by Helen Fields Hopping around in the Peruvian jungle, near the border with Brazil, is a menagerie of tiny poison dart frogs. Their wealth of colors and patterns—some have golden heads atop white-swirled bodies, others wear full-torso tattoos of black and neon-yellow stripes—act as the world's worst advertisement to predators: Don't eat me, I'm toxic. But why have so many designs evolved when a single one might do? Evolutionary biologist Mathieu Chouteau of the University of Montreal in Canada ventured into the rainforest to find out. He was on the trail of Ranitomeya imitator, a single species of poison dart frog that comes in about 10 different patterns. That variability should be confusing for predators, he says, because the warnings are supposed to be a message to them, and it would make more sense to give them only one design to keep track of. To figure out what was going on, Chouteau enlisted his girlfriend's help to make 3600 models of frogs, each 18 millimeters long. "It was, like, at least a month of working full-time," he says. They pressed black clay into frog-shaped molds and painted each one in one of two patterns: yellow striped or reticulated, like a giraffe, with green lines. They also made brown frogs as a nontoxic-looking control. Then Chouteau packed the frogs in his carryon baggage and flew to Peru. The models represent the frogs that live in two different sites: one in the Amazonian lowland and one in a valley at about 500 meters above sea level. The two sites are separated by a high ridge. In one very long day at each site, Chouteau set out 900 of the frogs on leaves along narrow trails used by locals to hunt in the forest. For the next 3 days, he went back and checked them to see whether the soft clay recorded evidence of attacks by birds. © 2010 American Association for the Advancement of Science

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 4: The Chemical Bases of Behavior: Neurotransmitters and Neuropharmacology
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Link ID: 15986 - Posted: 11.05.2011

By Tina Hesman Saey MONTREAL — Bigger, better human brains may be the result of a double dose of a gene that helps brain cells move around. At least twice in the past 3 million years, a gene called SRGAP2 has been duplicated within the human genome, says Megan Dennis of the University of Washington in Seattle. Dennis and her colleagues have now shown that extra copies of this gene may account for humans’ thicker brain cortex, the brain’s gray matter where thinking takes place. The team had previously discovered that SRGAP2 is one of 23 genes duplicated in humans but not in other primates. Dennis found that an ancient form of the gene, which is located on human chromosome 1, was partially duplicated on the same chromosome about 3.4 million years ago. That partial copy makes a shortened version of the SRGAP2 protein. Then, about 2.4 million years ago, a copy of the partial copy was created and added to the short arm of chromosome 1, Dennis reported October 13 at the International Congress of Human Genetics. But just having extra copies doesn’t mean the gene is evolutionarily important. So Dennis and her colleagues examined the duplicate genes in more than 150 people and found that the copy made 3.4 million years ago is missing in some people. But the younger version of the gene has become fixed in the human population, meaning that absolutely everyone has it. Millions of years may seem like a long time, but it is actually quite speedy for fixing duplicated genes, Dennis says. The rapid assimilation could indicate that the gene is important in human evolution. © Society for Science & the Public 2000 - 2011

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 0: ; Chapter 13: Memory, Learning, and Development
Link ID: 15913 - Posted: 10.15.2011

By Eric Michael Johnson Charles Darwin had more in common with chimpanzees than even he realized. Before he was universally known for his theory of natural selection, the young naturalist made a decision that has long been hailed as the type of behavior that fundamentally separates humans from other apes. In 1858, before Darwin published On the Origin of Species, his friend Alfred Russel Wallace​ mailed Darwin his own theory of evolution that closely matched what Darwin had secretly been working on for more than two decades. Instead of racing to publish and ignoring Wallace’s work, Darwin included Wallace’s outline alongside his own abstract so that the two could be presented jointly before the Linnean Society the following month. “I would far rather burn my whole book than that [Wallace] or any man should think that I had behaved in a paltry spirit,” Darwin wrote. This kind of prosocial behavior, a form of altruism that seeks to benefit others and promote cooperation, has now been found in chimps, the species that Darwin did more than any other human to connect us with. (This month's Science Agenda, about medical testing in chimps, notes other similarities that have been documented in chimps and humans.) In the study, published in the Proceedings of the National Academy of Sciences USA, primatologist Frans de Waal and his colleagues at the Yerkes National Primate Research Center at Emory University presented chimps with a simplified version of the choice that Darwin faced. Pairs of chimps were brought into a testing room where they were separated only by a wire mesh. On one side was a bucket containing 30 tokens that the chimpanzee could give to an experimenter for a food reward. Half of the tokens were of one color that resulted in only the chimpanzee that gave the token receiving a reward. The other tokens were of a different color that resulted in both chimpanzees receiving a food reward. If chimpanzees were motivated only by selfish interests, they would be expected to choose a reward only for themselves (or it should be 50–50 if they were choosing randomly). But individuals were significantly more likely to choose the prosocial outcome compared with the no-partner control. © 2011 Scientific American,

