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>For animals without eyelids, fish are surprisingly capable of catching some serious shut-eye.</p><p>When zebrafish (<i>Danio rerio</i>) doze off, they catch their z’s much like people do, <a href="https://www.nature.com/articles/s41586-019-1336-7">new research</a> shows. These striped swimmers even appear to experience the piscine equivalent of REM sleep, the stage in which humans dream—and something that, until now, has only been reported in mammals, birds, and reptiles.</p><p>That doesn’t necessarily mean that fish are dreaming, or even that their version of sleep is completely identical to ours. Even so, the study, published today in the journal <i>Nature,</i> suggests that multistage snoozing could be common among vertebrates—the group of animals that includes mammals, birds, reptiles, amphibians, and fish—and may have arisen more than 450 million years ago.</p><p>“This paper is a long time coming,” says <a href="https://faculty.sites.uci.edu/audreychenlew/">Audrey Chen Lew</a>, a neurobiologist at the University of California, Irvine who was not involved in the study. “It’s really nice work that...demonstrates similarities between fish and humans and other mammals that we haven’t seen before.”</p></div>
  

  
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      <div class="rich-text"><p>That sleep is more or less ubiquitous among complex animals such as vertebrates, which all have the neural circuitry that makes up the spinal cord, might sound like a no-brainer. But in the world of neurobiology, things aren’t so black and white.</p><p>One issue is that sleep isn’t always easy to measure or identify. In some creatures, it’s an easy behavior to pick out: As they doze off, many animals will settle into a relaxed posture, stop most of their movements, and become less aware of their surroundings for an extended period of time (without entering a coma or other difficult-to-reverse state of being).</p><p>Other organisms, however, don’t abide by these criteria, prompting researchers to search for a more cellular definition of sleep—something that might be universally detectable among all those who do, in fact, engage in regular slumber.</p>
            <figure class="richtext-image full-width"><img alt="Zebrafish95-300.jpg" class="richtext-image full-width" height="260" width="800"
            src="/wgbh/nova/media/images/Zebrafish95-300.width-800.jpg"/><figcaption><p>Zebrafish are transparent during their first few weeks of life. Shown here is a larva, or juvenile. Image Credit: Shawn Burgess, NHGRI, Wikimedia Commons</p><div class="credit"><p></p></div></figcaption>
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            <p>That’s actually something that scientists have more or less nailed down in mammals, birds, and reptiles, all of which exhibit similar patterns of electrical activity in the brain when hitting the hay. Fish, on the other hand, have remained mostly mysterious, due in part to the fact that many sleep research methods are tailored to humans and other land-based species.</p><p>But even though they’re separated by at least 400 million years of evolution, fish and humans <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3703927/">aren’t all that different</a>. Throughout the piscine body are familiar hallmarks of human physiology, down to the genes written into their DNA. When it comes to fish, all the right machinery is there for human-like sleep, says study author <a href="https://profiles.stanford.edu/philippe-mourrain">Philippe Mourrain</a>, a neurobiologist at Stanford University. It’s just that no one had yet found a way to check if it was doing the same thing.</p><p>So a team of scientists led by Mourrain decided to invent a method of their own. In <a href="https://www.mayoclinic.org/tests-procedures/polysomnography/about/pac-20394877">human sleep studies</a>, sensors hooked up to a person’s body record their brain activity, heart rate, breathing, and muscle movements. Taking inspiration from this comprehensive suite of measurements, the researchers developed what was, in effect, a whole-body scan for a zebrafish—a striped, inch-long minnow that develops with a transparent body during its first few weeks of life.</p><p>This see-through skin was key to the experiment’s success, as it allowed the researchers to peer directly into the fish’s organs without the need for surgeries or other invasive procedures, says study author <a href="https://profiles.stanford.edu/louis-leung">Louis Leung</a>, who conducts research under Mourrain’s supervision. In humans, many sleep study measurements are collected by recording electrical signals by way of electrodes on the skin. But the fish’s transparency allowed the researchers to gather the same kinds of data by simply putting fluorescent markers into cells, which then lit up in the presence of electrical signals, yielding a pictorial play by play of individual cells’ behavior over time.</p></div>
  

