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<p>The relationships these winged mammals forge in captivity are strong enough to survive the jarring transition back into the wild.</p>

Vampire bats form lasting bonds of ‘friendship,’ just like us

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<p>Researchers used artificial intelligence to reevaluate elevations vulnerable to rising sea levels.</p>

New study more than triples estimates of people at risk from rising seas

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<p>In a new study, brain-like organoids made from human cells were slower to mature than their chimpanzee and macaque counterparts.</p>

Lab-grown mini-brains highlight developmental differences between humans and great apes

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NOVA Next is NOVA’s award-winning digital publication that provides answers from the cutting edge of science and technology.

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<p>NOVA Next is NOVA’s award-winning digital publication that provides answers from the cutting edge of science and technology.</p>

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<p>Scientists are using artificial cervices and 3D models of the uterus to better understand pregnancy and childbirth.</p>

How mechanical engineering could revolutionize the study of preterm birth





  
      <div class="rich-text"><p>As an artist, he used science to understand the human body. As an anatomist, he used art to illuminate secrets beneath the flesh.</p><p>Five hundred years after Leonardo da Vinci’s death, his anatomical drawings are as powerful and poignant as they were in his time. Their beauty is breathtaking, their accuracy a testament to the genius of an artist willing to go to extremes to depict the human form.</p></div>
  

  
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      <div class="rich-text"><h3><b>Gifts to science</b></h3><p>About a dozen cadavers lie sealed in blue body bags on stainless steel tables in the anatomy lab at the Boston University School of Medicine. Trudy Van Houten unzips one of the bags to reveal the body of a tall, elderly man. Prepared with embalming fluids, the body is ready for dissection.</p><p>Van Houten, an assistant professor of anatomy and neurobiology at the school, has taught clinical anatomy for 30 years. She leans over the body, glasses perched on the edge of her nose.</p><p>Her young assistant passes her a scalpel. She makes a neat incision into the skin of the upper right arm. Minutes later, she uses forceps to lift the <a href="https://www.healthline.com/human-body-maps/biceps-brachii#1">biceps brachii muscle</a>, which extends between the shoulder and elbow. Next to her, a television monitor displays a magnified image of <a href="https://www.rct.uk/collection/919013/recto-the-muscles-of-the-shoulder-and-arm-verso-the-muscles-of-the-shoulder-and">one of da Vinci&#x27;s drawings</a> of a dissected arm. The muscles appear long and lithe, shaded in with lines that blend into a yellowed background.</p><p>The scene is being filmed for the NOVA documentary “<a href="https://www.pbs.org/wgbh/nova/video/decoding-da-vinci/">Decoding da Vinci</a>,” which probes the mysteries behind some of da Vinci’s most brilliant work. “His depictions of the human body were beautiful,” Van Houten later says. “And so accurate that we can actually use them to teach.”</p><p>Van Houten insists images are critical in teaching anatomy. “It’s something that anyone who teaches anatomy faces,” she says. “You can’t teach it without pictures.”</p><p>And although educators can now draw on 3D imagery and other computer-based models, Van Houten prefers the real thing. “The best models we have are dissected human bodies,” she says.</p>
            <figure class="richtext-image full-width"><img alt="Leonardo_da_Vinci_Story_Image.jpg" class="richtext-image full-width" height="478" width="800"
            src="/wgbh/nova/media/images/Leonardo_da_Vinci_Story_Image.width-800.jpg"/><figcaption><p>Anatomical studies of the shoulder. Image Credit: Wikimedia Commons, Leonardo da Vinci.</p><div class="credit"><p></p></div></figcaption>
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            <p>The bodies are donated to the school through its <a href="https://www.bumc.bu.edu/anatneuro/anatomical-gifts/">anatomical gift program</a><b>.</b></p><p>Hundreds of students dissect the bodies, working in groups of eight. “They dissect from skin to skeleton,” says the program’s director, Robert Bouchie. “We start with the back and limbs.”</p><p>After the dissections are done, Bouchie leads a <a href="https://www.youtube.com/watch?v=mvbfH5YoEwo">memorial ceremony</a> for each body, which is then cremated. He and the students place the body in a coffin. There is a moment of silence. Family of the deceased often attend, he says.</p><p>Bouchie returns cremains in person to a handful of families each year. He explains why. “You can’t send it UPS, you can’t send it FedEx,” he says. “You have to send it USPS.”</p><p>Bouchie recalls once being asked the value of packed cremains by a postal worker. He told her the package was priceless. “So the clerk said I had to declare a value of zero,” he says. “I wasn’t comfortable with that.”</p></div>
  

