Making North America: Life Hero

How did life emerge on our primeval continent? Why was North America home to so many iconic dinosaurs like T. rex? 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.

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

Making North America: Life

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

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

NOVA Wonders Can We Make Life? Hero

&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? NOVA Wonders explores the benefits and the burden of risk surrounding the controversial new technology.

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

Can We Make Life?

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Evolution

Koch Foundation

Draper

Fossilized fish uncovered in North Dakota appear to preserve the catastrophic fallout of the asteroid impact that wiped out the dinosaurs.
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.
Stunning Fossil Discovery Could Offer Glimpse into Day the Dinosaurs DiedPublished: April 22, 2019Onscreen: 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.Jay Melosh: 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.Onscreen: 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.Robert DePalma: 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.Onscreen: Sixty-six million years ago, an asteroid smashed into Earth along the coast of Mexico setting off a chain reaction of apocalyptic events.David Kring: 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.Onscreen: Scientists think the impact also launched molten rock into the atmosphere where it formed little beads, called tektites, that rained back down to Earth.Jan Smit: 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.DePalma: 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.Onscreen: Team members say the site holds much more evidence that will keep them busy for years to come.DePalma: 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.Smit: There are lots of open questions to answer all the beautiful observations we have. We are just at the beginning.

Fossilized fish uncovered in North Dakota appear to preserve the catastrophic fallout of the asteroid impact that wiped out the dinosaurs.

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

<div class="rich-text">The history of human evolution might be getting yet another rewrite.According to a <a href="https://www.nature.com/articles/s41586-019-1067-9">study</a> published today in the journal Nature, 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 Homo luzonensis could add yet another branch to our ever-growing family tree.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.“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.”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.”</div>
 

 
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 <div class="rich-text">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.No matter how peculiar, though, a single fossil isn’t enough to tell a story. So Mijares and his team dug deeper.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.
 <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>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<div class="credit"></div></figcaption>
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 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.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 Homo luzonensis] 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.”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">Homo floresiensis</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 Australopithecus 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.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.”
 <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>Two premolars and three molars from the upper jaw of a Homo luzonensis individual, viewed from the tongue&#x27;s perspective (top) and the cheek&#x27;s perspective (bottom). Image Credit: Callao Cave Archaeology Project<div class="credit"></div></figcaption>
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 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 Homo floresiensis, 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 Homo luzonensis lives up to its name, she says.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 Homo sapiens still carry traces of Neanderthal in our DNA.“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.”</div>
 

 
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 <div class="rich-text">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.“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.”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 Homo erectus 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 Homo sapiens.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.”
 <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>Armand Mijares&#x27; team during an excavation at Callao Cave. Image courtesy of Armand Mijares, University of the Philippines Diliman<div class="credit"></div></figcaption>
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 In many ways, the unfurling tale of these fossils parallels the mysterious trajectory of Homo floresiensis, 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.“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.”</div>
 

 
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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.

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

<div class="rich-text">For Waffles, the only direction to go was up.And as the lowest-ranking female in her clan of spotted hyenas (Crocuta crocuta), she had little to lose. Among her peers, Waffles was neither the biggest nor the brawniest; by all accounts, she was—physically speaking—unremarkable.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.“She was just so persistent,” Holekamp says. “It was absolutely stunning.”</div>
 

 
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 <div class="rich-text">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 PNAS, 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.“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.”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 years’ worth of data, tracking over 12,500 aggressive interactions among 249 adult female hyenas in Kenya.“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.”
 <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>This hyena, named Waffles, ascended to become the alpha female of her social group through coalitionary support from her allies. Image Credit: Tracy Montgomery.<div class="credit"></div></figcaption>
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 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.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.</div>
 

 
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 <div class="rich-text">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.”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).When these revolutions did occur, however, it wasn’t the females with the hardiest physiques that were overthrowing their superiors—but the ones with the most robust friendships.In the realm of the hyena, it seemed, the name of the throne-toppling game was camaraderie.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.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.”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.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.”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.
 <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>Spotted hyenas have primate-like societies in which individual hyenas form strong social bonds with their preferred partners. Image Credit: David Green. <div class="credit"></div></figcaption>
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 “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.”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.“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.”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.“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.”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.”</div>
 