  
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      <div class="rich-text"><p>When the team analyzed the brain waves of a school of juvenile zebrafish in repose, they discovered two familiar patterns of electrical activity. The first bore a striking resemblance to what’s known in humans as deep or slow-wave sleep, so named because it produces a series of synchronized, low-frequency brain waves. In people, deep sleep is marked by low brain activity, and is thought to give the body the opportunity to recuperate. It may also play a role in memory consolidation.</p><p>If that’s also true in fish, Mourrain says, it makes a lot of sense. Even in animals for whom life goes along swimmingly, there’s always a need for some R&amp;R. And fish, too, need to learn. But Mourrain was far more taken aback to see another hallmark of human sleep echoed in zebrafish: the state in which people dream.</p><p>So-called rapid-eye movement (REM) sleep is actually bursting with brain activity, on par with measurements taken during waking hours. The big difference, of course, is that the rest of the body <i>isn’t</i> awake, and is actually mostly immobilized (except for the eyes, which, in humans, jerk back and forth).</p><p>Much of this also appears to be true for zebrafish, except for their eyes, which kept quiet along with the rest of the body, Mourrain says. (Many other animals also keep their eyes still during REM sleep.)</p><p>Neither deep sleep nor REM sleep was completely identical between humans and fish, points out <a href="https://www.ucl.ac.uk/~ucbtjr3/People.html">Guliz Ozcan</a>, a neurobiologist and zebrafish expert at University College London who was not involved in the study. For one thing, the zebrafish equivalent of slow-wave sleep was a lot, well, <i>slower.</i> Despite these differences, Ozcan says, the neural “signatures” of both states are clearly recognizable—implying that the human version of sleep might be far less human than once thought.</p><p>With these new findings, Leung says, zebrafish can now join the growing list of vertebrates in which sleep has been pinpointed on a more molecular level. Without testing every single vertebrate in existence, it’s hard to say whether multistage sleep is <i>universal</i> in this group<i>,</i> he adds. But as a representative for fish—which comprise around half of all known vertebrate species—the zebrafish and its startling slumber hint that multistage sleep may have been present in a common ancestor of mammals, birds, reptiles, and fish, which lived at least 450 million years ago.</p><p>Amphibians are likely to share the trait as well, since they’re more closely related to us than fish are, Mourrain says. The next step, he adds, will be to see if the same signatures extend even further back in evolutionary time.</p>
            <figure class="richtext-image full-width"><img alt="combo.jpg" class="richtext-image full-width" height="668" width="800"
            src="/wgbh/nova/media/images/combo.width-800.jpg"/><figcaption><p>Top: A zebrafish larva with a fluorescent central nervous system. Cells light up as they become active. Bottom: The central nervous system and muscles of the zebrafish, illuminated with the same fluorescence. Using this system, researchers were able to record cellular signatures of sleep without invasive procedures. Image Credit: Courtesy of Louis Leung, Stanford University</p><div class="credit"><p></p></div></figcaption>
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            <p>Such deep-rooted implications make this paper “a total breakthrough,” says <a href="https://www.neuro.duke.edu/people/faculty/eva-naumann">Eva Naumann</a>, a neurobiologist at Duke University who was not involved in the study. “I can’t overstate it: [Finding these patterns of brain activity] was the missing piece of the puzzle...I’ve been waiting for a study like this to come out ever since I started working in this field.”</p><p>The big picture here doesn’t paint humans as primitive, though. Rather, these results should “elevate the zebrafish as a model system to study neural phenomena like sleep,” Naumann adds.</p><p>The study’s results also showed that, when deprived of sleep or treated with sleeping pills, zebrafish react similarly to humans both behaviorally and physiologically, hinting that they could also be useful in screening drugs to treat irregular or disordered sleep, Ozcan says.</p><p>There’s still, however, the elephant in the room: Despite being so widespread, sleep and all its stages continue to puzzle researchers trying to suss out their true purpose. But whatever it is that dozing is doing, if it really did evolve this long ago, and stuck around in so many species, “that points to something really essential,” Leung says.</p><p>As for whether zebrafish dream during their version of REM, that’s still an open question. If dreaming is a product of learning and memorization, it’s certainly possible, Mourrain says.</p><p>After all, most breakthroughs come from the most unexpected places, he says. Including the ones people (or any other species, perhaps) never even dreamed of.</p></div>
  

  
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<p>Deep sleep and REM sleep could be universal among vertebrates, stretching 450 million years back in evolutionary time.</p>

Like us, fish experience the ‘dreaming’ stage of sleep





  
      <div class="rich-text"><p>In November of 1978, an observer in a Boston institution hurriedly scrawled down a short note that, unbeknownst to them, would eventually send waves through the research field of language development.</p><p>“He says ‘Hoover’ in plain English,” the page read. “I have witnesses.”</p><p>That sentence wouldn’t have been remarkable, save for one detail: The “he” in question—Hoover—was a harbor seal.</p></div>
  

