Making North America: Life Hero

<p></p><p>How did life emerge on our primeval continent? Why was North America home to so many iconic dinosaurs like <i>T. rex</i>? And how did a huge sea filled with giant marine reptiles end up covering Kansas? We tell the surprising intertwined story of life and the landscape in North America.</p>

<p>How did massive volcanic eruptions, inland seas, and land bridges pave the way for life?</p>

Making North America: Life

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<p>A new study provides compelling evidence that children can inherit mitochondrial DNA from both their parents.</p>

Not Your Mom’s Genes: Mitochondrial DNA Can Come from Dad

NOVA Wonders Can We Make Life? Hero

<p></p><p>&quot;It&#x27;s alive!&quot; Since Dr. Frankenstein spoke those famous words, we&#x27;ve been alternately enthralled and terrified by the idea of creating life in the lab. Now, a revolution in genetic engineering and thrilling innovations in synthetic biology are bringing that dream—or nightmare, as the case may be—closer to reality. New tools allow researchers to use cells to create their own DNA and edit it into existing genomes with more ease and less cost than ever before. Along with renewed hopes for treating some genetic diseases, there&#x27;s serious talk of using the newest technologies to bring long-extinct animals back from the dead – like the team hoping to resurrect the woolly mammoth. Science fiction is quickly becoming science fact. Another daring genetic experiment to bioengineer animals could prevent Lyme disease. But the power to make life comes with deep ethical questions. What are the potential rewards—and dangers—of tinkering with nature? <i>NOVA Wonders</i> explores the benefits and the burden of risk surrounding the controversial new technology.</p><p></p><p></p>

<p>A revolution in gene editing enables scientists to create and edit DNA like never before.</p>

Can We Make Life?

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Evolution

Koch Foundation

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      <div class="rich-text"><p>Don’t be fooled by their charming name: <a href="http://medent.usyd.edu.au/fact/bedbugs.html">Bed bugs</a> don’t need beds to set up shop. These intrepid insects will colonize pretty much any place where people pile up, including hotels, movie theaters, libraries, even the <a href="http://gothamist.com/2014/08/06/bed_bugs_on_the_n_train.php">occasional subway</a>—ready and waiting to ruin a human life with their bloodsucking mouthparts and death-defying durability.</p><p>It’s easy to dismiss bed bugs as loathsome pests that exist to make humans miserable. But in reality, bed bugs predate humans by leaps and bounds, making <i>us</i> the unwanted interlopers that first crossed into their turf.</p></div>
  

  
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      <div class="rich-text"><p>According to a newly mapped bed bug family tree, these puny pests have been guzzling the blood of other animals for more than 100 million years, long before the rise of both modern humans and bats, their most common host. The <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(19)30477-4?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982219304774%3Fshowall%3Dtrue">research</a>, published today in the journal <i>Current Biology,</i> shows that the bed bug timeline stretches further back than even the <a href="https://www.pbs.org/wgbh/nova/article/new-fossils-mass-extinction-wiped-out-dinosaurs/">mass extinction</a> that wiped out 75 percent of Earth’s plant and animal species, including all dinosaurs, 66 million years ago.</p><p>The surprising longevity of bed bugs means we’re no longer certain of the identity of these bloodthirsty buggers’ first host. But the study’s findings could still offer clues on how bed bugs once made the jump to humans, and if that transition will have an encore act in the future.</p><p>“Bed bugs didn’t evolve on humans,” says study author <a href="https://www.sheffield.ac.uk/aps/staff-and-students/acadstaff/siva-jothy">Michael Siva-Jothy</a>, an entomologist and evolutionary biologist at the University of Sheffield in the United Kingdom. “We just happen to be their current host at the moment—which means they’re very good at what they do.”</p>
            <figure class="richtext-image full-width"><img alt="iStock-165162859.jpg" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/iStock-165162859.width-800.jpg"/><figcaption><p>Bed bug bites are caused primarily by two species—Cimex lectularius and Cimex hemipterus—which pierce human skin and drink blood with their sucking mouthparts. Luckily, neither is thought to transmit disease. Image Credit: smuay, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>The scourge of bed bugs on humankind is believed to stretch back to the very dawn of our species. But only three species—<i>Cimex lectularius</i>, <i>Cimex hemipterus</i>, and, less commonly, <i>Leptocimex boueti</i>—routinely spend their nights supping on human blood. At least 100 other types of bed bugs exist worldwide, feeding mostly on bats and, to a lesser extent, birds, and researchers still don’t have a good understanding of these insects’ origins, and how species have split and diversified over time.</p><p>To generate a more complete bed bug catalog, an international team of scientists led by <a href="http://www.dresden-ipp.de/research/research-groups/klaus-reinhardt/">Klaus Reinhardt</a>, a molecular and evolutionary biologist at the Dresden University of Technology in Germany, set out to amass insects from around the world.</p><p>A handful of specimens weren’t too hard to come by, arriving via the generosity of natural history museums, or scientific colleagues who had seen the team’s requests for help on Twitter. Collecting the lion’s share of the data, however, required some pretty gnarly field trips that featured amateur cliff scaling, treks through knee-deep guano, and hikes into remote mountaintop caves—all in search of nondescript insects just millimeters long.</p><p>In all, sample collection alone took the study’s 15 authors the better part of 15 years. But the result was an unprecedented collection of pristine bed bug DNA, representing 34 species hailing from 62 localities around the globe.</p><p>“It’s really difficult to collect these specimens,” says <a href="https://heteroptera.ucr.edu/index.php/people/christiane-weirauch">Christiane Weirauch</a>, a systematic entomologist at the University of California, Riverside who was not involved in the study. “It’s just so cool that this team has pulled this together.”</p></div>
  

