tag:theconversation.com,2011:/id/topics/evolutionary-20666/articlesevolutionary – The Conversation2022-10-06T13:45:35Ztag:theconversation.com,2011:article/1910892022-10-06T13:45:35Z2022-10-06T13:45:35Z‘Sea monsters’ were real millions of years ago. New fossils tell about their rise and fall<figure><img src="https://images.theconversation.com/files/488531/original/file-20221006-19-8xaxr1.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Thalassotitan teeth.
</span> <span class="attribution"><span class="source">Nicholas Longrich</span></span></figcaption></figure><p>Sixty six million years ago, sea monsters really existed. They were mosasaurs, huge marine lizards that lived at the same time as the last dinosaurs. Growing up to 12 metres long, mosasaurs looked like a Komodo dragon with flippers and a shark-like tail. They were also wildly diverse, evolving dozens of species that filled different niches. Some ate fish and squid, some ate shellfish or ammonites. </p>
<p>Now <a href="https://www.sciencedirect.com/science/article/pii/S0195667122001793?dgcid=author">we’ve found a new mosasaur</a> preying on large marine animals, including <em>other</em> mosasaurs.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=817&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=817&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=817&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1026&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1026&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487600/original/file-20221002-27126-grh6vs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1026&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The mosasaur Thalassotitan attacks a smaller mosasaur species, Halisaurus. Art by Andrey Atuchin.</span>
</figcaption>
</figure>
<p>The new species, <a href="https://www.sciencedirect.com/science/article/pii/S0195667122001793?dgcid=author"><em>Thalassotitan atrox</em></a>, was dug up in the Oulad Abdoun Basin of Khouribga Province, an hour outside Casablanca in Morocco. </p>
<p>At the end of the Cretaceous period, <a href="https://doi.org/10.1016/j.gloplacha.2013.12.007">sea levels were high</a>, flooding much of Africa. Ocean currents, driven by the trade winds, pulled nutrient-rich bottom waters to the surface, creating a <a href="https://doi.org/10.1016/j.cub.2017.04.043">thriving marine ecosystem</a>. The seas were full of fish, attracting predators – the mosasaurs. They brought their own predators, the giant <em>Thalassotitan</em>. Nine metres long and with a massive, 1.3 metre-long head, it was the deadliest animal in the sea. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487604/original/file-20221002-20-9yoxbu.jpg?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">
<figcaption>
<span class="caption">Thalassotitan size.</span>
</figcaption>
</figure>
<p>Most mosasaurs had long jaws and small teeth to catch fish. But <em>Thalassotitan</em> was built very differently. It had a short, wide snout and strong jaws, shaped like those of a killer whale. The back of the skull was wide to attach large jaw muscles, giving it a powerful bite. The anatomy tells us this mosasaur was adapted to attack and tear apart large animals.</p>
<p>The massive, conical teeth <a href="https://www.int-res.com/articles/ab2010/11/b011p213.pdf">resemble the teeth of orcas</a>. And the tips of those teeth are chipped, broken and ground down. This heavy wear – not found in fish-eating mosasaurs – suggests <em>Thalassotitan</em> damaged its teeth biting into the bones of marine reptiles like plesiosaurs, sea turtles and other mosasaurs.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=598&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=598&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=598&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=751&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=751&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487601/original/file-20221002-27856-5899ly.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=751&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Thalassotitan skull.</span>
</figcaption>
</figure>
<p>At the same site we’ve found what look like the fossilised remains of its victims. The rocks producing <em>Thalassotitan</em> skulls and skeletons are full of partially digested bones from mosasaurs and plesiosaurs. The teeth of these animals, including those of half-metre skull from a long-necked <a href="https://www.sciencedirect.com/science/article/pii/S1342937X10001851">plesiosaur</a>, have been partially eaten away by acid. That suggests they were killed, eaten and digested by a large predator, which then <a href="https://www.tandfonline.com/doi/abs/10.1080/08912963.2011.631703">spat up the bones</a>. We can’t prove <em>Thalassotitan</em> ate them, but it fits the profile of the killer, and nothing else does, making it the prime suspect.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487602/original/file-20221002-12-xgatwm.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">Remains of a small mosasaur, Halisaurus, showing teeth eaten away by acids.</span>
</figcaption>
</figure>
