tag:theconversation.com,2011:/us/topics/biological-physics-79518/articlesBiological physics – The Conversation2021-03-30T00:18:18Ztag:theconversation.com,2011:article/1572292021-03-30T00:18:18Z2021-03-30T00:18:18ZWe’ve discovered a new rule of nature. It explains why animals’ pointy parts grow the way they do<figure><img src="https://images.theconversation.com/files/392120/original/file-20210329-21-14cm6og.jpg?ixlib=rb-1.1.0&rect=50%2C126%2C5557%2C3606&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Burker Museum / Elliot Trotter</span></span></figcaption></figure><p>Discoveries of new overarching rules or “laws” in nature are very rare.</p>
<p>Surprisingly, my colleagues and I have found a new rule of biological growth that explains unexpected similarities in sharp structures found across the tree of life — in teeth, horns, claws, beaks, animal shells, and even the thorns and prickles of plants.</p>
<p>The discovery could help us look forward in evolution to predict how animals, including humans, and their many parts are likely to evolve. Our findings are published today in the open access journal <a href="https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-021-00990-w">BMC Biology</a>.</p>
<h2>The power of laws</h2>
<p>Some patterns are very common in nature, such as logarithmic spirals that follow the <a href="https://en.wikipedia.org/wiki/Golden_ratio">golden ratio</a>. These patterns appear because of the very simple processes that generate them. For example, a <a href="https://mathworld.wolfram.com/LogarithmicSpiral.html">logarithmic spiral</a> is produced when a spiral grows faster on one side than the other.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dahlia flower with golden ratio spiral overlayed." src="https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391361/original/file-20210324-19-52sivr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Logarithmic spirals follow the ‘golden ratio’ (~1.618). This mathematical ratio can predict patterns across nature, including in shells and plants.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>We can describe such patterns as following rules of growth. These rules help us understand why animals and plants are the shapes they are. </p>
<p>In my research I am fascinated by patterns in nature. And for many years I have searched for a pattern in how teeth grow. By looking at hundreds of teeth and measuring how they get wider as they get longer, my team and I identified a simple mathematical formula that underpins tooth shape. </p>
<p>This is a “power law”, in which there’s a straight-line relationship between a tooth’s width and length when you take a logarithm of these measurements. <a href="https://en.wikipedia.org/wiki/Power_law">Power laws</a> are also found in the sizes of earthquakes, extinction rates of animals and movements of the stock market.</p>
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Read more:
<a href="https://theconversation.com/the-golden-mean-a-great-discovery-or-natural-phenomenon-20570">The Golden Mean: a great discovery or natural phenomenon?</a>
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</em>
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<h2>Thorns, horns and hooves</h2>
<p>We named the new power law the “power cascade”, as it describes how the surface of a tooth <em>cascades</em> down while following a specific pattern. We looked at teeth from huge sharks, <em>Tyrannosaurus rex</em>, mammoths and humans, and saw the power cascade pattern in all of them. </p>
<p>Amazingly, the rule also works for claws, hooves, horns, spider fangs, snail shells, antlers, and the <a href="https://www.britannica.com/science/beak">beaks</a> of mammals, birds and dinosaurs. We even observed it in the horns of a <em>Triceratops</em> skeleton to be displayed at Melbourne Museum.</p>
<p>Perhaps these structures have a common shape because many of them carry out the same job. For instance, a sharp dinosaur tooth is useful for puncturing the flesh of prey, as is a sharp claw.</p>
<p>Nonetheless, we still find the power cascade pattern in physical traits that aren’t for piercing and have different shapes overall, such as shells and backward-facing horns. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/4WwVkwamMuA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The power cascade can simulate the growth of animal teeth, including sabre-toothed cats, Tyrannosaurs and giant sharks.</span></figcaption>
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<h2>Is it really a law of nature?</h2>
<p>While I first noticed the power cascade about ten years ago using a technique I’d developed to measure 3D shapes, the long road to its discovery began much earlier. </p>