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

For Hyenas, Climbing the Social Ladder is Easier with Friends

<div class="rich-text">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>.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.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.Today, in the journal PLOS ONE, 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.</div>
 

 
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 <div class="rich-text">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.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.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.Finding that answer, of course, meant looking at things from the perspective of the fly. But Caro’s modus operandi 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.
 <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>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<div class="credit"></div></figcaption>
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 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.</div>
 

 
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 <div class="rich-text">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.“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.”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.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.
 <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>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<div class="credit"></div></figcaption>
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 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.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 that’s it, that’s all that’s going on.”</div>
 

 
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 <div class="rich-text">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.“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.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.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.“The more we can find out about stopping animals getting bitten, the better we will be at stopping the spread of disease,” Hall says.</div>

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

When Keeping Flies at Bay, Zebras Can Thank Their Lucky Stripes

<div class="rich-text">On this particular morning, as he checked the contents of his live traps in the Sand Hills of Nebraska, <a href="https://barrettlab.ca/">Rowan Barrett</a> found himself three for 800. It wasn’t a great start to the day.Not all the traps he’d set out were empty; far from it. But the cache of sunflower seeds within had mostly drawn unwelcome guests: pocket mice, grasshopper mice, and, bizarrely, rattlesnakes. Only a handful contained the deer mice Barrett, now an evolutionary ecologist at McGill University, was after.For weeks on end, Barrett and his team had been rising before the sun, scouring the dusty landscape for traps jiggling with a catch. Their mission was simple: collect about 500 wild deer mice in a variety of colors, and monitor their survival in the Sand Hills—a cascading series of grass-speckled dunes where the shades of soil range from brown to beige.
 <figure class="richtext-image full-width"><img alt="light4.jpg" class="richtext-image full-width" height="397" width="800"
 src="/wgbh/nova/media/images/light4.width-800.jpg"/><figcaption>The Sand Hills of Nebraska, where a team of researchers led by biologists Rowan Barrett and Hopi Hoekstra conducted a large-scale experiment to monitor the survival of a population of deer mice. Image Credit: Rowan Barrett, McGill University<div class="credit"></div></figcaption>
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 Common sense would predict that rodents with coats that blend into their surroundings should be better camouflaged from hungry birds of prey, while mismatched mice, like brunettes on pale sands, would stick out and be quickly gobbled up (spoiler alert: that is, in fact, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aav3824">exactly what they found</a>).It sounds simple; even obvious. “You might think, ‘Well, duh, the camouflaged mice survive better,’” Barrett says. “But actually demonstrating that? It’s different than having an intuition about something.”</div>
 