  
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      <div class="rich-text"><p>By comparing DNA sequences across species, Reinhardt, Siva-Jothy, and their colleagues were able to trace the evolutionary relationships between the bed bugs they’d collected. The researchers then combined their data with evidence from known insect fossils to pinpoint when bed bug lineages had split in the past. And when the bed bug family tree was finally mapped, the team was met with a set of findings that flew in the face of almost everything they’d expected.</p><p>Because bats remain the most common host of bed bugs (technically, bat bugs) today, Siva-Jothy says, most researchers have assumed that the first bed bugs to scuttle the Earth also gorged on the blood of these winged mammals. Cozied up to cave-dwelling bats, bed bugs would’ve then had an easy time making the hop to our human ancestors seeking shelter some 2 million years ago, and evolved alongside the genus <i>Homo</i> ever since.</p><p>Neither of these theories panned out.</p><p>The researchers’ analysis now places the origin of bedbugs around 115 million years ago, during the Cretaceous—a whopping 30 to 50 million years before bats are believed to have come onto the scene. It’s not yet clear what species first drew the bed bug straw, but a good candidate might be a small, social, cave-dwelling mammal, Reinhardt says.</p><p>Others, however, aren’t ready to completely rule out bats, or at least an early bat-like ancestor. “The fossil records for [both bed bugs and mammals] are patchy...that makes it hard to make definitive statements,” says <a href="http://runewarkbiology.rutgers.edu/ware%20lab/Welcome.html">Jessica Ware</a>, an entomologist and evolutionary biologist at Rutgers University who was not involved in the study. “It’s possible bats are older, and we’ve just underestimated.”</p><p>Some 70 more bed bug species have yet to be analyzed in this way, and the family tree could still change with the addition of new data, Ware says. “That being said, this is the first and maybe most comprehensive analysis people have done for [this group of insects].”</p><p>Regardless of where, and on whom, bed bugs got their start, it appears these insects were hardy enough to weather a mass extinction—and have remained alarmingly adaptable ever since. The researchers’ findings suggest that, throughout their evolutionary history, several bed bug species went from bothering bats to terrorizing birds and vice versa. Along the way, at least three species dipped their spindly legs into human stock. Surprisingly, all three species appear to have evolved independently, with each making a separate jump to human hosts.</p><p>In other words, we humans didn’t actually do much to shape the evolution of one of our most iconic pests, who were perfectly content binging on the blood of bats and birds. It just so happened that, when an unlucky member of the genus <i>Homo</i> stumbled onto their path, certain bed bugs were flexible enough to expand their palates.</p>
            <figure class="richtext-image full-width"><img alt="Bat and bed bug - credit Mark Chappell, Univ Cailf, Riverside.jpg" class="richtext-image full-width" height="555" width="800"
            src="/wgbh/nova/media/images/Bat_and_bed_bug_-_credit_Mark_Chappell_Univ_Ca.width-800.jpg"/><figcaption><p>Bats were once thought to be the first host of bed bugs. But a newly mapped family tree shows that bed bugs predate bats by 30 to 50 million years. Image Credit: Mark Chappell, University of California, Riverside</p><div class="credit"><p></p></div></figcaption>
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            <p>There’s even a chance <i>another</i> bed bug species might one day develop a taste for human blood, Reinhardt says (in fact, it might <a href="https://watermark.silverchair.com/ae58-0058.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAjkwggI1BgkqhkiG9w0BBwagggImMIICIgIBADCCAhsGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMeB773wO7vsgeI0ahAgEQgIIB7N3OJjzz28ZhRu_7P4PiFqmG8uOc6RN7f07X1arxgqKyPIIi-Rm3W2HkKYAndcL7MM7mHpjWgzTx8KjUlA0ayFEopPC49PuO4tOesgkIjWOr3ySJ1HFdaIrgU8BVZ0rkPly5GFRymZP9D3RNIYdgpbfG-ojmCzoZZ2-g8hFnrm8a2dWUIy8ixBQP0Fh4lv5nrRaj3dVdycN8QemKpacQai_ekTZ5yVfLxl1racHHJ1lzTyEZhoVgpGytkWps0Tc4AEXhNPu4aNyGaBvfq64AUh9_4RkhaGK45DUcXzuMIew493CzpNgtOCXkcOWHmlU0pOzVY96BcykJVTEtTkBxROjBaQkC0qbF8iUJhMA6EwNUFpuuusk6EiJd77u2lAMWYBWg7ei5Qp350RkLa2zdt7JEmX48IUM2du4eW3m7x83OkyGcHP3V6-OPnRWHISarVsldy1zpsBBJxyAUVnOZf1VH2LJiuyi-n_sVJEbprGBYej3Idx-VuIIOK9tV9BkSpHcAxAzOnWt-CoBqJH7J7DqneKvmmQBqxHacHRLRsS16PcOilRPodQlov3zR0VZ23JDorQaYXyfROnz0DlPRmqT-ynoy3gjBgos4B0FQ8ey9UoQiXcPg6Itt8kXSLLPOHwUdzvuJ-2r-Ydlhgg">already be happening</a>). Based on the historical data, these transitions happen roughly every half a million years.</p><p>But the more pressing concern might be the enemies we already know, Siva-Jothy says. “With human populations expanding, and our reliance on animals, and the way cities grow and communicate…there will be more opportunities for the species we’ve already got to become more widespread.”</p><p>Given the stubbornness of bed bug infestations, that’s not great news. It’s enough to make us wonder if bed bugs have the apocalyptic armor to outlive us all.</p><p>We might not have made our bed bugs. But we still have to lie with them.</p></div>
  

  
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<p>The rise of bed bugs preceded modern humans by at least 100 million years. They survived the extinction that killed the dinosaurs. Could they outlive us all?</p>

Bed Bugs Don’t Need Beds, or Humans, to Survive. They Never Did





  
      <div class="rich-text"><p>Some 5,000 years ago, <i>Homo</i> domesticated <i>Equus</i>—and the histories of human and horse intertwined.</p><p>In the millennia since, peoples worldwide have leveraged the speed and power of these once-wild creatures to plow fields, stage hostile takeovers, and carry everything from goods to diseases across contentious borders. Even a good number of modern human languages owe their roots to equines: Before the ancestral tongue of Proto-Indo-European splintered into hundreds of linguistic descendants still spoken today, it was ferried throughout the Eurasian continent on horseback.</p></div>
  

  
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      <div class="rich-text"><p>Horses have dramatically shaped the human civilization—but researchers still know surprisingly little about how we have shaped them. To this day, even the identity of the wild ancestor of the modern domestic horse remains mysterious.</p><p>But now, thanks to a new analysis of ancient DNA, an international team of scientists has constructed the <a href="https://www.cell.com/cell/fulltext/S0092-8674(19)30384-8">largest collection of horse genomes to date</a>, spanning tens of thousands of years of equine history across Europe and Asia. Their <a href="https://www.cell.com/cell/fulltext/S0092-8674(19)30384-8">study</a>, published today in the journal <i>Cell,</i> suggests that the genetic diversity of domestic horses has deteriorated only in the last few hundred years, underscoring the toll recent animal husbandry practices have taken on modern breeds.</p><p>“This study is brilliant,” says <a href="https://scholar.harvard.edu/vagheesh/home">Vagheesh Narasimhan</a>, a mathematical genomicist at Harvard University who was not involved in the study. “Just to see data of this scale being produced for a species other than humans is spectacular.”</p>
            <figure class="richtext-image full-width"><img alt="iStock-865176640.jpg" class="richtext-image full-width" height="532" width="800"
            src="/wgbh/nova/media/images/iStock-865176640.width-800.jpg"/><figcaption><p>Today, only two lineages of horses remain: the modern domestic horse and its small, stocky cousin, the endangered Przewalski&#x27;s horse. Image Credit: LifeJourneys, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>To map out a timeline of equines past, a team of researchers led by <a href="http://amis.cnrs.fr/?Orlando-Ludovic&amp;lang=fr">Ludovic Orlando</a>, a molecular archaeologist and geneticist at the French National Center for Scientific Research, the University of Toulouse, and the University of Copenhagen, turned to the best source of information it had: ancient DNA, extracted from 250 fossils strewn across sites from Spain to Mongolia.</p><p>“DNA is nature’s own written history,” says <a href="http://animal.ifas.ufl.edu/faculty/brooks/index.shtml">Samantha Brooks</a>, a horse geneticist at the University of Florida who was not involved in the study. “Horses can’t write or speak their side of their story, but we can read a little bit about the events based on their DNA.”</p></div>
  