  
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      <div class="rich-text"><p>Over the next several months, Hoover’s trainers at Boston’s New England Aquarium discovered that their unusual flippered friend could do far more than speak his own name. Rewarded with treats of fish whenever he spoke, the seal quickly began verbally greeting aquarium employees and patrons alike.</p><p>On these occasions, Hoover would adopt a straight-backed posture and square his shoulders (or, at least, the seal equivalent of shoulders) before <a href="https://www.youtube.com/watch?v=prrMaLrkc5U">yelping out phrases</a> like “hello there, how are you,” “come over here,” or “get out of here” in a thick, rumbling New England accent, punctuated by raucous barks. He also appeared to be capable of “laughter,” scientists <a href="https://www.nrcresearchpress.com/doi/abs/10.1139/z85-157#.XRJIPGJKjOQ">noted in a 1985 study</a>, and once emitted a “blood-curdling scream” so alarming that an observer logged it as a data point in Hoover’s file.</p><div style="padding-bottom: 74.94553376906318%;" class="responsive-object">
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<p>Researchers later realized that Hoover had picked up several of these quirks from the Maine fisherman who had rescued him from the shores of Cundys Harbor when he was a pup. “Hoover sounds much like a male human with a Boston accent,” they <a href="https://www.nrcresearchpress.com/doi/abs/10.1139/z85-157#.XRJIPGJKjOQ">wrote</a>. Others, however, seemed to be Hoover-specific idiosyncrasies: “He often sounds somewhat inebriated,” the paper reads, “probably because of his tendency to slur together sounds representing separate human words.”</p><p>Unsurprisingly, Hoover’s remarkable ability to mimic human speech made him a hit—and people from all over flocked to Massachusetts to visit and converse with the world’s one and only “talking seal.” Hoover seemed to enjoy the spotlight, even staging the occasional fit, complete with “raspy breathing” and “strange cries,” to garner the attention of exasperated aquarium staff.</p><p>Even after Hoover died in 1985, scientists continued to puzzle over his startling verbosity. While Hoover was clearly producing the sounds of human speech, it was unclear <i>how</i> exactly he’d managed the feat—and researchers weren’t sure if this uncanny ability was just a fishy fluke.</p><p>Now, decades later, new research might finally help seal the deal. Reporting last week in the journal <i>Current Biology,</i> a team of scientists at the University of St. Andrews in the United Kingdom provides a fresh batch of evidence that <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(19)30685-2?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982219306852%3Fshowall%3Dtrue">seals can indeed learn and imitate many of the complex sounds fundamental to human speech</a>. Not only can pups belt out clear vowels—a skill that many of our closest primate relatives can’t achieve—but they can also <a href="https://www.youtube.com/watch?v=-ahW_f5Sd3Q">recognizably “sing”</a> the first few notes of tunes like the <i>Star Wars</i> theme song and “Twinkle, Twinkle, Little Star.”</p><p>“This is the proof we’ve been waiting for,” says <a href="http://www.cbd.cmu.edu/directory/fellows/postdoctoral-researchers/">Morgan Wirthlin</a>, a computational biologist studying language development at Carnegie Mellon University who was not involved in the study. “It’s long been thought that [seals and their relatives] have this incredible capacity for vocal learning...but this paper is the first to demonstrate it in a really clearly defined way.”</p><div style="padding-bottom: 56.25%;" class="responsive-object">
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<p>In the study, University of St. Andrews biologists Amanda Stansbury and <a href="https://risweb.st-andrews.ac.uk/portal/en/persons/vincent-janik(72f80aa4-1961-44bb-8923-27832001f7d7).html">Vincent Janik</a> trained three young gray seals named Zola, Janice, and Gandalf to copy tones played from a computer by rewarding them with fish. At first, the researchers focused on notes that were within their species’ vocal repertoire, or something a seal might normally hear from a herdmate in the wild.</p><p>Once the seals were comfortable with this task, Stansbury upped the ante, and began including sounds at high, unfamiliar frequencies, as well as sequences that incorporated vowels from human speech. Stansbury even remixed some combinations to recall common jingles and songs that no seal would be expected to produce under natural circumstances.</p><p>The renditions were imperfect, and they might not sound as wicked smart as a Mainer from the 1970s. But the accuracy the seals achieved with unfamiliar melodies and human vowel sounds was impressive—especially considering that this is something that non-human primates tend to struggle with, says Stansbury, who is now at the El Paso Zoo in Texas. “Seals are the closest non-human analog we’ve found this behavior in,” she says.</p></div>
  

  
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      <div class="rich-text"><p>“This is really the first example of a non-human animal that seems to be using vocal learning in the same way we are,” adds <a href="https://directory.whoi.edu/profile/lsayigh/">Laela Sayigh</a>, an animal behaviorist studying dolphin communication at the Woods Hole Oceanographic Institution who was not involved in the study. “The ability to produce these [vowel sounds]...is so central to our own speech as humans. It’s incredibly fascinating to see that seals have this capability, and that it’s so closely aligned with our own.”</p><p>On the whole, animals with vocal capabilities flexible enough to expand in this way are rare. Seals, however, have a rare combination of traits that many other creatures lack, including a key anatomical advantage: a larynx, or voice box—much like the one found in humans.</p><p>“The top of the larynx is what allows people to change between vowels, which linguists will tell you is the most basic building block of language,” says <a href="https://babylab.cornell.edu/people/samantha-carouso/">Samantha Carouso-Peck</a>, a behavioral biologist studying songbirds at Cornell University who was not involved in the study. <a href="https://www.smithsonianmag.com/science-nature/zebra-finches-dream-little-dream-melody-180969925/">Songbirds</a>, she adds, can accomplish something similar with an analogous structure called a syrinx. But a true larynx affords an animal more precise control over the production of sound.</p><p>Of course, hardware alone doesn’t make an adept vocal learner—the neural software needs to be in place, too, Wirthlin explains. “What’s impressive...isn’t really that they [can make these vowel sounds], but that they’re able to copy the structure of a human vowel that isn’t part of their normal repertoire,” she says. “That’s about having the right kinds of neural connections and being able to control the vocal apparatus in a way that other animals can’t.”</p>
            <figure class="richtext-image full-width"><img alt="Janice.JPG" class="richtext-image full-width" height="373" width="800"
            src="/wgbh/nova/media/images/Janice.width-800.jpg"/><figcaption><p>Janice, one of the gray seals trained in the study. After a year of working with the researchers, Janice (as well as the other two seals, Zola and Gandalf) was released to the wild. Image Credit: Courtesy of Amanda Stansbury, El Paso Zoo (formerly University of St. Andrews)</p><div class="credit"><p></p></div></figcaption>
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            <p>It’s still unclear why seals in particular have this exceptional ability, but Carouso-Peck thinks it’s likely got something to do with their dynamic social structure. “There’s a very interesting lesson here about how being highly social, being intelligent, and being a vocal learner seem to be a package deal,” she says. Combined with a keen ear, a sharp tongue and flexible learning style may help mothers and pups find each other over the cacophony of large pods, or give bachelor(ette) seals an edge during mating season.</p><p>Whatever the reason behind the chatter, the new findings reinforce the idea that humans are far from the only ones with the gift of the gab—and, at long last, validate Hoover’s loquacious legacy.</p><p>“Before this, Hoover’s story was an anecdote,” Sayigh says. “This study really cements the reality that seals are capable of modifying their own vocal production based on new sounds they’ve heard...and Hoover was definitely doing that.”</p><p>It’s only fitting, then, that the star of this story gets the last word. Now <i>get outta here!</i></p></div>
  

