Chapter 6. Evolution of the Brain and Behavior
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By Virginia Morell Two years ago, scientists showed that dolphins imitate the sounds of whales. Now, it seems, whales have returned the favor. Researchers analyzed the vocal repertoires of 10 captive orcas (Orcinus orca), three of which lived with bottlenose dolphins (Tursiops truncatus) and the rest with their own kind. Of the 1551 vocalizations these seven latter orcas made, more than 95% were the typical pulsed calls of killer whales. In contrast, the three orcas that had only dolphins as pals busily whistled and emitted dolphinlike click trains and terminal buzzes, the scientists report in the October issue of The Journal of the Acoustical Society of America. (Watch a video as bioacoustician and co-author Ann Bowles describes the difference between killer whale and orca whistles.) The findings make orcas one of the few species of animals that, like humans, is capable of vocal learning—a talent considered a key underpinning of language. © 2014 American Association for the Advancement of Science.
by Michael Marshall When we search for the seat of humanity, are we looking at the wrong part of the brain? Most neuroscientists assume that the neocortex, the brain's distinctive folded outer layer, is the thing that makes us uniquely human. But a new study suggests that another part of the brain, the cerebellum, grew much faster in our ape ancestors. "Contrary to traditional wisdom, in the human lineage the cerebellum was the part of the brain that accelerated its expansion most rapidly, rather than the neocortex," says Rob Barton of Durham University in the UK. With Chris Venditti of the University of Reading in the UK, Barton examined how the relative sizes of different parts of the brain changed as primates evolved. During the evolution of monkeys, the neocortex and cerebellum grew in tandem, a change in one being swiftly followed by a change in the other. But starting with the first apes around 25 million years ago through to chimpanzees and humans, the cerebellum grew much faster. As a result, the cerebellums of apes and humans contain far more neurons than the cerebellum of a monkey, even if that monkey were scaled up to the size of an ape. "The difference in ape cerebellar volume, relative to a scaled monkey brain, is equal to 16 billion extra neurons," says Barton. "That's the number of neurons in the entire human neocortex." © Copyright Reed Business Information Ltd.
Carl Zimmer As much as we may try to deny it, Earth’s cycle of day and night rules our lives. When the sun sets, the encroaching darkness sets off a chain of molecular events spreading from our eyes to our pineal gland, which oozes a hormone called melatonin into the brain. When the melatonin latches onto neurons, it alters their electrical rhythm, nudging the brain into the realm of sleep. At dawn, sunlight snuffs out the melatonin, forcing the brain back to its wakeful pattern again. We fight these cycles each time we stay up late reading our smartphones, suppressing our nightly dose of melatonin and waking up grumpy the next day. We fly across continents as if we could instantly reset our inner clocks. But our melatonin-driven sleep cycle lags behind, leaving us drowsy in the middle of the day. Scientists have long wondered how this powerful cycle got its start. A new study on melatonin hints that it evolved some 700 million years ago. The authors of the study propose that our nightly slumbers evolved from the rise and fall of our tiny oceangoing ancestors, as they swam up to the surface of the sea at twilight and then sank in a sleepy fall through the night. To explore the evolution of sleep, scientists at the European Molecular Biology Laboratory in Germany study the activity of genes involved in making melatonin and other sleep-related molecules. Over the past few years, they’ve compared the activity of these genes in vertebrates like us with their activity in a distantly related invertebrate — a marine worm called Platynereis dumerilii. The scientists studied the worms at an early stage, when they were ball-shaped 2-day-old larvae. The ocean swarms with juvenile animals like these. Many of them spend their nights near the ocean surface, feeding on algae and other bits of food. Then they spend the day at lower depths, where they can hide from predators and the sun’s ultraviolet rays. © 2014 The New York Times Company
It's not just humans who want the latest gadget. Wild chimpanzees that see a friend making and using a nifty new kind of tool are likely to make one for themselves, scientists report. "Our study adds new evidence supporting the hypothesis that some of the behavioural diversity seen in wild chimpanzees is the result of social transmission and can therefore be interpreted as cultural," an international research team writes today in the journal PLOS ONE. The findings suggest that the ability of individuals to learn from one another originated long ago in a common ancestor of chimpanzees and humans, the researchers add. "This study tells us that chimpanzee culture changes over time, little by little, by building on previous knowledge found within the community," said Thibaud Gruber, a co-author of the study, in a statement. "This is probably how our early ancestors' cultures also changed over time." Scientists already knew that chimpanzees in different groups have certain behaviours unique to their group, such as using a particular kind of tool. They suspected that wild chimpanzees learn those behaviours from other chimpanzees within their group, as scientists have observed in captive chimps. But they could never be sure. The new study documents the spread of two new behaviours among chimpanzees living in Uganda's Budongo Forest. It shows that chimps learned one of them — the making and use of a new tool called a moss sponge — by observing other chimps who had already adopted the behaviour. Chimps dip the tool in water and then put it in their mouth to drink. © CBC 2014