<p><em>Thalassotitan</em>, sitting at the top of the food chain, also tells a lot about ancient marine food chains, and how they evolved in the Cretaceous.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/scientists-have-found-dust-from-the-asteroid-that-wiped-out-the-dinosaurs-inside-the-crater-it-left-156232">Scientists have found dust from the asteroid that wiped out the dinosaurs inside the crater it left</a>
</strong>
</em>
</p>
<hr>
<h2>Evolution of a killer</h2>
<p>The discovery of <em>Thalassotitan</em> tells us about marine ecosystems just before the asteroid hit 66 million years ago, ending the age of the dinosaurs. </p>
<p><em>Thalassotitan</em> was just one of a dozen mosasaur species living in the waters off of Morocco. Mosasaurs made up a fraction of all the thousands of species living in the oceans, but the fact that predators were so diverse implies that lower levels of the food chain were diverse too, for the oceans to be able to feed them all. This means that the marine ecosystem wasn’t in decline before the asteroid hit. </p>
<p>Instead, mosasaurs and other animals – plesiosaurs, giant sea turtles, ammonites, countless species of fish, molluscs, sea urchins, crustaceans – flourished, then died out suddenly when the <a href="https://www.science.org/doi/10.1126/science.1177265">10-kilometre wide Chicxulub asteroid slammed into the earth</a>, launching dust and soot into the air, and blocking out the sun. Mosasaur extinction wasn’t the predictable result of gradual environmental changes. It was the unpredictable result of a sudden catastrophe. Like a lightning strike from a clear blue sky, their end was swift, final, unpredictable. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=185&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=185&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=185&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=232&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=232&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487610/original/file-20221002-18-6lu4ah.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=232&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An asteroid approaching Earth.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>But mosasaur evolution may also have <em>started</em> with a catastrophe. Curiously, the evolution of the giant carnivorous mosasaurs resembles that of another family of predators – the <em>Tyrannosauridae</em>. The giant <em>T. rex</em> evolved on land at about the same time that mosasaurs became top predators in the seas. Is that a coincidence? Maybe not. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487608/original/file-20221002-3194-gtqfpd.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">The tyrannosaur Tarbosaurus, from Mongolia.</span>
<span class="attribution"><span class="source">Nick Longrich</span></span>
</figcaption>
</figure>
<p>Both mosasaurs and <a href="https://www.nature.com/articles/s41559-019-0888-0">tyrannosaurs start to diversify</a> and become larger at the same time, around 90 million years ago, in the <a href="https://www.sciencedirect.com/science/article/abs/pii/S0031018213002514">Turonian stage of the Cretaceous</a>. This followed major extinctions <a href="https://pubs.geoscienceworld.org/gsa/gsabulletin/article/109/5/560/183244/Nonmarine-extinction-across-the-Cenomanian?casa_token=EPiZkxT68YkAAAAA:1qGLmu4DhCdd7-h4BC3E0V3dfvjFGvTwz3GTuZ_FLpAa-PT-dJEe7wMknDCAgsCTMticuA">on land</a> and <a href="https://archives.datapages.com/data/sepm_sp/fg4/Biotic_Patterns_Across.htm">in the sea</a> around 94 million years ago, at the Cenomanian-Turonian boundary.</p>
<p>These extinctions are associated with extreme global warming – a “supergreenhouse” climate – driven by <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020PA004016">volcanoes releasing C02</a> into the atmosphere. In the aftermath, <a href="https://www.sciencedirect.com/science/article/abs/pii/S0195667119305373">giant predatory plesiosaurs</a> disappeared from the seas and <a href="https://www.nature.com/articles/ncomms3827">giant allosaurid predators</a> were wiped out on land. With predator niches left vacant, mosasaurs and tyrannosaurs moved into the top predator niche. Although they were wiped out by a mass extinction, <em>Thalassotitan</em> and <em>T. rex</em> only evolved in the first place because of a mass extinction.</p>
<h2>The bigger they are, the harder they fall</h2>
<p>Top predators are fascinating because they’re big, dangerous animals. But their size and position at the top of the food chain also make them vulnerable. You have fewer animals as you move up the food chain. It takes many small fish to feed a big fish, many big fish to feed a small mosasaur, and many small mosasaurs to feed one giant mosasaur. That means top predators are rare. And apex predators need lots of food, so they’re in trouble if the food supply is disrupted. </p>
<p>If the environment deteriorates, dangerous predators can quickly become endangered species.</p>