  
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      <div class="rich-text"><h3><b>Human dissection: A unique learning tool</b></h3><p>Before the advent of modern imaging, dissections revealed the complicated inner workings of the human body when there was, perhaps, no other way. Da Vinci yearned to witness these mechanics for himself. Though he lacked any formal medical training, he is believed to have dissected more than <a href="https://www.rct.uk/collection/themes/exhibitions/leonardo-da-vinci/the-queens-gallery-buckingham-palace/leonardo-and-dissection">30 bodies</a> in his lifetime.</p><p>Though human dissections date back to <a href="https://www.britannica.com/biography/Herophilus">about the third century BCE</a>, the first <a href="https://link.springer.com/article/10.1007/s11999-016-5213-5">recorded public dissection</a> took place around 1315, when Italian physician and anatomist Mondino de Luzzi performed a dissection on an <a href="https://books.google.com/books?id=GeCFKXHYYEEC&amp;pg=PA177&amp;lpg=PA177&amp;dq=Mondino+de%E2%80%99+Liuzzi,+dissection,+1315,+criminal&amp;source=bl&amp;ots=TjzcVTNm84&amp;sig=ACfU3U25gW3Yz86tGnsQsSvVky7kQ_mNpQ&amp;hl=en&amp;sa=X&amp;ved=2ahUKEwjnkLaWlanlAhWtVt8KHSBlCOoQ6AEwEHoECAoQAQ#v=onepage&amp;q=Mondino%20de%E2%80%99%20Liuzzi%2C%20dissection%2C%201315%2C%20criminal&amp;f=false">executed criminal</a>.</p><p>The seminal anatomical book collection “<a href="https://www.metmuseum.org/toah/works-of-art/53.682/">De Humani Corporis Fabrica</a><i>”</i> (On the Structure of the Human Body)<i>,</i> by Flemish anatomist and physician Andreas Vesalius, was published in 1543. The books dispelled anatomical theories that had been entrenched since the second century. Vesalius, however, also pillaged cemeteries <a href="https://www.joh.cam.ac.uk/library/andreas-vesalius-and-challenge-galen">in search of corpses</a> for dissection.</p><p>Grave-robbing became a serious problem in the 18th and 19th centuries in some parts of Europe as well as the United States, where African American graves were especially vulnerable. Iron coffins and cage-like structures, known as <a href="https://www.atlasobscura.com/places/greyfriars-cemetery-mortsafes">mortsafes</a>, were used to protect graves from body snatchers in England and Scotland. In a notorious case, <a href="https://www.youtube.com/watch?v=FyE3MyaLD-U">William Burke and William Hare</a> murdered at least 16 people in Edinburgh, selling their bodies for dissection.</p><p>The British Parliament passed the <a href="https://www.youtube.com/watch?v=SPdhgnN9DbA">Anatomy Act</a> in 1832, which made it legal for medical schools to dissect unclaimed bodies from workhouses and hospitals. The law curbed the practice of body snatching in Britain but disproportionately <a href="https://kingscollections.org/exhibitions/specialcollections/charles-dickens-2/italian-boy/anatomy-act">affected the poor</a>.</p><p>For centuries, laws in Europe and the United States allowed dissections of <a href="https://www.ncbi.nlm.nih.gov/books/NBK481735/">executed criminals</a>. However, da Vinci was able to procure bodies from hospitals across Italy. In Florence, he befriended a centenarian who he then witnessed peacefully pass away.</p><p>He later dissected the man’s body. The study led to da Vinci’s very early description of arteriosclerosis.</p>
            <figure class="richtext-image full-width"><img alt="VetruvianSquare.jpg" class="richtext-image full-width" height="753" width="753"
            src="/wgbh/nova/media/images/VetruvianSquare.width-800.jpg"/><figcaption><p>&quot;Vitruvian Man&quot; by Leonardo da Vinci. Image Credit: Wikimedia Commons, Leonardo da Vinci.</p><div class="credit"><p></p></div></figcaption>
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            <h3><b>Science meets art</b></h3><p>Da Vinci was not the only <a href="https://www.metmuseum.org/toah/hd/anat/hd_anat.htm">Renaissance artist</a> who performed human dissections. And his findings were <a href="https://www.theguardian.com/science/2012/may/13/leonardo-da-vinci-anatomy-drawings">not always correct</a>. Yet, his anatomical studies remain scientifically significant.</p><p>He correctly described the heart as the center of the blood system and was the first to describe it as a muscle with <a href="https://www.cdc.gov/ncbddd/heartdefects/howtheheartworks.html">four chambers</a>. He discovered how small vortices of blood help shut the aortic valve, but because his scientific papers and anatomical drawings went unpublished for centuries, this mechanism wasn’t <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2804084/">confirmed</a> until the late 1960s.</p><p>“He started with an interest of understanding the body to improve his art,” explains “Decoding da Vinci” producer Doug Hamilton. “But he clearly went further. He clearly became fascinated by understanding the human body<i>.”</i></p><p>Da Vinci often dissected <a href="https://fn.bmj.com/content/77/3/F249">by candlelight</a>, taking left-handed, <a href="https://www.mos.org/leonardo/activities/mirror-writing">mirrored notes</a> throughout the process. “There&#x27;s no refrigeration, he&#x27;s sometimes doing it in the dark of night,” says Hamilton. “It’s a messy, smelly business. And yet, when you look at his drawings they don&#x27;t convey any of that. They convey the beauty of the body.”</p><p>More than <a href="https://www.bl.uk/collection-items/leonardo-da-vinci-notebook">7,000 pages</a> of Da Vinci’s notes and drawings still survive. A painter, sculptor, architect, and engineer, da Vinci made visionary drawings of a giant crossbow, a simplistic machine gun, winged flying machines, and a self-propelled cart—which <a href="https://www.wired.com/brandlab/2016/03/a-brief-history-of-autonomous-vehicle-technology/">some say</a> is the first design of a <a href="https://www.pbs.org/wgbh/nova/video/look-whos-driving/?fbclid=IwAR3Vacc_vkYq6hwc-RA5CoIsJfu6A66fgpPKWMyM7d8U-Q2OcBKThQKU3OA">self-driving vehicle</a><b>.</b> He also designed canal locks, buildings, and bridges.</p><p>Then there were masterpieces like “Mona Lisa,” “The Last Supper,” and “<a href="https://news.harvard.edu/gazette/story/2017/11/author-walter-isaacson-profiles-the-ultimate-renaissance-man-leonardo-da-vinci/">Vitruvian Man</a>,” a drawing that perfectly illustrates the fusion of art and science in da Vinci’s work.</p><p>Leonardo didn’t draw distinctions between art and science the way we do today, Hamilton says. The documentary, he says, is “an extraordinary story of how his scientific understanding went beyond what he needed to know to paint.”</p><p><i>Tune in or stream “</i><a href="https://www.pbs.org/wgbh/nova/video/decoding-da-vinci/"><i>Decoding da Vinci</i></a><i>” on November 13 at 9/8c on PBS to learn more about the science behind Leonardo da Vinci’s art.</i></p></div>
  

  
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<p>Leonardo da Vinci dissected some 30 cadavers in his lifetime, leaving behind a trove of beautiful—and accurate—anatomical drawings.</p>

Anatomy professor uses 500-year-old da Vinci drawings to guide cadaver dissection





  
      <div class="rich-text"><p>Of the many animals <a href="https://www.globalwildlife.org/team/andrew-tilker/">Andrew Tilker</a> studies, there are plenty he’s never actually seen in person.</p><p>It can feel a bit like chasing after mythical beasts, admits the Global Wildlife Conservation biologist. But that’s par for the course, he says, when you’re searching for species considered <a href="https://www.globalwildlife.org/search-for-lost-species/">“lost” to science</a>.</p><p>That’s certainly been the case for the <a href="https://www.globalwildlife.org/silver-backed-chevrotain/">silver-backed chevrotain</a> (<i>Tragulus versicolor</i>)—a fanged, cat-sized deer relative that looks like it lowered itself halfway into a bath of metallic paint before changing its mind. Though Western researchers have known about this skittish creature for more than a century, they’ve collected only five specimens, all corpses obtained from hunters in Vietnam.</p></div>
  

  
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      <div class="rich-text"><p>The last of these appeared nearly three decades ago, in 1990. No Western biologist—Tilker included—has ever glimpsed a silver-backed chevrotain alive.</p><p>But now, with the help of local knowledge and a cluster of well-placed camera traps, Tilker and his team have snapped the first-ever photos and videos of the silver-backed chevrotain in the wild. Their <a href="https://www.nature.com/articles/s41559-019-1027-7">findings</a>, published today in the journal <i>Nature Ecology &amp; Evolution,</i> go beyond the glamour shot: They confirm that, despite decades of illegal poaching and habitat destruction, this mysterious mini-mammal remains alive and well in its native Vietnam—for now.</p><p>“We should think that we’re still pretty damn lucky that this species is still around,” says <a href="https://www.uwo.ca/biology/directory/faculty/zanette.html">Liana Zanette</a>, a conservation biologist at Western University in Canada who wasn’t involved in the study. “We’ve been given another opportunity to try and preserve it, and that’s where the focus needs to be now.”</p><p>This scientific rediscovery is another notch in the belt of Global Wildlife Conservation, which, in 2017, launched a <a href="https://www.globalwildlife.org/lost-species-list/">campaign</a> to scour the world for 1,200 species lost to science. The silver-backed chevrotain is the first mammal checked off the organization’s 25 “most wanted” list, joining several other “found” plants and animals, including a <a href="https://www.globalwildlife.org/jacksons-climbing-salamander/">golden salamander</a> salamander in Guatemala, a <a href="https://www.globalwildlife.org/fernandina-galapagos-tortoise/">gargantuan tortoise</a> in Ecuador, a <a href="https://www.globalwildlife.org/wallaces-giant-bee/">giant bee</a> in Indonesia, and a <a href="https://www.globalwildlife.org/velvet-pitcher-plant/">flesh-hungry pitcher plant</a> in Canada.</p>
            <figure class="richtext-image full-width"><img alt="ncs016__ct016__2018-04-22__16-23-56(3)__Silver backed chevrotain.JPG" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/ncs016__ct016__2018-04-22__16-23-563__Silver_b.width-800.jpg"/><figcaption><p>A silver-backed chevrotain shows off its metallic backside. Image Credit: SIE/GWC/Leibniz-IZW/NCNP Copyright holder: Andrew Tilker</p><div class="credit"><p></p></div></figcaption>
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            <p>Like many of its predecessors, the silver-backed chevrotain (sometimes called the Vietnam mouse-deer) is as enigmatic as it is elusive. It first came onto the scientific scene in 1907, after a biologist collected four dead specimens near Nha Trang, Vietnam. Like other chevrotains, they sported short, spindly legs that could help them scuttle through the forest, and odd, elongated fangs that males might use for fighting. But in contrast to the more common lesser chevrotain (<i>Tragulus kanchil</i>), a close relative also native to the region, the silver-backed species lacked a distinctive stripe on its throat and “looked as though someone had dunked two thirds of it in silver,” Tilker says.</p><p>There was only so much scientists could figure out from the bodies, which were filed away into collections in the hopes that more individuals would appear. But then the trail went cold.</p>
            <figure class="richtext-image full-width"><img alt="setting camera trap (2).jpg" class="richtext-image full-width" height="450" width="800"
            src="/wgbh/nova/media/images/setting_camera_trap_2_e9GXfzy.width-800.jpg"/><figcaption><p>Researchers set up a camera trap to capture images of the elusive silver-backed chevrotain near Nha Trang, Vietnam. Image Credit: SIE/GWC/Leibniz-IZW/NCNP</p><div class="credit"><p></p></div></figcaption>
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            <p>The next chevrotain didn’t appear until 83 years later, when a team of Vietnamese and Russian scientists nabbed another hunter-killed specimen in Gia Lai, a province more than a hundred miles away from the original site.</p><p>By the time the species blipped onto the radar of Tilker and his colleagues some two decades later, it was clear in that the silver-backed chevrotain might be in some trouble. Poaching and habitat destruction had already triggered the decline of several other animals in the region—and scientists began to worry that they’d lose the strange little creature before it had truly been found.</p></div>
  