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 15: Emotions, Aggression, and Stress
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Link ID: 15868 - Posted: 10.04.2011

Our brains followed a twisting path of development through creatures that swam, crawled and walked the Earth long before we did. Here are a few of these animals, and how they helped make us what we are. Our single-celled ancestors had sophisticated machinery for sensing and responding to the environment. Once the first multicellular animals arose, this machinery was adapted for cell-to-cell communication. Specialised cells that could carry messages using electrical impulses and chemical signals – the first nerve cells – arose very early on. The first neurons were probably connected in a diffuse network across the body of a creature like this hydra. This kind of structure, known as a nerve net, can still be seen in the quivering bodies of jellyfish and sea anemones

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior
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Link ID: 15851 - Posted: 09.29.2011

by David Robson IT IS 30,000 years ago. A man enters a narrow cave in what is now the south of France. By the flickering light of a tallow lamp, he eases his way through to the furthest chamber. On one of the stone overhangs, he sketches in charcoal a picture of the head of a bison looming above a woman's naked body. In 1933, Pablo Picasso creates a strikingly similar image, called Minotaur Assaulting Girl. That two artists, separated by 30 millennia, should produce such similar work seems astonishing. But perhaps we shouldn't be too surprised. Anatomically at least, our brains differ little from those of the people who painted the walls of the Chauvet cave all those years ago. Their art, part of the "creative explosion" of that time, is further evidence that they had brains just like ours. How did we acquire our beautiful brains? How did the savage struggle for survival produce such an extraordinary object? This is a difficult question to answer, not least because brains do not fossilise. Thanks to the latest technologies, though, we can now trace the brain's evolution in unprecedented detail, from a time before the very first nerve cells right up to the age of cave art and cubism. The story of the brain begins in the ancient oceans, long before the first animals appeared. The single-celled organisms that swam or crawled in them may not have had brains, but they did have sophisticated ways of sensing and responding to their environment. "These mechanisms are maintained right through to the evolution of mammals," says Seth Grant at the Wellcome Trust Sanger Institute in Cambridge, UK. "That's a very deep ancestry." © Copyright Reed Business Information Ltd.

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Link ID: 15839 - Posted: 09.27.2011

by Ferris Jabr Slimy and often sluggish they may be, but some molluscs deserve credit for their brains – which, it now appears, they managed to evolve independently, four times. The mollusc family includes the most intelligent invertebrates on the planet: octopuses, squid and cuttlefishMovie Camera. Now, the latest and most sophisticated genetic analysis of their evolutionary history overturns our previous understanding of how they got so brainy. The new findings expand a growing body of evidence that in very different groups of animals – molluscs and mammals, for instance – central nervous systems evolved not once, but several times, in parallel. Kevin Kocot of Auburn University, Alabama, and his colleagues are responsible for the new evolutionary history of the mollusc family, which includes 100,000 living species in eight lineages. They analysed genetic sequences common to all molluscs and looked for differences that have accumulated over time: the more a shared sequence differs between two species, the less related they are. The findings, which rely on advanced statistical analyses, fundamentally rearrange branches on the mollusc family tree. In the traditional tree, snails and slugs (gastropods) are most closely related to octopuses, squid, cuttlefish and nautiluses (cephalopods), which appears to make sense in terms of their nervous systems: both groups have highly centralised nervous systems compared with other molluscs and invertebrates. Snails and slugs have clusters of ganglia – bundles of nerve cells – which, in many species, are fused into a single organ; cephalopods have highly developed central nervous systems that enable them to navigate a maze, use tools, mimic other species, learn from each other and solve complex problems. © Copyright Reed Business Information Ltd.

