe the continents’ capacity to host diverse species. </p>
<p>Here we also found a striking correlation (see below) between our variable and plant diversification for the past 400 million years. This highlights how changes in landscape also have a strong influence on species diversifying on land. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=232&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=232&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=232&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=291&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=291&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=291&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sediment cover in continental regions (black line) versus the long-term trend in land-plant diversity. Illustrations from Rebecca Horwitt.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>We hypothesise that as Earth’s surface was gradually covered with thicker soil, richer in nutrients deposited by rivers, plants could develop and diversify with more elaborate root systems. </p>
<p>As plants slowly expanded across the land, the planet ended up hosting varied environments and habitats with favourable conditions for plant evolution, such as the emergence of flowering plants some 100 million years ago.</p>
<h2>A living planet</h2>
<p>Overall, our findings suggest the diversity of life on our planet is strongly influenced by landscape dynamics. At any given moment, Earth’s landscapes determine the maximum number of different species continents and oceans can support.</p>
<p>This shows it’s not just tectonics or climates, but their interactions that determine the long-term evolution of biodiversity. They do this through sediment flows and changes to the landscapes at large.</p>
<p>Our findings also show that biodiversity has always evolved at the pace of plate tectonics. That’s a pace incomparably slower than the current rate of extinction caused by human activity.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-ways-you-can-help-stop-biodiversity-loss-in-your-area-and-around-the-world-196746">Five ways you can help stop biodiversity loss in your area – and around the world</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/217286/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This research was undertaken with resources from the National Computational Infrastructure supported by the Australian Government and from Artemis HPC supported by the University of Sydney. This work was supported by an Australian Research Council grant.</span></em></p><p class="fine-print"><em><span>Beatriz Hadler Boggiani, Laurent Husson, and Manon Lorcery do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>For decades, scientists have tried to uncover the cause of long-term changes in Earth’s biodiversity. New simulations point at geography playing a critical role.Tristan Salles, Senior Lecturer, University of SydneyBeatriz Hadler Boggiani, PhD Candidate, University of SydneyLaurent Husson, Earth sciences researcher, Université Grenoble Alpes (UGA)Manon Lorcery, PhD Candidate, Université Grenoble Alpes (UGA)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2152222023-11-21T13:27:15Z2023-11-21T13:27:15ZClimate change is already forcing lizards, insects and other species to evolve – and most can’t keep up<figure><img src="https://images.theconversation.com/files/558259/original/file-20231108-29-upppm0.jpg?ixlib=rb-1.1.0&rect=2%2C2%2C1615%2C1069&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Temperature sensitivity makes western fence lizards vulnerable to climate change.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/blmoregon/47961427128">Greg Shine/BLM</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Climate change is threatening the survival of plants and animals around the globe as temperatures rise and habitats change.</p>
<p>Some species have been able to meet the challenge with rapid evolutionary adaptation and other changes in behavior or physiology. Dark-colored dragonflies are <a href="https://doi.org/10.1073/pnas.2101458118">getting paler</a> in order to reduce the amount of heat they absorb from the sun. Mustard plants are <a href="https://doi.org/10.1098/rspb.2012.1051">flowering earlier</a> to take advantage of earlier snowmelt. Lizards are <a href="https://doi.org/10.1098/rsbl.2020.0625">becoming more cold-tolerant</a> to handle the extreme variability of our new climate.</p>
<p>However, scientific studies show that climate change is occurring much faster than species are changing.</p>
<figure class="align-center ">
<img alt="A tiny, royal blue fish with gold stripes looks into the camera. The downward slant of its mouth and shadow at the top of its eye give it an annoyed look." src="https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&rect=8%2C8%2C5599%2C3724&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558243/original/file-20231108-23-xs3oy9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Zebrafish have evolved to thrive in water a degree or so warmer than normal, but they struggle to survive at higher temperatures.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/brachydanio-rerio-royalty-free-image/154930602?adppopup=true">isoft/E+ Getty Images</a></span>