  
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      <div class="rich-text"><p>To deduce how humans might have sculpted the biology of their hoofed companions, the researchers compared ancient genomes from across time and space, and explored how they stacked up against modern breeds. This large-scale approach allowed them to both track the rise and fall of certain traits within the equine gene pool and link those shifts to events throughout human history.</p><p>Horses were first bridled by humans sometime between the fourth and third millennium BCE. Through their analysis, the researchers found that breeding priorities have undergone several revolutions in the centuries since. For instance, around 1,000 years ago, strong, sturdy builds came into fashion, ushering in the lasting age of the Arabian horses, which still frequent many a stable today. Traits like speed and the ability to amble—a medium-speed gait that’s considered more comfortable for riders—also became common fixtures in the equine lineage.</p><p>Despite these reproductive restrictions, the genomic time series showed that domesticated horses remained relatively genetically diverse for the first 4,000 years or so of their close coexistence with humans. It was only around 200 or 300 years ago that these levels took a sharp downturn.</p><p>“This is the moment that genetic diversity started to collapse,” says study author <a href="http://amis.cnrs.fr/?Fages-Antoine&amp;lang=fr">Antoine Fages</a>, a paleogenomicist at the University of Toulouse. “It’s quite amazing that it happened so quickly and so recently.”</p><p>The turning point coincides neatly with the latter half of the 18th century, when horse racing began in earnest, paring down the list of “desirable” equine traits, Fages says. As agility and power skyrocketed in importance, breeders began to select only a handful of stallions to sire future generations, keeping large parts of the population from throwing their genetic hats into the ring.</p><p>The dip isn’t shocking, though, and it parallels what humans have seen in other domesticated species, like dogs and livestock, Brooks says. The timing, she says, also coincides with cultural and technological evolutions in our history. As humans became less dependent on horses for farming and transportation, the relationship between the two species began to change. Eventually, equines settled into a newer, more specialized niche—recreation—giving breeders less incentive to keep their stables stocked with a diverse set of animals.</p><p>Even today, the genetic diversity of horses is in decline, says <a href="https://www.equine.umn.edu/bio/equine-genomics-genetics-team/molly-mccue">Molly McCue</a>, a horse geneticist at the University of Minnesota who was not involved in the study. This is “critically important” to keep in mind, she says, because populations with less genetic variation are more vulnerable to accumulating mutations, some of which might lead to disease.</p><p>Still, this downward trajectory isn’t a foregone conclusion, Fages says. It’s worth remembering the fact that humans were able to manage horses for thousands of years without negatively impacting their genetics.</p>
            <figure class="richtext-image full-width"><img alt="Horse-racing-1.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/Horse-racing-1.width-800.jpg"/><figcaption><p>The best of today&#x27;s thoroughbreds can race at speeds up to 55 miles per hour, and have a substantially different genetic makeup than the horses that thundered across the steppes and plains of Eurasia thousands of years ago. Image Credit: Softeis~commonswiki, Wikimedia Commons</p><div class="credit"><p></p></div></figcaption>
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            <p>Regardless of what awaits horses in the future, though, one key gap in their past has yet to be filled. While Przewalski’s horses—the only other lineage of horse still alive today—are known to hail from <a href="https://science.sciencemag.org/content/360/6384/111">Botai horses</a>, the ancestors that once gave rise to our modern domesticates remain anonymous.</p><p>Even with so many genomes at their disposal, the researchers were surprised to find themselves no closer to an answer. Their search, however, did rule out two previously unknown candidates: two long-gone lineages that once independently roamed Iberia and Siberia. While both were still thriving during some of the early days of domestication, the DNA in their remains bore little resemblance to that of today’s horses, suggesting that neither lineage directly gave rise to modern breeds before they died out. “These are sort of the horse equivalent of what Neanderthals and Denisovans are to humans,” Orlando says.</p><p>Several branches, it seems, are still missing from the equine family tree. But in the meantime, these new lineages add some much-needed complexity to the enigmatic tale of the horse—and, in turn, our own storied past.</p><p>“Human cultures and civilizations are what they are today in part because some people had horses, and others did not,” Brooks says. “Knowing more about their history tells us a lot about ourselves.”</p><p><i>To learn more about the rich history of horse domestication, watch “</i><a href="https://www.pbs.org/wgbh/nova/video/first-horse-warriors/"><i>First Horse Warriors</i></a><i>,” premiering at 9 p.m. EDT/8 p.m. CDT on Wednesday, May 15 on PBS.</i></p></div>
  

  
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<p>A sweeping genomic study expands the equine family tree and pinpoints how humans might have reshaped the equine gene pool.</p>

Domestic Horses Have Existed for Millennia. Modern Breeding Reduced Their Genetic Diversity in Just a Few Hundred Years.





  
      <div class="rich-text"><p>Given the choice between a wolf and a dog for a companion, you might be more inclined to choose a floppy-eared mutt.</p><p>For what it’s worth, that’s probably the right choice—as long as you’re human.</p><p>According to a <a href="https://doi.org/10.1371/journal.pone.0215444">study</a> published today in the journal <i>PLOS ONE</i>, wolves appear to be more inclined than dogs to be generous with their pack mates. When given the choice, wolves deliver food to their friends, even if they don’t benefit themselves. Dogs, on the other hand, quickly lose interest in the absence of personal payoff.</p><p>So far, these differences have only been noted with dogs raised in packs, and can’t be extrapolated to any pooches that live as pets. But the results hint at a surprising possibility: To become humans’ best friends, dogs might have had to reroute their loyalties—and snub their own species in the process.</p><p>“[These results] should encourage the scientific community to reexamine the hypotheses about the purpose of domestication,” says <a href="https://www.nps.gov/yell/learn/nature/wolves.htm">Kira Cassidy</a>, a wolf research at Yellowstone National Park who was not involved in the study. “[While] wolves have evolved to cooperate in order to survive...perhaps, after many generations of domestication, dogs now see humans as their family.”</p></div>
  