Link ID: 20141 - Posted: 10.01.2014
By Jia You Fish larvae emit sound—much to the surprise of biologists. A common coral reef fish in Florida, the gray snapper—Lutjanus griseus (pictured above)—hatches in the open ocean and spends its juvenile years in food-rich seagrass beds hiding from predators before settling in the reefs as an adult. To study how larval snappers orient themselves in the dark, marine biologists deployed transparent acrylic chambers equipped with light and sound sensors under the water to capture the swimming schools as they travel to the seagrass beds on new-moon nights. The larval snappers make a short “knock” sound that adults also make, as well as a long “growl” sound, the team reports online today in Biology Letters. The researchers suspect that the larvae use the acoustic signals to communicate with one another and stay together in schools. If so, human noise pollution could be interrupting their communications—even adult fish have been found to “yell” to be heard above boat noises. © 2014 American Association for the Advancement of Science.
Wild marmosets in the Brazilian forest can learn quite successfully from video demonstrations featuring other marmosets, Austrian scientists have reported, showing not only that marmosets are even better learners than previously known, but that video can be used successfully in experiments in the wild. Tina Gunhold, a cognitive biologist at the University of Vienna, had worked with a population of marmoset monkeys in a bit of Brazilian forest before this particular experiment. The forest is not wilderness. It lies near some apartment complexes, and the marmosets are somewhat used to human beings. But the monkeys are wild, and each extended family group has its own foraging territory. Dr. Gunhold and her colleagues reported in the journal Biology Letters this month that they had tested 12 family groups, setting up a series of video monitors, each with a kind of complicated box that they called an “artificial fruit.” All the boxes contained food. Six of the monitors showed just an unchanging image of a marmoset near a similar box. Three of them showed a marmoset opening the box by pulling a drawer, and three others a marmoset lifting a lid to get at the food. Marmosets are very territorial and would not tolerate a strange individual on their turf, but the image of a strange marmoset on video didn’t seem to bother them. Individual marmosets “differed in their reactions to the video,” Dr. Gunhold said. “Some were more shy, some more bold. The younger ones were more attracted to the video, perhaps because of greater curiosity.” © 2014 The New York Times Company
Posted by James Owen in Weird & Wild Bigger males may get a lot of attention, but sometimes being smaller—and sneakier—is more successful when it comes to mating. In the East African cichlid fish, Lamprologus callipterus, males come in two sizes: giants or dwarves that are 40 times smaller than their beefier rivals. (Watch a video of male cichlid fish fighting.) It’s an example of male polymorphism, a phenomenon in which males of the same species take different forms. Though people vary in height, men don’t come in two different sizes like the cichlids. Several research studies suggest that tall men—those over 5’7″—are more successful in dating and in their careers—but they get divorced at higher rates. But the variation in L. callipterus, which are found only in Lake Tanganyika (map), is “the most extreme there is,” said Michael Taborsky, co-director of the Institute of Ecology and Evolution at the University of Bern, Switzerland. “It’s an enormous size difference.” In a new study, published September 17 in the Proceedings of the Royal Society B, Taborsky and his team linked this gulf in size to the female’s unusual habit of laying eggs in empty snail shells. To attract females, the giant males collect hundreds of these shells, using their mouths to create nesting sites. But while their hefty build is ideal for lugging about the heavy shells and chasing off rivals, the giants can’t access the chambers of their female harem, instead releasing their sperm outside the shell, Taborsky explained. (Also see “Small Squid Have Bigger Sperm—And Their Own Sex Position.”) © 1996-2013 National Geographic Societ
Keyword: Sexual Behavior
Link ID: 20127 - Posted: 09.29.2014
by Greg Laden I heard yesterday that my friend and former advisor Irven DeVore died. He was important, amazing, charming, difficult, harsh, brilliant, fun, annoying. My relationship to him as an advisee and a friend was complex, important to me for many years, and formative. For those who don’t know he was instrumental in developing several subfields of anthropology, including behavioral biology, primate behavioral studies, hunter-gatherer research, and even ethnoarchaeology. He was a cultural anthropologist who realized during his first field season that a) he was not cut out to be a cultural anthropologist and b) most of the other cultural anthropologists were not either. Soon after he became Washburn’s student and independently invented the field study of complex social behavior in primates (though some others were heading in that direction at the same time), producing his famous work on the baboons of Kenya’s Nairobi National Park. For many years, what students learned about primate behavior, they learned from that work. Later he and Richard Lee, along with John Yellen, Alison Brooks, Henry Harpending, and others started up the study of Ju/’hoansi Bushmen along the Namibian/Botswana border. One of the outcomes of that work was the famous Werner Gren conference and volume called “Man the Hunter.” That volume has two roles in the history of anthropology. First, it launched modern forager studies. Second, it became one of the more maligned books in the field of Anthropology. I have yet to meet a single person who has a strong criticism of that book that is not based on having not read it. For many years, much of what students learned about human foragers, they learned from that work.