  
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<p>In the late 1970s, a harbor seal named Hoover began catcalling passersby at the New England Aquarium in a thick Maine accent. A new study confirms seals’ uncanny ability to copy human speech.</p>

‘Talking’ seals mimic sounds from human speech, and validate a Boston legend





  
      <div class="rich-text"><p>You know the look. Everyone does. The wide, winsome eyes; the forlorn, furrowed brow. It’s enough to melt your heart—and send your hand reaching for the treat bag.</p><p>But the next time your dog fixes you with that sorrowful stare, take comfort (or chagrin) in the knowledge that she—and the rest of the world’s pet pooches—could owe their expressive eyes entirely to us.</p></div>
  

  
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      <div class="rich-text"><p>According to <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1820653116">new research</a> published today in the journal <i>PNAS</i>, the allure of puppy dog eyes may be a product of domestication, acquired as a lineage of charismatic canines split off from wolves. While their wild ancestors lack the necessary facial anatomy to raise their inner eyebrows, dogs possess certain muscles that, when put to use, make their mugs resemble ours—something that may have piqued the interest of ancient peoples.</p><p>These brow-raising results hint that, on the road to becoming our closest companions, dogs may have evolved a way to hijack, or at least mimic, a core tenet of human communication: eye contact.</p>
            <figure class="richtext-image full-width"><img alt="iStock-871215928.jpg" class="richtext-image full-width" height="534" width="800"
            src="/wgbh/nova/media/images/iStock-912167862.width-800.jpg"/><figcaption><p>It&#x27;s hard to stay mad at a face like this. Image Credit: RalchevDesign, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>“Eye contact is central to human communicative skills,” says <a href="https://www.aleahbowie.com/">Aleah Bowie</a>, a conservation psychologist at Duke University who was not involved in the study. “So it makes sense if we’re selecting for non-human animals [like dogs], we’re going to look for the same kind of traits.”</p><p>In other words, the power of puppy dog eyes is rooted not so subtly in a bit of egocentrism: Wide, expressive eyes <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0082686">remind us of human babies</a>, or a person on the verge of tears—emotive extremes of ourselves.</p></div>
  

