Chapter 6. Evolution of the Brain and Behavior

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By Jonathan Webb Science reporter, BBC News Living in total darkness, the animals' eyes have disappeared over millions of years A study of blind crustaceans living in deep, dark caves has revealed that evolution is rapidly withering the visual parts of their brain. The findings catch evolution in the act of making this adjustment - as none of the critters have eyes, but some of them still have stumpy eye-stalks. Three different species were studied, each representing a different subgroup within the same class of crustaceans. The research is published in the journal BMC Neuroscience. The class of "malocostracans" also includes much better-known animals like lobsters, shrimps and wood lice, but this study focussed on three tiny and obscure examples that were only discovered in the 20th Century. It is the first investigation of these mysterious animals' brains. "We studied three species. All of them live in caves, and all of them are very rare or hardly accessible," said lead author Dr Martin Stegner, from the University of Rostock in Germany. Specifically, his colleagues retrieved the specimens from the coast of Bermuda, from Table Mountain in South Africa, and from Monte Argentario in Italy. One of the species was retrieved from caves on the coast of Bermuda The animals were preserved rather than living, so the team could not observe their tiny brains in action. But by looking at the physical shape of the brain, and making comparisons with what we know about how the brain works in their evolutionary relatives, the researchers were able to assign jobs to the various lobes, lumps and spindly structures they could see under the microscope. © 2015 BBC.

Keyword: Evolution; Vision
Link ID: 20769 - Posted: 04.08.2015

Tom Bawden Scientists have deciphered the secrets of gibbon “speech” – discovering that the apes are sophisticated communicators employing a range of more than 450 different calls to talk to their companions. The research is so significant that it could provide clues on the evolution of human speech and also suggests that other animal species could speak a more precise language than has been previously thought, according to lead author Dr Esther Clarke of Durham University. Her study found that gibbons produce different categories of “hoo” calls – relatively quiet sounds that are distinct from their more melodic “song” calls. These categories of call allow the animals to distinguish when their fellow gibbons are foraging for food, alerting them to distant noises or warning others about the presence of predators. In addition, Dr Clarke found that each category of “hoo” call can be broken down further, allowing gibbons to be even more specific in their communication. A warning about lurking raptor birds, for example, sounds different to one about pythons or clouded leopards – being pitched at a particularly low frequency to ensure it is too deep for the birds of prey to hear. The warning call denoting the presence of tigers and leopards is the same because they belong to the same class of big cats, the research found. © independent.co.uk

Keyword: Language; Evolution
Link ID: 20768 - Posted: 04.08.2015

by Jan Piotrowski It's not the most charismatic fossil ever found, but it may reveal secrets of our earliest evolution. Unearthed in Ethiopia, the broken jaw with greying teeth suggests that the Homo lineage – of which modern humans are the only surviving member – existed up to 400,000 years earlier than previously thought. The fragment dates from around 2.8 million years ago, and is by far the most ancient specimen to bear the Homo signature. The earliest such fossil was one thought to be up to 2.4 million years ages old. Showing a mixture of traits, the new find pinpoints the time when humans began their transition from primitive, apelike Australopithecus to the big-brained conquerer of the world, says Brian Villmoare from the University of Nevada, Las Vegas, whose student made the find. Geological evidence from the same area, also reported this week in a study led by Erin DiMaggio from Pennsylvania State University, shows that the jaw's owner lived just after a major climate shift in the region: forests and waterways rapidly gave way to arid savannah, leaving only the occasional crocodile-filled lake. Except for the sabre-toothed big cat that once roamed these parts, the environment ended up looking much like it does today. It was probably the pressure to adapt to this new world that jump-started our evolution into what we see looking back at us in the mirror today, according to Villmoare. © Copyright Reed Business Information Ltd.