<p>The pattern builds on an idea first put forward in 1659 by <a href="http://www.bbc.co.uk/history/historic_figures/wren_christopher.shtml">Sir Christopher Wren</a>, a polymath anatomist, physicist, mathematician and the architect of St Paul’s Cathedral in London.</p>
<p>Wren considered a snail shell may be a cone twisted around a logarithmic spiral. We now know shells and other shapes such as teeth and horns follow the power cascade shape, called a “power cone”. </p>
<p>The power cascade then seems to be the missing piece of a 350-year-old puzzle of how animals grow. But despite how common it is, can we really deem it a “law” of nature?</p>
<p>It was reasonably common for previous generations of biologists to refer to strong patterns (including the logarithmic spiral) as biological laws. </p>
<p>Biologists these days are very hesitant to use this term as it implies an unbreakable rule, such as the law of gravity. However, we can show there are very simple processes of growth which produce the power cascade pattern. </p>
<p>Therefore, when animals and plants grow in this way they will inevitably produce the power cascade shape, just as is the case with logarithmic spirals.</p>
<p>Certainly this rule can be bent, as seen by grooved snake fangs. But given the immense variety of animal parts it works for and the many shapes it makes, there’s a strong case to be made for classifying it as a power law of nature. </p>
<p>Future research will be able to confirm this.</p>
<h2>Predicting evolution (and life-like dragons)</h2>
<p>What can we do with this newly discovered rule? Well, to start it can help us think about the likely course of evolution. </p>
<p>The evolution of animals is usually thought to include a lot of “random” factors. This makes it difficult to know exactly what animals will end up looking like many millennia from now.</p>
<p>That said, the power cascade is perhaps the simplest way for a pointed structure to form when an animal is growing as an embryo or juvenile. Thus, we’d expect this shape to be very common both now and in the future — and we know the former to be true.</p>
<p>We can even apply the power cascade to imagine what shapes the teeth, horns and claws of mythical creatures might look like if they followed rules in nature. In other words, we can now design dragons in Game of Thrones and fantastic beasts in Harry Potter to look as realistic as possible.</p>
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<a href="https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Still of dragon's face from Game of Thrones" src="https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391373/original/file-20210324-17-xyacvl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Perhaps it’s not such a bad thing we won’t ever get to inspect the teeth of a Game of Thrones dragon up close.</span>
<span class="attribution"><a class="source" href="https://www.imdb.com/title/tt3866826/?ref_=ttmi_tt">Game of Thrones ('The Dance of Dragons') / IMDB</a></span>
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</figure>
<p>Moreover, many structures such as horns have evolved independently in different animals. So each time this happens in the future, it will probably follow the power cascade shape. Humans with horns remain may an unlikely reality, but at least we’ll know what this would look like.</p>
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<p>
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<strong>
Read more:
<a href="https://theconversation.com/how-animals-got-their-spots-and-stripes-according-to-maths-85053">How animals got their spots and stripes – according to maths</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/157229/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alistair Evans receives funding from the Australian Research Council and Monash University, and is an Honorary Research Affiliate with Museums Victoria.</span></em></p>Teeth, horns, claws, beaks, shells and even plant prickles — the power cascade rule can be observed far and wide throughout nature, much like the famous golden ratio.Alistair Evans, Associate Professor, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1311892021-03-26T12:24:27Z2021-03-26T12:24:27ZHow humans became the best throwers on the planet<figure><img src="https://images.theconversation.com/files/391246/original/file-20210323-13-1dlrzok.jpg?ixlib=rb-1.1.0&rect=20%2C20%2C3407%2C2312&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New York Yankees closer Aroldis Chapman routinely tops 100 mph with his fastball.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/aroldis-chapman-of-the-new-york-yankees-in-action-against-news-photo/1278868402?adppopup=true">Jim McIsaac/Getty Images Sport via Getty Images</a></span></figcaption></figure><p>Pitchers’ fastballs are getting better and better.</p>