 
 <div class="ad"></div>
 

 
 <div class="rich-text">In fact, the discovery Barrett truly sought was much bigger than mice, an elusive goal biologists have chased for centuries: Capturing a snapshot of <a href="https://www.pbs.org/wgbh/nova/labs/lab/evolution/">evolution</a> happening in real time.It was a daunting task, requiring a tricky trifecta of variables: genes, traits, and survival. Plenty of studies have shown how genetics affect outward characteristics, like <a href="https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet">BRCA mutations</a> increasing the risk of breast cancer; others clearly demonstrate that observable, physical features can make the difference between life and death, as with black moths that blend into a backdrop of <a href="https://theconversation.com/natural-selection-in-black-and-white-how-industrial-pollution-changed-moths-43061">soot-covered trees</a>. But few have brought all three elements together in a single experiment, pinpointing how genes can dictate survival—especially in mammals.The work of Barrett and his team, <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aav3824">published today</a> in the journal Science, highlights how the stresses of the natural environment can directly alter the fate of one gene—all within the span of a single generation. In light of our rapidly-changing world, these findings underscore the idea that, even against the complex backdrop of nature, one small shift can permanently tip the scales for an entire population.“This is a beautiful study,” says <a href="https://nature.berkeley.edu/rosenblum/people.html">Obed Hernández-Gómez</a>, an evolutionary biologist and geneticist at the University of California, Berkeley who was not involved in the study. “Recently we’ve looked at genes and understood that evolutionary processes act very quickly. To see that confirmed in this study, and not in a human-mediated environment... This could end up being one of those prominent examples we use to teach biology students in the future.”
 <figure class="richtext-image full-width"><img alt="IMG_1802.JPG" class="richtext-image full-width" height="533" width="800"
 src="/wgbh/nova/media/images/IMG_1802.width-800.jpg"/><figcaption>A young, dark-colored deer mouse on dark soil studded with bright green grass. This rodent might be better camouflaged from birds of prey because it carries a functioning copy of the Agouti gene, which contributes to fur pigmentation. Image Credit: Rowan Barrett, McGill University<div class="credit"></div></figcaption>
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 It’s been over a century and a half since Darwin first put forth his theories on evolution. Scientists have understood the basics of the process for decades. But putting this knowledge to work to forecast the fates of the species that populate the planet, including our own, is still mostly an exercise in futility.“Even after decades of evolutionary research, we’re only beginning to integrate the different types of approaches we need to truly understand the action of evolution,” says <a href="https://lucyaptran.weebly.com/">Lucy Tran</a>, an evolutionary biologist at Arizona State University. Tran is now a postdoctoral researcher in the lab of study author Susanne Pfeifer, but was not directly involved in the study.One thing, though, is certain: Evolution isn’t exclusively the slow, plodding process that Darwin originally envisioned. <a href="https://www.orlandosentinel.com/news/os-evolution-green-brown-lizards-20141101-story.html">Time</a> and <a href="https://www.the-scientist.com/multimedia/infographic-watching-evolution-in-real-time-31599">time</a> again, researchers have shown that it can be <a href="https://www.pbs.org/wgbh/nova/article/darwins-finches-mating-parents/">witnessed</a> in just a matter of years—or even within the span of a single <a href="https://news.harvard.edu/gazette/story/2014/02/evolution-in-real-time/">experiment</a>.“We took our motivation from microbes in lab environments,” Barrett says. One particularly well-known experiment has been monitoring bacteria <a href="http://myxo.css.msu.edu/">for decades</a>. “The crazy idea was, can we do this with a mammal in nature?”</div>
 

 
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 <div class="rich-text">For their test subjects, the team chose deer mice (Peromyscus maniculatus). In these rodents, the two halves of the equation were already there: The general importance of stealth for survival, and a gene, Agouti, known to control the color of fur. “I wanted to put the two bits of this puzzle together,” Barrett says. “No one had done that before.”In retrospect, Barrett says, there was probably a reason for that. The setup was far from trivial.To test mouse survival, the team needed a way to simulate the natural environment. That meant building eight 80-foot-by-80-foot enclosures, four each on dark and light soil. Six enclosures would house between 75 and 100 microchipped mice each; two others would remain empty. This required finding a lot of flat, rodent-friendly land—in a place named for its hills—and corralling herds of mice onto distinctly colored patches of dirt.Easier said than done. “Deer mice are like little ninjas,” Barrett says. “They burrow, they climb. People told me, ‘You’ll never hold them.’”
 <figure class="richtext-image full-width"><img alt="IMG_9116.jpg" class="richtext-image full-width" height="469" width="800"
 src="/wgbh/nova/media/images/IMG_9116.width-800.jpg"/><figcaption>Evolutionary biologist Rowan Barrett basks in the triumph of the research team&#x27;s manmade mouse enclosures in Nebraska&#x27;s Sand Hills. Image Credit: Naomi Man in’t Veld<div class="credit"></div></figcaption>
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 But with steel plate walls buried two-and-a-half feet into the ground, the barriers held. And while each enclosure started off with a mix of light- and dark-colored mice, by the end of three months, their compositions had changed drastically. First off, the populations had been decimated: Hundreds of mice had died, likely picked off by keen-eyed owls. And the surviving mice were only a very particular subset of the original population. Mice with fur to match the soil—like light mice on cream-colored soil—had been the ones to emerge victorious. Their standout brethren, on the other hand, had not.“I didn’t really think that we would see much change over such a short-term experiment,” Barrett says. “This was kind of a Hail Mary.”And when the researchers sequenced the mice’s DNA, they found they had the genes to match. Surviving mice on the dark side tended to carry a normal version of the Agouti gene, which aided the production of pigment in their coats, while the remaining mice in the light enclosures were more likely to carry a broken copy of Agouti that kept them blonde.</div>
 