Keyword: Evolution
Link ID: 20654 - Posted: 03.05.2015

By Nicholas Weiler The grizzled wolf stalks from her rival’s den, her mouth caked with blood of the pups she has just killed. It’s a brutal form of birth control, but only the pack leader is allowed to keep her young. For her, this is a selfish strategy—only her pups will carry on the future of the pack. But it may also help the group keep its own numbers in check and avoid outstripping its resources. A new survey of mammalian carnivores worldwide proposes that many large predators have the ability to limit their own numbers. The results, though preliminary, could help explain how top predators keep the food chains beneath them in balance. Researchers often assume that predator numbers grow and shrink based on their food supply, says evolutionary biologist Blaire Van Valkenburgh of the University of California, Los Angeles, who was not involved in the new study. But several recent examples, including an analysis of the resurgent wolves of Yellowstone National Park, revealed that some large predators keep their own numbers in check. The new paper is the first to bring all the evidence together, Van Valkenburgh says, and presents a “convincing correlation.” Hunting and habitat loss are killing off big carnivores around the world, just as ecologists are discovering how important they are for keeping ecosystems in balance. Mountain lions sustain woodlands by hunting deer that would otherwise graze the landscape bare. Coyotes protect scrub-dwelling birds by keeping raccoons and foxes in line. Where top carnivores disappear, these smaller predators often explode in numbers, with potentially disastrous consequences for small birds and mammals. © 2015 American Association for the Advancement of Science

Keyword: Sexual Behavior; Evolution
Link ID: 20629 - Posted: 02.28.2015

By Elizabeth Pennisi Last week, researchers expanded the size of the mouse brain by giving rodents a piece of human DNA. Now another team has topped that feat, pinpointing a human gene that not only grows the mouse brain but also gives it the distinctive folds found in primate brains. The work suggests that scientists are finally beginning to unravel some of the evolutionary steps that boosted the cognitive powers of our species. “This study represents a major milestone in our understanding of the developmental emergence of human uniqueness,” says Victor Borrell Franco, a neurobiologist at the Institute of Neurosciences in Alicante, Spain, who was not involved with the work. The new study began when Wieland Huttner, a developmental neurobiologist at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany, and his colleagues started closely examining aborted human fetal tissue and embryonic mice. “We specifically wanted to figure out which genes are active during the development of the cortex, the part of the brain that is greatly expanded in humans and other primates compared to rodents,” says Marta Florio, the Huttner graduate student who carried out the main part of the work. That was harder than it sounded. Building a cortex requires several kinds of starting cells, or stem cells. The stem cells divide and sometimes specialize into other types of “intermediate” stem cells that in turn divide and form the neurons that make up brain tissue. To learn what genes are active in the two species, the team first had to develop a way to separate out the various types of cortical stem cells. © 2015 American Association for the Advancement of Science

Keyword: Development of the Brain; Evolution
Link ID: 20628 - Posted: 02.27.2015

By Elizabeth Pennisi Researchers have increased the size of mouse brains by giving the rodents a piece of human DNA that controls gene activity. The work provides some of the strongest genetic evidence yet for how the human intellect surpassed those of all other apes. "[The DNA] could easily be a huge component in how the human brain expanded," says Mary Ann Raghanti, a biological anthropologist at Kent State University in Ohio, who was not involved with the work. "It opens up a whole world of possibilities about brain evolution." For centuries, biologists have wondered what made humans human. Once the human and chimp genomes were deciphered about a decade ago, they realized they could now begin to pinpoint the molecular underpinnings of our big brain, bipedalism, varied diet, and other traits that have made our species so successful. By 2008, almost two dozen computerized comparisons of human and ape genomes had come up with hundreds of pieces of DNA that might be important. But rarely have researchers taken the next steps to try to prove that a piece of DNA really made a difference in human evolution. "You could imagine [their roles], but they were just sort of 'just so' stories,” says Greg Wray, an evolutionary biologist at Duke University in Durham, North Carolina. Wray is particularly interested in DNA segments called enhancers, which control the activity of genes nearby. He and Duke graduate student Lomax Boyd scanned the genomic databases and combed the scientific literature for enhancers that were different between humans and chimps and that were near genes that play a role in the brain. Out of more than 100 candidates, they and Duke developmental neurobiologist Debra Silver tested a half-dozen. They first inserted each enhancer into embryonic mice to learn whether it really did turn genes on. Then for HARE5, the most active enhancer in an area of the brain called the cortex, they made minigenes containing either the chimp or human version of the enhancer linked to a “reporter” gene that caused the developing mouse embryo to turn blue wherever the enhancer turned the gene on. Embryos’ developing brains turned blue sooner and over a broader expanse if they carried the human version of the enhancer, Silver, Wray, and their colleagues report online today in Current Biology. © 2015 American Association for the Advancement of Science