  
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      <div class="rich-text"><p>All domestic dogs can trace their genetic roots back to a fierce, wolf-like ancestor—but today, few dog breeds still look or act the part. Over the course of human-driven domestication, this once-wild lineage grew tame, eventually accumulating enough genetic changes that an entirely new species arose. Now, modern mutts lounge in our living rooms and nibble at scraps from the edges of our plates; they’ve even learned to <a href="https://science.sciencemag.org/content/298/5598/1634.long">tune in to the subtleties</a> of <a href="https://www.smithsonianmag.com/science-nature/why-most-helpful-dogs-keep-calm-and-carry-180969731/">human emotion</a>.</p><p>Dogs’ persisting partnership with people might make it tempting to give humans all the credit for canine congeniality. But gray wolves, the other direct descendants of that long-gone lupine ancestor, aren’t exactly slouches at cooperation. In the wild, wolves rely on their pack mates for everything from food to caring for their young. The charitable nature of domestic dogs might be a product of human intervention—but it could just as easily be an age-old trait passed down from their pack-living predecessors.</p><p>To suss out whether dogs or wolves had the upper paw, a team of researchers led by <a href="https://www.wolfscience.at/en/aboutus/team/racheldale/">Rachel Dale</a> decided to see if two groups of canines would be willing to perform the ultimate act of altruism: give without getting in return.</p></div>
  

  
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      <div class="rich-text"><p>But the cushy, human-centric lifestyle of pet dogs can be hard to compare to the the close-knit, pack culture of wolves. To level the playing field, Dale and her team conducted their experiments using captive wolves and dogs raised in cohorts of their own species at the Wolf Science Center in Austria.</p><p>Nine wolves and six dogs were given the opportunity to deliver a tasty treat to a pack mate by pressing their noses to a “giving” symbol on a touchscreen. (To make sure the wolves weren’t just having fun nosing the touchscreens, the researchers also included a “withhold” option on the interface.) None of the donors were able to access the food themselves, but if they behaved selflessly, they could watch their friends chow down in their place.</p><p>To Dale’s surprise, the wolves repeatedly bested their domestic canine cousins in the realm of generosity. While the wolves booped the “giving” option time and time again to reward their pack mates, dogs were less likely to be team players.The wolves also showed an obvious preference for familiar faces, quickly losing interest in the tasks when they didn’t recognize the recipient. Dogs, on the other hand, didn’t seem eager to gift grub to other members of their species, regardless of whether they’d spent time with them or not.</p><p>These results were “surprising at first,” but in hindsight, there are several reasonable explanations, says <a href="https://www.ripon.edu/faculty/julia-meyers-manor/">Julia Meyers-Manor</a>, a dog behavior expert at Ripon College who was not involved in the study. In the wild, teamwork is often a matter of life and death—but within the cozy confines of human civilization, independence might be a more useful strategy. As dogs exchanged a lifestyle of hunting for scavenging human scraps, there might have been less pressure for groups of canines to act as cohesive units, and instead fend for themselves.</p>
            <figure class="richtext-image full-width"><img alt="199204.jpg" class="richtext-image full-width" height="325" width="800"
            src="/wgbh/nova/media/images/199204.width-800.jpg"/><figcaption><p>Because the wolf on the right pressed the &quot;giving&quot; symbol, its partner on the left was rewarded with a piece of sausage while the donor watched. Image Credit: Rachel Dale, Wolf Science Center</p><div class="credit"><p></p></div></figcaption>
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            <p>“Domestication hasn’t necessarily made dogs more tolerant of, or cooperative with, each other,” Dale says. “Some people have assumed this…but just because they’ve been selected to work so well with humans, that doesn’t mean they’ll do it with each other as a byproduct.” In fact, Dale says, it’s possible that the <i>inverse</i> might be true: Through domestication, humans might have inadvertently encouraged canines to choose person over pup.</p><p>For now, that’s still a theory. Additionally, because the dogs in the study grew up in packs, the results don’t have any bearing on how pet dogs, which spend most of their time around humans, might behave. In fact, Dale’s previous work suggests that dogs raised in the presence of people will happily share resources with <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0167750#pone.0167750.ref005">their own kind</a>.</p><p>It’s not yet clear why dogs might differ as pets or pack mates, but Dale has a theory. While pack dogs live by their own set of rules, most of the mutts that hang out with humans are rewarded for being chummy, she says. That sort of positive reinforcement could bring out the best in these dogs under all kinds of circumstances.</p><p>In other words, there’s nothing to show that dogs have lost the ability to lend a helping paw. After all, plenty of canines can still be counted on to have each other’s backs—and they were doing it long before we humans entered the picture.</p><p>“Sometimes we think, ‘Humans can cooperate, and it’s something other animals don’t have,’” says <a href="https://dogs.arizona.edu/people/gitanjali-gnanadesikan">Gitanjali Gnanadesikan</a>, who studies social behavior in dogs at the University of Arizona, but was not involved in the study. “But we see examples of this behavior throughout the animal kingdom...it’s naive to think other animals wouldn’t have ways of collaborating.”</p></div>
  

  
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<p>Dogs might be less inclined to be generous to their pack mates, hinting that domestication hasn’t necessarily improved canine social skills.</p>

Wolves Boop Their Snoots to Touch Screens to Feed Their Friends. Dogs? Not So Much.

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<p>Fossilized fish uncovered in North Dakota appear to preserve the catastrophic fallout of the asteroid impact that wiped out the dinosaurs.</p>
<p>Newly uncovered fossils in North Dakota appear to be the victims of one of the most catastrophic days in Earth’s history—the day the dinosaurs died 66 million years ago. A team of researchers led by paleontologist Robert DePalma reports chaotic debris created by two huge waves that surged up a river from an ancient inland sea. They say the site holds much more evidence that will keep them busy for years to come.</p>
<p><b>Stunning Fossil Discovery Could Offer Glimpse into Day the Dinosaurs Died</b></p><p>Published: April 22, 2019</p><p></p><p><b>Onscreen:</b> Newly uncovered fossils in North Dakota appear to be the victims of the most catastrophic day in Earth’s history… the day the dinosaurs died.</p><p><b>Jay Melosh:</b> You basically get a snapshot at the time that all these critters were dying. I think of this as the paleontological discovery of the century.</p><p><b>Onscreen</b>: A team of researchers led by paleontologist Robert DePalma says they uncovered chaotic debris created by two huge waves that surged up a river from an ancient inland sea.</p><p><b>Robert DePalma:</b> Essentially what you are looking at is a cross-section of what was alive at the time and you’re looking at a moment-by-moment record of conditions right after impact.</p><p><b>Onscreen</b>: Sixty-six million years ago, an asteroid smashed into Earth along the coast of Mexico setting off a chain reaction of apocalyptic events.</p><p><b>David Kring:</b> Massive earthquakes, immense landslides, and tsunamis or tidal waves that radiated across the Gulf of Mexico basin and for those of us in the United States, incursions of flood waters up onto the continent.</p><p><b>Onscreen</b>: Scientists think the impact also launched molten rock into the atmosphere where it formed little beads, called tektites, that rained back down to Earth.</p><p><b>Jan Smit:</b> DePalma pried out a region of the gills, and there was a collection of tektites stuck in the gills right there on the spot. From then I was totally convinced that he had something fantastic in that area.</p><p><b>DePalma:</b> What we see is these ejecta beads, these ejecta spherules caught in the gills of the fish. So that shows that these fish were alive right up until the time they were buried in the mud. They were entombed relatively instantaneously that’s why they are so well preserved. They are three-dimensionally preserved. That’s how we know that this was a very rapid event.</p><p><b>Onscreen</b>: Team members say the site holds much more evidence that will keep them busy for years to come.</p><p><b>DePalma:</b> This site and the research actually directly applies to what we’ve got going on today because this impact is one of our only test beds to see how the world ecology responds to major natural hazards and extinction-level events.</p><p><b>Smit:</b> There are lots of open questions to answer all the beautiful observations we have. We are just at the beginning.</p>
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<p>Fossilized fish uncovered in North Dakota appear to preserve the catastrophic fallout of the asteroid impact that wiped out the dinosaurs.</p>