</figcaption>
</figure>
<h2>What is evolutionary adaptation?</h2>
<p>The word “adaptation” is used in many ways by climate scientists, but it has a very specific meaning to biologists: It refers to genetic changes that are passed on from one generation to the next and improve a species’ ability to survive in its environment.</p>
<p>These genetic modifications make evolutionary adaptation different from “acclimation” or “acclimatization,” which involve advantages that are not passed on to offspring. For example, when people move to high-altitude cities, they <a href="http://dx.doi.org/10.1136/bjsports-2013-092840">start producing more red blood cells</a> as they acclimate to the low oxygen.</p>
<p>All over the world, plants and animals have adapted to many different warm and dry habitats, prompting scientists to <a href="https://doi.org/10.1098/rstb.2018.0176">question</a> <a href="https://doi.org/10.1038/s41586-019-1520-9">whether</a> <a href="https://doi.org/10.1111/gcb.14881">species</a> <a href="https://doi.org/10.1073/pnas.1406314111">might</a> <a href="https://doi.org/10.1111/evo.13862">also</a> <a href="https://doi.org/10.1126/science.1063656">adapt</a> <a href="https://doi.org/10.1073/pnas.0608379104">to</a> <a href="https://doi.org/10.1111/ele.14072">our</a> <a href="https://doi.org/10.1126/science.aba9287">rapidly</a> <a href="https://doi.org/10.1126/science.abj7484">changing</a> <a href="https://doi.org/10.1126/science.aaf3343">climate</a>, <a href="https://doi.org/10.1038/nclimate2628">too</a>.</p>
<p>Thus far, the answer <a href="https://doi.org/10.1002/wcc.852">seems to be no</a> for most species.</p>
<h2>Evolving, fast and slow</h2>
<p>A <a href="https://doi.org/10.1038/s41467-019-10924-4">recent study</a> of the populations of 19 bird and mammal species, including owls and deer, shows one potential barrier to adaptation. </p>
<p>In animals that take several years to reach breeding age, the climate has already shifted by the time their offspring are born. Genes that gave the parents an advantage – like hatching at exactly the right time or growing to the best size – are no longer as beneficial for the offspring.</p>
<p>Populations of these slow-maturing animals are adapting to climate change, but not enough during each generation to thrive in the changing conditions. In fact, the rate of evolution is so mismatched to the rate of global warming that the study’s authors estimate that nearly 70% of the local populations they studied are already vulnerable to climate-driven extinction over the coming decades.</p>
<figure class="align-center ">
<img alt="A dragonfly with dark bands on its wings." src="https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=512&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=512&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558246/original/file-20231108-27-yipcvj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=512&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Black bands on dragonflies heat up their bodies. Research shows some dragonflies have evolved smaller black bands as the climate warms.</span>
<span class="attribution"><span class="source">Michael P. Moore</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A heat map clearly shows that the dark bands on the wings absorb more heat." src="https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558248/original/file-20231108-27-nr1728.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In this heat map of the same dragonfly, white areas are the warmest and purple areas are cooler. The dark bands on the wings stand out.</span>
<span class="attribution"><span class="source">Michael P. Moore</span></span>
</figcaption>
</figure>
<p>Small-bodied animals, such as many fish, insects and plankton, typically mature quickly. Yet, recent research on <a href="https://doi.org/10.1073/pnas.2011419117">small fish</a> and a type of <a href="https://doi.org/10.1098/rspb.2011.0542">fast-maturing plankton called a copepod</a> revealed another hurdle for rapid genetic adaptation to climate change.</p>
<p>Many species possess genes that permit them to live in environments that are 1 to 2 degrees Celsius (about 2 to 4 Fahrenheit) warmer than today, but new genetic mutations must arise to enable survival if climates reach 4 to 5 C (about 7 to 9 F) warmer, as is possible in some regions, particularly if greenhouse gas emissions continue at a high rate.</p>
<p>To test species’ resilience, scientists warmed populations of these fast-maturing species over many generations to observe their genetic changes. They found that both the copepods and the small fish were able to adapt to the first couple degrees of warming, but populations soon went extinct above that. This was because genetic mutations that increased their ability to live in hotter conditions occurred at a slower rate than the temperatures rose.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A tiny nearly translucent oval creature with a tail and egg sacks trailing behind it." src="https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558242/original/file-20231108-29-dkylc9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A live copepod with egg sacs at 10 times magnification. These ocean creatures produce new generations quickly, allowing for speedier evolution.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/copepod-micrograph-royalty-free-image/170025374?adppopup=true">NNehring/E+ Getty Images</a></span>