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 1: Biological Psychology: Scope and Outlook
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Link ID: 15812 - Posted: 09.17.2011

by Alison George He has already revealed that early humans interbred with Neanderthals and discovered a whole new type of hominin from its DNA alone. Now Svante Pääbo is setting his sights on even more exotic discoveries. He tells Alison George why he thinks the bombshells will keep coming Last year you revealed a previously unknown type of hominin, called the Denisovans, from DNA in a pinkie bone found in a cave in Denisova, Siberia. Tell me about this. We knew people had lived in this cave, but thought they were either Neanderthals or modern humans. When we sequenced the DNA, I was in the US so a postdoc called me to tell me the results. He said: "Are you sitting down?" because it was immediately clear this was some other form of human; not a Neanderthal, not a modern human. We were totally shocked. This is the first time that a new form of human has been defined totally from molecular data, not from the morphology of fossils. I think this will happen much more in the future - that just from a tiny speck of bone we can determine the whole genome and reconstruct much of the history. You recently visited this cave. What was it like? The cave is in the Altai mountains in central Asia and it was the first time I had seen it. It is really beautiful. It's big, almost cathedral-like with light coming in through a natural chimney. And you know that in this cave there have been both the Denisovans and modern humans and perhaps Neanderthals too. I went there for a meeting where anatomists, palaeontologists and archaeologists came together for the first time to try to sort out what we can say about this group of humans. © Copyright Reed Business Information Ltd.

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior
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Link ID: 15770 - Posted: 09.06.2011

by Michael Marshall WHEN wondering about the origins of our brain, don't look to Homo sapiens, chimpanzees, fish or even wormsMovie Camera. Many key components first appeared in single-celled organisms, long before animals, brains and even nerve cells existed. Dirk Fasshauer of the University of Lausanne, Switzerland, and colleagues were studying a pair of essential neural proteins called Munc18/syntaxin1 when they decided to look for them in very simple, single-celled organisms. Choanoflagellates are aquatic organisms found in oceans and rivers around the globe. Being a single cell, they do not have nerves, yet the team found both proteins in the choanoflagellate Monosiga brevicollis, and the interaction between the two was the same as in neurons (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1106189108). These proteins are found in every nerve cell and control the release of the chemicals which neurons use to talk to each other, called neurotransmitters. The finding is intriguing on its own, but much more significant when combined with a growing body of evidence that essential brain components evolved in choanoflagellates before multicellular life appeared. In 2008, Xinjiang Cai of Duke University in Durham, North Carolina, discovered that M. brevicollis has the same calcium channels in its cells as those used by neurons (Molecular Biology and Evolution, DOI: 10.1093/molbev/msn077). Then, in 2010, it emerged that M. brevicollis also has several proteins that neurons use to process signals from their neighbours (BMC Evolutionary Biology, DOI: 10.1186/1471-2148-10-34). © Copyright Reed Business Information Ltd

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Link ID: 15757 - Posted: 09.03.2011

Matt Kaplan The discovery of stone axes in the same sediment layer as cruder tools indicates that hominins with differing tool-making technologies may have coexisted. The axes, found in Kenya by Christopher Lepre, a palaeontologist at Columbia University in New York, and his team are estimated to be around 1.76 million years old. That's 350,000 years older than any other complex tools yet discovered. The finding, described today in Nature1, includes another important discovery: the hand axes, usually associated with the emergence around 1.5 million years ago of Homo erectus as the dominant hominin species, were found alongside primitive chopping tools that had already been in use for at least a million years. "This supports the idea that the two earliest stone-tool manufacturing techniques and traditions were, at least sometimes, utilized contemporaneously," says palaeoanthropologist Briana Pobiner at the Smithsonian Institution in Washington DC. Chip off the old block The hand axes, which have a distinctive, carefully made oval shape, are part of the Acheulian technology — those tools thought to have been developed around 1.6 million years ago. The more primitive tools, typically chunks of stone with crudely-chipped edges, belong to the earlier Oldowan toolkit. Because H. erectus is often associated with Acheulian tools, Lepre and his colleagues suggest that the hand axes they found might have been made by H. erectus, and the Oldowan tools by the less cognitively-capable Homo habilis. © 2011 Nature Publishing Group,