  
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      <div class="rich-text"><p>And dogs, it seems, have reaped the benefits of this facial familiarity. There’s even evidence to suggest mutts who raise their inner eyebrows more often even <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0082686">get adopted more quickly from shelters</a>.</p><p>Of course, shelters didn’t exist tens of thousands of years ago, when people first cozied up with a subset of unusually friendly wolves. But that doesn’t mean a similar process wasn’t happening in the early days of domestication: In gravitating toward friendlier canines, humans might have inadvertently reshaped an entire lineage, altering traits both physical and psychological.</p><p>If that’s the case, then wolves might be expected to show less puppy-eyed prowess—or even lack some of the anatomical accoutrements necessary to maneuver their brows.</p><p>To put this theory to the test, a team of researchers led by <a href="http://www2.port.ac.uk/department-of-psychology/staff/dr-juliane-kaminski.html">Juliane Kaminski</a> and <a href="http://www2.port.ac.uk/department-of-psychology/staff/dr-bridget-waller.html">Bridget Waller</a>, both comparative psychologists at the University of Portsmouth in the United Kingdom, compared the facial muscles of six modern mutts and four gray wolves—a stand-in for domestic dogs’ long-gone wild ancestor. Though the two species’ faces were almost identical, almost all dogs tested possessed two extra muscles around their eyes that helped them raise their brows and pull their eyelids in certain directions—both movements that are, scientifically speaking, adorable.</p><p>“To see this kind of soft tissue change in the timespan of [dog domestication] is remarkable,” Waller says. The wolves, however, weren’t a “completely blank slate,” she adds. While the wolves didn’t have fully developed muscles, a few sparse muscle fibers existed in their place—just enough, she says, for evolution to “grab hold and make bigger, more uniform, and more stable in the dogs.”</p><p>Soft tissue like muscle doesn’t fossilize well, and a face-off between two modern species is just an approximation for gazing backwards in time. But already, the study presents a tantalizing hint of how these muscles may have beefed up over time. Only one dog breed studied lacked one of the two critical eye muscles: the Siberian Husky, which is more closely related to wolves than most other dog breeds. “This is suggestive of [an intermediate stage], but we need to follow up on this with other breeds,” Waller says.</p>
            <figure class="richtext-image full-width"><img alt="203461.jpg" class="richtext-image full-width" height="888" width="800"
            src="/wgbh/nova/media/images/203461.width-800.jpg"/><figcaption><p>Most dogs appear to possess two muscles that wolves lack: the levator anguli oculi medialis muscle (LAOM) and the retractor anguli oculi lateralis muscle (RAOL). The pair help dogs maneuver their eyebrows and eyelids. Image Credit: Juliane Kaminski et al., PNAS, 2019</p><div class="credit"><p></p></div></figcaption>
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            <p>To complement their anatomical findings, the researchers next filmed 27 shelter dogs and nine captive wolves for two minutes after a stranger approached them. As expected, dogs came out ahead in this face-off as well: On average, they raised their inner eyebrows more often, and seemed capable of producing more exaggerated movements with their eyes than their wolf cousins—findings in keeping with the team’s dissection.</p><p>“It’s really exciting to see a study exploring the connection between anatomy and behavior,” says <a href="https://dogs.arizona.edu/people/gitanjali-gnanadesikan">Gitanjali Gnanadesikan</a>, a cognitive biologist studying dog domestication at the University of Arizona who was not involved in the study. “In the process of domestication, both have changed in remarkable ways...and many of these changes are intertwined. Trying to understand how these different pieces fit together is extremely important.”</p><p>As eye-opening as the findings are, however, Gnanadesikan cautions that they raise “just as many questions as they answer...we still don’t know if these gazes contain information, or if dogs are intentionally trying to communicate with them.”</p>
            <figure class="richtext-image full-width"><img alt="iStock-871215928.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-871215928.width-800.jpg"/><figcaption><p>Wolves can twitch their brows, but those subtle movements are nothing compared to the heartwrenching stares of dogs. Image Credit: Nastasic, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>Figuring that out, she says, will require more studies on how these heart-wrenching stares are used in different contexts. Dogged gazes may tug on our heartstrings, but it’s important not to attribute <i>too</i> much to our canine comrades.</p><p>Even so, the study underscores the importance of facial expressions in communication, Waller says. That seems obvious. But it’s nonetheless notable, she says, just how much humans’ penchant for emotion has shaped our interactions—with both our own species and others.</p><p>It may not have been intentional on our part, or theirs. Either way, these pooches’ expressive eyes continue to get them out of the doghouse. And for anyone who’s ever fed Fido scraps under the table, or forgiven the massacre of an unlucky shoe, it’s clear that these looks of longing have yet to lose their luster.</p><p>You sly dog, you.</p></div>
  

  
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<p>Wolves lack the facial muscles required to raise their eyebrows—a feature that makes dogs especially endearing to people.</p>

Canines evolved puppy dog eyes to woo human companions





  
      <div class="rich-text"><p>With its loose, bunchy skin and sun-starved complexion, the naked mole-rat (<i>Heterocephalus glaber</i>) recalls an uncooked bratwurst dried on permanent press—and it might be one of the last creatures you’d expect to have superpowers.</p><p>But scientists have known for years that these wrinkly wonders boast an astounding set of death-defying qualities: They live decades longer than other rodents, <a href="https://www.pbs.org/wgbh/nova/article/once-thought-immune-to-cancer-naked-mole-rats-found-with-tumors/">almost never get cancer</a>, and can <a href="https://www.pbs.org/wgbh/nova/article/naked-mole-rats-make-like-a-plant-to-survive-in-zero-oxygen/">survive without oxygen for more than 18 minutes</a>. They’re even impervious to certain types of pain.</p><p>Now, new research suggests that some of these rodents’ oddball characteristics may not be as unusual as once thought. According to a <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.aau0236">study</a> published today in the journal <i>Science,</i> the inability to feel pain is something of a family trait—one that runs rampant across the mole-rat phylogenetic tree.</p></div>
  

