Chapter 6. Evolution of the Brain and Behavior
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Are you good at picking someone out of a crowd? Most of us are better at recognising faces than distinguishing between other similar objects, so it’s long been suspected there’s something mysterious about the way the brain processes a face. Now further evidence has emerged that this is a special, highly evolved skill. A study of twins suggests there are genes influencing face recognition abilities that are distinct from the ones affecting intelligence – so it’s not that people who are good with faces just have a better memory, for instance. “The idea is that telling friend from foe was so important to survival that there was very strong pressure to improve that trait,” says Nicholas Shakeshaft of King’s College London. Previous studies using brain scanning have suggested there is a part of the brain dedicated to recognising faces, called the fusiform face area. But others have suggested this region may in fact just be used for discriminating between any familiar objects. Wondering if genetics could shed any light, Shakeshaft’s team tested more than 900 sets of UK twins – including both identical and non-identical pairs – on their face recognition skills. The ability turned out to be highly heritable, with identical twins having more similar abilities than fraternal ones. The same went for intelligence, which had earlier been tested as part of a long-running study. © Copyright Reed Business Information Ltd.
By Michael Balter Are some animals smarter than others? It’s hard to say, because you can’t sit a chimpanzee or a mouse down at a table for an IQ test. But a new study, in which scientists tested wild robins on a variety of skills, concludes that they do differ in the kind of “general intelligence” that IQ tests are supposed to measure. General intelligence is usually defined as the ability to do well on multiple cognitive tasks, from math skills to problem solving. For years, researchers have questioned whether measurable differences exist in humans and nonhumans alike. In humans, factors like education and socioeconomic status can affect performance. When it comes to animals, the problem is compounded for two main reasons: First, it is very difficult to design and administer tests that pick up on overall smarts instead of specific skills, such as the keen memories of food-hoarding birds or the fine motor skills of chimpanzees that make tools for finding insects in trees. Second, differences in animal test scores can depend on how motivated they are to perform. Because most experiments award would-be test-takers with food, an empty (or a full) stomach might be all it takes to skew the results. Thus, even studies that suggest variations in intelligence among mice, birds, and apes all carry the caveat that alternative explanations could be at play. To get around some of these limitations, a team led by Rachael Shaw, an animal behavior researcher at Victoria University of Wellington, turned to a population of New Zealand North Island robins for a new round of experiments. The robins live at the Zealandia wildlife sanctuary, a 225-hectare nature paradise in Wellington where more than 700 of the birds live wild and protected from predators in the middle of the city. © 2015 American Association for the Advancement of Science.
By JAMES GORMAN Among the deep and intriguing phenomena that attract intense scientific interest are the birth and death of the universe, the intricacies of the human brain and the way dogs look at humans. That gaze — interpreted as loving or slavish, inquisitive or dumb — can cause dog lovers to melt, cat lovers to snicker, and researchers in animal cognition to put sausage into containers and see what wolves and dogs will do to get at it. More than one experiment has made some things pretty clear. Dogs look at humans much more than wolves do. Wolves tend to put their nose to the Tupperware and keep at it. This evidence has led to the unsurprising conclusion that dogs are more socially connected to humans and wolves more self-reliant. Once you get beyond the basics, however, agreement is elusive. In order to assess the latest bit of research, published in Biology Letters Tuesday by Monique Udell at Oregon State University, some context can be drawn from an earlier experiment that got a lot of attention more than a decade ago. In a much publicized paper in 2003, Adam Miklosi, now director of the Family Dog Project, at Eotvos Lorand University in Budapest, described work in which dogs and wolves who were raised by humans learned to open a container to get food. Then they were presented with the same container, modified so that it could not be opened. Wolves persisted, trying to solve the unsolvable problem, while dogs looked back at nearby humans. At first glance it might seem to a dog lover that the dogs were brilliant, saying, in essence, “Can I get some help here? You closed it; you open it.” But Dr. Miklosi didn’t say that. He concluded that dogs have a genetic predisposition to look at humans, which could have been the basis for the intense but often imperfect communication that dogs and people engage in. © 2015 The New York Times Company