</figcaption>
</figure>
<p>Cold-blooded species, such as lizards, frogs and fish, are especially vulnerable to climate change because they have a limited capacity to regulate their own body temperatures. Their ability to evolve in response to climate change is expected to be critical for their survival.</p>
<p>However, rapid adaptation to climate change often comes <a href="https://doi.org/10.1007/BF02984069">at a cost</a>: Populations get smaller due to the deaths of individuals that cannot tolerate new, hotter temperatures. Therefore, even if species do evolve to survive with climate change, their smaller populations may still go extinct due to problems such as inbreeding, harmful new mutations or plain old bad luck, such as a disease epidemic.</p>
<p><a href="https://doi.org/10.1126/science.1184695">In a now-classic study</a>, researchers studying lizards in Mexico discovered that the high death rates of just the heat-sensitive individuals – representing only a subset of the entire population – caused 12% of all lizard populations in Mexico to go extinct between 1975 and 2009. Even with some heat-tolerant adult lizards surviving in each population under the warmer conditions, the researchers estimated climate change would kill so many heat-sensitive adults within each population that 54% of all populations would go extinct by 2080.</p>
<h2>Evolutionary adaptation isn’t species’ only option</h2>
<p>Another way species adjust to rising temperatures is acclimation, sometimes called “phenotypic plasticity.” For example, <a href="https://doi.org/10.1126/science.1157174">great tits in the U.K.</a> – small birds that are common in yards and forests – lay their eggs earlier in warmer years so that their nestlings hatch right as the winter weather ends, no matter when that happens.</p>
<figure class="align-center ">
<img alt="A small bird with a yellow body and black head with white cheeks sits on a branch." src="https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558258/original/file-20231108-21-3e6t6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A great tit – <em>Parus major</em>. In the U.K., these common birds have been laying their eggs earlier in warm years.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/hedera_baltica/49433487712/in">Hedera.Baltica via Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>However, a <a href="https://www.nature.com/articles/s41467-022-32953-2">recent analysis</a> of more than 100 beetle, grasshopper and other insect species all over the world found that acclimation may not help those species enough. The study’s authors found that the species they reviewed gained an average of only 0.1 C (about 0.2 F) greater heat tolerance when acclimating to 1 C (about 2 F) warmer air temperatures during their development. Thus, the rate of global warming seems to be outstripping species’ abilities to acclimate, too.</p>
<p>Plants and animals could also escape the impacts of global warming by migrating to cooler habitats. A <a href="https://doi.org/10.1038/s41559-020-1198-2">global analysis</a> of more than 12,000 different plants and animal species recently showed that many species are migrating toward the poles fast enough to keep pace with rising temperatures, and many <a href="https://doi.org/10.1111/ele.13762">tropical species are moving upslope</a> to higher elevations as well.</p>
<p>Nonetheless, migration has its limits. Research shows that <a href="https://doi.org/10.1073/pnas.1804224115">tropical birds that already live high in the mountains could be doomed</a> because there is no room for them to migrate any farther upward. Tropical species, therefore, may be on what the authors call an “escalator to extinction.”</p>
<figure class="align-center ">
<img alt="A yellow-and-black moth sits on a yellow flower in an alpine field with snow-covered mountains in the background." src="https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=789&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=789&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=789&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=992&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=992&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558253/original/file-20231108-21-ad3ofx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=992&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Police car moths living at high elevations have little room to migrate to escape increasing heat.</span>
<span class="attribution"><span class="source">Michael P. Moore</span></span>
</figcaption>
</figure>