Link ID: 20114 - Posted: 09.25.2014
By John Horgan On this blog, in my book The End of War and elsewhere (see Further Reading and Viewing), I have knocked the deep roots theory of war, which holds that war stems from an instinct deeply embedded in the genes of our male ancestors. Inter-community killings are rare among chimpanzees and non-existent among bonobos, according to a new report in Nature, undercutting the theory that the roots of war extend back to the common ancestor of humans and chimps. Proponents of this theory—notably primatologist Richard Wrangham—claim it is supported by observations of inter-community killings by chimpanzees, Pan troglodytes, our closest genetic relatives. Skeptics, including anthropologists Robert Sussman and Brian Ferguson, have pointed out that chimpanzee violence might be not an adaptation but a response to environmental circumstances, such as human encroachment. This “human impacts” hypothesis is rejected in a new report in Nature by a coalition of 30 primatologists, including Wrangham and lead author Michael Wilson. In “Lethal aggression in Pan is better explained by adaptive strategies than human impacts,” Wilson et al. analyze 152 killings in 18 chimpanzee communities and find “little correlation with human impacts.” Given that the primary interest in chimp violence is its alleged support of the deep-roots theory, it might seem odd, at first, that Wilson et al. do not mention human warfare. Actually, this omission is wise, because the Nature report undermines the deep-roots theory of war, and establishes that the “human impact” issue is a red herring. © 2014 Scientific American,
By Virginia Morell Living in a complex social world—one with shifting alliances and competitors—is often cited as the key reason humans, dolphins, and spotted hyenas evolved large brains. Now, researchers say that social complexity also underlies the braininess of parrots, which have big brains relative to their body size. To understand the social lives of these birds, the scientists observed wild populations of monk parakeets (Myiopsitta monachus), a small parrot, in Argentina and captive ones in Florida. They recorded how often the birds (pictured) were seen with other individuals and how they interacted—and then analyzed the parakeets’ social networks. The birds, the researchers report online today in The Auk: Ornithological Advances, prefer to spend time with one specific individual, usually their mate. In the captive populations, the birds also had strong associations with one or two other individuals, numerous more moderate relationships, and only a few that were weak. The scientists also recorded aggressive interactions among the captive birds, revealing that monk parakeets have a dominance hierarchy based on which birds won or lost confrontations. Thus, the parakeets’ society has layers of relationships, similar to those documented in other big-brained animals. Living in such a society requires that the birds recognize and remember others, and whether they are friend or foe—mental tasks that are thought to be linked to the evolution of significant cognitive skills. © 2014 American Association for the Advancement of Science
Link ID: 20087 - Posted: 09.18.2014
By Sarah Zielinski The marshmallow test is pretty simple: Give a child a treat, such as a marshmallow, and promise that if he doesn’t eat it right away, he’ll soon be rewarded with a second one. The experiment was devised by Stanford psychologist Walter Mischel in the late 1960s as a measure of self-control. When he later checked back in with kids he had tested as preschoolers, those who had been able to wait for the second treat appeared to be doing better in life. They tended to have fewer behavioral or drug-abuse problems, for example, than those who had given in to temptation. Most attempts to perform this experiment on animals haven’t worked out so well. Many animals haven’t been willing to wait at all. Dogs, primates, and some birds have done a bit better, managing to wait at least a couple of minutes before eating the first treat. The best any animal has managed has been 10 minutes—a record set earlier this year by a couple of crows. The African grey parrot is a species known for its intelligence. Animal psychologist Irene Pepperberg, now at Harvard, spent 30 years studying one of these parrots, Alex, and showed that the bird had an extraordinary vocabulary and capacity for learning. Alex even learned to add numerals before his death in 2007. Could an African grey pass the marshmallow test? Adrienne E. Koepke of Hunter College and Suzanne L. Gray of Harvard University tried the experiment on Pepperberg’s current star African grey, a 19-year-old named Griffin. In their test, a researcher took two treats, one of which Griffin liked slightly better, and put them into cups. Then she placed the cup with the less preferred food in front of Griffin and told him, “wait.” She took the other cup and either stood a few feet away or left the room. After a random amount of time, from 10 seconds to 15 minutes, she would return. If the food was still in the cup, Griffin got the nut he was waiting for. Koepke and colleagues presented their findings last month at the Animal Behavior Society meeting at Princeton. © 2014 The Slate Group LLC.