Stunning Fossil Discovery Could Offer Glimpse into the Day the Dinosaurs Died





  
      <div class="rich-text"><p>The history of human evolution might be getting yet another rewrite.</p><p>According to a <a href="https://www.nature.com/articles/s41586-019-1067-9">study</a> published today in the journal <i>Nature,</i> a vast, chambered cave in the Philippines holds the remains of a previously unknown, small-bodied population of early humans who lived some 67,000 years ago. If confirmed to be a distinct species, the newly-dubbed <i>Homo luzonensis</i> could add yet another branch to our ever-growing family tree.</p><p>Regardless of species designation, though, the presence of any ancient human remains on this remote island locale reaffirms the role Southeast Asia played in shaping our evolution—and suggests our ancestors weren’t quite as landlocked as once thought.</p><p>“This is a really welcome and exciting addition,” says <a href="https://anthropology.missouri.edu/people/ward">Carol Ward</a>, a biological anthropologist at the University of Missouri who was not involved in the study. “We now have evidence of [ancient humans] in a time and place that has been very poorly understood, and yet was undoubtedly important for the biology and evolution of our species.”</p><p>But Ward and others remain cautious about assigning an entirely new species to the remains, which contain just 13 fossils: a smattering of hand and foot bones, a few teeth, and a partial femur. Additionally, at least two adults and one child are jumbled up in the mix, muddying the picture of what a full skeleton might look like. “New fossils are always exciting,” Ward says. “But they always raise more questions than they answer.”</p></div>
  

  
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      <div class="rich-text"><p>The first fossil in the collection—<a href="https://www.sciencedirect.com/science/article/pii/S0047248410000850?via%3Dihub">a petite, curiously curved foot bone</a>—was unearthed in 2007 in Callao Cave on the Philippine island of Luzon. It clearly came from a member of the group known as hominins, which encompasses the human lineage after it split from the chimpanzee and bonobo line. But study author <a href="http://asp.upd.edu.ph/faculty/armandmijares.html">Armand Mijares</a>, an archaeologist at the University of Philippines Diliman, was struck by the bone’s anatomy, which didn’t fall neatly within the bounds of any known human species.</p><p>No matter how peculiar, though, a single fossil isn’t enough to tell a story. So Mijares and his team dug deeper.</p><p>It was no easy task. In the years that followed, the team hacked its way through foot after foot of sticky, unyielding clay with little success. Finally, in 2011, they hit pay dirt: Clustered within a few square feet of soil were six tiny teeth and four bones from dainty-looking hands and feet. The fragmented remains of an adolescent’s femur followed soon after. Another excavation in 2015 revealed one final tooth.</p>
            <figure class="richtext-image full-width"><img alt="DSC7588.jpg" class="richtext-image full-width" height="531" width="800"
            src="/wgbh/nova/media/images/DSC7588.width-800.jpg"/><figcaption><p>A toe bone from Homo luzonensis. Its shape bears similarities to that of Australopithecus afarensis, a species that predates the new fossils by a 2 to 3 million years. Image Credit: Callao Cave Archaeology Project</p><div class="credit"><p></p></div></figcaption>
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            <p>Mijares credits the discoveries to his team’s patience and perseverance—but also to a tried-and-true Beach Boys soundtrack that now carries a bit of mythos among his colleagues. “Once the Beach Boys are playing, the fossils come out,” Mijares attests.</p><p>The remains were next shuttled to study author <a href="https://www.researchgate.net/profile/Florent_Detroit">Florent Détroit</a>, an anthropologist at France’s National Museum of Natural History in Paris. It was soon apparent to Détroit that the remains featured a puzzling mosaic of traits both modern and ancient. “Each of the features [of <i>Homo luzonensis</i>] corresponds to some hominin or another,” he says. “But the combination makes for something really unique. There’s no known species with this same suite of features.”</p><p>A couple of the bones from the feet, for instance, hint at a very diminutive stature—an adaptation that’s also been observed in <a href="http://humanorigins.si.edu/evidence/human-fossils/species/homo-floresiensis"><i>Homo floresiensis</i></a>, who had to cope with limited food availability on the Indonesian island of Flores. They’re also shaped in a way that bears a striking resemblance to our <i>Australopithecus</i> predecessors, who lived some 3 million years ago—a similarity that’s “extraordinary for something so young in geological age,” says <a href="https://www.gc.cuny.edu/Page-Elements/Academics-Research-Centers-Initiatives/Doctoral-Programs/Anthropology/Faculty-Listing/William-Harcourt-Smith">William Harcourt-Smith</a>, a physical anthropologist at Lehman College who was not involved in the study.</p><p>But it’s perhaps the teeth—seven upper jaw premolars and molars, five of which are from the same individual—that are most fascinating, says <a href="https://www.luc.edu/anthropology/faculty/drkristinlkrueger/">Kristin Krueger</a>, a paleoanthropologist at Loyola University Chicago who was not involved in the study. While molars typically dwarf premolars in modern humans and many of our extinct relatives, the newly uncovered teeth are all fairly small and uniform, stacking hefty premolars up against molars that are fairly puny by modern standards. “Overall, the dental differences...present the strongest indication of a new species,” Krueger says. “I am cautiously optimistic.”</p>
            <figure class="richtext-image full-width"><img alt="teeth comp.jpg" class="richtext-image full-width" height="626" width="800"
            src="/wgbh/nova/media/images/teeth_comp_t2V7TOd.width-800.jpg"/><figcaption><p>Two premolars and three molars from the upper jaw of a <i>Homo luzonensis</i> individual, viewed from the tongue&#x27;s perspective (top) and the cheek&#x27;s perspective (bottom). Image Credit: Callao Cave Archaeology Project</p><div class="credit"><p></p></div></figcaption>
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            <p>However, without a skull, mandible, or DNA evidence (which has been unrecoverable so far), it’s still possible these individuals are just unusual members of an already-characterized species like <i>Homo floresiensis</i>, says <a href="https://www.ashleyshammond.com/">Ashley Hammond</a>, a paleoanthropologist at the American Museum of Natural History who was not involved in the study. Only time—and more fossil evidence—will tell if <i>Homo luzonensis</i> lives up to its name, she says.</p><p>In the meantime, it might not be worth it to quibble over the finer points of species distinctions, which can carry a kind of social baggage, says <a href="http://www.wennergren.org/news/professor-leslie-c-aiello">Leslie Aiello</a>, an anthropologist at the Wenner-Gren Foundation for Anthropological Research who was not involved in the study. Though these boundaries are often drawn on the basis of reproductive incompatibility, evidence for interbreeding between species has surfaced time and time again throughout human evolution. Even we <i>Homo sapiens</i> still carry traces of Neanderthal in our DNA.</p><p>“The natural world doesn’t care what labels we put on things,” says <a href="https://anthropology.dartmouth.edu/people/jeremy-desilva">Jeremy DeSilva</a>, a paleoanthropologist at Dartmouth University who was not involved in the study. “Species are much more fluid and interesting than the distinct groupings that we as humans arbitrarily put them in.”</p></div>
  