  
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      <div class="rich-text"><p>But for these rodents, the evolution of a pain-free existence comes with a twist. Rather than being passed down in carbon copy as mole-rats split off into separate species, resistance to pain seems to have arisen independently in separate lineages—and it doesn’t always manifest in the same way. While some species of these subterranean critters live in blissful ignorance of the sting of acid burns, others are immune only to acrid substances commonly found in plants.</p><p>“This is a fabulous study and a very thorough investigation,” says <a href="https://www.calicolabs.com/team-member/rochelle-shelley-buffenstein/">Rochelle Buffenstein</a>, a biologist studying naked mole-rats at Calico Labs in San Francisco who was not involved in the study. “The researchers have provided a little window into how these animals are able to shut down different kinds of pain in different situations.”</p>
            <figure class="richtext-image full-width"><img alt="6257899504_ac3b1b7070_o.jpg" class="richtext-image full-width" height="546" width="800"
            src="/wgbh/nova/media/images/6257899504_ac3b1b7070_o.width-800.jpg"/><figcaption><p>The naked mole-rat (<i>Heterocephalus glaber</i>), a super-social burrowing rodent native to parts of East Africa. These sausage-shaped critters are impervious to chemical pain from acid and capsaicin. Image Credit: Smithsonian&#x27;s National Zoo, flickr</p><div class="credit"><p></p></div></figcaption>
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            <p>For all its simplicity, the word “pain” encompasses an awful lot. Many different flavors of unpleasantness exist, but one of the body’s most important pain-sensing systems exists solely to detect the types of dangerous chemicals that tend to lurk in snake venom or poisonous shrubs.</p><p>This makes it all the weirder that the naked mole-rat <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0060013">can’t feel two pretty universally agonizing kinds of chemicals</a>: acid and capsaicin (the spicy substance that gives chili peppers their heat). Though the reason behind these insensitivities hasn’t been completely worked out, it probably has something to do with these rodents’ underground habitats, where they’re exposed to a bevy of extreme conditions. Here, adaptations that eased the nuisance of pain could be a way to make a tough life more bearable.</p></div>
  

  
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      <div class="rich-text"><p>Naked mole-rats, however, aren’t the only rodents tunneling in the sands of sub-Saharan Africa. Dozens of other African mole-rat species exist, each with its own unique environmental quirks—but no one had ever tested whether the naked mole-rat’s closest cousins shared its insensitivity to pain.</p><p>So a team of researchers led by <a href="https://www.mdc-berlin.de/lewin">Gary Lewin</a>, a molecular physiologist at the Max Delbrück Center, decided to construct a family tree of mole-rat pain tolerance. After amassing nine evolutionarily distant species of African rodents (including the OG naked mole-rat), the team injected the rodents with three odious chemicals: dilute hydrochloric acid, capsaicin, and allyl isothiocyanate (AITC)—the sinus-clearing compound that gives wasabi and horseradish their pungent taste.</p><p>Right off the bat, it was clear that pain tolerance was not a universal mole-rat attribute. Like their distant mouse relatives (and humans, for that matter), four out of nine rodent species expressed discomfort in the presence of all three chemicals. Of the five remaining, two species, the Cape mole-rat (<i>Georychus capensis</i>) and the East African root rat (<i>Tachyoryctes splendens</i>), had no response to hydrochloric acid, while another, the Natal mole-rat (<i>Cryptomys hottentotus natalensis</i>), was insensitive to capsaicin. As before, the naked mole-rat was indifferent to both. Oddly, pain sensitivity combinations didn’t match up by relatedness, suggesting that several lineages had found their own way to the same pain-free outcome.</p><p>Every species tested, however, had a strong reaction to AITC—a compound known for its destructive powers in most animal bodies—except for one: the highveld mole-rat (<i>Cryptomys hottentotus pretoriae</i>), which became “the star of this particular study,” Lewin says. “This insensitivity [to AITC] is, as far as we know, completely unique in the animal kingdom.”</p><p>To track down the basis of this enigmatic trait, Lewin and his team extracted and compared genetic material from all nine species. The analysis revealed two subtle differences in the highveld mole-rat. One was a mutation in a gene that made AITC tougher to detect. Another boosted the expression of a protein that jettisoned signaling molecules out of pain receptive cells, compromising their ability to relay the presence of AITC.</p>
            <figure class="richtext-image full-width"><img alt="iStock-172383652.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-172383652.width-800.jpg"/><figcaption><p>Horseradish is among the many plant roots that contain allyl isothiocyanate (AITC), a pungent, spicy chemical that burns when eaten. Image Credit: blowbackphoto, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>But neither of these alterations had completely removed the AITC detection system from the highveld mole-rat. The genetic hardware was still in place—the lines of communication had just been gummed up. When the researchers next treated the rodents with a chemical that plugged up the protein that made pain receptive cells leaky, they became just as sensitive to AITC as their horseradish-hating cousins.</p><p>A drug that did the exact opposite of this and <i>increased</i> the leakiness of the protein could someday have value as a therapy for chronic pain, Lewin says.</p><p>It’s still unclear why only the highveld mole-rat has adopted AITC insensitivity, but as with its cousins, the trait is probably a product of its unusual lifestyle, says study author <a href="https://www.linkedin.com/in/ole-eigenbrod/?originalSubdomain=de">Ole Eigenbrod</a>, who completed his PhD in Lewin’s lab. It’s possible these rodents have become tolerant to AITC to cope with the spicy roots in their diets, or the stinging bites of the Natal droptail ants that frequent highveld hovels.</p><p>A pain-free coexistence with ants could confer “a huge advantage” on highveld mole-rats, which would be able to populate areas without any challenge from other rodent species, which are presumably sensitive to the insects’ nips and nibbles, Lewin says. It’s even possible that highveld mole-rats have expanded the typical vegetarian palate of their kin to include these ants, which could be a serious perk in times of scarcity.</p>
            <figure class="richtext-image full-width"><img alt="iStock-1124742136.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-1124742136.width-800.jpg"/><figcaption><p>A common mole-rat (<i>Cryptomys hottentotus hottentotus</i>). This species of burrowing African rodent can feel all three types of chemical pain. Image Credit: avstraliavasin, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>That said, there are trade-offs to any kind of pain tolerance—and it remains to be seen what cost the highveld mole-rat may be paying for these ant-ics. There’s probably a reason researchers haven’t yet found a mole-rat—or any other animal—that’s completely impervious to all three of these painful chemicals, says <a href="https://medicine.yale.edu/bbs/people/elena_gracheva.profile">Elena Gracheva</a>, a neuroscientist at Yale University who was not involved in the study. (Were that hypothetical animal to be discovered, though, it would still presumably be vulnerable to myriad other types of pain, including cold burns and the agony of flesh wounds.) Pain, after all, is a memorable tutor—and a life without clear signs of danger <a href="https://ghr.nlm.nih.gov/condition/congenital-insensitivity-to-pain">would probably be a short one</a>.</p><p>But the work done on this family of stoic rodents just goes to show that “pain, while important, can still be very fluid,” says <a href="http://www.childrenshospital.org/research/labs/woolf-laboratory/people/post-doctoral-research-fellows/simmie-foster">Simmie Foster</a>, a neuroscientist and pain expert at Harvard Medical School and Boston Children’s Hospital who was not involved in the study. “Pain responds to a changing environment...and there are instances in which it’s beneficial to adapt.”</p><p>Given what these critters have to deal with on a daily basis, pain tolerance might just be another notch in the mole-rat superpower belt. After all, it’s in the harshest environments that the most creative solutions for survival often arise. “[These rodents] have been forced to defy dogmas and figure out how to live in these circumstances,” Buffenstein says. “They don’t read the textbooks on how a mammals should behave...they’ve figured out their <i>own</i> best way.”</p><p>Naked or not, mole-rats can clearly take the heat.</p></div>
  