  
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      <div class="rich-text"><p>But “species shouldn’t be written off just because they haven’t been seen,” Tilker says. So he and his colleague <a href="https://www.globalwildlife.org/team/an-nguyen/">An Nguyen</a> decided to do some scientific sleuthing of their own. The best bet for pinpointing a chevrotin population, Nguyen says, would be to go back to the source: Nha Trang, where four of the five precious specimens had first been recovered—and, they later learned, where a photo of an oddly colored young chevrotain had supposedly been taken in 2004.</p><p>In 2017, a team led by Nguyen began interviewing residents around Nha Trang. While Western scientists have yet to glimpse a living silver-backed chevrotin, he says, the animals—known to the Vietnamese as <i>cheo cheo—</i>were nothing new to locals: About a quarter of the 35 people the researchers interviewed said they had recently spotted gray-looking chevrotains nearby.</p><div style="padding-bottom: 74.94553376906318%;" class="responsive-object">
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<p>That fall, the researchers planted three camera traps—which, when triggered by motion, snap images and record videos of their surroundings—near where the sightings had occurred. These devices, Zanette explains, give scientists a way to keep tabs on rare animals in remote regions without making the trek themselves.</p><p>When the team collected the traps the next spring, Nguyen wasn’t expecting to see much. But within the first 30 photos, a small, silver-speckled creature flashed onto his screen. Then there was another—and another. All three cameras had captured silver-backed chevrotains.</p><p>“I got very excited,” Nguyen says. “It was a joy to see.”</p>
            <figure class="richtext-image full-width"><img alt="ncs015__ct015__2018-06-06__15-41-54(1)__Silver backed chevrotain.JPG" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/ncs015__ct015__2018-06-06__15-41-541__Silver_b.width-800.jpg"/><figcaption><p>The silver-backed chevrotain is a baffling mishmash of traits: a round body, sharp fangs, spindly legs, even-toed hooves, and a splash of metallic fur. Image Credit: SIE/GWC/Leibniz-IZW/NCNP Copyright holder: Andrew Tilker</p><div class="credit"><p></p></div></figcaption>
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            <p>Eager for more, the team returned to the region, this time setting ten times as many traps as before. Within three months, they’d amassed evidence of another 208 sightings.</p><p>“This was a classic case of an animal that wasn’t that hard to find as long as somebody looked for it in the right place,” Tilker says.</p><p>One of the most exciting parts about this story is how critical local voices were to the scientists’ success, says <a href="https://www.mairinbalisi.com/">Mairin Balisi</a>, a paleontologist and evolutionary biologist at La Brea Tar Pits who wasn’t involved in the study. “[Conservation] can’t just be scientists working together. It has to be scientists and local community members working together.”</p><p>That human element, in combination with the cutting-edge technology of camera traps, makes this “a fantastic detective story,” Zanette says. “You need the pictures to prove a species exists. Now we can do all that.”</p>
            <figure class="richtext-image full-width"><img alt="IMG_20191101_121507_2.jpg" class="richtext-image full-width" height="600" width="800"
            src="/wgbh/nova/media/images/IMG_20191101_121507_2.width-800.jpg"/><figcaption><p>Study author An Nguyen gets a new tally mark on his wrist tattoo each time he discovers a mammal in the wild that he’s never detected before. The silver-backed chevrotain marks his fiftieth find. Image Credit: Courtesy of An Nguyen</p><div class="credit"><p></p></div></figcaption>
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            <p>The most important next step is to get a better sense of how many chevrotains are left, Tilker says, which is hard to do with just photos and videos. But, he notes, most of the team’s interviewees noted a recent and sharp decline in chevrotain numbers. Hunting and habitat destruction have stripped Vietnam and surrounding countries of many of their animals, where “<a href="http://enbt.jbrj.gov.br/mestrado_profissional/seminario/7_Redford%201992.pdf">empty forest syndrome</a>” has spread like contagion, Tilker says.</p><p>As such, Tilker and his colleagues have also been careful not to disclose too much about the chevrotain’s whereabouts. Awareness, he explains, is a double-edged sword: Hunters have previously used published scientific data to <a href="https://www.independent.co.uk/news/science/endangered-species-scientists-urged-not-publish-location-poachers-find-hunt-kill-animals-chinese-a7763156.html">home in on their marks</a>.</p><p>Even though it’s been found in the forest, the silver-backed chevrotain isn’t yet out of the woods.</p><p>“We...have this remarkable opportunity in our hands to protect a species that has come back onto the radar,” Tilker says. “Second chances like this don’t come around that often.”</p><p><i>To learn more about how scientists are spying on the world’s creatures, stream “</i><a href="https://www.pbs.org/wgbh/nova/video/animal-espionage/"><i>Animal Espionage</i></a><i>” or tune in on November 27 at 9/8c on PBS. </i></p></div>
  

  
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<p>The images confirm the species, which has been “lost” to science for 29 years, is alive and well in its native Vietnam.</p>

Feast your eyes on the first-ever photos of a silver-backed chevrotain in the wild





  
      <div class="rich-text"><p>With 7.7 billion members and counting, humankind has yet to run its course. But a controversial new study argues it’s possible all of us can trace our roots back to the same starting line: a single spot on the African continent where the ancestors of today’s people arose roughly 200,000 years ago, before dispersing in waves and populating the rest of the world.</p><p>Where exactly modern humans came to be remains a topic of intense contention, as does the question of <a href="https://www.nature.com/scitable/content/out-of-africa-versus-the-multiregional-hypothesis-6391/">whether it even <i>is</i> just one point</a>. Now, an interdisciplinary team of researchers has entered the fray with a new theory that one place was of certain significance: The “homeland” of modern humans, they argue, might lie south of the Zambezi River, in what’s now northern Botswana.</p></div>
  