  
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      <div class="rich-text"><p>Aiello would much rather spend her time thinking about the potentially “tantalizing” new narrative that’s surfaced so far. New species or not, these fossils point to the presence of early humans in a time and place that they were not previously known to occupy. “This changes the role of the Philippines in the human evolution debate,” Mijares says. And that’s a tremendous contribution in and of itself.</p><p>“This tells us that hominins could really get all over the place,” Hammond says. “To see them making it to a place where we weren’t really expecting much interchange…that’s pretty exciting.”</p><p>What’s not yet clear, though, is how these people got there, and when. Last year, a separate <a href="https://www.nature.com/articles/s41586-018-0072-8">study</a> identified stone tools and butchered animal remains on Luzon that date to 700,000 years ago. The discovery of these artifacts sparked many theories on their makers, ranging from seafaring <i>Homo erectus</i> clans (which is pretty unlikely) to castaways washed ashore in the wake of a catastrophic tsunami. For now, these more recent human fossils are the oldest in the region. But the possibility remains: Early humans might have established themselves on the island and spent hundreds of thousands of years adjusting, adapting, perhaps even speciating—long before the eventual arrival of today’s <i>Homo sapiens.</i></p><p>Détroit and Mijares say it’s too early to speculate on the lineage of their fossils. Another group of globetrotters could have settled Luzon—perhaps purposefully—many years after those early tools were crafted, and still have had plenty of time to evolve. If that’s the case, Krueger says, it’s of “great consequence...it represents the ingenuity of our ancestors.”</p>
            <figure class="richtext-image full-width"><img alt="56917860_948050815341857_1880177764103880704_n.jpg" class="richtext-image full-width" height="564" width="800"
            src="/wgbh/nova/media/images/56917860_948050815341857_1880177764103880704_n.width-800.jpg"/><figcaption><p>Armand Mijares&#x27; team during an excavation at Callao Cave. Image courtesy of Armand Mijares, University of the Philippines Diliman</p><div class="credit"><p></p></div></figcaption>
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            <p>In many ways, the unfurling tale of these fossils parallels the mysterious trajectory of <i>Homo floresiensis,</i> presumably stranded on Flores. This hints that there might be other isolated outcrops, holding the remnants of more populations, yet undiscovered. Mijares is already planning a return trip to Callao Cave, and several nearby sites in the Philippines. After all, he says, if they made it to Luzon, there was likely little keeping them off other islands.</p><p>“Understanding human evolution is like building a jigsaw puzzle: It’s one picture, even if you just have a few of the pieces,” Ward says. “Whether this is a new species or a population is an interesting question. But the important aspect of this is that we now have a new part of the puzzle started.”</p></div>
  

  
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<p>Seven teeth, five hand and foot bones, and a partial femur point to a previously unknown population of early humans. Time will tell if it was truly a distinct lineage.</p>

50,000-Year-Old Fossils in the Philippines Hint at a New Species of Early Human





  
      <div class="rich-text"><p>For Waffles, the only direction to go was up.</p><p>And as the lowest-ranking female in her clan of spotted hyenas (<i>Crocuta crocuta</i>), she had little to lose. Among her peers, Waffles was neither the biggest nor the brawniest; by all accounts, she was—physically speaking—unremarkable.</p><p>But to the amazement of <a href="https://straussed.github.io/">Eli Strauss</a> and <a href="https://www.holekamplab.org/">Kay Holekamp</a>, the Michigan State University evolutionary biologists tracking the hyenas’ behavior, over the course of just a single year, Waffles steadily ascended her group’s hierarchy, unseating high-ranking female after high-ranking female—until, at long last, the former underdog had attained the coveted alpha position.</p><p>“She was just so persistent,” Holekamp says. “It was absolutely stunning.”</p></div>
  

  
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      <div class="rich-text"><p>The secret to Waffles’ success? According to Strauss and Holekamp’s <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1810384116">research</a>, published today in the journal <i>PNAS</i>, Waffles battled her way to the top not by leveraging stature or might, but by arming herself with the most powerful weapon of all: a troupe of loyal comrades at her side. And though her case was extraodinary, Waffles was—by several metrics—far from alone. Even when born into a low station in life, with ironclad alliances to bolster confrontations with higher-ranked individuals, female spotted hyenas can shirk the lottery of birth and clamber atop the social pyramid.</p><p>“The quality of this work is outstanding,” says <a href="https://sites.nd.edu/archielab/">Elizabeth Archie</a>, a behavioral ecologist at the University of Notre Dame who was not involved in the study. “This shows that animals that navigate the social arena can turn a hierarchy on its head.”</p><p>This tactic sounds simple, but it was an answer hard won. To arrive at these chummy conclusions, Strauss and Holekamp had to sift through 27 <i>years’</i> worth of data, tracking over 12,500 aggressive interactions among 249 adult female hyenas in Kenya.</p><p>“Such a huge sample size over such a long time is not something we have the luxury of doing in behavioral research very often,” says <a href="https://suzannemacdonald.ca/">Suzanne MacDonald</a>, a biologist who studies primate behavior at York University and was not involved in the study. “They’ve gotten data we often theorize about, but can’t often test. It’s awesome.”</p>
            <figure class="richtext-image full-width"><img alt="Waffles.jpg" class="richtext-image full-width" height="531" width="800"
            src="/wgbh/nova/media/images/Waffles.width-800.jpg"/><figcaption><p>This hyena, named Waffles, ascended to become the alpha female of her social group through coalitionary support from her allies. Image Credit: Tracy Montgomery.</p><div class="credit"><p></p></div></figcaption>
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            <p>It turns out hyena social climbing, even on a small scale, is a relative rarity (making Waffles all the more anomalous). Their hierarchies are actually remarkably stable—perhaps due in part to the fact that, like many primates, spotted hyenas are intelligent, highly adept puzzle solvers capable of cultivating <a href="https://royalsocietypublishing.org/doi/abs/10.1098/rstb.2006.1993">rich social networks</a>. A single spotted hyena can individually recognize each member of a clan of dozens, and will invest this social savvy in allies and adversaries alike.</p><p>While many other animals give top billing to individuals with the most prominent or powerful physical attributes—like the seal with the greatest girth, or the bird with the flashiest feathers—spotted hyenas structure their societies like female-centric monarchies. Offspring inherit ranks directly below that of their mothers and above those of their older siblings. In this nepotistic system, might and stature hold little sway, and even small, frail, and sickly individuals can hold dominion over their peers through heritage alone.</p></div>
  