 
 <div class="newsletter"></div>
 

 
 <div class="rich-text">Too many mice died in those early months for the experiment to look past the initial cohort of 500 mice, Barrett says. But one look at the Agouti genes of the remaining mice in each enclosure told him that it would be essentially impossible for their offspring to be very diverse, in terms of coat color. For the most part, lighter mice carrying broken Agouti had been left on light soil, and vice versa; future generations would likely reflect this as well. And for Barrett, this probably represented a sped-up version of what had happened naturally on the Sand Hills over the course of many years, ultimately partitioning the rodents by color.“Typically, we would say, for this to be evolution, you need to see if it’s reflected in the next generation,” he says. “But we know [the traits are] going to be transmitted, because we showed changes at the genetic level.”Others, like Tran, are slightly more hesitant to make this conclusion, however. “Multiple generations would provide stronger evidence [of evolution],” she says. “What’s missing in the study is whether these changes are definitely heritable.”Regardless, the study’s ability to link natural selection in the field to a specific gene makes it a “rare gem,” says <a href="http://blog.uvm.edu/mpespeni/">Melissa Pespeni</a>, an evolutionary biologist at the University of Vermont who was not involved in the research.In the future, Barrett and his colleagues hope to extend the study into a multi-generational approach. “This is just the first step in a long-term project,” says study author <a href="https://hoekstra.oeb.harvard.edu/">Hopi Hoekstra</a>, an evolutionary geneticist at Harvard University. But the staggering rates of change the researchers found might still have a lot to say in other contexts—including species conservation.
 <figure class="richtext-image full-width"><img alt="5907607580_da47cdab55_o.jpg" class="richtext-image full-width" height="533" width="800"
 src="/wgbh/nova/media/images/5907607580_da47cdab55_o.width-800.jpg"/><figcaption>“This study is sure to be a classic example of how natural selection works on both an animal’s [physical characteristics] and the genetics associated with them out in the wild,” says <a href="https://www.colorado.edu/ebio/rebecca-safran">Rebecca Safran</a>, an evolutionary ecologist at the University of Colorado Boulder who was not involved in the study. Image Credit: Rowan Barrett, McGill University<div class="credit"></div></figcaption>
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 “The more we can learn about how organisms adapt, the more we’ll know about how organisms might adapt to, for instance, a changing climate,” Hoekstra says.Already, it’s clear that shifts in global temperatures and other human-motivated changes have done some <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5769427/">serious damage</a> to Earth’s inhabitants. <a href="https://www.nature.com/articles/ncomms1213">Owls</a> are molting out of paler shades in response to warming winters; <a href="https://www.pbs.org/wgbh/nova/article/feminized-turtle-populations-in-trouble/">sea turtle</a> populations with temperature-dependent sex determination systems are skewing heavily female.“A major lesson here is to preserve genetic diversity,” Hernández-Gómez says. “We might lose genes that might be beneficial in the future if we don’t.”Some species may be flexible in the face of harsh environmental change. With others, though, one variable could be all it takes to transform an entire population in just a handful of weeks.As for passing these changes down through the generations? Well—that’s a mouse of a different color.</div>

By watching a population of deer mice shift in the span of a single generation, scientists have captured evolution in action, connecting genes to survival in the wild.

Seeing “Evolution in Real Time”: Mice Blend in to Survive

<div class="rich-text">She hadn’t eaten in days.While her cousins in the next room over had eagerly scarfed down a smorgasbord of treats, she refused each item placed before her. And the situation was getting dire: If her hunger strike continued, it could soon spell trouble—not just for her own body, but for another life burgeoning within.Or, at least, that was the idea. There was no way to tell if she was actually pregnant—or, really, even that she was a she. But entomologist <a href="https://cals.arizona.edu/ento/content/wendy-moore">Wendy Moore</a>, the de facto caretaker of this stubborn <a href="http://tolweb.org/Ozaena_lemoulti">Ozaena lemoulti</a> ground beetle, had chosen to roll the dice.</div>
 