  
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      <div class="rich-text"><p>Their <a href="https://www.nature.com/articles/s41586-019-1714-1">study</a>, published last week in the journal <i>Nature,</i> intertwines genetic, geological, and climatological data to map out the probable migratory routes of one of the earliest groups of modern humans identified.</p><p>The early group, known as L0, was the first to diverge away from the enigmatic population that included “Mitochondrial Eve”—the hypothetical maternal ancestor of all living humans—and is considered the oldest branch on our species’ evolutionary tree. Pinpointing the place where L0 first emerged, the researchers say, may be one of our best bets for identifying the elusive geographic origins of <i>Homo sapiens</i> itself.</p><p>But other experts stress an important distinction: While the new study helps to position the L0 lineage in time and space, it can’t do the same for the earlier group that Mitochondrial Eve belonged to, says <a href="https://scholar.harvard.edu/vagheesh/home">Vagheesh Narasimhan</a>, a genomicist studying human evolution at Harvard University who wasn’t involved in the study. That leaves the biggest question of all—the one that addresses the true origin of all modern humans—unanswered, he says.</p><p>All humans inherit a form of genetic information known as mitochondrial DNA exclusively from their mothers. Trace all those maternal lines far back enough, and you’ll end up at what scientists call Mitochondrial Eve: The woman all living humans supposedly descended from.</p><p>But Mitochondrial Eve is long gone, and in the 200,000 years since, her lineage has splintered substantially. The closest we can get to rewinding the clock with modern data is tracing the roots of the oldest mitochondrial lineage that still survives today: L0, says study author <a href="https://www.garvan.org.au/people/vanhay">Vanessa Hayes</a>, a genomicist at the Garvan Institute of Medical Research and the University of New South Wales in Australia.</p><p>To home in on where L0 got its start, Hayes and her colleagues compared 1,217 modern mitochondrial genomes, 198 of which they collected from living southern Africans.</p><p>Since it first arose, L0 has diverged into its own set of subgroups. But the vast majority of its members have remained on the African continent, Hayes says, some never straying more than a few miles from the land their ancestors occupied for generations. That’s effectively created genetic sublineages that are also culturally, linguistically, and geographically distinct, she says, allowing the researchers to map out not just <i>when</i> different L0 subgroups had last shared a common ancestor, but <i>where</i>.</p>
            <figure class="richtext-image full-width"><img alt="Screen Shot 2019-10-27 at 5.18.29 PM.png" class="richtext-image full-width" height="364" width="800"
            src="/wgbh/nova/media/images/Screen_Shot_2019-10-27_at_5.18.29_PM.width-800.png"/><figcaption><p>Geographical distribution of the 1,217 L0 mitochondrial genomes used in the study, 198 of which were newly collected. The map on the right shows the distribution of KhoeSan populations, which tend to be genetically, culturally, linguistically, and geographically distinct. Most KhoeSan individuals reside south of the Zambezi river, while non-KhoeSan individuals live north of the river. Image Credit: Chan et al., Nature, 2019</p><div class="credit"><p></p></div></figcaption>
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            <p>Remarkably, Hayes says, all the genomes seemed to unspool from a single knot: A population that once resided in the Kalahari region of the Zambezi river basin, about 200,000 years ago. This group, she says, is ancestral to all humans alive on Earth today.</p><p>Having tied these threads together, the researchers then spun them out again, this time overlaying geologic and paleontologic data that suggested that this early group’s biggest migrations—and resulting genetic splits—had been driven by changes in the region’s climate.</p><p>Nowadays, the Zambezi river basin is arid and inhospitable, speckled with the salty remnants of long-gone lakes. But hundreds of thousands of years ago, it was a wetland that blanketed much of the northern part of modern Botswana, says study author <a href="https://ibsclimate.org/people/axel-timmermann/">Axel Timmermann</a>, a researcher at the Institute for Basic Science and Pusan National University in South Korea. While nearby regions were plagued with frequent droughts, this resource-rich oasis was sustained by the (inland) Okavango delta and the fragments of a once-gargantuan lake called Makgadikgadi, he says, creating prime real estate for humans and animals alike.</p>
            <figure class="richtext-image full-width"><img alt="18828107511_ba7211f09b_o.jpg" class="richtext-image full-width" height="532" width="800"
            src="/wgbh/nova/media/images/18828107511_ba7211f09b_o.width-800.jpg"/><figcaption><p>Botswana&#x27;s Makgadikgadi salt pans, the remnants of what was once a vast lake that covered much of the country&#x27;s northern region. Image Credit: JJ Vos, flickr</p><div class="credit"><p></p></div></figcaption>
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            <p>This “homeland” appears to have hosted an early population of modern humans for about 70,000 years, Timmermann says. Then, around 130,000 years ago, as Earth <a href="https://www.jpl.nasa.gov/news/news.php?feature=6332">wobbled on its axis</a>, the landscape began to shift. Previously parched conditions to the northeast gave way to warmer, wetter climes, prompting at least one subgroup to leave and subsequently branch into their own lineage. About 20,000 years later, a second hospitable corridor emerged to the southwest, sparking another wave of dispersal—and another round of genetic fracture.</p><p>Once they reached their respective destinations north and south of home base, many of these early migrants settled for good, Hayes says, establishing family lines that have endured for more than 100,000 years. There’s even a population she believes may have never left the homeland at all: the Kalahari KhoeSan, who have maintained many aspects of their hunter-gatherer way of life and complex, click-consonant language since, it seems, L0 first arose. “Genetically, this is the oldest population on the planet,” Hayes says.</p></div>
  