<p>It’s this sensitivity to environmental change that makes predators like <em>Thalassotitan</em> so interesting for studying extinction. They suggest being a top predator is a risky evolutionary strategy. Over short timescales, evolution drives the evolution of larger and larger predators. Their size means they can compete for and take down prey. But over long timescales, specialisation for the apex predator niche increases vulnerability to disasters. Eventually, a mass extinction wipes the top predators out, and the cycle starts again.</p><img src="https://counter.theconversation.com/content/191089/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>Fossils of a giant killer mosasaur have been discovered, alongside the fossilised remains of its prey.Nicholas R. Longrich, Senior Lecturer in Paleontology and Evolutionary Biology, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1220392019-10-01T03:05:22Z2019-10-01T03:05:22ZCurious Kids: how do scientists know evolution is real?<figure><img src="https://images.theconversation.com/files/294299/original/file-20190926-51410-1evvi4s.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6165%2C4135&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Darwin wondered: what if species change over time in response to their environment?</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><hr>
<blockquote>
<p><strong>How do scientists know that evolution is real? – Emily, age 11.</strong></p>
</blockquote>
<hr>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>In science, we look at the evidence and try to find the theory that best explains it. And that’s what happened when it came to figuring out evolution. </p>
<p>We can see life evolving all around us. Plants, animals and even bacteria are adapting to different conditions (like climate change), to new predators and diseases. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=803&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=803&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=803&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1008&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1008&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294685/original/file-20190930-185379-1q7amur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1008&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 is a portrait of the young Charles Darwin by artist George Richmond.</span>
<span class="attribution"><span class="source">George Richmond/Wikimedia</span></span>
</figcaption>
</figure>
<p>A young man named Charles Darwin was one of the first to realise how this happens. He lived in England nearly 190 years ago and decided to sail around the world (because he didn’t really know what to do with his life). </p>
<h2>Spot the difference</h2>
<p>For two years people on the boat mapped the shore and explored South America and Australia. Darwin’s job was to check out the plants and animals they found. Sound fun? Not if you were seasick like poor Darwin.</p>
<p>He began to wonder why animals were so different to those back in England. He had the revolutionary idea that they weren’t always that way. Maybe these species had changed over time in response to their environment, he thought.</p>
<p>He noticed that little brown birds that they called finches, living on a group of islands called the Galápagos, looked similar to each other but had different-shaped beaks on different islands. </p>
<p>Darwin realised that the beaks were good for getting different kinds of food: big heavy beaks for crushing tough nuts that grew on one island; little beaks for eating fruit; sharp beaks for probing cactus; and long beaks for catching insects on other islands.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/294300/original/file-20190926-51421-5tvw1p.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>
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<span class="caption">Darwin looked closely at the beaks of finches on the Galápagos Islands.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>Darwin twigged that the birds all started off the same, but those on an island with nuts developed heavier beaks, whereas those on an island with cactus developed sharp beaks. How?</p>
<p>He suggested the beaks of individual ancestor birds were all a bit different, and the differences were passed down from parents to chicks. Birds with slightly heavier beaks did better on the island with nuts, and they laid more eggs and had more chicks than other birds. These chicks also had heavier beaks, and did better than other birds, and laid more eggs. He called this “natural selection”. </p>
<p>Darwin suggested animals or plants that survived in different environments would eventually become so different they couldn’t get together to have chicks. This is how one species splits into two.</p>
<h2>The evidence piles up</h2>
<p>During Darwin’s day, these ideas seemed shocking. Most people believed species of plants and animals had always been the way they were; that they were created that way. But soon, people began to find new evidence that fit Darwin’s theory, or reconsider old evidence in light of what he proposed. </p>
<p>People found dinosaur bones and realised these enormous creatures once roamed the Earth but were now extinct. Now we know, from comparing skeletons, they are related to birds, and we even have <a href="https://www.nhm.ac.uk/discover/why-are-birds-the-only-surviving-dinosaurs.html">fossils</a> of feathered dinosaurs.</p>