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Link ID: 15752 - Posted: 09.01.2011

By Matt McGrath Science reporter, BBC World Service Sexual relations between ancient humans and their evolutionary cousins are critical for our modern immune systems, researchers report in Science journal. Mating with Neanderthals and another ancient group called Denisovans introduced genes that help us cope with viruses to this day, they conclude. Previous research had indicated that prehistoric interbreeding led to up to 4% of the modern human genome. The new work identifies stretches of DNA derived from our distant relatives. In the human immune system, the HLA (human leucocyte antigen) family of genes plays an important role in defending against foreign invaders such as viruses. The authors say that the origins of some HLA class 1 genes are proof that our ancient relatives interbred with Neanderthals and Denisovans for a period. At least one variety of HLA gene occurs frequently in present day populations from West Asia, but is rare in Africans. The researchers say that is because after ancient humans left Africa some 65,000 years ago, they started breeding with their more primitive relations in Europe, while those who stayed in Africa did not. BBC © 2011

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 0: ; Chapter 11: Emotions, Aggression, and Stress
Link ID: 15727 - Posted: 08.27.2011

By ALEXANDRA HOROWITZ and AMMON SHEA HUMANS have long been fascinated with animal intelligence. Scientific studies have asked if animals use language or tools; have culture; can imitate, cooperate, empathize or deceive. Inevitably, the results of these studies invite comparison with our own cognitive faculties. In such comparisons, humans nearly always come out on top. An impartial observer might suggest that the deck is stacked. After all, we are the ones running these tests. But if we look at some of the subtler aspects of animal behavior, the beasts begin to offer surprisingly stiff competition. A few recent research papers describe animal competence at social and cognitive tasks that humans often struggle with — mastering conversational etiquette, understanding botanical classification, competing on game shows and figuring out how to get a drink when you’re thirsty and the only glass of water is glued to the table and your hands are tied behind your back. “Aping Expressions? Chimpanzees Produce Distinct Laugh Types When Responding to Laughter of Others,” in the journal Emotion (2011). You’re at a dinner party. Your hostess regales you with a long, meandering tale of her recent back surgery. It ends with attempted humor: she laughs and glances at you. You laugh in response, trying to convey an appreciation for her humor that you don’t actually feel. Congratulations: you are now at the level of social politeness of chimpanzees. © 2011 The New York Times Company

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 17: Learning and Memory
Related chapters from MM:Chapter 0: ; Chapter 13: Memory, Learning, and Development
Link ID: 15701 - Posted: 08.23.2011

Gayathri Vaidyanathan Thump! Thump! Thump! As the hollow sound echoes through the Liberian rainforest, Vera Leinert and her fellow researchers freeze. Silently, Leinert directs the guide to investigate. Jefferson 'Bola' Skinnah, a ranger with the Liberian Forestry Development Authority, stalks ahead, using the thumping to mask the sound of his movement. In a sunlit opening in the forest, Skinnah spots a large adult chimpanzee hammering something with a big stone. The chimpanzee puts a broken nut into its mouth then continues pounding. When Skinnah tries to move closer, the chimp disappears into the trees. By the time Leinert and her crew get to the clearing, the animal is long gone. For the past year, Leinert has been trekking through Sapo National Park, Liberia's first and only protected reserve, to study its chimpanzee population. A student volunteer at the Max Planck Institute for Evolutionary Anthropology (EVA) in Leipzig, Germany, Leinert has never seen her elusive subjects in the flesh but she knows some of them well. There's an energetic young male with a big belly who hammers nuts so vigorously he has to grab a sapling for support. There are the stronger adults who can split a nut with three blows. And there are the mothers who parade through the site with their babies. They've all been caught by video cameras placed strategically throughout Sapo. Chimpanzees in the wild are notoriously difficult to study because they flee from humans — with good reason. Bushmeat hunting and human respiratory diseases have decimated chimpanzee populations1, while logging and mining have wiped out their habitat. Population numbers have plunged — although no one knows by exactly how much because in most countries with great apes, the animals have never been properly surveyed. © 2011 Nature Publishing Group,