  
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<p>Some African mole-rats seem to tolerate the burn of spicy plants or biting insects that cause most other animals excruciating pain.</p>

The naked mole-rat is impervious to certain kinds of pain. It’s not alone





  
      <div class="rich-text"><p>Seeing someone else suffer a big disappointment can have a pretty damaging effect on your own morale. That’s definitely the case with people—and it may be true for ravens, too.</p><p>New research suggests that, like humans and many other mammals, common ravens (<i>Corvus corax</i>) can read and internalize the emotional states of others. In the <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1817066116">study</a>, published today in the journal <i>PNAS,</i> ravens watch their friends grapple with a frustrating task in which they’re denied a tasty treat. Though the onlookers aren’t deprived of anything, they then seem to mirror their partners’ discontent, and start behaving pessimistically themselves.</p></div>
  

  
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      <div class="rich-text"><p>Unlike people, ravens can’t speak freely about their emotional distress. But these results hint at the tantalizing possibility that humans aren’t alone in their interconnectedness, and could provide early evidence of something akin to empathy in birds.</p><p>“This paper is a tremendous step forward in being able to understand the evolutionary roots of empathy,” says <a href="https://corvidresearch.blog/">Kaeli Swift</a>, an animal behaviorist and corvid expert at the University of Washington who was not involved in the study. “I think it would be too far to say that [this paper shows] ravens are empathetic…but this work could be foundational in eventually arriving at that conclusion.”</p>
            <figure class="richtext-image full-width"><img alt="iStock-1081629534.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/iStock-1081629534.width-800.jpg"/><figcaption><p>In many ways, raven intelligence rivals that of primates. These birds are adept at problem solving, deception, and even mimicking human speech. Image Credit: Tom Meaker, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>Showing that non-human animals have empathy—the ability to understand and share the feelings of others—is no easy task. A big part of the challenge is obvious: Researchers can’t ask their subjects how they’re feeling, says <a href="https://sites.lsa.umich.edu/prestos-lab/">Stephanie Preston</a>, a neuroscientist studying emotion and behavior at the University of Michigan who was not involved in the study.</p><p>But some researchers argue that empathy can be broken down and tested through its more manageable components. For instance, you can’t have empathy without emotional contagion, or the tendency of the feelings and behaviors of an emotional reaction to hop from individual to individual even in the absence of what triggered them. Emotional contagion is, in a sense, a way to experience by proxy—and it can come with serious perks.</p></div>
  