<p>One famous example of fossils that showed earlier “versions” of contemporary animals is the “<a href="https://evolution.berkeley.edu/evolibrary/article/evograms_03">walking whale</a>” – fossils that indicated that earlier versions of whales had legs. People couldn’t believe that natural selection could turn a hippo-like land animal into a whale, that lost its legs as it became a better swimmer. But recently whale fossils with legs were discovered. (Even today, we can see that whale embryos develop four masses of cells called limb buds, but which don’t grow into legs.)</p>
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<span class="caption">The skeleton of Ambulocetus natans, an extinct ‘walking whale’.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/w/index.php?curid=16486662">By Ghedoghedo - Own work, CC BY-SA 3.0</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>In Darwin’s day nobody knew the Earth’s crust changes dramatically; land under the ocean can buckle upward to form mountains. That’s why <a href="https://books.google.com.au/books?id=4rwB5Fam1RQC&pg=PA11&lpg=PA11&dq=cockle+shells+top+of+andes&source=bl&ots=WI3WwNVGMt&sig=ACfU3U0i2lSZ0Eu0jU-F4cabTOLq_mFgnA&hl=en&sa=X&ved=2ahUKEwj_6PjTwe3kAhWN6XMBHf8jBLsQ6AEwFHoECAYQAQ#v=onepage&q=cockle%20shells%20top%20of%20andes&f=false">cockle shells</a> can be found at the top of huge mountains. All this evidence supports the idea that environments change and animals adapt.</p>
<p>Splitting one species into two takes millions of years, but we can sometimes catch this happening. Little groups of wallabies that live in rocky outcrops in Queensland are a famous example because they show a lot of intermediates (meaning populations that are starting to get so different from each other that they don’t interbreed well and are close to becoming two new species).</p>
<p>A huge new source of evidence for evolution came with the discovery of DNA, which is shared by all life on Earth. DNA changes slowly as mutations accumulate. DNA is similar for species that are closely related (like Darwin’s finches, or like hippos and whales) and more different between species that are distant (like humans and whales, or humans and plants). This is a pretty big clue supporting Darwin’s idea that living things are related and have changed over time. </p>
<p>Scientists have looked at the huge piles of evidence and concluded that evolution is the best explanation we’ve heard so far on how life on Earth came to be as it is today.</p>
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Read more:
<a href="https://theconversation.com/curious-kids-are-humans-going-to-evolve-again-116990">Curious Kids: are humans going to evolve again?</a>
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<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p><img src="https://counter.theconversation.com/content/122039/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jenny Graves receives funding from the Australian Research Council. </span></em></p>In science, we look at the evidence and try to find the theory that best explains it. And that’s what happened when it came to figuring out evolution.Jenny Graves, Distinguished Professor of Genetics, La Trobe UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/912882018-02-07T00:03:26Z2018-02-07T00:03:26ZHow bombardier beetles survive being eaten – and other amazing animal defence mechanisms<p>In Disney’s film version of Pinnochio, the boy-puppet rescues his creator Geppetto by lighting a fire inside Monstro the whale, who has swallowed them both. The fire causes the whale to sneeze, freeing Pinnochio and Geppetto from their gastric prison.</p>
<p>Before you dismiss this getaway as incredible fantasy, consider that new research shows that a kind of fire in the belly can actually be an effective strategy for escaping predators in the real world. In fact, the animal kingdom is full of amazing examples of unusual defence mechanisms that help small creatures avoid a nasty fate.</p>
<p>In a new paper <a href="http://rsbl.royalsocietypublishing.org/lookup/doi/10.1098/rsbl.2017.0647">in Biology Letters</a>, scientists at Kobe University in Japan describe how bombardier beetles can survive being eaten by a toad by releasing a hot chemical spray that makes the hungry amphibian vomit.</p>
<p>Bombardier beetles are so-named because, when threatened, they emit a boiling, irritating substance from their backsides <a href="http://news.bbc.co.uk/2/hi/science/nature/422599.stm">with remarkable accuracy</a>, to deter potential predators. They produce the caustic mixture by <a href="https://www.wired.com/2014/05/absurd-creature-of-the-week-bombardier-beetle/">combining hydrogen peroxide, hydroquinones and chemical catalysts</a> in a specially reinforced chamber at the base of their abdomen, which shields the beetle’s own organs from the resulting explosive reaction.</p>
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<p><a href="http://rsbl.royalsocietypublishing.org/lookup/doi/10.1098/rsbl.2017.0647">The Japanese researchers</a> fed two different species of bombardier beetles to captive toads. They were then able to confirm that the beetles used their weapon inside the toads by listening carefully for the explosive pop that accompanies each discharge. </p>
<p>Toads are ambush predators, quite used to swallowing first and asking questions later. When they start to feel a dose of diner’s remorse, they can literally turn <a href="https://indianapublicmedia.org/amomentofscience/how-to-heave-your-guts/">their stomachs inside out and scrape out the contents</a>, rather than suffering meekly from indigestion. Many of the toads in this experiment did just that, disgorging the beetles up to 107 minutes after ingestion. Remarkably, the ejected beetles all survived.</p>