 
 <div class="ad"></div>
 

 
 <div class="rich-text">In her two decades of field work in the state of Arizona, Moore had collected fewer than ten individuals of this species, all full-grown. Their rarity made this bug, and whatever cargo it might carry, incalculably precious. A windfall like this might never come again.So Moore persevered. Nothing she offered—mealworms, waxworms, flies—seemed to suit the beetle’s taste. But then Moore remembered that the Emory oak trees that Ozaena beetles are known to frequent always seemed to be teeming with the tawny bodies of carpenter ants.Into the chamber went a handful of wriggling ants. And though Moore never saw the beetle take a single bite, the ants’ thick, segmented bodies slowly began to disappear. Then, one morning, Moore peered into the beetle’s studio apartment to find the greatest gift of all: a tiny, beautiful Ozaena egg.
 <figure class="richtext-image full-width"><img alt="Fig.2.png" class="richtext-image full-width" height="624" width="800"
 src="/wgbh/nova/media/images/Fig.2.width-800.png"/><figcaption>An Ozaena lemoulti beetle egg. Eventually, this egg might have hatched a parasitic larva that would suck the juice out of ants in their nests. Image Credit: Andrea Di Giulio, Universita Roma Tre<div class="credit"></div></figcaption>
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 Barely a millimeter and a half long, the egg would soon hatch into the first Ozaena larva ever scientifically described. Today, in a <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0209790">study</a> published in the journal PLOS ONE, Moore and her colleagues report that these rare and exquisite larvae are noteworthy for another reason, too: Just like their mothers, these insect infants appear eerily well-equipped to feast on the innards of unsuspecting ants—and may do so by infiltrating their nests.This finding flies in the face of Ozaena evolutionary history. These bugs belong to a group of beetles that’s best known for a macabre hunting method called burrow trapping. Take their close relatives in the Goniatropus genus: After hatching, Goniatropus larvae will dig headfirst into a patch of soil, plugging the hole to its burrow with the hypersensitive, disc-like appendage that fans out from its rear end. When an insect stumbles over this butt-borne umbrella, the disturbance prompts the larva to rear up and ambush its prey like a living landmine. After latching onto its victim, the larvae will drag it into the burrow to be eviscerated and consumed.</div>
 

 
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 <div class="rich-text">But when Moore peered at her lone Ozaena larva under the microscope (sadly, its tenure on this earth was short-lived: just days after its birth, it was boiled and preserved for further study), she found that it bore none of the traits the burrow-trapping lifestyle demands.Gone were the critical sensory structures that burrow-trapping beetles touted on their rears, as well as the powerful jaws that enabled typical burrow-bound larvae to grasp onto their prey. The Ozaena larva also lacked the classic, U-shaped body type of their close relatives—a flexible physique that allowed burrow-bound larvae to bend nearly in half to reach insects wandering past their bums—and it was completely blind. Despite the place it held on the beetle family tree, Ozaena was no garden-variety burrow trapper.So how, then, were Ozaena sustaining themselves?When the researchers split open the guts of eight previously preserved, fully grown Ozaena beetles, they found them sloshing with the bodily juices of carpenter ants—the same ones that had reinvigorated Moore’s lethargic mother-to-be. This in combination with the oddball larval physique, Moore explains, pointed not to the varied diet of a burrow trapper, but that of a highly specialized parasite that subsisted exclusively on ants throughout its lifetime.<div style="padding-bottom: 74.94553376906318%;" class="responsive-object">
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Ozaena are by no means the first beetles to take advantage of ants. A distantly-related group—Paussus beetles—have actually achieved a small degree of infamy for this behavior. Paussus beetles are the Trojan horses of the insect world: After conning their way into ant nests, female Paussus will lay eggs that hatch into sweet-smelling larvae, thought to exude an irresistible bouquet of ant attractants. Lured in by the scent, ants approach—only to be punctured and sucked dry by the ravenous, vampiric larvae. Paussus adolescents thus spend their early days gorging on an essentially unlimited, self-sustaining supply of protein-rich food.When beetles invade ant nests, they initiate “an exploitative relationship,” says <a href="https://www.lsuagcenter.com/profiles/bowens">Brittany Owens</a>, an entomologist at the Louisiana State University Agricultural Center who was not involved in the study. “The ants really get a bum deal.”And from the beetle’s perspective, it’s a pretty cushy lifestyle compared to, say, the toils of burrow trapping. “If you are able to socially integrate inside ant colonies and gain acceptance inside nests, you have no predators,” says <a href="https://www.beetles.caltech.edu/">Joseph Parker</a>, an entomologist who studies beetle-ant relationships at the California Institute of Technology who was not involved in the study. “There are infinite resources for you to feed on. You’re in a really safe, stable environment. The payoff is really big.”</div>
 