<p>From 2008 to 2020, the average speeds of all major league baseball pitches combined <a href="https://www.theringer.com/mlb/2021/3/15/22331075/pitching-mound-move-distance">rose by between 1.5 mph and 2 mph</a>. In the 2019 season, nearly 90% of the 281 pitchers who threw more than 1,000 pitches <a href="https://baseballsavant.mlb.com/leaderboard/pitch-arsenals?year=2019&min=1000&type=avg_speed&hand=">threw fastballs that averaged over 90 mph</a>. The 100 mph fastball – once a newsworthy event – <a href="https://www.usatoday.com/story/sports/mlb/2017/03/30/with-all-the-100-mph-pitchers-how-long-will-the-arms-last/99813546/">is now relatively common</a>.</p>
<p>But MLB pitchers aren’t the only expert throwers; most healthy people can throw faster than our <a href="https://doi.org/10.1038/nature12267">much stronger chimpanzee relatives</a>, who max out at around 30 mph. <a href="https://doi.org/10.1177/036354659602400506">A study of boys</a> from the ages of 8 to 14 who were only moderately trained in throwing could still throw two times faster than chimps.</p>
<p>So how and why did humans evolve to become expert throwers? </p>
<p>In two papers in The Quarterly Review of Biology, we explored the <a href="https://doi.org/10.1086/696721">ecological causes</a> and <a href="https://doi.org/10.1086/698225">evolutionary consequences</a> of throwing in humans. </p>
<h2>Sticks and stones that break bones</h2>
<p>Humans are the only species that can throw well enough to kill rivals and prey. Because throwing requires the highly coordinated and extraordinarily rapid movements of multiple body parts, there was likely a long history of selection favoring the evolution of expert throwing in our ancestors.</p>
<p>Most people probably don’t think throwing is important outside of sports because they’ve forgotten its usefulness. Part of that has to do with the fact that people have been using weapons like bows and firearms <a href="https://www.simonandschuster.com/books/Technology-and-War/Martin-Van-Creveld/9780029331538#">for centuries</a>.</p>
<p><a href="https://books.google.com/books/about/Throwing_Fire.html?id=vyFxldb2GJQC">But before the invention of these weapons</a>, our hunter-gatherer ancestors threw darts, knives, spears, sticks and stones at rivals and prey. Even today, stones remain effective weapons; <a href="https://www.reuters.com/article/us-health-coronavirus-india/migrant-workers-throw-stones-at-police-in-india-in-protest-against-lockdown-idUSKBN22L0JZ">you’ll see protesters heave stones at police</a> and <a href="https://www.rferl.org/a/afghan-rights-group-investigates-video-of-woman-being-stoned-to-death/30414665.html">stoning used as a form of punishment</a> in some places.</p>
<p>Darwin considered the evolution of throwing to be critical to the success of our ancestors. As he wrote in “<a href="https://books.google.com/books?id=Na9LAAAAMAAJ&printsec=frontcover&dq=darwin+1871+descent+of+man&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiZuKzpwu3nAhVOip4KHWVTDF0Q6AEwAXoECAUQAg#v=onepage&q=darwin%201871%20descent%20of%20man&f=false">The Descent of Man, and Selection in Relation to Sex</a>,” it allowed “the progenitors of man” to better “defend themselves with stones or clubs, to attack their prey, or otherwise to obtain food.”</p>
<p>The development of the skill begins with the evolution of bipedal locomotion, or walking on two feet. <a href="https://doi.org/10.1007/978-3-642-27800-6_48-3">This happened about 4 million years ago</a>, and it freed the arms and hands to learn new abilities like making tools, carrying goods and throwing.</p>
<p>The Australopithecines, the relatively small-brained, bipedal ancestors of our genus that lived in Africa <a href="https://doi.org/10.1016/B978-0-12-802652-6.00010-4">somewhere between 1 million and 4 million years ago</a>, probably threw projectiles as well, since <a href="https://doi.org/10.1046/j.1469-7580.2003.00144.x">their hand bones</a> hint at their ability to grip objects and throw them. </p>
<p>But just because you can throw doesn’t mean you can throw well. Anatomical adaptations like a tall mobile waist that decoupled the hips and thorax allowed for more torso rotation. A laterally oriented shoulder joint that better aligned the main axis of the upper arm with the action of chest muscles allowed for a greater range of motion. Both are necessary for high-speed throwing, <a href="https://doi.org/10.1038/nature12267">and these first appeared together in <em>Homo erectus</em></a> – the first member of our genus – about 2 million years ago. </p>