James Gorman If spiders had nightmares, the larvae of ichneumonid wasps would have to star in them. The wasp lays an egg on the back of an orb weaver spider, where it grows fat and bossy, and occupies itself with turning the spider into a zombie. As Keizo Takasuka and his colleagues point out in The Journal of Experimental Biology, this is a classic case of “host manipulation.” Using more colorful language, he described the larva turning the spider into a “drugged navvy.” The larva forces the spider to turn its efforts away from maintaining a sticky, spiral web to catch prey, and to devote itself to building a safe and sturdy web to serve as a home for the larva’s cocoon, in which it will transform itself into a wasp. This process was well known, but Dr. Takasuka and Kaoru Maeto at Kobe University, working with other Japanese researchers, wanted to explore how the wasp overlords controlled their spiders. They suspected that the larvae were co-opting a natural behavior of the spiders. Turning on a behavior already in the spiders’ repertoire would be much easier than controlling every step of modifying a sticky web. So they compared the cocoon web to one that the spiders themselves build to rest in when they are molting. It’s called a resting web. The similarities were striking. In both the resting and cocoon webs, the sticky, spiraling threads that make the webs of orb weavers so appealing were gone. Instead, the spokes of the web remained, decorated with fibrous spider silk that the researchers found reflected ultraviolet light. That would be a highly useful quality to warn away birds and some large insects from flying into the web because those creatures can see in the ultraviolet spectrum. The strength of the two silk webs was also similar. © 2015 The New York Times Company
Mo Costandi At some point back in deep time, a group of fish were washed into a limestone cave somewhere in northeastern Mexico. With no way out and little more than bat droppings to eat, the fish began to adapt to their new troglodytic lifestyle. Unable to see other members of their group in the dark, they lost their colourful pigmentation. Then they lost their eyesight, their eyes gradually got smaller, and then disappeared altogether. This was accompanied by a dramatic reduction in the size of the brain’s visual system. Yet, the question of why the blind cave fish lost its eyes and a large part of its brain remains unresolved. Now, biologists in Sweden believe they have found the answer. In new research published today, they report that loss of the visual system saves the fish a substantial amount of energy, and was probably key to their stranded ancestors’ survival. The blind cave fish Astyanax mexicanus is adapted to its subterranean environment in other ways. As its vision regressed, it became more reliant on smell and taste, and its taste buds grew larger and more numerous. They also developed an enhanced ability to detect changes in mechanical pressure, which made them more sensitive to water movements. Last year, Damian Moran of Lund University and his colleagues reported that blind cave fish eliminated the circadian rhythm in their metabolism during their course of evolution, and that this leads to a massive 27% reduction in their energy expenditure. This new study was designed test whether or not they lost their visual system for the same reason. © 2015 Guardian News and Media Limited
