Chapter 6. Evolution of the Brain and Behavior
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by Bob Holmes Lions might be one of the biggest threats to hyenas, but that doesn't stop the smaller animals teaming up to steal from the big cats. Nora Lewin from Michigan State University in East Lansing and her colleagues observed the mobbing behaviour at the Masai Mara National Reserve in Kenya. Hyenas were also spotted banding together to keep lions away from their dens. The mobbing involves a surprising degree of cooperation and communication. Male lions, which actively pursue and kill hyenas, are much more of a danger than females, who usually just make threats. This could be why the hyenas in the video above are confronting females. The team suggests the hyenas can identify their opponent's age and sex before deciding as a group whether or not to mob it. Levin and her colleagues are now investigating how the hyenas communicate to make a group decision. The findings were reported on 13 June at the annual meeting of the Animal Behavior Society in Anchorage, Alaska. © Copyright Reed Business Information Ltd.
By David Shultz Not usually lauded for their cuddly appearance, opossums were long thought to have a social inclination to match their looks; the marsupials have mostly been observed lurking alone and hissing at others who encroach on their personal space. However, a new study published online today in Biology Letters suggests that opossums sometimes live in groups and may form pair bonds with mates before the mating season starts. Based on 17,127 observations of 312 artificial nests over 8 years, scientists at the Federal University of Pernambuco in Recife, Brazil, discovered 10 instances of multiple opossums sharing the same den with no signs of hostility or ongoing reproductive activity. An additional observation made on the university campus revealed a group of 13 opossums from three separate age groups all sharing a single den. The researchers speculate that this type of “gregarious denning” may be relatively common in the wild and that males and females may work cooperatively to build a nest—a ritual that could trigger the onset of an estrous cycle in females. Furthermore, the group of 13 animals was discovered in a large concrete box housing electrical equipment, much bigger than the typical artificial dens used by scientists studying opossums. The team suspects that building larger artificial dens may promote more social interactions like the ones they observed. © 2015 American Association for the Advancement of Science
Link ID: 21059 - Posted: 06.17.2015
by Michael Le Page It is perhaps the most extraordinary eye in the living world – so extraordinary that no one believed the biologist who first described it more than a century ago. Now it appears that the tiny owner of this eye uses it to catch invisible prey by detecting polarised light. This suggestion is also likely to be greeted with disbelief, for the eye belongs to a single-celled organism called Erythropsidinium. It has no nerves, let alone a brain. So how could it "see" its prey? Fernando Gómez of the University of São Paulo, Brazil, thinks it can. "Erythropsidinium is a sniper," he told New Scientist. "It is waiting to see the prey, and it shoots in that direction." Erythropsidinium belongs to a group of single-celled planktonic organisms known as dinoflagellates. They can swim using a tail, or flagellum, and many possess chloroplasts, allowing them to get their food by photosynthesis just as plants do. Others hunt by shooting out stinging darts similar to the nematocysts of jellyfishMovie Camera. They sense vibrations when prey comes near, but they often have to fire off several darts before they manage to hit it, Gómez says. Erythropsidinium and its close relatives can do better, Gómez thinks, because they spot prey with their unique and sophisticated eye, called the ocelloid, which juts out from the cell. "It knows where the prey is," he says. At the front of the ocelloid is a clear sphere rather like an eyeball. At the back is a dark, hemispherical structure where light is detected. The ocelloid is strikingly reminiscent of the camera-like eyes of vertebrates, but it is actually a modified chloroplast. © Copyright Reed Business Information Ltd.