// by Richard Farrell Conventional thinking has long held that pelvic bones in whales and dolphins, evolutionary throwbacks to ancestors that once walked on land, are vestigial and will disappear millions of years from now. But researchers from University of Southern California and the Natural History Museum of Los Angeles County (NHM) have upended that assumption. The scientists argue in a paper just published in the journal Evolution that cetacean (whale and dolphin) pelvic bones certainly do have a purpose and that they're specifically targeted, by selection, for mating. The muscles that control a cetacean's penis are attached to the creature's pelvic bones. Matthew Dean, assistant professor at the USC Dornsife College of Letters, Arts and Sciences, and Jim Dines, collections manager of mammalogy at NHM, wanted to find out if pelvic bones could be evolutionarily advantageous by impacting the overall amount of control an individual creature has with its penis. The pair spent four years examining whale and dolphin pelvic bones, using a 3D laser scanner to study the shape and size of the samples in extreme detail. Then they gathered as much data as they could find -- reaching back to whaler days -- on whale testis size relative to body mass. The testis data was important because in nature, species in "promiscuous," competitive mating environments (where females mate with multiple males) develop larger testes, relative to their body mass, in order to outdo the competition. © 2014 Discovery Communications, LLC.
Ewen Callaway Caffeine's buzz is so nice it evolved twice. The coffee genome has now been published, and it reveals that the coffee plant makes caffeine using a different set of genes from those found in tea, cacao and other perk-you-up plants. Coffee plants are grown across some 11 million hectares of land, with more than two billion cups of the beverage drunk every day. It is brewed from the fermented, roasted and ground berries of Coffea canephora and Coffea arabica, known as robusta and arabica, respectively. An international team of scientists has now identified more than 25,000 protein-making genes in the robusta coffee genome. The species accounts for about one-third of the coffee produced, much of it for instant-coffee brands such as Nescafe. Arabica contains less caffeine, but its lower acidity and bitterness make it more flavourful to many coffee drinkers. However, the robusta species was selected for sequencing because its genome is simpler than arabica’s. Caffeine evolved long before sleep-deprived humans became addicted to it, probably to defend the coffee plant against predators and for other benefits. For example, coffee leaves contain the highest levels of caffeine of any part of the plant, and when they fall on the soil they stop other plants from growing nearby. “Caffeine also habituates pollinators and makes them want to come back for more, which is what it does to us, too,” says Victor Albert, a genome scientist at the University of Buffalo in New York, who co-led the sequencing effort. The results were published on 4 September in Science1. © 2014 Nature Publishing Group
by Sandrine Ceurstemont Screening an instructional monkey movie in a forest reveals that marmosets do not only learn from family members: they also copy on-screen strangers. It is the first time such a video has been used for investigations in the wild. Tina Gunhold at the University of Vienna, Austria, and her colleagues filmed a common marmoset retrieving a treat from a plastic device. They then took the device to the Atlantic Forest near Aldeia in Pernambuco, Brazil, and showed the movie to wild marmosets there. Although monkeys are known to learn from others in their social group, especially when they are youngMovie Camera, little is known about their ability to learn from monkeys that do not belong to the same group. Marmosets are territorial, so the presence of an outsider – even a virtual one on a screen – could provoke an attack. "We didn't know if wild marmosets would be frightened of the video box but actually they were all attracted to it," says Gunhold. Compared to monkeys shown a static image of the stranger, video-watching marmosets were more likely to manipulate the device, typically copying the technique shown (see video). Young monkeys spent more time near the video box than older family members, suggesting that they found the movie more engaging – although as soon as one monkey mastered the task, it was impossible to tell whether the others were learning from the video or from their relative. "We think it's a combination of both," says Gunhold. © Copyright Reed Business Information Ltd.