<p>In a further experiment, the researchers poked beetles with forceps to deplete their spray reserves. Compared to those with full tanks of fuel, the exhausted beetles were much less likely to be ejected. This showed that it really was their chemical arsenals that saved them, rather than just their taste or behaviour in the gut.</p>
<figure> <img src="https://media.giphy.com/media/26DN4S3rQgsgvzEY0/giphy.gif"><figcaption>“I guess I’ll die another day.” Sugiura & Sato, Kobe University</figcaption></figure>
<p>The bombardier beetle is of course not the only animal escape artist. The diverse getaway tactics of animals are a testament to the fascinating creativity of evolution. Subject to millions of years of abuse and exploitation by predators, natural selection has shaped an array of ingenious strategies for cheating death in the face of would-be devourers.</p>
<h2>Animal Houdinis</h2>
<p>Some examples are probably familiar to most people. For instance, many lizards drop their tails to distract a predator or <a href="https://academic.oup.com/bioscience/article/59/8/728/256547">escape from its venom</a>. But others are more exotic. Sea cucumbers don’t have tails so they <a href="http://echinoblog.blogspot.ca/2012/01/sea-cucumber-evisceration-defense.html">eject and regenerate their internal organs instead</a>. Loud sounds (<a href="http://thatslifesci.com.s3-website-us-east-1.amazonaws.com/2016-12-26-How-Pistol-Shrimp-Kill-With-Bubbles-AStrauss/">such as the “gunshots” of snapping shrimp</a>) and bright colours (as on <a href="https://www.ucpress.edu/ebook.php?isbn=9780520952461">banded wing grasshoppers</a>) are also effective means of <a href="https://pdfs.semanticscholar.org/5742/afd010a4e1b889d1097f28f6f5741f10d33e.pdf">startling predators</a>. Mantid insects unite movement, sound and colour in an elaborate display that can stop an attack or at least give them a chance to escape.</p>
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<p>Some animals fight back, such as the frogs that can <a href="http://rsbl.royalsocietypublishing.org/content/4/4/355">erect sharp bony splinters</a> from their claws that <a href="https://www.newscientist.com/article/dn13991-horror-frog-breaks-own-bones-to-produce-claws/">pierce their own skin</a>, like X-Men’s Wolverine. Other animals, including <a href="https://doi.org/10.1098%252Frspb.2001.1708">the mimic octopus</a>, prefer to pretend to be being dangerous, <a href="https://www.nature.com/scitable/blog/accumulating-glitches/the_mimic_octopus_master_of">adopting the appearance of more deadly prey</a> when threatened.</p>
<p>The stunning variety of defensive mechanisms would be impressive even if we only counted variations of chemical warfare, similar to the bombardier beetle’s steam treatment. There are the defensive toxins in <a href="https://www.nationalgeographic.com/animals/fish/group/pufferfish/">pufferfish</a> and <a href="http://www.bbc.com/earth/story/20150422-the-worlds-most-poisonous-animal">poison arrow frogs</a>, the nauseating <a href="https://www.newscientist.com/article/mg12717282-900-science-the-seven-deadly-smells-of-a-skunk/">odours of skunks</a>, the charmingly named but actually revolting <a href="http://www.bbc.com/earth/story/20150623-millipedes-use-chemical-weapons">repugnatorial glands of some millipedes</a>, and the <a href="http://www.nydailynews.com/life-style/vomit-bird-throws-defense-predators-eurasian-roller-nestlings-emit-foul-smelling-fluid-protection-article-1.1037423">projectile vomiting</a> and <a href="https://wildfowl.wwt.org.uk/index.php/wildfowl/article/view/562">faecal egg decorating</a> of some birds.</p>
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<img alt="" src="https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/205061/original/file-20180206-14107-1lzimnd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">I wouldn’t eat me if I were you.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/strawberry-poison-dart-frog-dendrobates-pumilio-110478725?src=wsqFvxedepyW5_6CPNI-NQ-1-3">Maiquez/Shutterstock</a></span>
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<p>Why should nature have created such an impressive array of defensive tactics? One possible explanation can be summarised as the <a href="http://evosophos.com/life-dinner-principle/">life-dinner principle</a>, articulated by biologists <a href="http://rspb.royalsocietypublishing.org/content/205/1161/489">Richard Dawkins and John Krebs in the late 1970s</a>. The argument is that predator and prey often face asymmetrical selection pressures, meaning that the stakes are different for the two competitors. If a predator fails to capture its target, it loses dinner, but if the prey fails to escape, it loses its life. Because the stakes are greater for prey, we shouldn’t be surprised they have developed so many impressive defences.</p>