  
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      <div class="rich-text"><p>The first people Hayes and her team shared their data with were the participants themselves. Many of Hayes’ KhoeSan contacts were unsurprised by the findings, which affirmed their oral histories, she says. “The first thing one of them said was...‘We know we’ve always been here,’” she says.</p><p><a href="http://hennlab.ucdavis.edu/">Brenna Henn</a>, a population geneticist at the University of California, Davis who was not involved in the study, calls the team’s findings striking. “This really fits the pattern for a single origin in Africa,” she says.</p><p>But a “homeland” shouldn’t be confused with an <i>origin</i>—a term that might imply the discovery of one individual, the first <i>Homo sapiens,</i> who gave rise to us all, Hayes says.</p><p>That means we’re still a long way off from finding where modern humans really got their start, Narasimhan says. And, given the complexities of human history, more research could reveal a drastically different, and far less simple, answer. It’s still possible, for instance, that a more ancient group arose in East Africa before migrating southwest and segregating into distinct genetic lineages. Just last month, Naramsimhan authored a <a href="https://scholar.harvard.edu/files/vagheesh/files/eaat7487.full_.pdf">study</a> that profiled a diverse set of lineages that had branched in South Asia, but actually emerged thousands of miles away. “Where a population diverges isn’t always where it originates,” he says.</p>
            <figure class="richtext-image full-width"><img alt="214896.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/214896.width-800.jpg"/><figcaption><p>Study author Vanessa Hayes learning how to make fire with Juǀ’hoansi hunters in the greater Kalahari of Namibia. From left to right: Nǂamce Sao, ǀkun Nǂamce, Vanessa Hayes, and ǀkunǀkunta. Image Credit: Chris Bennett, Evolving Picture</p><div class="credit"><p></p></div></figcaption>
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            <p>Really nailing our origins will take more data, says <a href="https://www.genome.gov/staff/Charles-N-Rotimi-PhD">Charles Rotimi</a>, director of the National Institutes of Health’s Center for Research on Genomics and Global Health, who was not involved in the study. If the study’s findings are correct, the authors have found only “the geographical origin of the woman who carried the L0 lineage.”</p><p>But our timeline stretches further back than the root of L0. And while L0 is the oldest branch on our tree, most living humans aren’t a part of it, belonging instead to one of six other groups that emerged from the original lineage (that is, the trunk) after L0 peeled off. The ultimate goal, Narasimhan says, is identifying the common ancestor of <i>all</i> these groups.</p><p>This would be a difficult task, Hayes says. Right now, researchers don’t have an easy and ethical way to even <i>collect</i> such a comprehensive set of modern mitochondrial genomes, let alone the computational tools to systematically analyze all of them at once.</p><p>For now, scientists might have more success going beyond just mitochondrial DNA, which makes up just a small fraction of the genome, Rotimi says. There’s a paternal lineage, too—one that endures in the Y chromosome. Researchers have also had luck tracing ancestry by comparing mutations that occur across individuals’ <a href="https://ghr.nlm.nih.gov/primer/dtcgenetictesting/ancestrytesting">entire genomes</a>, as well as by extracting ancient DNA from fossils.</p>
            <figure class="richtext-image full-width"><img alt="Image One.jpeg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/Image_One.width-800.jpg"/><figcaption><p>Study author Vanessa Hayes speaking with ǀkunǀkunta, one of the many participants who donated a mitochondrial genome to the research. ǀkunǀkunta comes from an extended Juǀ’hoansi family that lives in the semi-desert Kalahari region of Namibia. &quot;They know the stories of themselves,&quot; Hayes says. &quot;The most important part of this process isn’t talking… it’s listening. It’s their project, at the end of the day.&quot; Image Credit: Chris Bennett, Evolving Picture</p><div class="credit"><p></p></div></figcaption>
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            <p>The new findings may also have a bone to pick with fossil finds that point to an alternative to the “single origin” story, Henn says. Fossils with a wide array of <i>Homo sapiens</i> features speckle the African landscape, including some <a href="https://www.nature.com/articles/nature03258">195,000-year-old remains</a> from the Omo Kibish rock formation in Ethiopia, the <a href="https://alchetron.com/Florisbad-Skull">260,000-year-old Florisbad skull</a> from South Africa, and a <a href="https://www.npr.org/sections/health-shots/2017/06/07/531804528/315-000-year-old-fossils-from-morocco-could-be-earliest-recorded-homo-sapiens">315,000-year-old skull</a> unearthed from Morocco’s Jebel Irhoud site. The age and far-flung locales of these fossils, researchers argue, show that multiple disparate populations arose in different spots, then mixed and mingled until our exact mishmash of contemporary features arose. The <i>Homo sapiens</i> tree, in other words, may not be a tree at all, but a tangle of vines that crisscross later in our timeline.</p><p>The so-called multiregionalism hypothesis isn’t well supported by genetics, which seem to bat instead for Team Mitochondrial Eve, Timmermann says. Perhaps many populations existed, then died out, he says, leaving behind only one that successfully seeded today’s humans.</p><p>That remains to be seen. But whatever their answers, Hayes says, these questions will keep researchers busy for some time. Understanding our past, after all, is key to understanding our future, she says. “Ancestry fascinates all of us,” she says. “It’s where we come from...it’s who we are.”</p></div>
  

  
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<p>But many questions remain about the true origin of the <i>Homo sapiens</i> species.</p>

In a controversial study, DNA from today’s southern Africans hints at possible “homeland” for modern humans





  
      <div class="rich-text"><p>Age is kind to no one.</p><p>Unfortunately, that includes the books, scrolls, and scrawlings of ages past. Thanks to centuries of floods, fires, volcanic eruptions, and plain old wear and tear, many ancient texts have degraded past the point of legibility—leaving countless chapters of human history as inscrutable as the words that once chronicled them.</p><p>But the key to deciphering the past might just lie in the technologies of the future. Thanks to recent advances, researchers can now digitally unravel, read, and translate texts once considered lost to time. Here are three of the most powerful methods scientists are using to put a new lens on the past.</p></div>
  

  
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      <div class="rich-text"><h3>Unveiling the innards of a scroll</h3><p>Nowadays, the 1,700-year-old En-Gedi Scroll—one of the most ancient snippets of the Old Testament ever uncovered—isn’t much to look at. Ravaged by a fire that consumed a Jewish synagogue around 600 CE, the document transformed from a supple scroll into a charred, brittle cylinder of charcoal. The artifact is so delicate that, for decades, scholars dared not even attempt to peel back its layers for fear of destroying it for good.</p><p>But several years ago, a team of computer scientists led by University of Kentucky’s <a href="https://www.engr.uky.edu/directory/seales-brent">Brent Seales</a> managed to <a href="https://advances.sciencemag.org/content/2/9/e1601247">crack the scroll’s contents</a> without physically unfurling it. The non-invasive method, called “virtual unwrapping,” extracted intel from the burnt scroll with a combination of scans and image-processing algorithms.</p><p>The scroll itself made only a brief cameo in the team’s investigation, when X-rays were shot through its layers from several angles to visualize what was inside. These computerized tomography (CT) scans, Seales says, are the same ones radiologists perform on human patients with internal injuries—only instead of searching for bone breaks and tissue damage, researchers hunt for hidden text.</p><p>“Tomography is really powerful,” Seales says. “It gives you the ability to infer what’s inside something by taking views from all the way around, with a signal that goes all the way through.”</p>
            <figure class="richtext-image full-width"><img alt="the charred En-Gedi scroll damaged by a synagogue fire" class="richtext-image full-width" height="454" width="800"
            src="/wgbh/nova/media/images/Scroll-Natural.width-800.jpg"/><figcaption><p>The charred En-Gedi Scroll. Image courtesy of the Leon Levy Dead Sea Scrolls Digital Library, IAA. Photo: S. Halevi. Pictured in Seales et al. Science Advances 2016</p><div class="credit"><p></p></div></figcaption>
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            <p>After the document was imaged, it went back into storage, and the team switched to a computational approach. What’s produced by a CT scan, Seales says, isn’t the type of picture you’d get from a typical camera. Instead, these machines generate cross sections—2-D “slices” of the inside of an object, like a front-on view of a cut loaf of bread. After collecting a series of these images, the team fed them into an algorithm that determined where one layer of the animal-skin scroll ended and another began.</p><p>Accomplishing this is especially difficult when a document’s pages have been warped, deformed, and smashed up against each other, says <a href="https://www.cardiff.ac.uk/people/view/118139-lai-yukun">Yukun Lai</a>, a visual computing expert at Cardiff University who, together with his colleagues, has published a series of papers that have <a href="https://www.nature.com/articles/s41598-018-29037-x">digitally recovered</a> the contents of other <a href="http://users.cs.cf.ac.uk/Yukun.Lai/papers/parchmentTIP.pdf">damaged historic texts</a>. One way to deal with this, he says, is to use the typical thickness of parchment and other materials as a guide to digitally peel pages apart.</p><h3>Interpreting (almost) invisible ink</h3><p>Piecing together a page isn’t the same as reading what’s on it—and it’s not always easy to identify where ink has been laid down.</p><p>Relatively speaking, the text of the En-Gedi Scroll was fairly straightforward to detect, Seales says. Different materials block X-rays to different extents, and dense, metal-rich inks tend to pop when they’re printed on something carbon-based, like plant fibers or, in the case of the scrolls, the skin of an animal.</p>
            <figure class="richtext-image full-width"><img alt="computerized tomography scan of the En-Gedi scroll showing a slice" class="richtext-image full-width" height="299" width="800"
            src="/wgbh/nova/media/images/Sealesfig4.width-800.png"/><figcaption><p>A cross section of the En-Gedi Scroll, as imaged by a CT scanner. Image Credit: Seales et al. Science Advances 2016</p><div class="credit"><p></p></div></figcaption>
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            <p>Things get more complicated when you’re dealing with a document that’s carbon on carbon, as in the case of the Herculaneum scrolls—a trove of papyrus that survived the fateful eruption of <a href="https://www.pbs.org/wgbh/nova/video/the-next-pompeii/">Mount Vesuvius</a> in 79 CE. The scrolls’ scribes used a substance called carbon black as their ink of choice, which, from an X-ray’s perspective, is just as dense as the stuff on which it sits, Seales says.</p><p>But subtle differences still exist between material that’s been written on and material that hasn’t. For instance, the addition of carbon ink alters the shape of plant fibers, creating tiny bumps on the surface of a sheet of papyrus. Though these mini-mountains can’t be picked out by human eyes, Seales says, they can be made obvious to a well-trained machine. For the past few months, Seales and his team have been <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0215775">training an algorithm</a> to search for the structural signatures of ink in data produced from CT scans of scrolls.</p><p>The researchers have yet to apply the method to the Herculaneum papyri. But ideally, that’s where this research is headed, Seales says. With a bit more tinkering, he says, the “lost” texts of Herculaneum might soon be found.</p>
            <figure class="richtext-image full-width"><img alt="Herculaneum papyri viewed from the side" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/Herculaneum2.width-800.jpg"/><figcaption><p>Even with CT scans, Herculaneum scrolls are particularly challenging to analyze because the ink and paper block X-rays to the same extent. Image Credit: The Digital Restoration Initiative, University of Kentucky</p><div class="credit"><p></p></div></figcaption>
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            <h3>Reviving a dead language</h3><p>The En-Gedi Scroll is emblazoned with Hebrew, and the Herculaneum papyri with Greek and occasionally Latin. But many other texts were inscribed in languages that have since disappeared from common use.</p><p>“Just because you can read the letters, that doesn’t mean you know what they mean,” says <a href="https://people.csail.mit.edu/regina/">Regina Barzilay</a>, a computer scientist at the Massachusetts Institute of Technology.</p><p>Barzilay, whose work in artificial intelligence has spanned applications from early cancer detection to drug discovery, is now working with her graduate student <a href="https://github.com/j-luo93">Jiaming Luo</a> to <a href="http://people.csail.mit.edu/j_luo/assets/publications/NeuroDecipher.pdf">decipher lost languages</a>.</p></div>
  