<p>High-latitude and high-elevation habitats also present numerous challenges for species to overcome besides temperature. Our own research across 800 species of insects all over the Earth shows that butterflies, bees and other flying insects are <a href="https://doi.org/10.1038/s41558-023-01794-2">especially hindered from migrating to higher elevations</a> because there is not enough oxygen for them to survive. </p>
<h2>Many species lack obvious climate strategies</h2>
<p>Overall, evolutionary adaptation appears to help lessen the impacts of global warming, but the evidence thus far shows that it is insufficient to overcome current rates of climate change. Acclimation and migration provide faster solutions, but research shows that those may not be enough, either.</p>
<p>Of course, not all evolution is driven by warming temperatures. Plant and animal species appear to be also gradually adapting to other kinds of environments, including <a href="https://doi.org/10.1111/evo.14191">human-created ones like cities</a>. But the fast pace of global warming makes it <a href="https://nca2023.globalchange.gov/chapter/8#fig-8-2">one of the major threats</a> that species must respond to immediately.</p>
<p>The <a href="https://nca2023.globalchange.gov/chapter/8#fig-8-2">evidence indicates</a> that humanity cannot simply assume that plants and animals will be able to save themselves from climate change. To protect these species, humans will have to stop the activities that are fueling climate change.</p><img src="https://counter.theconversation.com/content/215222/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From dark dragonflies becoming paler to plants flowering earlier, some species are slowly evolving with the climate. Evolutionary biologists explain why few will evolve fast enough.Michael P. Moore, Assistant Professor of Biology, University of Colorado DenverJames T. Stroud, Assistant Professor of Ecology and Evolution, Georgia Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2150352023-11-13T13:33:33Z2023-11-13T13:33:33ZClimate change is altering animal brains and behavior − a neuroscientist explains how<figure><img src="https://images.theconversation.com/files/558492/original/file-20231108-17-uomc0i.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1998%2C1501&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Animal nervous systems may lose their adaptive edge with climate change.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/melting-brain-royalty-free-image/1279693246">PM Images/DigitalVision via Getty Images</a></span></figcaption></figure><p>Human-driven climate change is increasingly <a href="https://doi.org/10.1098/rstb.2019.0104">shaping the Earth’s living environments</a>. Rising temperatures, rapid shifts in rainfall and seasonality, and ocean acidification are presenting altered environments to many animal species. How do animals adjust to these new, often extreme, conditions?</p>
<p>Animal nervous systems play a central role in both enabling and limiting how they respond to changing climates. Two of my main research interests as a <a href="https://scholar.google.com/citations?user=qFFX_9KiimwC&hl=en">biologist and neuroscientist</a> involve understanding how <a href="https://doi.org/10.1371/journal.pone.0271250">animals accommodate</a> <a href="https://doi.org/10.1016/j.cois.2017.06.004">temperature extremes</a> and identifying the forces that shape the <a href="https://doi.org/10.1093/biolinnean/blx150">structure and function of</a> <a href="https://doi.org/10.1007/s00040-022-00873-5">animal nervous systems</a>, especially brains. The intersection of these interests led me to explore the effects of climate on nervous systems and how animals will likely respond to rapidly shifting environments.</p>
<p>All major functions of the nervous system – sense detection, mental processing and behavior direction – are critical. They allow animals to navigate their environments in ways that enable their survival and reproduction. Climate change will likely affect these functions, often for the worse.</p>
<h2>Shifting sensory environments</h2>
<p>Changing temperatures shift the energy balance of ecosystems – from plants that produce energy from sunlight to the animals that consume plants and other animals – subsequently altering the sensory worlds that animals experience. It is likely that climate change will challenge all of their senses, from sight and taste to smell and touch. </p>
<p>Animals like mammals perceive temperature in part with <a href="https://doi.org/10.1038/nature02732">special receptor proteins</a> in their nervous systems that respond to heat and cold, discriminating between moderate and extreme temperatures. These receptor proteins help animals <a href="https://doi.org/10.1038/nature07001">seek appropriate habitats</a> and may play a critical role in how animals respond to changing temperatures.</p>