<p>Understanding nature’s tremendous capacity to adapt should make us be careful. Humans interact with other organisms all the time, and usually we’re the predators. When we try to take action against other creatures to stop them spreading disease or eating crops, we should be mindful that evolutionary innovation can produce remarkable adaptations. For example, our widespread use of <a href="https://www.myjoyonline.com/lifestyle/2018/february-3rd/high-levels-of-antibiotic-resistance-found-worldwide-who.php">antibiotics</a> and <a href="https://guardian.ng/features/malaria-cases-rise-as-insecticide-resistance-spreads/">pesticides</a> has spurred the evolution of organisms that are resistant to these methods.</p>
<p>Only by having a healthy respect for the relentless power of evolution can we hope to generate sustainable solutions to these kinds of problems. If we grow complacent and inattentive, we may some day soon find ourselves facing newly evasive diseases and pests, sputtering to breathe and dyspeptic amid all the fire and smoke in our bellies.</p><img src="https://counter.theconversation.com/content/91288/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luc Bussiere 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>Meet the brawny bug with a concoction so caustic it’ll make a toad vomit.Luc Bussiere, Lecturer in Biological Sciences, University of StirlingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/504162015-11-25T12:33:43Z2015-11-25T12:33:43ZHomo naledi may be two million years old (give or take)<figure><img src="https://images.theconversation.com/files/101607/original/image-20151111-9400-17a11sc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Professor Lee Berger from the University of the Witwatersrand holding the skull of Homo Naledi.</span> <span class="attribution"><span class="source">EPA/Shiraaz Mohamed</span></span></figcaption></figure><p>There has been global interest in the announcement of new fossils from a cave called Rising Star in the <a href="http://www.maropeng.co.za/videos/entry/sterkfontein-caves-unesco-world-heritage-site">Cradle of Humankind World Heritage Site</a> in South Africa.</p>
<p>These fossils were recently reported by <a href="http://dx.doi.org/10.7554/eLife.09560">Lee Berger</a> and his team, who described the discovery of more than 1500 fossils as representing a new species of the genus Homo. It has been called Homo naledi, associated with a name for star in the Sesotho language.</p>
<p>But the age of Homo naledi is not yet known with certainty. The new species has not yet been dated. Unsuccessful attempts had been made by <a href="http://dx.doi.org/10.7554/eLife.09561">Paul Dirks</a> and members of the Rising Star team to obtain an age. They used techniques applied previously to date a range of fossils. These included Australopithecus africanus, such as the famous <a href="http://www.encounter.co.za/article/58.html">“Mrs Ples”</a> skull, as more than two million years old, and fossils of <a href="http://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-robustus">Paranthropus</a> robustus and <a href="http://www.livescience.com/41048-facts-about-homo-erectus.html">Homo erectus</a>.</p>
<p>In a new <a href="http://www.sajs.co.za/sites/default/files/publications/pdf/SAJS%20111_11-12_Thackeray_Sci%20Cor.pdf">paper</a> in the South African Journal of Science I suggest that Homo naledi lived two million years ago (plus or minus 500,000 years). If shown to be correct, this will help to place Homo naledi in the family tree of human relatives.</p>
<p>The variance is based on the fact that the earliest date for Homo rudolfensis is about 2.5 million years, and the date for certain African Homo erectus samples is about 1.5 million years.</p>
<p>Although different, Homo naledi is most similar to fossils attributed to Homo habilis (about 1.8 million years old), and to a lesser extent to fossils of Homo rudolfensis and Homo erectus.</p>
<p>Taken together I am suggesting that Homo naledi is in the order of two million years old, with upper and lower limits of about 1.5 and 2.5 million years respectively. </p>
<h2>Why is dating so important</h2>
<p>Estimating the age of <a href="http://antiquity.ac.uk/projgall/thackeray335/">fossils</a> is important because it allows palaeoanthropologists the opportunity to try to draw up a family tree. It shows the evolutionary relationships of distant relatives.</p>
<p>Some of the fossil species can be considered to represent possible ancestors of our own species, Homo sapiens, while other species such as <a href="http://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-robustus">Paranthropus</a> robustus can be considered to be evolutionary “dead ends”.</p>
<p>The big question being asked is: where does Homo naledi fit in the evolutionary tree?</p>
<p>It had a small brain of about 500 cubic centimetres in volume. This makes it similar to fossils of Australopithecus. On the other hand, bones of parts of the skeleton, especially the foot, indicate that this species was in some respect remarkably like Homo. </p>
<p>Dating such enigmatic fossils is crucial for an understanding of evolutionary relationships of Homo naledi, compared to more than ten other species which are recognised by palaeontologists.</p>
<p>My approach has been to assess the degree of similarity or dissimilarity between skulls. This can help to assess the age and affinities of fossils.</p>
<h2>Quantifying degrees of similarity between fossils</h2>