By Kate Wong In 1871 Charles Darwin surmised that humans were evolutionarily closer to the African apes than to any other species alive. The recent sequencing of the gorilla, chimpanzee and bonobo genomes confirms that supposition and provides a clearer view of how we are connected: chimps and bonobos in particular take pride of place as our nearest living relatives, sharing approximately 99 percent of our DNA, with gorillas trailing at 98 percent. Yet that tiny portion of unshared DNA makes a world of difference: it gives us, for instance, our bipedal stance and the ability to plan missions to Mars. Scientists do not yet know how most of the DNA that is uniquely ours affects gene function. But they can conduct whole-genome analyses—with intriguing results. For example, comparing the 33 percent of our genome that codes for proteins with our relatives' genomes reveals that although the sum total of our genetic differences is small, the individual differences pervade the genome, affecting each of our chromosomes in numerous ways. © 2014 Scientific American
By Jonathan Webb Science reporter, BBC News Monkeys at the top and bottom of the social pecking order have physically different brains, research has found. A particular network of brain areas was bigger in dominant animals, while other regions were bigger in subordinates. The study suggests that primate brains, including ours, can be specialised for life at either end of the hierarchy. The differences might reflect inherited tendencies toward leading or following, or the brain adapting to an animal's role in life - or a little of both. Neuroscientists made the discovery, which appears in the journal Plos Biology, by comparing brain scans from 25 macaque monkeys that were already "on file" as part of ongoing research at the University of Oxford. "We were also looking at learning and memory and decision-making, and the changes that are going on in your brain when you're doing those things," explained Dr MaryAnn Noonan, the study's first author. The decision to look at the animals' social status produced an unexpectedly clear result, Dr Noonan said. "It was surprising. All our monkeys were of different ages and different genders - but with fMRI (functional magnetic resonance imaging) you can control for all of that. And we were consistently seeing these same networks coming out." BBC © 2014
|By Madhuvanthi Kannan We humans assume we are the smartest of all creations. In a world with over 8.7 million species, only we have the ability to understand the inner workings of our body while also unraveling the mysteries of the universe. We are the geniuses, the philosophers, the artists, the poets and savants. We amuse at a dog playing ball, a dolphin jumping rings, or a monkey imitating man because we think of these as remarkable acts for animals that, we presume, aren’t smart as us. But what is smart? Is it just about having ideas, or being good at language and math? Scientists have shown, time and again, that many animals have an extraordinary intellect. Unlike an average human brain that can barely recall a vivid scene from the last hour, chimps have a photographic memory and can memorize patterns they see in the blink of an eye. Sea lions and elephants can remember faces from decades ago. Animals also have a unique sense perception. Sniffer dogs can detect the first signs of colon cancer by the scents of patients, while doctors flounder in early diagnosis. So the point is animals are smart too. But that’s not the upsetting realization. What happens when, for just once, a chimp or a dog challenges man to one of their feats? Well, for one, a precarious face-off – like the one Matt Reeves conceived in the Planet of the Apes – would seem a tad less unlikely than we thought. In a recent study by psychologists Colin Camerer and Tetsuro Matsuzawa, chimps and humans played a strategy game – and unexpectedly, the chimps outplayed the humans. Chimps are a scientist’s favorite model to understand human brain and behavior. Chimp and human DNAs overlap by a whopping 99 percent, which makes us closer to chimps than horses to zebras. Yet at some point, we evolved differently. Our behavior and personalities, molded to some extent by our distinct societies, are strikingly different from that of our fellow primates. Chimps are aggressive and status-hungry within their hierarchical societies, knit around a dominant alpha male. We are, perhaps, a little less so. So the question arises whether competitive behavior is hard-wired in them. © 2014 Scientific American