By JOHN NOBLE WILFORD Acting on a tip from spelunkers two years ago, scientists in South Africa discovered what the cavers had only dimly glimpsed through a crack in a limestone wall deep in the Rising Star Cave: lots and lots of old bones. The remains covered the earthen floor beyond the narrow opening. This was, the scientists concluded, a large, dark chamber for the dead of a previously unidentified species of the early human lineage — Homo naledi. The new hominin species was announced on Thursday by an international team of more than 60 scientists led by Lee R. Berger, an American paleoanthropologist who is a professor of human evolution studies at the University of the Witwatersrand in Johannesburg. The species name, H. naledi, refers to the cave where the bones lay undisturbed for so long; “naledi” means “star” in the local Sesotho language. In two papers published this week in the open-access journal eLife, the researchers said that the more than 1,550 fossil elements documenting the discovery constituted the largest sample for any hominin species in a single African site, and one of the largest anywhere in the world. Further, the scientists said, that sample is probably a small fraction of the fossils yet to be recovered from the chamber. So far the team has recovered parts of at least 15 individuals. “With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage,” Dr. Berger said. The finding, like so many others in science, was the result of pure luck followed by considerable effort. Two local cavers, Rick Hunter and Steven Tucker, found the narrow entrance to the chamber, measuring no more than seven and a half inches wide. They were skinny enough to squeeze through, and in the light of their headlamps they saw the bones all around them. When they showed the fossil pictures to Pedro Boshoff, a caver who is also a geologist, he alerted Dr. Berger, who organized an investigation. © 2015 The New York Times Company
Link ID: 21396 - Posted: 09.11.2015
Bill McQuay and Christopher Joyce Acoustic biologists who have learned to tune their ears to the sounds of life know there's a lot more to animal communication than just, "Hey, here I am!" or "I need a mate." From insects to elephants to people, we animals all use sound to function and converse in social groups — especially when the environment is dark, or underwater or heavily forested. "We think that we really know what's going on out there," says Dartmouth College biologist Laurel Symes, who studies crickets. But there's a cacophony all around us, she says, that's full of information still to be deciphered. "We're getting this tiny slice of all of the sound in the world." Recently scientists have pushed the field of bioacoustics even further, to record whole environments, not just the animals that live there. Some call this "acoustic ecology" — listening to the rain, streams, wind through the trees. A deciduous forest sounds different from a pine forest, for example, and that soundscape changes seasonally. Neuroscientist Seth Horowitz, author of the book The Universal Sense: How Hearing Shapes the Mind, is especially interested in the ways all these sounds, which are essentially vibrations, have shaped the evolution of the human brain. "Vibration sensitivity is found in even the most primitive life forms," Horowitz says — even bacteria. "It's so critical to your environment, knowing that something else is moving near you, whether it's a predator or it's food. Everywhere you go there is vibration and it tells you something." © 2015 NPR
By Ann Gibbons From the moment in 2013 when paleoanthropologist Lee Berger posted a plea on Facebook, Twitter, and LinkedIn for “tiny and small, specialised cavers and spelunkers with excellent archaeological, palaeontological and excavation skills,” some experts began grumbling that the excavation of a mysterious hominin in the Rising Star Cave in South Africa was more of a media circus than a serious scientific expedition. Daily blogs recorded the dangerous maneuvers of “underground astronauts” who squeezed through a long, narrow chute to drop 30 meters into a fossil-filled cavern, while Berger, who is based at the University of the Witwatersrand in Johannesburg, South Africa, became the “voice from the cave” in radio interviews. When it came time to analyze the fossils, Berger put out a call for applications from “early career scientists” to study them at a workshop in Johannesburg in March 2014. Handing over much of the analysis of such potentially important specimens to inexperienced researchers didn’t inspire confidence among Berger’s colleagues either, though it did win him the nickname Mr. Paleodemocracy. Many thought the expedition “had more hype than substance,” paleoanthropologist Chris Stringer of the Natural History Museum in London writes in a commentary accompanying the fossils’ official presentation this week in the journal eLIFE. But the substance has now been unveiled, and few dispute that the findings are impressive. In their report, Berger and his team describe 1550 fossils representing more than 15 ancient members of a strange new kind of hominin, which they named Homo naledi. (Naledi means “star” in the Sotho language spoken in the region of the cave.) © 2015 American Association for the Advancement of Science.