<p>Recognising that the new fossils have features of both Australopithecus and Homo, we need to know how old they are. One way of addressing this is to use a technique that I have previously described, based on measurements of <a href="https://theconversation.com/species-without-boundaries-a-new-way-to-map-our-origins-42646">skulls</a>.</p>
<p>Statistics are calculated by taking one set of measurements for specimen A, plotted against the corresponding measurements of specimen B. When A and B are the same species, the values for the two specimens are typically distributed along a straight line, with little scatter around that linear pattern. </p>
<p>When measurements of two specimens (C and D) of different species are plotted against each other, there is a high degree of scatter. The degree of scatter around the line can be quantified using a statistic that I have called log sem, based on a standard mathematical technique that is known as least squares linear regression. </p>
<p>Remarkably, a pattern has been found for comparisons of modern skulls of the same species, whether these are of mammals, birds or reptiles. The mean log sem value for comparisons of pairs of modern species has central tendency around a particular number with a value of -1.61 (plus or minus 0.1), which I have regarded as an approximation of a biological species constant called <a href="http://www.scielo.org.za/pdf/sajs/v103n11-12/a0210312.pdf">T</a>.</p>
<h2>How does this help to date Homo naledi</h2>
<p>Comparisons have been made between the skull measurements of Homo naledi and those of more than ten other recognised species. </p>
<p>It is possible to say that Homo naledi is indeed different because in all cases the log sem statistics for such comparisons is significantly greater than -1.61. </p>
<p>But what is exciting is the fact that of all such comparisons, Homo naledi is most similar to skulls attributed to Homo habilis known to date to about 1.8 million years, and to some extent to other fossils attributed to Homo rudolfensis between about two and 2.5 million years ago.</p>
<p>To a smaller extent Homo naledi is similar to fossil skulls of Homo erectus between about 1.5 and 1.8 million years ago. Using these results, based on comparisons of skulls, I suggest that Homo naledi is two million years old, plus or minus 500,000 years.</p><img src="https://counter.theconversation.com/content/50416/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Francis Thackeray received funding for this study from the National Research Foundation and the A.W. Mellon Foundation</span></em></p>The big question being asked is: where does Homo naledi fit in the evolutionary tree? Assessing the similarity or dissimilarity between fossil skulls has provided a possible clue to the answer.Francis Thackeray, Phillip Tobias Chair in Palaeoanthropology, Evolutionary Studies Institute, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/478402015-09-25T04:31:27Z2015-09-25T04:31:27ZHomo naledi: determining the age of fossils is not an exact science<figure><img src="https://images.theconversation.com/files/95463/original/image-20150920-11714-78ktva.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The skull of Homo naledi is built like those of early Homo species but its brain was just more than half the size of the average ancestor from 2 million years ago. </span> <span class="attribution"><span class="source">SUPPLIED</span></span></figcaption></figure><p>Age is nothing but a number when it comes to unravelling the relationships of species from our past. We do not know the actual geological age of the <a href="http://www.wits.ac.za/homonaledi/">Dinaledi fossils</a>, the single largest fossil hominin find in Africa, but the discovery of <a href="http://voices.nationalgeographic.com/blog/rising-star-expedition/">Homo naledi</a> still provides insight into how our ancestors evolved. </p>
<p>The Dinaledi fossil collection is one of the most complete ever discovered, representing nearly the entire anatomy of a previously unknown species. Yet our team made no statement or conclusion about the fossils’ geological age. I reviewed with Ed Yong some of the <a href="http://www.theatlantic.com/science/archive/2015/09/why-dont-we-know-the-age-of-the-new-human-ancestor-homo-naledi/405148/">reasons</a> why it is difficult to determine the age of the fossils. </p>
<p>The bottom line is that, for now, we have little idea how old the fossils may be. </p>
<p>Most fossil hominins are found in association with extinct animals, which give us at least a general indication of their age. Famous fossil discoveries from more than a century ago, such as the Spy Neanderthal skeletons from Belgium and the first Homo erectus from Java, were found together with long-extinct creatures that indicated they were of great antiquity. This won’t work for Homo naledi because we have found no other animals in association with the hominin bones. </p>
<p>Even today, with methods that rely upon radioactive isotopes to determine the absolute ages of rock layers, geologists often have to revise their initial ideas of the ages of fossils. </p>
<p>Across the last 45 years, the age of the famous KNM-ER 1470 skull of Homo rudolfensis, from Koobi Fora, Kenya, has swung upward and down by more than a half million years as geologists revised age estimates of the famous KBS Tuff. The age of the Sterkfontein Member 4 fossils has been notoriously difficult to determine. Different teams have produced very different ages for the famous Little Foot skeleton from the Silberberg Grotto of Sterkfontein, ranging over more than a million years. </p>