<p>Climate change disrupts the environmental cues animals rely on to solve problems like selecting a habitat, finding food and choosing mates. Some animals, such as <a href="https://doi.org/10.1016/j.jinsphys.2017.04.010">mosquitoes</a> that transmit <a href="https://doi.org/10.3389/fmicb.2020.584846">parasites and pathogens</a>, rely on temperature gradients to orient themselves to their environment. Temperature shifts are altering where and when mosquitoes search for hosts, leading to changes in disease transmission.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/aYH-KYdgXag?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Climate change is pushing more and more mosquitoes to take humans as their preferred hosts.</span></figcaption>
</figure>
<p>How climate change affects the chemical signals animals use to <a href="https://doi.org/10.1111/1365-2435.12128">communicate with each other</a> or <a href="https://doi.org/10.1071/EN13055">harm competitors</a> can be especially complex because chemical compounds are highly sensitive to temperature.</p>
<p>Formerly reliable sources of information like seasonal changes in daylight can lose its utility as they become uncoupled. This could cause a breakdown in the link between day length and <a href="http://hdl.handle.net/1773/37034">plant flowering and fruiting</a>, and interruptions to <a href="https://doi.org/10.1146/annurev-physiol-021909-135837">animal behavior</a> like hibernation and migration when day length no longer predicts resource availability.</p>
<h2>Changing brains and cognition</h2>
<p>Rising temperatures may disrupt how animal brains develop and function, with potentially negative effects on their ability to effectively adapt to their new environments. </p>
<p>Researchers have documented how temperature extremes can alter individual neurons at the <a href="https://doi.org/10.1002/jez.b.22736">genetic and</a> <a href="https://doi.org/10.1073/pnas.0400773101">structural levels</a>, as well as how the <a href="https://doi.org/10.1007/s10071-016-0993-2">brain is organized</a> as a whole.</p>
<p>In marine environments, researchers have found that climate-induced changes of water chemistry like ocean acidification can affect animals’ general cognitive performance and sensory abilities, such as odor tracking in <a href="https://doi.org/10.1038/nclimate2195">reef fish</a> and <a href="https://doi.org/10.1111/gcb.12678">sharks</a>.</p>
<h2>Behavior disruptions</h2>
<p>Animals may respond to climate adversity by shifting locations, from <a href="https://doi.org/10.1111/gcb.12439">changing the microhabitats</a> <a href="https://doi.org/10.1111/1365-2656.13309">they use</a> to <a href="https://doi.org/10.1073/pnas.1316145111">altering their</a> <a href="https://doi.org/10.1007/s00040-016-0504-0">geographic ranges</a>. </p>
<p>Activity can also shift to <a href="https://doi.org/10.1007/s00359-005-0030-4">different periods of the day</a> <a href="https://doi.org/10.1098/rspb.2010.1768">or to</a> <a href="https://doi.org/10.3354/cr00713">new seasons</a>. These behavioral responses can have major implications for the environmental stimuli animals will be exposed to.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Green snake slithering out of a nest after eating a bird" src="https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558495/original/file-20231108-27-homplj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Shifting climates are driving some snake species into forested habitats, and the subsequent increased predation on nesting birds may push above sustainable levels.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/green-pit-viper-trimeresurus-full-up-after-ate-royalty-free-image/1148122650">Rapeepong Puttakumwong/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>For example, fish in warming seas have shifted to cooler, deeper waters that have dramatically different <a href="https://doi.org/10.1098/rspb.2021.0396">light intensity and color range</a> than their visual systems are used to. Furthermore, because not all species will shift their behaviors in the same way, species that do move to a new habitat, time of day or season will <a href="https://doi.org/10.1016/j.ecolmodel.2015.05.031">confront new ones</a>, including food plants and prey animals, competitors and predators, and pathogens. </p>
<p>Behavioral shifts driven by climate change will restructure ecosystems worldwide, with complex and unpredictable outcomes.</p>
<h2>Plasticity and evolution</h2>
<p>Animal brains are remarkably flexible, developed to match <a href="https://doi.org/10.1007/s00040-022-00873-5">individual environmental experience</a>. They’re even substantially <a href="https://doi.org/10.1016/S0166-2236(00)01558-7">capable of changing</a> <a href="https://doi.org/10.31887/DCNS.2004.6.2/fgage">in adulthood</a>. </p>
<p>But studies comparing species have <a href="https://doi.org/10.1007/s00114-016-1353-4">seen strong</a> <a href="https://doi.org/10.1159/000006666">environmental effects</a> on brain evolution. Animal nervous systems evolve to match the sensory environments of each species’ activity space. These patterns suggest that new climate regimes will eventually shape nervous systems by forcing them to evolve. </p>