 
 <div class="newsletter"></div>
 

 
 <div class="rich-text">So there’s a big motivation to make the switch from burrow to nest. But beetles can’t just integrate into ant society willy-nilly. The change requires some substantial evolutionary rejiggering: Ozaena’s ancestors, which gave rise to burrow trappers, likely split off from the Paussus line at least 100 million years ago. This means Ozaena had to find its own way ant-ward—a feat that required these beetles to shed millions of years of adaptations that had tailored their relatives to burrows, and instead take on traits that would allow them to raid unfamiliar nests, lay their eggs in the presence of strangers, and meet their nutritional needs with only one source of food.The shift is so difficult and so extreme that it’s only happened a few times in beetles, Moore says. And if Ozaena beetles have indeed traded their lineage’s long history of burrow trapping for a life of juice-guzzling luxury, they would be the only members of their subfamily that parasitizes ants in the United States—making them the ant-munching black sheep of the family.“I’m always amazed by the adaptations that these insects show,” Parker says. “Your jaw hitting the floor is the standard response.”
 <figure class="richtext-image full-width"><img alt="Fig.3.png" class="richtext-image full-width" height="1223" width="800"
 src="/wgbh/nova/media/images/Fig.3.width-800.png"/><figcaption>Ozaena beetle larvae (top) lack many of the specialized structures that their close relatives in the Goniatropus genus (bottom) use for their burrow trapping lifestyle, including a disc-like appendage at their rear ends that helps the larvae sense when prey passes over their burrow. Image Credit: Wendy Moore, University of Arizona<div class="credit"></div></figcaption>
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 Despite their similarities, though, Ozaena isn’t simply a Paussus copycat—and in their time apart, Ozaena has come up with its own strategies to make the most out of nests. For instance, while Paussus larvae are pretty much immobile blobs that must wait for their meals to come waddling by, the Ozaena specimen boasted unusually long legs that might have helped it scurry around the nest to actively hunt its prey.“When we think about beetles, we only think about adults,” Moore says. “But larvae aren’t just big bags of goo. They represent this entire hidden world.”Besides, “it’s the most vulnerable stage,” Moore says of the larvae. “If they don’t make it, the species doesn’t make it.”</div>

Their closest relatives hide in burrows to ambush their prey. But Ozaena beetles have taken a different tack: infiltrating ant nests.

This Rare Beetle Bucks Family Tradition—By Sucking the Life Out of Ants

<div class="rich-text">Birds do it. Voles do it. Even poisonous frogs do it. When it comes to monogamous mating, there are countless ways to couple up. But while the modus operandi of commitment may differ across the tree of life, if you zoom in far enough, things can start to look awfully familiar.According to <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1813775116">a new study</a> published today in the journal PNAS, the brains of monogamous animals may share a common genetic signature. Though rodents, birds, frogs, and fish are separated by 450 million years of evolution—and a panoply of promiscuous predecessors—it seems that, in these species, evolution has fiddled with the same set of genes to keep commitment on the mind.“These species are so evolutionarily divergent,” says <a href="https://hoekstra.oeb.harvard.edu/">Hopi Hoekstra</a>, an evolutionary biologist who studies the genetics of animal behavior at Harvard University, but was not involved in the study. “There are so many reasons you might think you wouldn’t get this result... it’s really remarkable.”</div>
 