By Michael Balter Alcoholic beverages are imbibed in nearly every human society across the world—sometimes, alas, to excess. Although recent evidence suggests that tippling might have deep roots in our primate past, nonhuman primates are only rarely spotted in the act of indulgence. A new study of chimpanzees with easy access to palm wine shows that some drink it enthusiastically, fashioning leaves as makeshift cups with which to lap it up. The findings could provide new insights into why humans evolved a craving for alcohol, with all its pleasures and pains. Scientists first hypothesized an evolutionary advantage to humans’ taste for ethanol about 15 years ago, when a biologist at the University of California, Berkeley, proposed what has come to be called the “drunken monkey hypothesis.” Robert Dudley argued that our primate ancestors got an evolutionary benefit from being able to eat previously unpalatable fruit that had fallen to the ground and started to undergo fermentation. The hypothesis received a boost last year, when a team led by Matthew Carrigan—a biologist at Santa Fe College in Gainesville, Florida—found that the key enzyme that helps us metabolize ethanol underwent an important mutation about 10 million years ago. This genetic change, which occurred in the common ancestor of humans, chimps, and gorillas, made ethanol metabolism some 40 times faster than the process in other primates—such as monkeys—that do not have it. According to the hypothesis, the mutation allowed apes to consume fermented fruit without immediately getting drunk or, worse, succumbing to alcohol poisoning. Nevertheless, researchers had turned up little evidence that primates in the wild regularly eat windfall fruit or are attracted to the ethanol that such fruit contains. Now, a team led by Kimberley Hockings, a primatologist at the Center for Research in Anthropology in Lisbon, concludes from a 17-year study of chimps in West Africa that primates can tolerate significant levels of ethanol and may actually crave it, as humans do. © 2015 American Association for the Advancement of Science
James Gorman Chimpanzees have the cognitive ability to cook, according to new research, if only someone would give them ovens. It’s not that the animals are ready to go head-to-head with Gordon Ramsay, but scientists from Harvard and Yale found that chimps have the patience and foresight to resist eating raw food and to place it in a device meant to appear, at least to the chimps, to cook it. That is no small achievement. In a line that could easily apply to human beings, the researchers write, “Many primate species, including chimpanzees, have difficulty giving up food already in their possession and show limitations in their self-control when faced with food.” But they found that chimps would give up a raw slice of sweet potato in the hand for the prospect of a cooked slice of sweet potato a bit later. That kind of foresight and self-control is something any cook who has eaten too much raw cookie dough can admire. The research grew out of the idea that cooking itself may have driven changes in human evolution, a hypothesis put forth by Richard Wrangham, an anthropologist at Harvard and several colleagues about 15 years ago in an article in Current Anthropology, and more recently in his book, “Catching Fire: How Cooking Made Us Human.” He argued that cooking may have begun something like two million years ago, even though hard evidence only dates back about one million years. For that to be true, some early ancestors, perhaps not much more advanced than chimps, had to grasp the whole concept of transforming the raw into the cooked. © 2015 The New York Times Company
Link ID: 21016 - Posted: 06.03.2015
By Elahe Izadi Researchers classified two new species of Dusky Antechinus, mouse-like creatures that engage in suicidal reproduction, and published their findings last week in the peer-reviewed journal Memoirs of the Queensland Museum -- Nature. The Mainland Dusky Antechinus, found in southeastern Australia, has been elevated from sub-species to a distinct species. And the newly discovered Tasman Peninsula Dusky Antechinus, found in southeastern Tasmania, already faces the threat of extinction due in part to loss of habitat and feral pests, researchers said. Their proclivity for ferocious, suicidal sex frenzies aren't helping them any. "The breeding period is basically two to three weeks of speed-mating, with testosterone-fueled males coupling with as many females as possible, for up to 14 hours at a time," lead author Andrew Baker of the Queensland University of Technology said in a release. All of that testosterone "triggers a malfunction in the stress hormone shut-off switch" for the males, Baker said. The males then get so stressed out that their immune systems fail, and they die before the females actually give birth. Suicidal reproduction -- or semelparity-- is rare in mammals, and has so far just been documented in these kinds of marsupials.