  
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      <div class="rich-text"><p>Their strategy hinges on the predictable way languages change over time—a process that’s similar to how species split on the tree of life. Like organisms, languages can be grouped into families that share common traits, including the way their alphabets, vocabularies, and grammar look and sound. Even if words manifest differently between languages, they often remain recognizable: the French <i>terre</i> and the Spanish <i>tierra,</i> for instance, share the Latin root for “earth.&quot;</p><p>These similarities aren’t coincidences, Barzilay explains. If two languages share a point of origin, there are only so many evolutionary paths they can take, even as they’re diverging away from each other.</p><p>Feeding these rules into a machine can give it a structured way to translate a language, as long as it’s given appropriate familial context, Barzilay says. So far, she and Luo have successfully tested out their strategy with <a href="http://people.csail.mit.edu/j_luo/assets/publications/NeuroDecipher.pdf">two extinct languages</a>: Ugaritic, an early form of Hebrew, and Linear B, which shares roots with ancient Greek.</p>
            <figure class="richtext-image full-width"><img alt="En-Gedi scroll unrolled after virtual unwrapping" class="richtext-image full-width" height="378" width="800"
            src="/wgbh/nova/media/images/EnGedi_unrolled.width-800.jpg"/><figcaption><p>The digitally unwrapped En-Gedi scroll. Image Credit: Seales et al. Science Advances 2016</p><div class="credit"><p></p></div></figcaption>
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            <p>These were proof-of-concept experiments, as both languages had already been meticulously deciphered by (human) linguists before any algorithms got involved, Barzilay says. Now, she and Luo are interested in teaching a machine to do what a person hasn’t: decode a totally lost language—perhaps even one with deeply contested evolutionary roots.</p><p>One example is <a href="http://www.ancientscripts.com/iberian.html">Northeastern Iberian script</a>, which has yet to be firmly classified into a language family. That means the algorithms will have to reverse engineer yet another piece of the puzzle, predicting the script’s origins before tackling its translation.</p><p>Once that’s possible, these techniques and more could even enhance the identification of ink in damaged texts, Barzilay says. “Even if letters are missing, or you don’t understand all of them, maybe you can complete it,” she says. “With all this technology...it’s about tying the whole process together.”</p><p><i>To learn more about how researchers are uncovering and analyzing ancient texts, watch “</i><a href="https://www.pbs.org/wgbh/nova/video/dead-sea-scroll-detectives/"><i>Dead Sea Scroll Detectives</i></a><i>,” premiering on PBS at 9/8c on November 6.</i></p></div>
  

  
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<p>Recent breakthroughs in scanning, image processing, and machine learning are helping researchers read historic documents once considered lost to time.</p>

From ashes to AI: How technology puts a new lens on ancient texts





  
      <div class="rich-text"><p>In the conversation around wildfire risk, a couple factors tend to steal the spotlight.</p><p>Climate change is a big one, as droughts, rising temperatures, and powerful winds drive the intensity and spread of fires worldwide. Then there’s human disturbance: People and their homes continue to push into the wilderness, adding flames and fuels to places they’re not typically found.</p><p>Those two players can’t be ignored, says <a href="https://people.umass.edu/bethanyb/?_ga=2.13642039.1288577295.1572571486-1327202640.1568249647">Bethany Bradley</a>, a biogeographer and spatial ecologist at the University of Massachusetts, Amherst. But there’s more to the story than just <i>how</i> the burning begins, she says. It also matters <i>what’s</i> burning—which plants are around to catch a stray spark.</p></div>
  