Keyword: Development of the Brain; Genes & Behavior
Link ID: 20598 - Posted: 02.21.2015

By Warren Cornwall The green wings of the luna moth, with their elegant, long tails, aren’t just about style. New research finds they also help save the insect from becoming a snack for a bat. The fluttering tails appear to create an acoustic signal that is attractive to echolocating bats, causing the predators to zero in on the wings rather than more vital body parts. Scientists pinned down the tails’ lifesaving role by taking 162 moths and plucking the tails off 75 of them. They used fishing line to tether two moths—one with tails, the other without—to the ceiling of a darkened room. Then, they let loose a big brown bat. The bats caught 81% of the tailless moths, but just 35% of those with fully intact wings, they report in a study published online today in the Proceedings of the National Academy of Sciences. High-speed cameras helped show why. In 55% of attacks on moths with tails, the bats went after the tails, often missing the body. It’s the first well-documented example of an organism using body shape to confuse predators that use echolocation, the researchers say—the equivalent of fish and insects that display giant eyespots for visual trickery. © 2015 American Association for the Advancement of Science

Keyword: Hearing; Evolution
Link ID: 20587 - Posted: 02.18.2015

Madeline Bonin Bats and moths have been evolving to one-up each other for 65 million years. Many moths can hear bats’ ultrasonic echolocation calls, making it easy for the insects to avoid this predator. A few species of bat have developed echolocation calls that are outside the range of the moths’ hearing, making it harder for the moths to evade them1. But humans short-circuit this evolutionary arms race every time they turn on a porch light, according to a study in the Journal of Applied Ecology2. In field experiments, ecologist Corneile Minnaar of the University of Pretoria and his colleagues examined the diet of Cape serotine bats (Neoromicia capensis) both in the dark and under artificial light in a national park near Pretoria. The bat, an insect-eating species common in South Africa, has an echolocation call that moths can hear. Minnaar and his team determined both the species and quantity of available insect prey at the test sites using a hand-held net and a stationary trap. Cape serotine bats do not normally eat many moths. As the scientists expected, they caught more during the lighted trials than in the dark. What was surprising, however, was the discovery that the insects formed a greater share of the bats' diet during the lighted trials. The percentage of moths eaten in bright areas was six times larger than in dark zones, even though moths represented a smaller share of the total insect population under the lights than in the shade. But surprisingly, though moths represented a smaller share of the total insect population in the lighted areas, they played a larger role in the bats' diet. © 2015 Nature Publishing Group

Keyword: Hearing; Evolution
Link ID: 20565 - Posted: 02.09.2015

by Andy Coghlan Apple's the word. Chimpanzees can learn to grunt "apple" in two chimp languages – a finding that questions how unique our own language abilities are. Researchers have kept records of vocalisations of a group of adult chimps from the Netherlands before and after the move to Edinburgh zoo. Three years later, recordings show, the Dutch chimps had picked up the pronunciation of their Scottish hosts. The finding challenges the prevailing theory that chimp words for objects are fixed because they result from excited, involuntary outbursts. Humans can easily learn foreign words that refer to a specific object, and it was assumed that chimps and other animals could not, perhaps owing to their different brain structure. This has long been argued to be one of the talents making humans unique. The assumption has been that animals do not have control over the sounds they make, whereas we socially learn the labels for things – which is what separates us from animals, says Katie Slocombe of the University of York, UK. But this may be wrong, it seems. "The important thing we've now shown is that with the food calls, they changed the structure to fit in with their new group members, so the Dutch calls for 'apple' changed to the Edinburgh ones," says Slocombe. "It's the first time call structure has been dissociated from emotional outbursts." © Copyright Reed Business Information Ltd.