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Link ID: 15690 - Posted: 08.20.2011

Jo Marchant Hyenas can count up to three. Researchers playing recorded calls to the wily carnivores found that wild spotted hyenas (Crocuta crocuta) responded differently depending on whether they heard one, two or three individuals. The result adds numerical assessment to the list of cognitive abilities that hyenas share with primates, and supports the idea that living in complex social groups — as both primates and hyenas do — is key to the evolution of big brains. Sarah Benson-Amram, a zoologist at Michigan State University in East Lansing, and her colleagues played recordings of hyena calls, or whoops, to members of two hyena clans in the Masai Mara National Reserve in southwestern Kenya1. The recordings were made in Tanzania, Malawi and Senegal, so the calls were unfamiliar to the Kenyan clans, and would have been interpreted as belonging to potential intruders. The recordings each consisted of three bouts of whooping, from one, two or three different animals. In 39 trials involving resting adults — mostly lone females — Benson-Amram measured how vigilant the animals became while the recordings were playing by comparing the amount of time they spent facing the speaker with the amount of time they spent looking away or resting. Although some females became equally watchful in response to all of the recordings, most of the animals distinguished between one, two or three intruders, their attentiveness increasing with the number of unique calls they heard. The finding is published in Animal Behaviour. © 2011 Nature Publishing Group,

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 19: Language and Hemispheric Asymmetry
Related chapters from MM:Chapter 0: ; Chapter 15: Language and Our Divided Brain
Link ID: 15689 - Posted: 08.20.2011

By Susan Milius Acts of apparent altruism in European paper wasps can be explained by plain old self-interest, a new study finds. Polistes dominulus females can either establish their own nests to raise young or join other females for joint homemaking. In those joint nests, though, one female fights her way to the top and does most of the egg-laying while the others do most of the drudge work in taking care of the top wasp’s young. When a subordinate helps her sister, that’s not hard to explain: The underling may not end up with her own offspring, but her reproductive success includes an indirect share of her sister’s brood, because relatives share genes. Forgoing her own direct offspring counts as a kind of altruism, in which an individual helping kin trades direct for indirect benefit. Either way, the wasp’s self-interest is served. But some 15 to 35 percent of co-queens slaving away are not closely related to the top wasp, so biologists have been puzzled about why those strangely helpful females don’t go off to found their own nests. They do it because joining an unrelated queen’s nest offers a chance of grabbing the throne, says Ellouise Leadbeater of the Zoological Society of London. She and her colleagues tracked the fortunes of 1,113 foundresses in 228 nests in southern Spain. In this epic population analysis, females that started out as subordinates to a nonrelative occasionally took over the whole nest and laid their own eggs. Their triumphs were rare but dramatic enough so that, overall, the strategy worked out better than being a single mom: Lone nest foundresses hardly managed to produce any offspring, the researchers report in the Aug. 12 Science. © Society for Science & the Public 2000 - 2011

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Link ID: 15672 - Posted: 08.13.2011

by Sara Reardon Giving birth to twins is rough, especially in rural regions. They tend to be born smaller and weaker than single babies, and their mothers have more complications during childbirth. So why did twinning evolve? A new study in Gambia finds that women who have twins also tend to have single babies that are heavier than average at birth, which makes them more likely to survive. Since the 1950s, the U.K. Medical Research Council has been collecting data and providing medical care in Gambia. It's a highly unusual data set, says evolutionary anthropologist Rebecca Sear of Durham University in the United Kingdom, with a length and thoroughness that's "unheard of for populations without good access to medical care." Evolutionary biologist Ian Rickard of the University of Sheffield in the United Kingdom wondered whether the data could shed light on the biology of twins. Rickard and colleagues looked at the birth weights of 1889 single babies born to Gambian women over a 30-year period. Then they examined which of these mothers also had twins. Single babies born after twins were 226 grams heavier on average than single babies whose mothers had no twins, the team reports today in Biology Letters. This wasn't surprising, Rickard says, because carrying twins is thought to improve blood flow to the uterus and "prime" it for later children, allowing them to more easily receive nutrients. What did surprise the researchers was the discovery that when single babies were born before twins, the singles tended to be 134 grams heavier than average. © 2010 American Association for the Advancement of Science