  
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      <div class="rich-text"><p>Some of the most worrisome culprits are nonnative grasses <a href="https://www.usgs.gov/centers/werc/science/invasive-plants-and-fire-0?qt-science_center_objects=0#qt-science_center_objects">invading ecosystems</a> across the country. Given the chance, these hardy, fast-growing plants can <a href="https://www.fs.fed.us/rm/pubs/rmrs_gtr042_6/rmrs_gtr042_6_033_046.pdf">easily outcompete</a> their native kin, <a href="https://www.fs.fed.us/psw/publications/ff/psw_2014_ellsworth001.pdf">blanketing entire landscapes</a> with their thin, ignitable leaves. From there, a single trigger—a cigarette butt, a spark from a railroad track, a rogue firework—can lead to disaster.</p><p>Invasive grass isn’t your average kindling, Bradley says. There’s always more where it came from. It’s kindling that lives and breathes. It’s kindling that reproduces and spreads.</p><p>Now, Bradley and her team, led by ecologist <a href="https://gpls.cns.umass.edu/oeb/directory/emily-j.-fusco">Emily Fusco</a>, have intertwined decades of satellite and ground-based records to create a nationwide map of where eight of these incendiary species have taken hold. Their <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1908253116">findings</a>, published today in the journal <i>PNAS,</i> suggest that some of these grasses can more than triple a region’s likelihood of succumbing to wildfire, imperiling entire swaths of land from the shrublands of the West to the pine savannas of the southeast.</p><p>“This paper sheds light on an often-overlooked issue in the United States,” says <a href="https://marinalaforgia.weebly.com/">Marina LaForgia</a>, a grassland ecologist at the University of California, Davis who wasn’t involved in the study. “So much of the focus, especially in California, is on forest fires, and for good reason. But during fire season, it’s not just the forests that burn.”</p><p>The link between invasive grasses and wildfire isn’t new. Researchers have been aware of the connection since at least the early 1990s, when Californian ecologists <a href="https://labs.eemb.ucsb.edu/dantonio/carla/carla.html">Carla D’Antonio</a> and <a href="https://biology.stanford.edu/people/peter-vitousek">Peter Vitousek</a> raised the alarm in what’s considered <a href="https://labs.eemb.ucsb.edu/dantonio/carla/CV_Publications/dantonio_vitousek_1992.pdf">one of the field’s landmark studies</a>.</p><p>With their speedy growth cycles, invasive grasses outpace other plants, transforming landscapes into conduits for fire during dry summer months. They also tend to be remarkably resistant to disturbances like drought—and even when felled by fire, they’re some of the first species to spring back.</p>
            <figure class="richtext-image full-width"><img alt="4889082332_9aa669e6ea_o.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/4889082332_9aa669e6ea_o.width-800.jpg"/><figcaption><p>Cheatgrass, an invasive grass species, covers 100 million acres of the western United States. In the summer, it dries out into a continuous, easily ignitable carpet. Image Credit: .deeneg, flickr</p><div class="credit"><p></p></div></figcaption>
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            <p>“These grasses perpetuate this feedback loop between more fire, more grass, more fire, more grass,” says <a href="https://lisamellsworth.weebly.com/">Lisa Ellsworth</a>, a fire ecologist at Oregon State University who wasn’t involved in the study. “We see this across ecosystems, all over the world.”</p><p>Most infamous, perhaps, are the fire-starting feats of <a href="https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/idpmspg8317.pdf">cheatgrass</a> (<i>Bromus tectorum</i>)—a droopy, buff-colored species that, since its accidental introduction in the 1800s, has infiltrated some 100 million acres of the country’s western flank, throttling local plants out of existence. Last year, more than 400,000 acres of cheatgrass provided ample fodder for Nevada’s <a href="https://www.nasa.gov/image-feature/goddard/2018/nevadas-martin-fire-largest-in-us">Martin Fire</a>, birthing a plume of smoke so big it was visible from space.</p><p>It’s long been clear that where invasive grass goes, flames follow. But putting numbers to fire risk has been tough—in part because the data on both grass distribution and fire frequency has, until recently, been pretty spotty.</p><p>“In the early ‘90s, we didn’t have access to this kind of big-scale data...we had to dig and dig and dig,” says D’Antonio, who wasn’t involved in the new study. That’s changed in the past few years, she says, with the advent of widely-used digital repositories that are being constantly updated by researchers around the world. “Finally,” she says, “we’re seeing that data being used to address these questions.”</p>
            <figure class="richtext-image full-width"><img alt="3351247465_2130431b74_o.jpg" class="richtext-image full-width" height="533" width="800"
            src="/wgbh/nova/media/images/3351247465_2130431b74_o.width-800.jpg"/><figcaption><p>A controlled buffelgrass fire in Avra Valley, Arizona in May 2008. Image Credit: Daina Dajevskis, flickr</p><div class="credit"><p></p></div></figcaption>
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            <p>At least 176 grass species have been tenuously tied to wildfires in the United States. Fusco and her colleagues combed through records on all of them, scouring studies and databases for numbers that could help them pinpoint places the plants had infiltrated. In the end, there was only enough to map out 12 species. The team then overlaid information from 16 years of recent fire records, comparing the number, size, and likelihood of burns occurring in both invaded and uninvaded places.</p><p>Of the dozen grassy interlopers analyzed, eight were associated with increased fire risk in the areas they inhabited. Though cheatgrass was among them, it wasn’t the most problematic firestarter of the bunch. That title went instead to common Mediterranean grass (<i>Schismus barbatus</i>), a grass that sprouts in thin, threadlike clumps across the American southwest—and more than tripled the chance a region would burn. Similarly potent was buffelgrass (<i>Cenchrus ciliaris</i>), a particularly stubborn plant that’s plagued Arizona since the 1930s. Where its squat, recalcitrant tufts sprang up, the team found, the land was more than twice as likely to ignite.</p></div>
  

  
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      <div class="rich-text"><p>But it’s not only the West at risk. The team’s map of invaded areas covers land from coast to coast, with patches of plants like Japanese stiltgrass (<i>Microstegium vimineum</i>) and Chinese silvergrass (<i>Miscanthus sinensis</i>) extending as far north as Pennsylvania and New Jersey. “It’s just not where you expect to see fire,” D’Antonio says. “But it’s worth appreciating...this isn’t just a problem for the deserts.”</p><p>The picture painted isn’t exactly a cheery one, Bradley says. And the eight species highlighted in the paper are probably just a drop in the bucket—the ones the team could scrounge up enough data for. “My guess is there’s a heck of a lot more fire-prone grasses that we don’t have the numbers to back up yet,” she says.</p><p>Invasive grasses come in all shapes, sizes, and spark-promoting potential. But they have at least one crucial thing in common: they’re still being spread by humans, often as they’re pushing into wild environments. Though many introductions have been accidental, all it takes is a couple seeds stuck to the bottom of a shoe or embedded in a bale of hay to breach a barrier, Bradley says.</p>
            <figure class="richtext-image full-width"><img alt="pnas.201908253 copy.jpg" class="richtext-image full-width" height="570" width="800"
            src="/wgbh/nova/media/images/Katie_Figure1b.width-800.jpg"/><figcaption><p>Study areas for 12 invasive grass species. Colored polygons show where the researchers analyzed data for invasive grasses; yellow regions denote places with demonstrated fire impact. Image Credit: Fusco et al., PNAS, 2019</p><div class="credit"><p></p></div></figcaption>
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            <p>Complicating matters is the increasing influence of climate change. Droughts, heat waves, and other extreme weather events wipe out fragile local plants, clearing the way for invasive grasses to grow. Wetter years favor foreigners, too, allowing these species to bloom out of control. In a single season, an infiltrated ecosystem can become completely unrecognizable. As the world continues to shift around us, D’Antonio says, there are probably more grasslands—and more fires—in our future.</p><p>Once they take root, these pest-like plants are tough to exterminate. Grass-specific herbicides, carefully timed grazing by livestock, and firebreaks—natural or human-made gaps in flammable vegetation—can all help, Ellsworth says. But for the most part, where landscapes have already been overrun, “it’s not looking great,” she says.</p><p>Where researchers can still make a big difference are intact environments, says <a href="https://www.ars.usda.gov/plains-area/fort-collins-co/center-for-agricultural-resources-research/rangeland-resources-systems-research/people/lauren-porensky/">Lauren Porensky</a>, a restoration ecologist at the United States Department of Agriculture who wasn’t involved in the study. A combination of monitoring and early interventions can purge habitats of invaders before they have a chance to settle in. And even before their arrival, efforts can be made to boost the resilience of native plants. “We need to get more proactive on invasion,” she says, “and not just be reactive.”</p><p>All this will require raising awareness, and plenty of collaboration, Fusco says. But putting the focus on prevention means there’s hope, she says. Just because the kindling’s there doesn’t mean it has to burn.</p></div>
  