  
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      <div class="rich-text"><p>This dynastic dictum poses a bit of a puzzle, however. With tantalizing incentives, like better access to food and mates, high up on the social ladder, Holekamp says, you might expect big-bodied individuals to constantly be “beating up weaker, older, more fragile individuals higher up in the hierarchy to improve their position.”</p><p>Quite the opposite is true. In fact, only a small fraction of the thousands of encounters Strauss and Holekamp had tracked actually involved a lower-ranking female staging a successful coup d’état (far more actually involved females in the upper echelons reaffirming their dominance).</p><p>When these revolutions <i>did</i> occur, however, it wasn’t the females with the hardiest physiques that were overthrowing their superiors—but the ones with the most robust friendships.</p><p>In the realm of the hyena, it seemed, the name of the throne-toppling game was camaraderie.</p><p>A classic confrontation might go something like this. Two females team up and swagger, shoulder to shoulder, in the direction of their higher-ranking rival, tails bristled and ears cocked, using pure posture to communicate their intent, Strauss says. The hyena on the receiving end would then have a choice to make: reassert her dominance, or yield. If daunted by the pair loping towards her, she might simply hunker down and tuck her tail between her legs—a clear signal of defeat.</p><p>In other words, these weren’t necessarily violent mutinies, Strauss says. “When people think of aggression, they think of hair flying and blood and intestines,” he says. “That’s not what’s going on here.”</p><p>Occasionally, standoffs did escalate to the point of bodily harm—especially when a high-ranking female decided to stand her ground in the face of a challenge. Despite these risks, though, uprisings appeared to paid dividends: By ascending the social ladder, females and their accomplices boosted their reproductive success. The repercussions of these revolts were even passed on to future generations, who reaped the benefits of their mother’s newly acquired clout.</p><p>Although these status switchups weren’t happening on a daily basis, they support the idea that “rank inheritance isn’t a foregone conclusion,” Archie says. “There could be this impression that animals are born with a silver spoon in their mouth and they pass that on. But there’s nuance to that.”</p><p>The power of partnership isn’t terribly surprising, says <a href="http://tropbiolab.org/FMKU/">Floria Mora-Kepfer Uy</a>, who studies social behavior in animals at Cornell University and was not involved in the study. Hyenas, like many other social species, thrive on strong social bonds—and the allegiances that allow individuals to clamber up to higher echelons might be the same ones that <a href="https://www.nature.com/articles/s41559-018-0718-9?WT.feed_name=subjects_behavioural-ecology">reinforce the ranks</a> once they’ve resettled. In this way, social currency might form two sides of the same coin: It’s what maintains, and occasionally disrupts, the hyena hierarchy.</p>
            <figure class="richtext-image full-width"><img alt="Soc snf DSG-copy.jpg" class="richtext-image full-width" height="535" width="800"
            src="/wgbh/nova/media/images/Soc_snf_DSG-copy.width-800.jpg"/><figcaption><p>Spotted hyenas have primate-like societies in which individual hyenas form strong social bonds with their preferred partners. Image Credit: David Green. </p><div class="credit"><p></p></div></figcaption>
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            <p>“This is all the more reason animals on the bottom need to not kick their friends, but to hold them up,” says <a href="http://choosyfemale.com/index.html">Emily Weigel</a>, an evolutionary biologist at the Georgia Institute of Technology who was not involved in the study. “Social environment matters. And it’s shaping evolution way more than we thought.”</p><p>What’s more, spotted hyenas are unlikely to bear this congenial mantle alone. Other primates, like macaques and baboons, also inherit status through strict and stable matrilines. Such parallels hint that these “very impressive” results might translate into other species, says <a href="https://www.stefanokaburu.com/">Stefano Kaburu</a>, an evolutionary biologist and primatologist at the University of Wolverhampton in the United Kingdom who was not involved in the study.</p><p>“I was nodding as I was reading this paper,” MacDonald says. “This makes perfect sense. I was almost salivating, thinking that I should look at my own data with these methods.”</p><p>And there’s one other notable primate for whom these conventions might ring true: humans. Differences exist between the two species, of course—but there’s an undeniable familiarity to the idea that coalitions can make or break social standing, Holekamp says.</p><p>“Our own societies are largely convention-based,” she says. “My feeling is that, ultimately, it will be wonderful if we can take some of this knowledge and use it to someday make human society more egalitarian.”</p><p>But that won’t happen on its own, Holekamp says. “Social inequality, even though it is a highly common characteristic in human and animal societies, can be understood and quantified, and managed,” she says. “If we have the brains to do it.”</p></div>
  

  
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<p>In these female-dominated clans, the name of the throne-toppling game might just be camaraderie.</p>

For Hyenas, Climbing the Social Ladder is Easier with Friends





  
      <div class="rich-text"><p>When you hear hoof beats, think horses. Unless, that is, you’re on safari with <a href="http://wfcb.ucdavis.edu/people/faculty/caro-tim/caro-lab/">Tim Caro</a>.</p><p>Caro, an evolutionary ecologist at the University of California, Davis has spent a hefty chunk of his decades-long career chasing after zebras and their distinctive stripes, trying to figure out why these eccentric equines look the way they do.</p><p>The mystery of zebra stripes has plagued evolutionary biologists (albeit, a pretty specific subset of them) for over a century. Several theories have been batted back and forth, but Caro is among those who stand staunchly by one in particular: Stripes safeguard against bloodthirsty bugs.</p><p>Today, in the journal <i>PLOS ONE,</i> a team of researchers led by Caro publishes <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210831">the latest piece in the puzzle</a>, showing that horseflies appear to have trouble touching down on zebra-patterned flanks. Beyond bolstering the case for the benefits of stripes, the results might also point to potential strategies for deterring nippy insects from setting their sights on vulnerable flesh—including, perhaps, that of humans.</p></div>
  