<p>When genetics have strong effects on brain development, nervous systems that are finely adapted to the local environment may lose their adaptive edge with climate change. This may pave the way for new adaptive solutions. As the range and significance of sensory stimuli and seasonal cues shift, natural selection will favor those with new sensory or cognitive abilities.</p>
<p>Some parts of the nervous system are constrained by <a href="https://doi.org/10.1111/jeb.14188">genetic adaptations</a> while others are more plastic and responsive to environmental conditions. A greater understanding of how animal nervous systems adapt to rapidly changing environments will help predict how all species will be affected by climate change.</p><img src="https://counter.theconversation.com/content/215035/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sean O'Donnell does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Rapidly changing temperatures and sensory environments are challenging the nervous systems of many species. Animals will be forced to evolve to survive.Sean O'Donnell, Professor of Biodiversity, Earth and Environmental Science and Biology, Drexel UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2166392023-11-09T19:09:59Z2023-11-09T19:09:59ZA new theory linking evolution and physics has scientists baffled – but is it solving a problem that doesn’t exist?<figure><img src="https://images.theconversation.com/files/558544/original/file-20231109-17-qp5bsl.jpg?ixlib=rb-1.1.0&rect=10%2C42%2C7130%2C4710&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/leafless-tree-with-water-droplets-TYnHpsuAkBg">Tim Johnson / Unsplash</a></span></figcaption></figure><p>In October, a paper titled “<a href="https://www.nature.com/articles/s41586-023-06600-9">Assembly theory explains and quantifies selection and evolution</a>” appeared in the top science journal Nature. The authors – a team led by Lee Cronin at the University of Glasgow and Sara Walker at Arizona State University – claim their theory is an “interface between physics and biology” which explains how complex biological forms can evolve.</p>
<p>The paper provoked strong responses. On the one hand were headlines like “<a href="https://www.sciencealert.com/assembly-theory-bold-new-theory-of-everything-could-unite-physics-and-evolution">Bold New ‘Theory of Everything’ Could Unite Physics And Evolution</a>”.</p>
<p>On the other were reactions from scientists. One evolutionary biologist <a href="https://twitter.com/baym/status/1710815658890432679">tweeted</a> “after multiple reads I still have absolutely no idea what [this paper] is doing”. Another <a href="https://twitter.com/Irishpalaeo/status/1712450672476512424">said</a> “I read the paper and I feel more confused […] I think reading that paper has made me forget my own name.”</p>
<p>As a biologist who studies evolution, I felt I had to read the paper myself. Was assembly theory really the radical new paradigm its authors suggested? Or was it the “<a href="https://twitter.com/AdamRutherford/status/1711160807453569404">abject wankwaffle</a>” its critics decried?</p>
<h2>Hackle-raising claims</h2>
<p>When I sat down to read the paper, the very first sentence of the abstract had my hackles up: </p>
<blockquote>
<p>Scientists have grappled with reconciling biological evolution with the immutable laws of the Universe defined by physics.</p>
</blockquote>
<p>I had no idea we scientists grappled with this. No biologist I know has a problem with the laws of physics or sees any problem with reconciling them with evolution. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/life-modern-physics-cant-explain-it-but-our-new-theory-which-says-time-is-fundamental-might-203129">Life: modern physics can't explain it – but our new theory, which says time is fundamental, might</a>
</strong>
</em>
</p>
<hr>
<p>The abstract goes on to note that the laws of physics do not predict “life’s origin, evolution and the development of human culture and technology”, and claims we need a “new approach” to understand “how diverse, open-ended forms can emerge from physics without an inherent design blueprint”.</p>
<p>The complaint that biological evolution seems incompatible with the laws of physics, taken with the use of loaded terms like “design blueprint”, is reminiscent of creationist arguments against evolution. No wonder the blood pressure of evolutionary biologists was spiking.</p>
<p>In the words of <a href="https://www.nature.com/articles/s41586-023-06600-9#comment-6296992737">one Nature commenter</a>: “Why so many creationist tropes in the first few sentences?”</p>
<h2>Biology and physics</h2>
<p>Before I go further, I should note that I may, along with some of scientists quoted above, not fully understand the aim of the paper. But I have problems with what I do understand of it. </p>
<p>First of all, the claim that evolution is at odds with the immutable laws of physics does not seem to be supported. </p>
<p>The paper says “the open-ended generation of novelty does not fit cleanly in the paradigmatic frameworks of either biology or physics”, which doesn’t seem to make much sense. </p>
<figure class="align-center ">