By Virginia Morell Figaro, a Goffin’s cockatoo (Cacatua goffini) housed at a research lab in Austria, stunned scientists a few years ago when he began spontaneously making stick tools from the wooden beams of his aviary. The Indonesian parrots are not known to use tools in the wild, yet Figaro confidently employed his sticks to rake in nuts outside his wire enclosure. Wondering if Figaro’s fellow cockatoos could learn by watching his methods, scientists set up experiments for a dozen of them. One group watched as Figaro used a stick to reach a nut placed inside an acrylic box with a wire-mesh front panel; others saw “ghost demonstrators”—magnets that were hidden beneath a table and that the researchers controlled—displace the treats. Each bird was then placed in front of the box, with a stick just like Figaro’s lying nearby. The group of three males and three females that had watched Figaro also picked up the sticks, and made some efforts reminiscent of his actions. But only those three males, such as the one in the photo above, became proficient with the tool and successfully retrieved the nuts, the scientists report online today in the Proceedings of the Royal Society B. None of the females did so; nor did any of the birds, male or female, in the ghost demonstrator group. Because the latter group failed entirely, the study shows that the birds need living teachers, the scientists say. Intriguingly, the clever observers developed a better technique than Figaro’s for getting the treat. Thus, the cockatoos weren’t copying his exact actions, but emulating them—a distinction that implies some degree of creativity. Two of the successful cockatoos were later given a chance to make a tool of their own. One did so immediately (as in the video above), and the other succeeded after watching Figaro. It may be that by learning to use a tool, the birds are stimulated to make tools of their own, the scientists say. © 2014 American Association for the Advancement of Science.
Keyword: Learning & Memory
Link ID: 20027 - Posted: 09.03.2014
By Virginia Morell A dog’s bark may sound like nothing but noise, but it encodes important information. In 2005, scientists showed that people can tell whether a dog is lonely, happy, or aggressive just by listening to his bark. Now, the same group has shown that dogs themselves distinguish between the barks of pooches they’re familiar with and the barks of strangers and respond differently to each. The team tested pet dogs’ reactions to barks by playing back recorded barks of a familiar and unfamiliar dog. The recordings were made in two different settings: when the pooch was alone, and when he was barking at a stranger at his home’s fence. When the test dogs heard a strange dog barking, they stayed closer to and for a longer period of time at their home’s gate than when they heard the bark of a familiar dog. But when they heard an unknown and lonely dog barking, they stayed close to their house and away from the gate, the team reports this month in Applied Animal Behaviour Science. They also moved closer toward their house when they heard a familiar dog’s barks, and they barked more often in response to a strange dog barking. Dogs, the scientists conclude from this first study of pet dogs barking in their natural environment (their owners’ homes), do indeed pay attention to and glean detailed information from their fellows’ barks. © 2014 American Association for the Advancement of Science
By Michael Balter Humans are generally highly cooperative and often impressively altruistic, quicker than any other animal species to help out strangers in need. A new study suggests that our lineage got that way by adopting so-called cooperative breeding: the caring for infants not just by the mother, but also by other members of the family and sometimes even unrelated adults. In addition to helping us get along with others, the advance led to the development of language and complex civilizations, the authors say. Cooperative breeding is not unique to humans. Up to 10% of birds are cooperative breeders, as are meerkats and New World monkeys such as tamarins and marmosets. But our closest primate relatives, great apes such as chimpanzees, are not cooperative breeders. Because the human and chimpanzee lineages split between 5 million and 7 million years ago, and humans are the only apes that engage in cooperative breeding, researchers have puzzled over how this helping behavior might have evolved all over again on the human line. In the late 1990s, Sarah Blaffer Hrdy, now an anthropologist emeritus at the University of California, Davis, proposed the cooperative breeding hypothesis. According to her model, early in their evolution humans added cooperative breeding behaviors to their already existing advanced ape cognition, leading to a powerful combination of smarts and sociality that fueled even bigger brains, the evolution of language, and unprecedented levels of cooperation. Soon after Hrdy’s proposal, anthropologists Carel van Schaik and Judith Burkart of the University of Zurich in Switzerland began to test some of these ideas, demonstrating that cooperatively breeding primates like marmosets engaged in seemingly altruistic behavior by helping other marmosets get food with no immediate reward to themselves. © 2014 American Association for the Advancement of Science.