  
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      <div class="rich-text"><p>“This gives you the ability to learn information about something without having to experience it yourself,” Preston says. “There’s an advantage to not having to experience pain, or realize food makes you sick, or see that someone is threatening...it can also give you the information you need to provide help to another in distress. It’s an efficient way to learn in a social environment.”</p><p>Emotional contagion is a fixture of the human experience, but it’s also been demonstrated in other species, including rats and pigs, thought to be both clever and social. Though ravens have <a href="https://science.sciencemag.org/content/357/6347/202">both</a> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3064662/">these</a> qualities in spades, no one had yet investigated whether these black-feathered birds could mirror the feelings of their friends. So a team of researchers led by <a href="https://cogbio.univie.ac.at/people/phd-candidates/jessie-adriaense/">Jessie Adriaense</a>, a cognitive biologist at the University of Vienna, put a group (technically, an “unkindness”) of eight ravens raised at the Haidlhof Research Station in Austria to the test.</p><p>The researchers first sorted the most buddy-buddy birds into pairs. Then, one member of each raven duo, dubbed the “observer,” was placed in front of a closed, unfamiliar box—an ambiguous situation designed to probe the bird’s baseline emotional state. While an optimistic raven may eagerly toy with the container, expecting a reward, a pessimistic bird would more likely to regard it with skepticism. At the start of the experiment, the ravens curiously pecked at the box after only momentary hesitation.</p><p>Then, each observer raven looked on as its partner bird, the “demonstrator,” was emotionally manipulated by a scientist. Demonstrator ravens were shown two different food items of different appeal: scrumptious morsels of dried dog food and an unappealing nubbin of raw carrot. Then, a researcher took one food away and handled the remaining treat as if the bird was about to be fed. Those left ogling the kibble behaved enthusiastically, while those saddled with the unappetizing vegetable quickly lost interest. Though the spectating ravens couldn’t see the foods themselves, they remained privy to their friends’ reactions.</p><p>Immediately after watching this ordeal play out, each observer raven was presented once again with a mystery box. Not much changed for the birds who had just seen their friends zealously react to kibble. But the ravens who had witnessed their partners’ carroty chagrin waited much longer than before to start tinkering with the box—as if they had already resigned themselves to disappointment. (The birds later switched roles so that each raven in the study got to experience its own emotional rollercoaster.)</p>
            <figure class="richtext-image full-width"><img alt="201010.jpg" class="richtext-image full-width" height="530" width="800"
            src="/wgbh/nova/media/images/201010.width-800.jpg"/><figcaption><p>A raven in an experimental compartment at Haidlhof Research Station in Austria. Image Credit: Jessie E. C. Adriaense, University of Vienna</p><div class="credit"><p></p></div></figcaption>
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            <p>It’s not entirely clear why the effects of pessimism were stronger, but this finding isn’t entirely surprising, says <a href="https://www.lomapendergraft.com/">Loma Pendergraft</a>, a corvid cognition expert at the University of Washington who was not involved in the study. After all, there’s probably an evolutionary advantage to being a little more sensitive to negative outcomes. “If something is ambiguous...it’s better to tend towards caution, because the potential cost could include death,” he says.</p><p>But it seems something about the reactions of jilted demonstrators was, in fact, contagious. Had their partners “caught” their disillusionment?</p><p>It’s possible, but the study can’t guarantee that infectious element was <i>emotion,</i> says <a href="https://www.jennifervonk.com/">Jennifer Vonk</a>, a cognitive psychologist at Oakland University who was not involved in the study. The researchers weren’t able to test the emotional state of the demonstrator ravens, making it tough to confirm if the observers were actually picking up on feelings, or a set of behaviors associated with them. Behaviors, too, can be contagious—just step into a room full of people and yawn.</p>
            <figure class="richtext-image full-width"><img alt="Paul (53).JPG" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/Paul_53.width-800.jpg"/><figcaption><p>A raven at the Haidlhof Research Station in Austria. Image Credit: Jessie E. C. Adriaense, University of Vienna</p><div class="credit"><p></p></div></figcaption>
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            <p>Still, in many cases, emotions tend to come packaged up with a reliable set of behaviors, Preston says. “Each species has its own repertoire of behaviors that are common...you have to start somewhere.”</p><p>Going from emotional awareness to empathy remains a big jump, however. One crucial part of the equation that still needs to be addressed is whether infectious feelings come paired with concern and care for another individual in distress, Preston says. For that, an observer bird may be expected to soothe a disappointed demonstrator. (There is, however, separate evidence that ravens are capable of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2868892/">consoling</a> and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3064662/">reconciling</a> with each other after fights.)</p><p>None of that takes away from how exciting this find is, she adds—especially in birds. “These building blocks of empathy are present in diverse species,” she says. “Empathy is not something that defines us as humans. There is a long evolutionary history leading up to our ability to empathize.”</p></div>
  

  
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<p>These crafty birds might be capable of interpreting and internalizing the emotions of others.</p>

Seeing friends disappointed bums us out. The same may be true for ravens





  
      <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 may <a href="https://academic.oup.com/ae/article-pdf/58/1/58/18756174/ae58-0058.pdf">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 may 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 may 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 may 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 may 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>

Topic: Evolution

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