<p>The two main theories for why selection favored throwing are fighting and hunting. Most scholars have favored the <a href="https://doi.org/10.1016/0162-3095(82)90010-3">hunting hypothesis</a>. However, <a href="https://jhupbooks.press.jhu.edu/title/animal-tool-behavior">monkeys and apes</a> – especially chimpanzees, our closest relatives – frequently throw sticks, stones and vegetation during combat with each other and potential predators. Only rarely do they do so while hunting. Because throwing at other members of the same species is an ancestral trait in primates, <a href="https://doi.org/10.1086/696721">we argue that our throwing abilities evolved first in the context of combat and only later became a hunting tactic</a>.</p>
<h2>A skill that diverges by sex</h2>
<p>Once the ability to throw quickly and accurately became critical to success in combat and hunting, our male ancestors would have been more likely than females to develop, through natural selection, these skills, since anthropologists have shown that males <a href="https://global.oup.com/academic/product/war-in-human-civilization-9780199236633?cc=us&lang=en&">tended to fight</a> and <a href="https://www.jstor.org/stable/3773347">hunt big game</a>.</p>
<p>Over time, men who were better throwers became better warriors and hunters. This further accelerated the evolution of throwing ability in men because success in <a href="https://science.sciencemag.org/content/239/4843/985">war</a> and <a href="https://doi.org/10.1007/s12110-004-1013-9">hunting</a> increases male status within groups and influenced female mate choice.</p>
<p>Interestingly, while all modern humans can throw well relative to other primates, sex differences in throwing are among the <a href="https://doi.org/10.1037/0003-066X.60.6.581">largest behavioral differences between the sexes</a>. These differences emerge early in life and are not strongly influenced by experience or practice. </p>
<p>Anthropologists and biologists <a href="https://doi.org/10.1037/0033-2909.98.2.260">have extensively documented</a> this advantage in throwing velocity, distance and targeting ability, although a recent study <a href="https://doi.org/10.3389/fpsyg.2017.00212">suggests training may eliminate differences in throwing accuracy</a>.</p>
<p>Sex differences in throwing do not exist just because males are, on average, larger and stronger. <a href="https://doi.org/10.1086/698225">The relative size, shape and orientation of the shoulders of men</a> increase the range of motion of the arm during the cocking phase, which facilitates better throwing. Some of these differences begin early in life and exist even when taking into account sex differences in body size and the fact that males, from a young age, tend to throw more often than females.</p>
<p>Even among men, large size and strength do not always result in faster throwing. Throwing speed is influenced by a variety of factors including <a href="https://doi.org/10.1080/02701367.2006.10599378">the range of motion of the throwing arm</a> and <a href="https://doi.org/10.1080/02701367.2006.10599377">stride length</a>. That’s why relatively svelte pitchers like <a href="https://www.baseball-reference.com/players/l/linceti01.shtml">Tim Lincecum</a> and <a href="https://www.baseball-reference.com/players/m/martipe02.shtml">Pedro Martinez</a> were able to throw faster than most of their taller, stronger and bulkier counterparts.</p>
<p>Their bodies are the paragons of an evolutionary adaptation that has made humans the best throwers on the planet. If rising pitch speeds are any indication, the skill continues to develop. There are even some who argue that pitchers have become too good – and that <a href="https://www.theringer.com/mlb/2021/3/15/22331075/pitching-mound-move-distance">it’s high time to move back the mound</a>.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p><img src="https://counter.theconversation.com/content/131189/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>We’re the only species that can throw at speeds that kill.Michael P. Lombardo, Professor of Biology, Grand Valley State University Robert Deaner, Associate Professor of Psychology, Grand Valley State University Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1251942020-01-22T13:37:19Z2020-01-22T13:37:19ZWhat a bundle of buzzing bees can teach engineers about robotic materials<figure><img src="https://images.theconversation.com/files/308138/original/file-20191220-11904-19nzsit.jpg?ixlib=rb-1.1.0&rect=613%2C0%2C3987%2C3055&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Individuals working together as one.</span> <span class="attribution"><span class="source">Orit Peleg and Jacob Peters</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Gathered inside a small shed in the midst of a peaceful meadow, my colleagues and I are about to flip the switch to start a seemingly mundane procedure: using a motor to shake a wooden board. But underneath this board, we have a swarm of roughly 10,000 honeybees, clinging to each other in a single magnificent pulsing cone.</p>