Link ID: 21392 - Posted: 09.10.2015
By Steve Mirsky It's nice to know that the great man we celebrate in this special issue had a warm sense of humor. For example, in 1943 Albert Einstein received a letter from a junior high school student who mentioned that her math class was challenging. He wrote back, “Do not worry about your difficulties in mathematics; I can assure you that mine are still greater.” Today we know that his sentiment could also have been directed at crows, which are better at math than those members of various congressional committees that deal with science who refuse to acknowledge that global temperatures keep getting higher. Studies show that crows can easily discriminate between a group of, say, three objects and another containing nine. They have more trouble telling apart groups that are almost the same size, but unlike the aforementioned committee members, at least they're trying. A study in the Proceedings of the National Academy of Sciences USA finds that the brain of a crow has nerve cells that specialize in determining numbers—a method quite similar to what goes on in our primate brain. Human and crow brains are substantially different in size and organization, but convergent evolution seems to have decided that this kind of neuron-controlled numeracy is a good system. (Crows are probably unaware of evolution, which is excusable. Some members of various congressional committees that deal with science pad their reactionary résumés by not accepting evolution, which is astonishing.) © 2015 Scientific American
By Emily Chung, Whadd'ya at? Ow ya goin'? If you were at a picnic with a bunch of Newfoundlanders or Australians, those are the greetings you might fling around. Similarly, scientists who eavesdrop on sperm whales – Moby Dick's species — have found they also have distinct "dialects." And a new study suggests like human dialects, they arise through cultural learning. "Cultural transmission seems key to the partitioning of sperm whales into… clans," the researchers wrote in a paper published today in the journal Nature Communications. Sperm whales live around the world, mainly in deeper waters far offshore. The solitary males live in colder areas, and roam in Canadian waters in areas where the ocean depth is more than 1000 metres, says Mauricio Cantor, the Dalhousie University PhD. student who led the new study with Hal Whitehead, a Dalhousie biology professor. The females live in warmer, more southern waters, in loose family groups of around seven to 12 whales – sisters, aunts, grandmothers, cousins, and the occasional unrelated friend and their calves. Sometimes, they meet up with other families for gatherings of up to 200 whales, similar to human picnics or festivals. These can last from a few hours to a few days. The whales that gather in these groups, called clans, have distinct "dialects" of patterns of clicks called codas that are distinct from the clicks they use in echolocation when they're hunting for food. They use codas talk to each other when they surface between dives. ©2015 CBC/Radio-Canada.
Erin Wayman Nose picking isn’t a mark of distinction among people — but it is among monkeys. For the first time, researchers have reported a wild capuchin monkey using a tool to pick its nose and teeth. The monkey was caught in the act last year by Michael Haslam of the University of Oxford. For about five minutes, an adult female bearded capuchin (Sapajus libidinosus) in northeastern Brazil repeatedly inserted a twig or stem into its nostril, usually inducing a sneeze. The monkey also rubbed sticks back and forth against the base of its teeth, probably to dislodge debris, Haslam and Oxford colleague Tiago Falótico report in the July Primates. After picking its nose or teeth, the monkey often licked the tool tip, perhaps to wipe the stick clean. Bearded capuchins are quite handy, brandishing rocks to crack open nuts (SN Online: 4/30/15) and sticks to retrieve insects from crevices or to collect honey. But until now, no one had seen a wild capuchin use a tool as a nasal probe or toothpick. M. Haslam and T. Falótico. Nasal probe and toothpick tool use by a wild female bearded capuchin (Sapajus libidinosus). Primates. Vol. 56, July 2015, p. 211. doi: 10.1007/s10329-015-0470-6. © Society for Science & the Public 2000 - 2015
Link ID: 21382 - Posted: 09.08.2015