  
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      <div class="rich-text"><p>With their stark, vivid allure, zebra stripes are distinctive, to say the least. So perhaps it’s no surprise that this captivating coloration caught the eye of Charles Darwin, who famously debated the subject in the 1870s with his colleague Alfred Wallace. In the decades since, scientists have posited that stripes arose to protect against hungry predators, help individuals identify each other in big herds, or <a href="https://www.smithsonianmag.com/smart-news/heated-debate-do-zebra-stripes-keep-cool-180969581/">keep skin cool</a> under the hot savannah sun.</p><p>There’s not much evidence for most of these ideas, however. The only theory that still holds water, Caro says, is that stripes deter biting flies. The stakes for these creatures, after all, are high: Zebra coats aren’t very thick, and one nibble from a fly can usher in the myriad deadly microbes that cause trypanosomiasis, equine infectious anemia, African horse sickness, and equine influenza.</p><p>But while previous studies have shown that flies can be thwarted by stripes (at least, compared to more monochromatic options), exactly how this aerodynamic aversion plays out has remained unclear.</p><p>Finding that answer, of course, meant looking at things from the perspective of the fly. But Caro’s <i>modus operandi</i> has typically been to take the zebra’s point of view (in some of his most famous experiments, Caro has even <a href="https://www.universityofcalifornia.edu/news/biologist-earns-his-zebra-stripes-new-book">donned zebra stripes</a> to mimic the vivacious visage of his subject of study). So Caro teamed up with <a href="http://www.bristol.ac.uk/biology/people/martin-j-how/index.html">Martin How</a>, an ecologist and animal vision expert at the University of Bristol.</p>
            <figure class="richtext-image full-width"><img alt="WIKO PLAKAT_17_3.jpg" class="richtext-image full-width" height="677" width="800"
            src="/wgbh/nova/media/images/WIKO_PLAKAT_17_3_5R0fFFS.width-800.jpg"/><figcaption><p>Tim Caro often dons stripes in the name of science. While this particular onesie was never used for fieldwork, Caro has previously adopted the guise of a zebra to test some of his theories. Image Credit: Maurice Weiss</p><div class="credit"><p></p></div></figcaption>
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            <p>Together, the researchers and their colleagues monitored the flight behaviors of flies buzzing around a group of captive zebras and horses. From a distance, horses and zebras of all shades lured in thirsty flies to about the same extent. But things changed upon close approach. Though the flies sailed in to sate themselves on the hides of horses, they had lower rates of success landing on zebras, often simply ricocheting off their festive flanks, or missing them entirely.</p></div>
  

  
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      <div class="rich-text"><p>Next, the researchers conducted a stripy switcheroo, draping both species sequentially with black, white, and black-and-white striped coats. Once again, the insects seemed flummoxed in close proximity of striped surfaces, and had difficulty maneuvering during touchdown. In the end, flies had a much easier time landing on horses costumed in plain black or white than on those draped with striped cloth.</p><p>“It’s remarkable how effective stripes are at reducing landing success,” How says. “It’s a really dramatic effect, and we see it consistently—that’s the most startling thing.”</p><p>Much like aircraft, airborne insects probably need to decelerate as they prepare for final descent, Caro explains. “We think it’s about that last half second,” he says. “It’s a dangerous situation. The fly has to slow down and make sure it doesn’t break a leg or hit its eyes or head against the object.” But stripes might just befuddle the flies into crash landings, distracting them from their original mission: nabbing mouthfuls of blood.</p><p>It’s not yet clear what it is about stripes that discombobulate the flies, but Caro, How, and their team are currently testing a few theories. One possibility is that stripes create an optical illusion that disrupts the insects’ ability to estimate distance. After all, moving stripes can look pretty wonky: Think of the common <a href="https://www.opticalillusion.net/optical-illusions/the-barber-pole-illusion/">barber pole illusion</a>, in which the rotating poles found outside of traditional barber shops seem to show stripes traveling upwards.</p>
            <figure class="richtext-image full-width"><img alt="192864.JPG" class="richtext-image full-width" height="531" width="800"
            src="/wgbh/nova/media/images/192864.width-800.jpg"/><figcaption><p>As a part of their experiment, researchers placed coats of different colors and patterns on horses to test if this changed the behavior of flies trying to land on their skin. Image Credit: Tim Caro, UC Davis</p><div class="credit"><p></p></div></figcaption>
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            <p>When pestered, the horses and zebras behaved a little differently as well: While zebras were constantly lashing their tails and galloping away to fend off flies, horses were far less vigilant, responding with just the occasional body twitch or swish of the tail. Tails can only reach so far, though, so differences in biting can’t just be chalked up to horsey nonchalance. But it seemed zebras were going to greater lengths to avoid the mouthparts of their pint-sized nemeses.</p><p>This may all fall in line with the ultimate goal of disease avoidance, but that theory still needs rigorous testing. Additionally, <a href="https://www.ntu.ac.uk/staff-profiles/animal-rural-environmental-sciences/carol-hall">Carol Hall</a>, an animal behaviorist and equine expert at Nottingham Trent University in the UK who was not involved in the study, points out that stripes could still have other, non-insect-related perks. “This is a useful step along the way,” she says. “But I don’t know if there’s enough evidence to say <i>that’s it,</i> that’s all that’s going on.”</p></div>
  

  
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      <div class="rich-text"><p>In the meantime, it probably wouldn’t hurt to dust off striped apparel for equines and humans alike—especially if your next vacation destination overlaps with horsefly territory.</p><p>“A couple of years ago, I would’ve said I’m sure [wearing stripes] wouldn’t have any effect on avoiding flies,” Caro says. “But now I’m willing to entertain the idea that it might be useful for humans.” Football referees, rejoice.</p><p>And these effects might not be restricted to just horseflies, Caro says. Many insect eyes are built in similar ways—which means there’s a chance stripes could addle bug brains galore.</p><p>There’s not yet evidence of that, but such concerns may be increasingly relevant as the climate continues to change, Hall says. With global temperatures rising, tropical locales are expanding, allowing many insects that carry human diseases to flourish—and it’s a constant struggle to keep hungry mouths at bay.</p><p>“The more we can find out about stopping animals getting bitten, the better we will be at stopping the spread of disease,” Hall says.</p></div>
  



<p>To solve the mystery of zebra stripes, these researchers looked to a horse of a different color.</p>

Topic: Evolution

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