<p>As we share one last look of excited concern, the swarm, literally a chunk of living material, starts to move right and left, jiggling like jelly. </p>
<p>Who in their right minds would shake a honeybee swarm? My colleagues and I are studying swarms to deepen our understanding of these essential pollinators, and also to see how we can leverage that understanding in the world of robotics materials.</p>
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<a href="https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=376&fit=crop&dpr=1 754w, https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=376&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/307042/original/file-20191216-123998-19vuyqy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=376&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">Honeybee swarms adapt to different branch shapes.</span>
<span class="attribution"><span class="source">Orit Peleg and Jacob Peters</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Many bees create one swarm</h2>
<p>The swarms in our study occur as part of the <a href="https://www.scientificamerican.com/article/how-honeybees-find-a-home/">reproductive cycle of European honeybee colonies</a>. When the number of bees exceeds available resources, usually in the spring or summer, a colony divides into two groups. One group, and a queen, fly away in search of a new permanent location while the rest of the bees remain behind.</p>
<p>During that effort, the relocating bees temporarily form a highly adaptable swarm that can hang from tree branches, <a href="https://apnews.com/3565459f20454cf399310eccd3bfbadf/NYPD-bee-squad-ready-for-sting-operations-on-urban-swarms">roofs, fences or cars</a>. While suspended, they have no nest to protect them from the elements. Huddling together allows them <a href="https://doi.org/10.1098/rsif.2013.1033">to minimize heat loss to the colder outside environment</a>. They also need to adapt in real time to temperature variations, rain and wind – all of which could shatter the fragile protection they share as one unit.</p>
<p>The swarm is orders of magnitude larger than the size of an individual bee. A bee could potentially coordinate its activity with neighboring bees right next to it, but it certainly couldn’t coordinate directly with any bees at the far edge of the swarm.</p>
<p>So how do they manage to maintain mechanical stability in the face of something like strong wind – a test that requires near simultaneous coordination throughout the entire swarm?</p>
<p>My colleagues <a href="https://scholar.google.com/citations?user=YYtLjJoAAAAJ&hl=en&oi=sra">Jacob Peters</a>, <a href="https://scholar.google.com/citations?user=Xt6THm8AAAAJ&hl=en&oi=ao">Mary Salcedo</a>, <a href="https://scholar.google.com/citations?user=iiyj5MsAAAAJ&hl=en&oi=sra">L. Mahadevan</a> and I devised a series of experiments to address that question — which brings us back to intentionally shaking the swarm.</p>
<h2>Individual actions, whole swarm response</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=717&fit=crop&dpr=1 600w, https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=717&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=717&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=901&fit=crop&dpr=1 754w, https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=901&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/307045/original/file-20191216-124027-1k6kspl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=901&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Examining the experimental setup, with the pyramidal swarm hanging from the bottom of the board.</span>
<span class="attribution"><span class="source">Orit Peleg and Jake Peters</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>When we shook the swarm along its horizontal axis, the bees adjusted the shape of their swarm and within minutes became a wider, more stable cone. However, when the motion was vertical, the shape remained constant until a critical force was reached that caused the swarm to break apart.</p>