Allie Wilkinson For many species, reproduction is a duet between male and female. Now, for the first time, scientists report evidence of 'virgin birth' in a wild vertebrate, the smalltooth sawfish. The fish (Pristis pectinata) normally reproduces sexually, requiring contributions from both sexes. But the latest analysis estimates that nearly 4% of sawfish in a Florida estuary were born without any genetic contribution from a male, in a phenomenon known as parthenogenesis. This asexual reproduction is rare in vertebrates, and had previously been observed only in a handful of species in captivity, including snakes collected from the wild1 and Komodo dragons2. The latest findings appear in the 1 June issue of Current Biology3. Smalltooth sawfish are one of five large ray species that have chainsaw-like appendages protruding from their faces, and are in the same subclass as sharks. The smalltooth sawfish was once abundant along the US eastern and southern coastlines from North Carolina to Texas, but overfishing and coastal development have drastically reduced its numbers. The critically endangered fish are now found only off the coast of southwest Florida. Researchers discovered evidence of 'virgin births' among the sawfish while conducting a routine genetic analysis to determine whether they were inbreeding. Some of the 190 sawfish sampled in a Florida estuary showed unusually high levels of relatedness to other fish in the same population. © 2015 Nature Publishing Group
By Sarah C. P. Williams Bonobos, endangered great apes considered—along with chimpanzees—the closest living relative to humans, spend most of each day climbing through trees, collecting fruit and leaves. Compare that with the lives of early humans who traversed hot, barren landscapes and it begins to make sense why we’re the fattier, less muscular primate. Over the past 3 decades, two researchers analyzed the hard-to-come-by bodies of 13 bonobos that had died in captivity and compared them with already collected data on 49 human bodies donated by means of autopsy to help understand how evolution drove this change. Although some captive bonobos have become obese, the researchers found that, on average, the apes’ body mass—which is thought to resemble that of the closest common ancestor we share with them—is composed of 10% to 13% skin, whereas humans have only 6% skin. This thinner skin, the team hypothesizes, probably arose around the same time that Homo sapiens gained the ability to sweat, allowing more time spent in hot, open areas. The scientists also found that we pack on more fat than our ape relatives: Female and male humans average 36% and 20% body fat, whereas female and male bonobos average 4% and close to 0% body fat, respectively. Increased fat, the researchers hypothesize, allowed our species to survive—and reproduce—during times of low food availability. As for muscle, the team reports online today in the Proceedings of the National Academy of Sciences, bonobos come out on top, especially when it comes to upper body muscles needed for tree climbing and swinging, which became unnecessary when humans went strictly bipedal. The new findings, the researchers say, help illustrate the forces of natural selection that may have affected H. sapiens’s soft tissues even before our brains started expanding in size and tool use shaped the species. © 2015 American Association for the Advancement of Science.
Carl Zimmer For scientists who study human evolution, the last few months have been a whirlwind. Every couple of weeks, it seems, another team pulls back the curtain on newly discovered bones or stone tools, prompting researchers to rethink what we know about early human history. On Wednesday, it happened again. Yohannes Haile-Selassie of the Cleveland Museum of Natural History and his colleagues reported finding a jaw in Ethiopia that belonged to an ancient human relative that lived some time between 3.3 and 3.5 million years. They argue that the jaw belongs to an entirely new species, which they dubbed Australopithecus deyiremeda. While some experts agree, skeptics argued that the jaw belongs to a familiar hominid species, known as Australopithecus afarensis, that existed from about 3.9 to 3 million years ago. Studies like this one are adding fresh fuel to the debate over the pace of human evolution. Some researchers now believe the human family tree bore exuberant branches early on. “I’m so excited about these discoveries, I’m driving my friends crazy,” said Carol V. Ward, a paleoanthropologist at the University of Missouri. “It makes us stop and rethink everything.” In the 1990s, the broad outlines of human evolution seemed fairly clear. Early human ancestors — known as hominids — evolved from an ancestor shared with chimpanzees about six or seven million years ago. These hominids were short, bipedal apes with small brains and arms and legs still adapted for climbing trees. Until about three million years ago, experts thought, there weren’t a lot of hominid species. In fact, some researchers argued that most hominid fossils represented just a single species. © 2015 The New York Times Company
Link ID: 20993 - Posted: 05.28.2015
By Sarah C. P. Williams Here’s an easy way to tell if a female warbler is a year-round resident of the tropics or just a visiting snowbird: Females from species that spend their lives near the equator tend to have brighter plumage more typical of male birds. In contrast, females who fly north for the summer appear drab compared with their male counterparts. In the past, researchers thought the difference was due to the shorter breeding season in the north, hypothesizing that migrating males evolved bright colors to better compete for mates. But a new study hints that northern-breeding females may have evolved to be less colorful than males in order to be less conspicuous to predators during their long migrations. Researchers at Trinity University in San Antonio, Texas, studied the coloring, migration patterns, breeding locales, and ancestry of 109 warbler species. Migration distance, not the length of the breeding season, was the best predictor of color contrasts between male and female birds, they report online today in the Proceedings of the Royal Society B. Female bay-breasted warblers (Setophaga castanea), for instance, which migrate about 7000 kilometers between their breeding grounds in North America and their wintering grounds in the Caribbean, are a dull gray and white, whereas males boast more showy yellows and browns. But both male and female slate-throated redstarts (Myioborus miniatus), like the one shown above, flaunt bright colors in their year-round tropical homes in Mexico and Central America. For migrating warblers, the researchers hypothesize that the breeding benefits of brighter male colors outweigh the threat of being spotted by a hungry predator. © 2015 American Association for the Advancement of Science.