 
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 <div class="rich-text">Promiscuity may not be all that romantic, but in many animals, it’s the standard way of life. Less than 10 percent of mammalian species sustain steady relationships over long periods of time. And when you think about the economics of devotion, it actually makes a lot of sense to swing: Maintaining fidelity to just one partner or a single set of offspring takes time away from finding new mates and, by extension, new opportunities to pass genes on to the next generation—<a href="https://www.smithsonianmag.com/science-nature/neurochemistry-fatherhood-180969635/">especially if you’re male</a>. In other words, putting all your eggs (or sperm) in one basket can be quite a costly strategy.All the same, sometimes the payoff is worth the investment. Monogamous mating has evolved time and time again in vertebrate species—each instance independent of the others—and seems to help couples and their offspring thrive. Once prairie voles find a partner, their unions can <a href="https://www.smithsonianmag.com/science-nature/what-can-rodents-tell-us-about-why-humans-love-180949441/">last a lifetime</a>. Certain songbirds may serenade their mates into sticking around for good. Even amphibians like <a href="https://scienceblogs.com/grrlscientist/2010/03/29/evolution-monogamy-dendrobatid">poison dart frogs</a> can make for devoted dads that attentively parent their young.Fidelity doesn’t always manifest in exactly the same way, but it’s an option that animals from all walks (and flights and swims and waddles) of life have turned to time and time again. As a group, committed critters are more likely to bond intimately with their mates; aggressively defend their territory; be raised by both mothers and fathers; and look similar across the sexes (as opposed to peacocks or deer, whose males sport plumage or antlers—and tend to operate on the more philandering end of the spectrum). These common motifs suggest that, when it comes to monogamy, evolution could be capitalizing on a similar set of molecular tools.
 <figure class="richtext-image full-width"><img alt="Peacock_Plumage.jpg" class="richtext-image full-width" height="489" width="800"
 src="/wgbh/nova/media/images/Peacock_Plumage.width-800.jpg"/><figcaption>Promiscuous male peacocks flash their colorful plumage to attract females, which are noticeably more drably feathered. Males and females of monogamous bird species, on the other hand, tend to resemble each other more. Image Credit: Jatin Sindhu, Wikimedia Commons<div class="credit"></div></figcaption>
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 To test this possibility, a team of biologists led by <a href="https://devoevo.ccbb.utexas.edu/">Rebecca Young</a> and <a href="https://cichlid.biosci.utexas.edu/">Hans Hofmann</a> of the University of Texas at Austin extracted genetic material from five pairs of vertebrate species that haven’t shared a common ancestor for at least 400 million years. Each pair represented a separate instance in which a lineage had yielded a monogamous species, as well as a closely-related, non-monogamous counterpart: prairie voles (<a href="https://www.iucnredlist.org/species/42631/115196932">Microtus ochrogaster</a>) and meadow voles (<a href="https://www.iucnredlist.org/species/13452/115114123">Microtus pennsylvanicus</a>); California mice (<a href="https://www.iucnredlist.org/species/16654/22361553">Peromyscus californicus</a>) and deer mice (<a href="https://www.iucnredlist.org/species/16672/22360898">Peromyscus maniculatus</a>); water pipits (<a href="https://www.iucnredlist.org/species/22718571/131988012">Anthus spinoletta</a>) and dunnocks (<a href="https://www.iucnredlist.org/species/22718651/132118966">Prunella modularis</a>); mimic poison frogs (<a href="https://www.iucnredlist.org/species/56378936/43715994">Ranitomeya imitator</a>) and strawberry poison frogs (<a href="https://www.iucnredlist.org/species/55196/3025630">Oophaga pumilio</a>); and cichlid fishes <a href="https://www.iucnredlist.org/species/60711/12396736">Xenotilapia spiloptera</a> and <a href="https://www.iucnredlist.org/species/60719/12398029">Xenotilapia ornatipinnis</a>. In all cases, the researchers used only reproductive males, and focused entirely on brain tissue (as it turns out, love really is all in your head).</div>
 