<p>In other words, it pays to be cautious about geology. </p>
<h2>But how old is it?</h2>
<p>Our lack of a geological age for the fossils caught some other experts by surprise. Carol Ward, of the University of Missouri, <a href="http://www.theatlantic.com/science/archive/2015/09/homo-naledi-rising-star-cave-hominin/404362/">commented</a> to The Atlantic:</p>
<blockquote>
<p>“Without dates, the fossils reveal almost nothing about hominin evolution, beyond supporting the growing realisation that there was much more species diversity than previously thought.”</p>
</blockquote>
<p>William Jungers, from Stony Brook University, said in The <a href="http://www.theguardian.com/science/2015/sep/10/new-species-of-ancient-human-discovered-claim-scientist">Guardian</a>. </p>
<blockquote>
<p>“If they are as old as two million years, then they might be early South African versions of Homo erectus, a species already known from that region. If much more recent, they could be a relic species that persisted in isolation. In other words, they are more curiosities than game-changers for now.”</p>
</blockquote>
<p>Whether it turns out to be 20 000 years or 2 million years old, Homo naledi is equally distinct from Homo erectus either way. The age of the fossils is simply not relevant to their relationships with other hominins. In the study of anatomy, we focus on the shared features of different species, not their age. </p>
<p>Indeed, so-called relic species can be among the most important indicators of biological relationships, survivors that carry anatomical features from deep time. The coelacanth is much more than a curiosity: its anatomy provides vital clues that helped scientists understand how early land creatures could evolve from lobe-finned fish ancestors.</p>
<h2>How our ancestors evolved</h2>
<p>No matter its geological age, Homo naledi may provide vital clues about the way our ancestors stepped along a humanlike evolutionary path. This is where the real mystery comes in.</p>
<p>When we look across the skeleton of Homo naledi, we see some puzzling combinations of features. Homo naledi has a foot nearly the same as our own, much more humanlike than any early hominin we’ve discovered so far. Yet its hip and thighbone seem more primitive.</p>
<p>Likewise, Homo naledi had a hand and wrist that were largely humanlike, suitable for manipulating objects and possibly making tools. Yet powerful thumbs, curved finger bones and a shoulder canted upward like an ape’s shoulder suggest that its arms were used for climbing much more than any human today.</p>
<p>The skull of Homo naledi is built like those of early Homo species, especially Homo erectus, but its brain was just more than half the size of the average Homo erectus. Meanwhile, Homo naledi had teeth that were smaller than average for any early Homo species, a trait we have usually linked to eating better, more calorie-rich foods like meat or starchy tubers.</p>
<p>It’s almost as if Homo naledi evolved from the outside in. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=318&fit=crop&dpr=1 600w, https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=318&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=318&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=400&fit=crop&dpr=1 754w, https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=400&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/95560/original/image-20150921-31531-1530wz1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=400&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Homo naledi skull DH3 compared with an example of Homo erectus from East Africa.</span>
<span class="attribution"><span class="source">SUPPLIED</span></span>
</figcaption>
</figure>
<p>The traits in direct contact with its environment, used for walking, handling things, and eating, are the most humanlike. The core of Homo naledi’s body, its brain, ribcage and hips, were more like our very distant relatives, the australopiths.</p>
<p>These combinations make it hard to be sure exactly where Homo naledi fits on our family tree. If we trust the humanlike foot and hand, and the Homo erectus-like cranial form, then Homo naledi looks like it may be closer to us than Homo habilis, the famous handy man. </p>
<p>Whether it is closer or not, Homo naledi’s features show that the key changes leading to our genus may have had nothing to do with a large brain. Testing this will bring us closer to understanding the causes that made us human. </p>
<p><em>John <a href="http://johnhawks.net">Hawks</a> is a core scientist on the Rising Star Expedition team and co-author on the papers describing Homo naledi.</em></p><img src="https://counter.theconversation.com/content/47840/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Hawks 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>Despite claims about its age, puzzling combinations of features from Homo naledi gives it an uncanny resemblance to human beings.John Hawks, Paleoanthropologist, University of Wisconsin-MadisonLicensed as Creative Commons – attribution, no derivatives.