Alison Abbott Redouan Bshary well remembers the moment he realized that fish were smarter than they are given credit for. It was 1998, and Bshary was a young behavioural ecologist with a dream project: snorkelling in Egypt's Red Sea to observe the behaviour of coral-reef fish. That day, he was watching a grumpy-looking grouper fish as it approached a giant moray eel. As two of the region's top predators, groupers and morays might be expected to compete for their food and even avoid each other — but Bshary saw them team up to hunt. First, the grouper signalled to the eel with its head, and then the two swam side by side, with the eel dipping into crevices, flushing out fish beyond the grouper's reach and getting a chance to feed alongside. Bshary was astonished by the unexpected cooperation; if he hadn't had a snorkel in his mouth, he would have gasped. This underwater observation was the first in a series of surprising discoveries that Bshary has gone on to make about the social behaviour of fish. Not only can they signal to each other and cooperate across species, but they can also cheat, deceive, console or punish one another — even show concern about their personal reputations. “I have always had a lot of respect for fish,” says Bshary. “But one after the other, these behaviours took me by surprise.” His investigations have led him to take a crash course in scuba diving, go beach camping in Egypt and build fake coral reefs in Australia. The work has also destroyed the stereotypical idea that fish are dumb creatures, capable of only the simplest behaviours — and it has presented a challenge to behavioural ecologists in a different field. Scientists who study primates have claimed that human-like behaviours such as cooperation are the sole privilege of animals such as monkeys and apes, and that they helped to drive the evolution of primates' large brains. Bshary — quiet, but afraid of neither adventure nor of contesting others' ideas — has given those scientists reason to think again. © 2015 Nature Publishing Grou
Michael C. Corbalis In the quest to identify what might be unique to the human mind, one might well ask whether non-human animals have a theory of mind. In fiction, perhaps, they do. Eeyore, the morose donkey in Winnie-the-Pooh, at one point complains: ‘A little consideration, a little thought for others, makes all the difference.’ In real life, some animals do seem to show empathy toward others in distress. The primatologist Frans de Waal photographed a juvenile chimpanzee placing a consoling arm around an adult chimpanzee in distress after losing a fight, but suggests that monkeys do not do this. However, one study shows that monkeys won’t pull a chain to receive food if doing so causes a painful stimulus to be delivered to another monkey, evidently understanding that it will cause distress. Even mice, according to another study, react more intensely to pain if they perceive other mice in pain. It is often claimed that dogs show empathy toward their human owners, whereas cats do not. Cats don’t empathise—they exploit. Understanding what others are thinking, or what they believe, can be complicated, but perceiving emotion in others is much more basic to survival, and no doubt has ancient roots in evolution. Different emotions usually give different outward signs. In Shakespeare’s “Henry V,” the King recognises the signs of rage, urging his troops to . . . imitate the action of the tiger; Stiffen the sinews, summon up the blood, Disguise fair nature with hard-favour’d rage; Then lend the eye a terrible aspect . . . The human enemy will read the emotion of Henry’s troops, just as the antelope will read the emotion of the marauding tiger. Perhaps the best treatise on the outward signs of emotion is Charles Darwin’s “The Expression of the Emotions in Man and Animals,” which details the way fear and anger are expressed in cats and dogs, although he does not neglect the positive emotions: © 2015 Salon Media Group, Inc.