Bill McQuay The natural world is abuzz with the sound of animals communicating — crickets, birds, even grunting fish. But scientists learning to decode these sounds say the secret signals of African elephants — their deepest rumblings — are among the most intriguing calls any animal makes. Katy Payne, the same biologist who recognized song in the calls of humpback whales in the 1960s, went on to help create the Elephant Listening Project in the Central African Republic in the 1980s. At the time, Payne's team was living in shacks in a dense jungle inhabited by hundreds of rare forest elephants. That's where one of us — Bill McQuay — first encountered the roar of an elephant in 2002, while reporting a story for an NPR-National Geographic collaboration called Radio Expeditions. Here's how Bill remembers that day in Africa: I was walking through this rainforest to an observation platform built up in a tree — out of the reach of the elephants. I climbed up onto the platform, a somewhat treacherous exercise with all my recording gear. Then I set up my recording equipment, put on the headphones, and started listening. That first elephant roar sounded close. But I was so focused on the settings on my recorder that I didn't bother to look around. The second roar sounded a lot closer. I thought, this is so cool! What I didn't realize was, there was this huge bull elephant standing right underneath me — pointing his trunk up at me, just a few feet away. Apparently he was making a "dominance display." © 2015 NPR
Carl Zimmer You are what you eat, and so were your ancient ancestors. But figuring out what they actually dined on has been no easy task. There are no Pleistocene cookbooks to consult. Instead, scientists must sift through an assortment of clues, from the chemical traces in fossilized bones to the scratch marks on prehistoric digging sticks. Scientists have long recognized that the diets of our ancestors went through a profound shift with the addition of meat. But in the September issue of The Quarterly Review of Biology, researchers argue that another item added to the menu was just as important: carbohydrates, bane of today’s paleo diet enthusiasts. In fact, the scientists propose, by incorporating cooked starches into their diet, our ancestors were able to fuel the evolution of our oversize brains. Roughly seven million years ago, our ancestors split off from the apes. As far as scientists can tell, those so-called hominins ate a diet that included a lot of raw, fiber-rich plants. After several million years, hominins started eating meat. The oldest clues to this shift are 3.3-million-year-old stone tools and 3.4-million-year-old mammal bones scarred with cut marks. The evidence suggests that hominins began by scavenging meat and marrow from dead animals. At some point hominins began to cook meat, but exactly when they invented fire is a question that inspires a lot of debate. Humans were definitely making fires by 300,000 years ago, but some researchers claim to have found campfires dating back as far as 1.8 million years. Cooked meat provided increased protein, fat and energy, helping hominins grow and thrive. But Mark G. Thomas, an evolutionary geneticist at University College London, and his colleagues argue that there was another important food sizzling on the ancient hearth: tubers and other starchy plants. © 2015 The New York Times Company
Alison Abbott The octopus genome offers clues to how cephalopods evolved intelligence to rival the craftiest vertebrates. With its eight prehensile arms lined with suckers, camera-like eyes, elaborate repertoire of camouflage tricks and spooky intelligence, the octopus is like no other creature on Earth. Added to those distinctions is an unusually large genome, described in Nature1 on 12 August, that helps to explain how a mere mollusc evolved into an otherworldly being. “It’s the first sequenced genome from something like an alien,” jokes neurobiologist Clifton Ragsdale of the University of Chicago in Illinois, who co-led the genetic analysis of the California two-spot octopus (Octopus bimaculoides). The work was carried out by researchers from the University of Chicago, the University of California, Berkeley, the University of Heidelberg in Germany and the Okinawa Institute of Science and Technology in Japan. The scientists also investigated gene expression in twelve different types of octopus tissue. “It’s important for us to know the genome, because it gives us insights into how the sophisticated cognitive skills of octopuses evolved,” says neurobiologist Benny Hochner at the Hebrew University of Jerusalem in Israel, who has studied octopus neurophysiology for 20 years. Researchers want to understand how the cephalopods, a class of free-floating molluscs, produced a creature that is clever enough to navigate highly complex mazes and open jars filled with tasty crabs. © 2015 Nature Publishing Group