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 0: ; Chapter 13: Memory, Learning, and Development
Link ID: 15665 - Posted: 08.11.2011

By Alexandra Witze There’s just no getting ahead when you’re a hobbit. Anthropologists are arguing yet again over whether a tiny 18,000-year-old Indonesian skull represents a separate species of little human cousins, or an ordinary Homo sapiens with an abnormally small head. New data compare the fossil to a large group of modern humans with microcephaly, a genetic condition that makes the head smaller than usual. Measurements of the hobbit skull suggest its proportions fall within the range of microcephalic Homo sapiens, researchers report August 8 in the Proceedings of the National Academy of Sciences. “Previously published papers that seemed to show that it can’t be a microcephalic are open to doubt,” says coauthor Ralph Holloway, an anthropologist at Columbia University in New York. The hobbit story began in 2003, when archaeologists unearthed the skull and other bones of a female hominid on the island of Flores. Her discoverers argued she represented a member of a human genus that had survived until relatively recently, and dubbed it Homo floresiensis. But some scientists charged that because the hobbit’s skull is so small, it might have just been a microcephalic Homo sapiens. To test that question, anthropologist Dean Falk of Florida State University in Tallahassee compared the skull’s internal dimensions to those of nine microcephalic humans and 10 normal humans. In a 2007 paper, she concluded the hobbit skull was still best assigned to its own species. © Society for Science & the Public 2000 - 2011

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Link ID: 15657 - Posted: 08.09.2011

by Helen Fields Despite our wars and crime, humans tend to be nice. We bake for our neighbors, give directions to strangers, and donate money to far-off disaster victims. But does the same go for our closest cousin, the chimpanzee? A new study suggests that it does. People who study chimpanzees in the field have known for a long time that the apes console their comrades when they're upset and support each other in a fight. And when one chimp has a good hunting day and kills a nice, juicy monkey, it shares the meat with the other members of its group. But scientists have found that chimps don't share in lab experiments, creating a bit of a primatology mystery. For instance, when researchers gave captive chimps the opportunity to get rewards just for themselves or for both themselves and another chimpanzee from an apparatus with multiple interconnected trays, the apes were equally likely to choose the selfish and sharing options. Comparative psychologist Victoria Horner of Emory University in Atlanta thought she knew the reason why experiments didn't find sharing: the experimental setups other scientists used to test the chimps were just too confusing—"tables with pulley systems and whatnot." For one study, she says, "I had to read it several times before I understood the apparatus, and I'm a human." She thinks the chimps didn't understand how what they did affected their partner. With her colleagues at Emory, including renown primatologist Frans de Waal, Horner devised a new way to test chimps' generosity. "We did the same basic idea but from a more chimpy perspective," she says. In each experiment, two female chimps that live at the Yerkes National Primate Research Center in Lawrenceville, Georgia, were put in side-by-side rooms with a mesh-covered opening between them. Both chimps had been trained to "buy" food from the researchers with tokens, colored, 5-centimeter-long pieces of PVC pipe. © 2010 American Association for the Advancement of Science.