 
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 <div class="rich-text">At first glance, this list presents a veritable menagerie of misfits with little in common. But when the researchers compared gene expression in all five, they found that the same genetic shifts had been leveraged in each transition to commitment—a core suite of 24 genes that comprised monogamy’s molecular trademark.It wasn’t the content of the genes themselves that had changed, however. Rather, in monogamous species, evolution had tweaked the genetic equivalent of volume control, allowing some genes to blast their instructions to the cell’s protein-producing machinery on loudspeaker, while others were muffled into silence.Despite their outwardly differences, five species spanning millions of years of evolutionary change had managed to converge on the same playbook. Turns out, there may just be a sort of universal language of love—one inscribed in the very contents of the genetic code.<div style="padding-bottom: 56.25%;" class="responsive-object">
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“One might think that something like mammalian monogamy would be nothing like fish monogamy—that we would use higher, more complex processes,” says <a href="http://www.psychology.illinois.edu/people/jrhodes">Justin Rhodes</a>, a biologist studying genes affect behavior at the University of Illinois at Urbana-Champaign, but who was not involved in the study. “But this work is saying, well, no. There’s a lot of common molecules involved.”Among the genes that rose to prominence in steadfast species were factors that are thought to affect learning and memory, or make the brain more amenable to change—hinting at a sort of behavioral flexibility in monogamous males. Young thinks it’s possible that hardworking family guys may benefit from this kind of cognitive firepower.Until these genes are tested one by one, however, it’s too early to definitely say what’s actually going through the heads of monogamous males. “A clear next step could be manipulating these genes and seeing if that changes behavior,” Hoekstra says. “Can you get a promiscuous male to start providing parental care? That would be really cool.”</div>
 

 
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 <div class="rich-text">Of course, even if there are commonalities between species, the complexity of the researchers’ findings also shows that there isn’t just one “monogamy gene”—or even one way to be monogamous. “There’s a conserved theme at the molecular level, but also a lot of variation on that theme... even within populations and individuals,” Hofmann explains.For instance, “monogamous” isn’t always equivalent to “faithful”: The term refers not to a code of conduct, but a repetitive pattern of behavior. Getting attached to a single mate at a time certainly doesn’t preclude the tendency to stray—and many monogamous animals regularly engage in <a href="https://phys.org/news/2015-06-socially-monogamous-birds-promiscuous-previously.html">a little infidelity</a> here and there.Tinkering aside, monogamy’s encore act is telling, Hofmann says. The packaging may differ, but these sorts of evolutionary echoes indicate that, with the same building blocks lying around, there’s been little reason to reinvent the wheel.Moving forward, the researchers plan to test if these patterns hold true in other monogamous species. “I think we would go in with the prediction that we’d see the same genetic signature in other vertebrates,” Young says.
 <figure class="richtext-image full-width"><img alt="Anthus_spinoletta_-_Water_Pipit,_Kahramanmaraş_2016-11-18_02-3.jpg" class="richtext-image full-width" height="533" width="800"
 src="/wgbh/nova/media/images/Anthus_spinoletta_-_Water_Pipit_Kahramanmaras_.width-800.jpg"/><figcaption>The water pipit (Anthus spinoletta) is mainly monogamous, although both males and females will occasionally deviate from their pairs. Image Credit: Zeynel Cebeci, Wikimedia Commons<div class="credit"></div></figcaption>
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 Does that include primates—like us humans? It’s complicated. The topic of human monogamy remains a <a href="https://www.livescience.com/32146-are-humans-meant-to-be-monogamous.html">contentious topic</a>: On one hand, people do tend to get pretty attached to each other, and fathers regularly parent their kids. But not all hallmarks ring true—and many human cultures <a href="https://www.nytimes.com/2013/08/02/science/monogamys-boost-to-human-evolution.html">aren’t strict about the practice of monogamy</a>.The researchers didn’t include people in their study for a variety of reasons (including the ethical dubiousness of grinding up the brains of virile young men). Still, humans are vertebrates, and we share much of the anatomical and chemical machinery that enables monogamy in other species. As such, there are likely to be at least some overlaps in behavior, Hofmann says.From the outside, animals take just about every shape and form. But deep down—at the heart of it all—there exist some striking similarities. “We’re not apart from other animals,” Hofmann says. “We are animals. What happened millions of years ago still affects what we look like, our physiology, our behavior. And not acknowledging that is a mistake.”</div>

By fine-tuning the expression of a similar set of genes, mammals, birds, frogs, and fish may have all capitalized on a common toolkit in the transition to monogamy.

Topic: Evolution

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