Nell Greenfieldboyce Take a close look at a house cat's eyes and you'll see pupils that look like vertical slits. But a tiger has round pupils — like humans do. And the eyes of other animals, like goats and horses, have slits that are horizontal. Scientists have now done the first comprehensive study of these three kinds of pupils. The shape of the animal's pupil, it turns out, is closely related to the animal's size and whether it's a predator or prey. The pupil is the hole that lets light in, and it comes in lots of different shapes. "There are some weird ones out there," says Martin Banks, a vision scientist at the University of California, Berkeley. Cuttlefish have pupils that look like the letter "W," and dolphins have pupils shaped like crescents. Some frogs have heart-shaped pupils, while geckos have pupils that look like pinholes arranged in a vertical line. Needless to say, scientists want to know why all these different shapes evolved. "It's been an active point of debate for quite some time," says Banks, "because it's something you obviously observe. It's the first thing you see about an animal — where their eye is located and what the pupil shape is." For their recent study, Banks and his colleagues decided to keep things simple. They looked at just land animals, and just three kinds of pupils. "We restricted ourselves to just pupils that are elongated or not," Banks explains. "So they're either vertical, horizontal or round." © 2015 NPR
// by Richard Farrell Bonobos have a capacity to do something human infants have been shown to do: use a single sound whose meaning varies based on context, a form of "flexible" communication previously thought specific to humans. The finding was made by researchers from the University of Birmingham and the University of Neuchatel, in a paper just published in the journal Peer J. The newly identified bonobo call is a short, high-pitched "peep," made with a closed mouth. The scientists studied the call's acoustic structure and observed that it did not change between what they termed "neutral" and "positive" circumstances (for example, between activities such as feeding or resting), suggesting that other bonobos receiving the call would need to weigh contextual information to discern its meaning. Human babies do something similarly flexible, using sounds called protophones -- different from highly specific sounds such as crying or laughter -- that are made independent of how they are feeling emotionally. The appearance of this capability in the first year of life is "a critical step in the development of vocal language and may have been a critical step in the evolution of human language," an earlier study on infant vocalization noted. The find challenges the idea that calls from primates such as bonobos -- which, along with chimpanzees, are our closest relatives -- are strictly matched with specific contexts and emotions, whether those sounds are territorial barks or shrieks of alarm. © 2015 Discovery Communications, LLC.
By Michael Balter Have you ever wondered why you say “The boy is playing Frisbee with his dog” instead of “The boy dog his is Frisbee playing with”? You may be trying to give your brain a break, according to a new study. An analysis of 37 widely varying tongues finds that, despite the apparent great differences among them, they share what might be a universal feature of human language: All of them have evolved to make communication as efficient as possible. Earth is a veritable Tower of Babel: Up to 7000 languages are still spoken across the globe, belonging to roughly 150 language families. And they vary widely in the way they put sentences together. For example, the three major building blocks of a sentence, subject (S), verb (V), and object (O), can come in three different orders. English and French are SVO languages, whereas German and Japanese are SOV languages; a much smaller number, such as Arabic and Hebrew, use the VSO order. (No well-documented languages start sentences or clauses with the object, although some linguists have jokingly suggested that Klingon might do so.) Yet despite these different ways of structuring sentences, previous studies of a limited number of languages have shown that they tend to limit the distance between words that depend on each other for their meaning. Such “dependency” is key if sentences are to make sense. For example, in the sentence “Jane threw out the trash,” the word “Jane” is dependent on “threw”—it modifies the verb by telling us who was doing the throwing, just as we need “trash” to know what was thrown, and “out” to know where the trash went. Although “threw” and “trash” are three words away from each other, we can still understand the sentence easily. © 2015 American Association for the Advancement of Science.