  
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<p>New research quantifies the fire risks of eight species of invasive grass.</p>

Invasive, flammable grasses now blanket much of the United States





  
      <div class="rich-text"><p>If your anxious brain is keeping you up at night, <a href="https://www.researchgate.net/profile/Eti_Ben-Simon">Eti Ben Simon</a> has some not-so-great-news: The sleep you lose to stress might exact an additional emotional toll on your wellbeing the next day.</p><p>“Typically, people think of <a href="https://www.pbs.org/wgbh/nova/article/can-animals-survive-without-sleep/?utm_source=FBPAGE&amp;utm_medium=social&amp;utm_term=20190227&amp;utm_content=2152807857&amp;utm_campaign=NOVA+Next&amp;linkId=63940930">lost sleep</a> as a symptom of anxiety,” says the University of California, Berkeley neuroscientist. “But disturbed sleep can be an instigator of anxiety, too.”</p><p>Ben Simon and her colleagues have spent years studying the relationship between sleep deprivation and anxiety—two experiences that, from a neurobiological perspective, actually look pretty similar. The team’s <a href="https://www.nature.com/articles/s41562-019-0754-8">latest findings</a>, published today in the journal <i>Nature Human Behavior,</i> show that both affect brain regions that regulate emotions.</p></div>
  

  
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      <div class="rich-text"><p>Functionally, that means experiencing one can aggravate the other, fueling a cycle of stress and sleeplessness. It’s pretty much a two-way street, Ben Simon says. And it doesn’t take much to trip the system: Enduring even one session of low-quality shut-eye, the study suggests, can boost anxiety the next day.</p><p>But there’s a flip side to the findings, too. A good night’s sleep, Ben Simon says, could be a straightforward way to manage our emotions. With more research, she says, sleep therapy could someday offer an additional treatment option for those that struggle with chronic anxiety.</p><p>“This is a very elegant study,” says <a href="https://www.vanderbilt.edu/psychological_sciences/bio/bunmi-olatunji">Bunmi Olatunji</a>, an expert in anxiety disorders at Vanderbilt University who was not involved in the study. “They really went after the biological underpinnings of the relationship between sleep and anxiety, and that’s an important and unique contribution.”</p><p>Researchers have long been aware that low-quality sleep is intertwined with a number of mental health conditions. People with anxiety disorders frequently have <a href="https://adaa.org/understanding-anxiety/related-illnesses/sleep-disorders">trouble falling and staying asleep</a>, and insomnia can <a href="https://www.sleepfoundation.org/excessive-sleepiness/health-impact/complex-relationship-between-sleep-depression-anxiety">exacerbate the symptoms</a> of clinical anxiety. It’s an especially troubling connection, Ben Simon says, in a world where younger generations are <a href="http://sleepeducation.org/news/2019/07/18/college-students-are-not-getting-nearly-enough-sleep">staying up late</a> and feeling more <a href="https://gspp.berkeley.edu/centers/bifya/our-research-and-projects/mental-health-project/mental-health-project">stressed out</a> than ever.</p><p>But no one’s managed to compare the two experiences in a systematic way, she says, especially in the same individual. “We wanted to know if there was a shared neurobiological mechanism,” she explains.</p><p>To explore the link between the two conditions, Ben Simon and her colleagues recruited 18 healthy people for two overnight sessions: one where they were sent home for a normal night of rest, and another where they stayed at the lab and didn’t sleep at all. Before bedtime, the researchers scored the participants’ anxiety with a questionnaire. When they repeated the assessment the next morning, they found that a total lack of sleep triggered a 30% increase in anxiety levels.</p><p>To home in on the brain regions responsible for the uptick in stress, the researchers put the study subjects in a functional magnetic resonance imaging (fMRI) machine, which monitors blood flow as a proxy for brain activity, after each session. During the scan, participants watched a series of video clips, some of which featured distressing situations.</p><p>Compared to when they were well rested, sleep-deprived participants seemed to have trouble controlling their emotions when watching evocative scenes, Ben Simon says. In these people, emotive regions of the brain—like the amygdala and the dorsal anterior cingulate cortex—were quick to light up, while the prefrontal cortex, which can put the brakes on runaway feelings, stayed dim. Their brains, in other words, looked like they were experiencing anxiety in overdrive.</p></div>
  

  
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      <div class="rich-text"><p>“When you’re dealing with something emotional, you need to recruit the prefrontal cortex to help you regulate [your reaction],” Ben Simon says. It’s the region, she explains, that’s responsible for keeping us cool and collected in times of crisis. “You fail to do that when you’re sleep-deprived,” she says.</p><p>Sleep’s restorative powers are vast, Ben Simon says, and can equip the brain to cope with adversity. So-called deep sleep, a dreamless stage characterized by the <a href="https://www.pbs.org/wgbh/nova/article/zebrafish-sleep/">slow brain waves</a> it produces on an electroencephalogram (EEG), seems especially important for this process, she says. The more deep sleep participants got during their night of rest, the more active their prefrontal cortices were the day after—and the better managed their emotions.</p><p>“It’s a beautiful cycle,” Ben Simon says. “Being sleep deprived takes away your emotion regulation capabilities. And then sleep, specifically deep sleep, magically brings it back online, and lets you start your day calmer.”</p><p>Pulling an all-nighter is a drastic departure from a healthy snooze schedule. But that’s not the only way to deprive yourself of sleep, says <a href="https://www.binghamton.edu/psychology/people/profile.html?id=mcoles">Meredith Coles</a>, an expert in anxiety disorders at Binghamton University who wasn’t involved in the study.</p>
            <figure class="richtext-image full-width"><img alt="iStock-820818020.jpg" class="richtext-image full-width" height="534" width="800"
            src="/wgbh/nova/media/images/iStock-820818020.width-800.jpg"/><figcaption><p>Anxiety and sleep deprivation both affect the brain&#x27;s emotion processing centers, fueling a vicious cycle of stress and sleeplessness. Image Credit: amenic181, iStock</p><div class="credit"><p></p></div></figcaption>
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            <p>In a final experiment, Ben Simon and her team asked nearly 400 healthy people to fill out online surveys tracking their sleep quality and anxiety levels from the comfort of their own homes. Even minor disruptions to slumber, like frequent wake-ups, appeared to mess with people’s emotions: When they slept worse, they felt worse.</p><p>Historically, people have put “a lot of focus on the importance of sleep duration,” says <a href="https://case.fiu.edu/about/directory/profiles/mcmakin-dana.html">Dana McMakin</a>, a clinical psychologist who specializes in anxiety at Florida International University, but was not involved in the study. “But this makes it clear that sleep continuity and efficiency matter, too.”</p><p>Ben Simon hopes that sleep might someday play a role in the treatment of anxiety disorders. That has yet to be tested directly, as all the people studied in this particular paper were healthy individuals, McMakin points out. There are also probably more brain regions and pathways involved at the nexus of sleep and anxiety that have yet to be uncovered, Olatunji adds.</p><p>Still, the study hints at an exciting avenue for future research, he says, especially considering that many patients with anxiety disorders don’t respond to typical interventions.</p><p>Even for those hoping to ameliorate day-to-day stress, catching high-caliber z’s can be a powerful palliative, Coles says. After all, “there aren’t too many risks to just getting more sleep,” she says. “In my experience, the benefits to doing so...tend to come out even stronger than we predict.”</p></div>
  

  
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<p>From a neurobiology perspective, anxiety and sleep deprivation look very much alike.</p>

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