<p>Why did the bees respond to horizontal shaking, but not to vertical shaking? It’s all about how the <a href="https://doi.org/10.1038/s41567-018-0262-1">bonds bees create by “holding hands”</a> get stretched.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310361/original/file-20200115-134772-sfa6ua.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">Honeybees are essentially holding hands to create the dense swarm structure. How much the bonds between two bees stretch is important information that influences their actions for the good of the swarm.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/trust-teamwork-bees-linking-two-bee-262155599">Viesinsh/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>It turns out vertical shaking doesn’t disrupt these pair bonds as much as horizontal shaking does. Using a computational model, we showed that bonds between bees located closer to where the swarm attaches to the board stretch more than bonds between bees at the far tip of the swarm. Bees could sense these different amounts of stretching, and use them as a directional signal to move upwards and make the swarm spread. </p>
<p>In other words, bees move from locations where bonds stretch less, to locations where they stretch more. This behavioral response improves the collective stability of the swarm as a whole at the expense of increasing the average burden experienced by the individual bee. The result is a kind of “mechanical altruism”, as the one bee endures strain for the benefit of the swarm’s greater good.</p>
<h2>Engineering lessons, taught by bees</h2>
<p><a href="https://scholar.google.com/citations?user=xH5Ryy4AAAAJ&hl=en&oi=ao">As a broadly trained physicist studying animal behavior</a>, I am fascinated by this kind of evolved solution in nature. It’s amazing that honeybees can create multi-functional materials – made of their many individual bodies – that can shape shift without a global conductor telling them all what to do. No one is in charge, but together they keep the swarm intact. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jswSJznyvDI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Bee swarms exhibit emergent intelligence, behaving as one unit.</span></figcaption>
</figure>
<p>What if engineers could take those solutions and lessons from nature and apply them to buildings? Instead of a bundle of buzzing bees, could you imagine a bundle of buzzing robots that cling on each other to create adaptive structures in real time? I can <a href="https://www.arch2o.com/hypercell-thesis-aadrl/">envision shelters</a> that deploy rapidly in the face of natural disasters like hurricanes, or construction materials that can sense an earthquake’s vibrations and respond in the same way that these swarms react to a branch in wind.</p>
<p>Essentially, these bees create an autonomous material that – embedded within itself – has multiple abilities. The swarm can sense information from the nearby environment, based on how much the pair bonds are stretching. It can compute, in the sense that it figures out which regions have more bond stretching. And it can actuate, meaning move in the direction toward more stretching.</p>
<p>These properties are some of the longstanding aspirations in the fields of <a href="https://doi.org/10.1126/science.1261689">multi-functional materials and robotics materials</a>. The idea is to combine affordable robots that each have a minimal amount of mechanical components and sensors, like the <a href="http://news.mit.edu/2019/self-transforming-robot-blocks-jump-spin-flip-identify-each-other-1030">M-blocks</a>. Together they can sense their local environment, interact with neighboring robots and make their own decisions on where to move next. As Hiro, the young roboticist in the Disney movie “<a href="https://youtu.be/ep2-W1X65KI?t=55">Big Hero 6</a>” says, “The applications to this tech are limitless.”</p>
<p>For the moment, <a href="https://www.thisiscolossal.com/2019/12/spatial-bodies-aujik/?fbclid=IwAR1QWvNE_NiEiVsZR6pWZRFGoknPjsex0Ji05L-OFTDXmv8WlXDtlkiy7d8">this is still science fiction</a>. But the more researchers know about the honeybees’ natural solutions, the closer we get to making that dream come true.</p>
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<p class="fine-print"><em><span>Orit Peleg receives funding from the Human Frontiers Science Program. </span></em></p>A swarm of honeybees can provide valuable lessons about how a group of many individuals can work together to accomplish a task, even with no one in charge. Roboticists are taking notes.Orit Peleg, Assistant Professor of Computer Science, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.