<img alt="A microscope photo of fluorescent cells" src="https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558547/original/file-20231109-15-kojsc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Is there a conflict between biology and physics that needs to be explained?</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/a-close-up-of-a-cell-phone-case-sIqWYiNLiJU">National Cancer Institute / Unsplash</a></span>
</figcaption>
</figure>
<p>In the paradigm of biology, we understand there is a variation in biological forms through genetic drift, mutation and selection. Does this <em>need</em> to “fit the paradigm of physics”, as long as it doesn’t break any laws of physics?</p>
<p>Another troubling statement: “To comprehend how diverse, open-ended forms can emerge from physics without an inherent design blueprint, a new approach to understanding and quantifying selection is necessary.” </p>
<p>Is it? One of the tenets of evolutionary theory is that there is no “teleology” – no goal or aimed-for endpoint – in the process. So how could there be a “design blueprint”? Why would its absence need to be explained?</p>
<h2>Putting numbers on the odds of evolution</h2>
<p>So what is assembly theory trying to do? <a href="https://twitter.com/leecronin/status/1711356692720501103">According to Cronin</a>, it “aims to explain selection & evolution before biology”; as such its goal is a theory that unifies inert and living matter and seeks to explain their complexity or otherwise, in the same way.</p>
<p>The paper itself says it is a “framework that does not alter the laws of physics, but redefines the concept of an ‘object’ on which these laws act”. </p>
<blockquote>
<p>[Assembly theory] conceptualizes objects not as point particles, but as entities defined by their possible formation histories. This allows objects to show evidence of selection, within well-defined boundaries of individuals or selected units. </p>
</blockquote>
<p>The “object” in assembly theory is then what “laws of physics” act on. For any object, we can calculate its “assembly index”, a number that measures how complex the object would be to make. </p>
<p>Any object that is both abundant and has a high assembly index is unlikely to have arisen by chance, so it must be a product of evolution and selection. This, in itself, is neither problematic nor new – apart from this calculated “index”.</p>
<p>How do we figure out that assembly index? We count the number of steps it would take to build a molecule, say, or a bodily organ, or a whole organism. The higher the index, the more likely it is to have evolved. </p>
<p>So assembly theory is an attempt to quantify the complexity of something and the likelihood of it having evolved. </p>
<h2>A problem that doesn’t exist?</h2>
<p>Is this useful? It’s hard to say. </p>
<p>For one thing, it implies there is only one pathway to produce a complicated (high assembly index) object such as a biochemical molecule, which is simply not the case.</p>
<p>Also, as <a href="https://twitter.com/professor_dave/status/1710914156612710503">another scientist pointed out</a>: </p>
<blockquote>
<p>it’s obvious that if a molecule is complex and there are lots of copies of it, then it likely emerged from some process of evolution. And most chemists could spot such cases without the need for assembly theory. Although trying to put numbers on it is very neat.</p>
</blockquote>
<p>My own feeling is that this is a poorly written paper, as evidenced by the inability of many biologists to understand what it is trying to do, and much of the negative reaction to the work springs from the hard-to-follow framing and use of phrases that echo creationist talking points. </p>
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Read more:
<a href="https://theconversation.com/physics-has-long-failed-to-explain-life-but-were-testing-a-groundbreaking-new-theory-in-the-lab-215636">Physics has long failed to explain life – but we're testing a groundbreaking new theory in the lab</a>
</strong>
</em>
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<p>As for assembly theory itself, it seems to have been <a href="https://www.quantamagazine.org/a-new-theory-for-the-assembly-of-life-in-the-universe-20230504/">developed</a> in the course of Cronin and Walker’s efforts to find a general way to <a href="https://www.nature.com/articles/s41467-021-23258-x">recognise signs of life on alien planets</a>, and even <a href="https://www.mdpi.com/1099-4300/24/7/884">create artificial life</a>. And perhaps, in those contexts, it may prove useful.</p>
<p>However, as a sweeping new paradigm aiming to unify evolution and physics, assembly theory appears – to me and many others – to be addressing a problem that does not exist.</p><img src="https://counter.theconversation.com/content/216639/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bill Bateman does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>‘Assembly theory’ aims to explain evolution without biology. Is it a dazzling breakthrough or an attempt to answer questions nobody asked?Bill Bateman, Associate professor, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.