Nala Rogers Alzheimer’s disease may have evolved alongside human intelligence, researchers report in a paper posted this month on BioRxiv1. The study finds evidence that 50,000 to 200,000 years ago, natural selection drove changes in six genes involved in brain development. This may have helped to increase the connectivity of neurons, making modern humans smarter as they evolved from their hominin ancestors. But that new intellectual capacity was not without cost: the same genes are implicated in Alzheimer's disease. Kun Tang, a population geneticist at the Shanghai Institutes for Biological Sciences in China who led the research, speculates that the memory disorder developed as ageing brains struggled with new metabolic demands imposed by increasing intelligence. Humans are the only species known to develop Alzheimer's; the disease is absent even in closely related primate species such as chimpanzees. Tang and his colleagues searched modern human DNA for evidence of this ancient evolution. They examined the genomes of 90 people with African, Asian or European ancestry, looking for patterns of variation driven by changes in population size and natural selection. Marked by selection The analysis was tricky, because the two effects can mimic each other. To control for the effects of population changes ― thereby isolating the signatures of natural selection — the researchers estimated how population sizes changed over time. Then they identified genome segments that did not match up with the population history, revealing the DNA stretches that were most likely shaped by selection. © 2015 Nature Publishing Group
By Jason G. Goldman In 1970 child welfare authorities in Los Angeles discovered that a 14-year-old girl referred to as “Genie” had been living in nearly total social isolation from birth. An unfortunate participant in an unintended experiment, Genie proved interesting to psychologists and linguists, who wondered whether she could still acquire language despite her lack of exposure to it. Genie did help researchers better define the critical period for learning speech—she quickly acquired a vocabulary but did not gain proficiency with grammar—but thankfully, that kind of case study comes along rarely. So scientists have turned to surrogates for isolation experiments. The approach is used extensively with parrots, songbirds and hummingbirds, which, like us, learn how to verbally communicate over time; those abilities are not innate. Studying most vocal-learning mammals—for example, elephants, whales, sea lions—is not practical, so Tel Aviv University zoologists Yosef Prat, Mor Taub and Yossi Yovel turned to the Egyptian fruit bat, a vocal-learning species that babbles before mastering communication, as a child does. The results of their study, the first to raise bats in a vocal vacuum, were published this spring in the journal Science Advances. Five bat pups were reared by their respective mothers in isolation, so the pups heard no adult conversations. After weaning, the juveniles were grouped together and exposed to adult bat chatter through a speaker. A second group of five bats was raised in a colony, hearing their species' vocal interactions from birth. Whereas the group-raised bats eventually swapped early babbling for adult communication, the isolated bats stuck with their immature vocalizations well into adolescence. © 2015 Scientific American
Carl Zimmer Octopuses, squid and cuttlefish — a group of mollusks known as cephalopods — are the ocean’s champions of camouflage. Octopuses can mimic the color and texture of a rock or a piece of coral. Squid can give their skin a glittering sheen to match the water they are swimming in. Cuttlefish will even cloak themselves in black and white squares should a devious scientist put a checkerboard in their aquarium. Cephalopods can perform these spectacles thanks to a dense fabric of specialized cells in their skin. But before a cephalopod can take on a new disguise, it needs to perceive the background that it is going to blend into. Cephalopods have large, powerful eyes to take in their surroundings. But two new studies in The Journal Experimental Biology suggest that they have another way to perceive light: their skin. It’s possible that these animals have, in effect, evolved a body-wide eye. When light enters the eye of a cephalopod, it strikes molecules in the retina called opsins. The collision starts a biochemical reaction that sends an electric signal from the cephalopod’s eye to its brain. (We produce a related form of opsins in our eyes as well.) In 2010, Roger T. Hanlon, a biologist at the Marine Biological Laboratory in Woods Hole, Mass., and his colleagues reported that cuttlefish make opsins in their skin, as well. This discovery raised the tantalizing possibility that the animals could use their skin to sense light much as their eyes do. Dr. Hanlon teamed up with Thomas W. Cronin, a visual ecologist at the University of Maryland Baltimore County, and his colleagues to take a closer look. © 2015 The New York Times Company
by Karl Gruber "As clever as a guppy" is not a huge compliment. But intelligence does matter to these tropical fish: big-brained guppies are more likely to outwit predators and live longer than their dim-witted peers. Alexander Kotrschal at Stockholm University, Sweden, and his colleagues bred guppies (Poecilia reticulata) to have brains that were bigger or smaller than average. His team previously showed that bigger brains meant smarter fish. When put in an experimental stream with predators, big-brained females were eaten about 13 per cent less often than small-brained ones. There was no such link in males, and the researchers suspect that their bright colours may counter any benefits of higher intelligence. They did find, Kotrschal says , that large-brained males were faster swimmers and better at learning and remembering the location of a female. "This is exciting because it confirms a critical mechanism for brain size evolution," says Kotrschal. It shows, he adds, that interactions between predator and prey can affect brain size. It might seem obvious that bigger brains would help survival. Yet previous research simply found a correlation between the two, leaving the possibility open that some third factor may have been driving the effect. Now, direct brain size manipulation allowed Kotrschal's team to pin it down as a cause of better survival. "This is the first time anyone has tested whether a larger brain confers a survival benefit," says Kotrschal. "The fact that large-brained females survived better in a naturalistic setting is the first experimental proof that a larger brain is beneficial for the fitness of its bearer. This is like watching evolution happen and shows how brain size evolves." © Copyright Reed Business Information Ltd.