Related chapters from BP6e: Chapter 6: Evolution of the Brain and Behavior; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 0: ; Chapter 11: Emotions, Aggression, and Stress
Link ID: 15656 - Posted: 08.09.2011

THE extraordinary success of Homo sapiens is a result of four things: intelligence, language, an ability to manipulate objects dexterously in order to make tools, and co-operation. Over the decades the anthropological spotlight has shifted from one to another of these as the prime mover of the package, and thus the fundament of the human condition. At the moment co-operation is the most fashionable subject of investigation. In particular, why are humans so willing to collaborate with unrelated strangers, even to the point of risking being cheated by people whose characters they cannot possibly know? Evidence from economic games played in the laboratory for real money suggests humans are both trusting of those they have no reason to expect they will ever see again, and surprisingly unwilling to cheat them—and that these phenomena are deeply ingrained in the species’s psychology. Existing theories of the evolution of trust depend either on the participants being relatives (and thus sharing genes) or on their relationship being long-term, with each keeping count to make sure the overall benefits of collaboration exceed the costs. Neither applies in the case of passing strangers, and that has led to speculation that something extraordinary, such as a need for extreme collaboration prompted by the emergence of warfare that uses weapons, has happened in recent human evolution to promote the emergence of an instinct for unconditional generosity. Leda Cosmides and John Tooby, two doyens of the field, who work at the University of California, Santa Barbara, do not agree. They see no need for extraordinary mechanisms and the latest study to come from their group (the actual work was done by Andrew Delton and Max Krasnow, who have just published the results in the Proceedings of the National Academy of Sciences) suggests they are right. It also shows the value of applying common sense to psychological analyses—but then of backing that common sense with some solid mathematical modelling. © The Economist Newspaper Limited 2011.

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Link ID: 15642 - Posted: 08.04.2011

by Michael Balter "This town ain't big enough for the both of us," says ranch foreman Nick Grindell to lawman Tim Barrett in the 1932 film The Western Code. Biologists know the principle well: Two animal species can rarely occupy the same niche. The same, it seems, goes for human populations. A new study of Neandertal and modern human sites in the south of France concludes that the moderns so greatly outnumbered their evolutionary cousins that Neandertals had little choice but to go extinct. For more than 100,000 years, Neandertals had Europe all to themselves. Then, beginning roughly 40,000 years ago, modern humans—Homo sapiens—began migrating into the continent from Africa. Although researchers debate how long the Neandertals hung around, these ancient humans probably did not survive much longer than 5000 years. Just why they disappeared is also a matter of contention, but most experts agree that H. sapiens was able to outgun its rival in either direct or indirect competition for food and other resources. Some genetic studies, based on both modern and ancient DNA sequences, have suggested that modern human population growth quickly outstripped that of Neandertals, but estimating population levels from these kinds of data is very difficult and inexact. So Paul Mellars and Jennifer French, archaeologists at the University of Cambridge in the United Kingdom, decided to look directly at the archaeological evidence for the presence of both groups in the region where the most excavations have taken place: southwestern France, including the lush Dordogne region, as well known for its prehistoric sites as for its wine and foie gras. © 2010 American Association for the Advancement of Science

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Link ID: 15625 - Posted: 07.30.2011

by Carl Zimmer In 1758 the Swedish taxonomist Carolus Linnaeus dubbed our species Homo sapiens, Latin for “wise man.” It’s a matter of open debate whether we actually live up to that moniker. If Linnaeus had wanted to stand on more solid ground, he could have instead called us Homo megalencephalus: “man with a giant brain.” Regardless of how wisely we may use our brains, there’s no disputing that they are extraordinarily big. The average human brain weighs in at about three pounds, or 1,350 grams. Our closest living relatives, the chimpanzees, have less than one-third as much brain—just 384 grams. And if you compare the relative size of brains to bodies, our brains are even more impressive. As a general rule, mammal species with big bodies tend to have big brains. If you know the weight of a mammal’s body, you can make a fairly good guess about how large its brain will be. As far as scientists can tell, this rule derives from the fact that the more body there is, the more neurons needed to control it. But this body-to-brain rule isn’t perfect. Some species deviate a little from it. A few deviate a lot. We humans are particularly spectacular rule breakers. If we were an ordinary mammal species, our brains would be about one-sixth their actual size. Competing theories seek to explain the value of a big brain. One idea, championed by psychologist Robin Dunbar of the University of Oxford, is that complicated social lives require big brains (pdf). A relatively large-brained baboon can make a dozen alliances while holding grudges against several rivals. Humans maintain far more, and more complicated, relationships. © 2011, Kalmbach Publishing Co.

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Link ID: 15623 - Posted: 07.28.2011