By Andrea Alfano Forget the insult “fathead.” We may actually owe our extraordinary smarts to the fat in our brain. A study published in Neuron in February revealed that the variety of fat molecules found in the human neocortex, the brain region responsible for advanced cognitive functions such as language, evolved at an exceptionally fast rate after the human-ape split. The researchers analyzed the concentrations of 5,713 different lipids, or fat molecules and their derivatives, present in samples of brain, kidney and muscle tissues taken from humans, chimpanzees, macaques and mice. Lipids have a variety of critical functions in all cells, including their role as the primary component of a cell's membrane. They are particularly important in the brain because they enable electrical signal transmission among neurons. Yet until this study, it was unknown whether the lipids in the human brain differed significantly from lipids in other mammals. The team discovered that the levels of various lipids found in human brain samples, especially from the neocortex, stood out. Humans and chimps diverged from their common ancestor around the same time, according to much evolutionary evidence. Because the two species have had about the same amount of time to rack up changes to their lipid profiles, the investigators expected them to have roughly the same number of species-specific lipid concentrations, explains computational biologist and study leader Kasia Bozek of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Indeed, lipid changes in the cerebellum, a primitive part of the brain similar in all vertebrates, were comparable between humans and chimps. But the human neocortex has accumulated about three times more lipid changes than the chimpanzee cortex has since we split from our common ancestor. © 2015 Scientific American
Link ID: 21260 - Posted: 08.04.2015
Kill, Fido! Docile ants become aggressive guard dogs after a secret signal from their caterpillar overlord. The idea turns on its head the assumption that the two species exchange favours in an even-handed relationship. The caterpillars of the Japanese oakblue butterfly (Narathura japonica) grow up wrapped inside leaves on oak trees. To protect themselves against predators like spiders and wasps, they attract ant bodyguards, Pristomyrmex punctatus, with an offering of sugar droplets. The relationships was thought to be a fair exchange of services in which both parties benefit. But Masaru Hojo from Kobe University in Japan noticed something peculiar: the caterpillars were always attended by the same ant individuals. “It also seemed that the ants never moved away or returned to their nests,” he says. They seemed to abandon searching for food, and were just standing around guarding the caterpillar. Intrigued, Hojo and his colleagues conducted lab experiments in which they allowed some ants to interact with the caterpillars and feed on the secretions, and kept others separate. Ants that ate the caterpillar’s secretions remained close to the caterpillar. They didn’t return to their nest. And whenever the caterpillar everted its tentacles – flipped them so they turned inside out – the ants moved around rapidly, acting aggressively. © Copyright Reed Business Information Ltd.
Ewen Callaway Our ancestors were not a picky bunch. Overwhelming genetic evidence shows that Homo sapiens had sex with Neanderthals, Denisovans and other archaic relatives. Now researchers are using large genomics studies to unravel the decidedly mixed contributions that these ancient romps made to human biology — from the ability of H. sapiens to cope with environments outside Africa, to the tendency of modern humans to get asthma, skin diseases and maybe even depression. The proportion of the human genome that comes from archaic relatives is small. The genomes of most Europeans and Asians are 2–4% Neanderthal1, with Denisovan DNA making up about 5% of the genomes of Melanesians2 and Aboriginal Australians3. DNA slivers from other distant relatives probably pepper a variety of human genomes4. But these sequences may have had an outsize effect on human biology. In some cases, they are very different from the corresponding H. sapiens DNA, notes population geneticist David Reich of Harvard Medical School in Boston, Massachusetts — which makes it more likely that they could introduce useful traits. “Even though it’s only a couple or a few per cent of ancestry, that ancestry was sufficiently distant that it punched above its weight,” he says. Last year, Reich co-led one of two teams that catalogued the Neanderthal DNA living on in modern-day humans5, 6. The studies hinted that Neanderthal versions of some genes may have helped Eurasians to reduce heat loss or grow thicker hair. But the evidence that these genes were beneficial was fairly weak. To get a better handle on how Neanderthal DNA shapes human biology, Corinne Simonti and Tony Capra, evolutionary geneticists at Vanderbilt University in Nashville, Tennessee, turned to genome-wide association studies (GWAS) that had already compared thousands of DNA variants in people with and without a certain disease or condition. © 2015 Nature Publishing Group,
Link ID: 21240 - Posted: 07.30.2015