by Ashley Yeager New Caledonian crows are protective of their tools. The birds safeguard the sticks they use to find food and become even more careful with the tools as the cost of losing them goes up. Researchers videotaped captive and wild Corvus moneduloides crows and tracked what the birds did with their sticks. In between eating, the birds tucked the tools under their toes or left them in the holes they were probing. When higher up in the trees, the birds dropped the tools less often and were more likely to leave them in the holes they were probing than when they were on the ground. The finding, published May 20 in the Proceedings of the Royal Society B, shows how tool-protection tactics can prevent costly losses that could keep the crows from chowing down. © Society for Science & the Public 2000 - 2015
By James Gorman and Robin Lindsay Before human ancestors started making stone tools by chipping off flakes to fashion hand axes and other implements, their ancestors may have used plain old stones, as animals do now. And even that simple step required the intelligence to see that a rock could be used to smash open a nut or an oyster and the muscle control to do it effectively. Researchers have been rigorous in documenting every use of tools they have found find in animals, like crows, chimpanzees and dolphins. And they are now beginning to look at how tools are used by modern primates — part of the scientists’ search for clues about the evolution of the kind of delicate control required to make and use even the simplest hand axes. Monkeys do not exhibit human dexterity with tools, according to Madhur Mangalam of the University of Georgia, one of the authors of a recent study of how capuchin monkeys in Brazil crack open palm nuts. “Monkeys are working as blacksmiths,” he said, “They’re not working as goldsmiths.” But they are not just banging away haphazardly, either. Mr. Mangalam, a graduate student who is interested in “the evolution of precise movement,” reported in a recent issue of Current Biology on how capuchins handle stones. His adviser and co-author was Dorothy M. Fragaszy, the director of the Primate Behavior Laboratory at the university. Using video of the capuchins’ lifting rocks with both hands to slam them down on the hard palm nuts, he analyzed how high a monkey lifted a stone and how fast it brought it down. He found that the capuchins adjusted the force of a strike according to the condition of the nut after the previous strike. © 2015 The New York Times Company
by Andy Coghlan When a fly escapes being swatted, what is going on in its head? Is it as terrified as we would be after a close shave with death? Or is buzzing away from assailantsMovie Camera a momentary inconvenience that flies shrug off? It now seems that flies do become rattled. "In humans, fear is something that persists on a longer timescale than a simple escape reflex," says William Gibson of the California Institute of Technology in Pasadena, California. "Our observations suggest flies have a persistent state of defensive arousal, which is not necessarily fear, but which has some similarities to it." This doesn't mean that flies share the same emotional responses to fear as humans, but they do seem to have the same behavioural building blocks of fear as us. Evasive action Gibson and his colleagues exposed fruit flies to overhead shadows resembling aerial predators, such as birds. The more shadows they were exposed to, the more the flies resorted to evasive behaviour, such as hopping, jumping or freezing. When the shadow passed over once per second, by the time the shadow had fallen 10 times, the average running speed of the flies had doubled, for example. Their average number of hops trebled after just two passes. They also offered starved flies food, and part way through the meal threatened them with shadows. The more often the meal was interrupted, the longer the flies took to return to their meal after flying away. © Copyright Reed Business Information Ltd.
Tina Hesman Saey COLD SPRING HARBOR, N.Y. — Taming animals makes an impression on their DNA. Domesticated animals tend to have genetic variants that affect similar biological processes, such as brain and facial development and fur coloration. Alex Cagan of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, reported the results May 6 at the Biology of Genomes conference. Cagan and colleagues examined DNA in Norway rats (Rattus norvegicus) that had been bred for 70 generations to be either tame or aggressive toward humans. Docility was associated with genetic changes in 1,880 genes in the rats. American minks (Neovison vison) bred for tameness over 15 generations had tameness-associated variants in 525 genes, including 82 that were also changed in the rats. The researchers also compared other domesticated animals, including dogs, cats, pigs and rabbits, with their wild counterparts. The domestic species and the minks had tameness-associated changes in genes for epidermal growth factor and associated proteins that stimulate growth of cells. Those proteins are important for the movement of neural crest cells within an embryo. That finding seems to support a recent hypothesis that changes in neural crest cells could be responsible for domestication syndrome, physical traits, including floppy ears, spotted coats and juvenile faces, which accompany tameness in many domestic animals. © Society for Science & the Public 2000 - 2015.