Keyword: Language; Evolution
Link ID: 20560 - Posted: 02.07.2015

by Sandrine Ceurstemont Malte Andersson from the University of Gothenburg in Sweden has been testing whether Norwegian lemmings (Lemmus lemmus), like the one in the video above, deter predators by warning them of their aggressive nature with their shrieks. The vivid markings on the fur also indicate to predators that this critter isn't for eating. Having such warning colours – a phenomenon known as aposematism – is common in insects, snakes and frogs, but unusual in herbivorous mammals. This combination of hues made the lemmings easier to spot than their plain-looking neighbours, grey-sided voles. When a predator, played by humans in Andersson's test, is far away, these lemmings prefer to go unnoticed, he found. But when predators get closer, to within a few metres, these lemmings were much more likely to give out a warning call than their browner relatives. The conspicuous colours, aggressive calls and threatening postures together let predators know to expect a fight, and potentially damage, if they attempt to eat a Norwegian lemming. In contrast with the voles, these lemmings aggressively resist attacks by predatory birds. © Copyright Reed Business Information Ltd.

Keyword: Aggression
Link ID: 20558 - Posted: 02.07.2015

By Monique Brouillette When the first four-legged creatures emerged from the sea roughly 375 million years ago, the transition was anything but smooth. Not only did they have to adjust to the stress of gravity and the dry environment, but they also had to wait another 100 million years to evolve a fully functional ear. But two new studies show that these creatures weren’t deaf; instead, they may have used their lungs to help them hear. Fish hear easily underwater, as sound travels in a wave of vibration that freely passes into their inner ears. If you put a fish in air, however, the difference in the density of the air and tissue is so great that sound waves will mostly be reflected. The modern ear adapted by channeling sound waves onto an elastic membrane (the eardrum), causing it to vibrate. But without this adaptation, how did the first land animals hear? To answer this question, a team of Danish researchers looked at one of the closest living relatives of early land animals, the African lungfish (Protopterus annectens). As its name suggests, the lungfish is equipped with a pair of air-breathing lungs. But like the first animals to walk on land, it lacks a middle ear. The researchers wanted to determine if the fish could sense sound pressure waves underwater, so they filled a long metal tube with water and placed a loudspeaker at one end. They played sounds into the tube in a range of frequencies and carefully positioned the lungfish in areas of the tube where the sound pressure was high. Monitoring the brain stem and auditory nerve activity in the lungfish, the researchers were surprised to discover that the fish could detect pressure waves in frequencies above 200 Hz. © 2015 American Association for the Advancement of Science

Keyword: Hearing; Evolution
Link ID: 20551 - Posted: 02.05.2015

David Cox Bernd Heinrich was on a hike through the woods of New England when he observed something which would go on to change our perception of animal psychology. A group of ravens had gathered to feed on a dead moose. But rather than choosing to keep the bounty for themselves, they were making a strange call, one which seemed to be deliberately attracting more ravens to the feast. A biologist at the University of Vermont, Heinrich was initially confused. By helping their competitors, the ravens appeared to be defying all natural biological instinct. But as it transpired, their motivation was actually deeply selfish. The birds were juveniles who had discovered the moose in an adult raven’s territory. By inviting other ravens to join them, their intrusion was more likely to go unchallenged. Last month, an astonishing video emerged of a rhesus macaque successfully resuscitating another of its species which had been electrocuted at a train station in India. It is tempting to describe the sustained display of persistence and apparent concern as almost human. But there is a danger in viewing animal behaviour through the misty lens of human emotion. What both Heinrich’s “sharing ravens’ and the macaques of Kampur do provide is a window into the gradual evolution of one of the most human of traits – altruism. Altruism in its purest form should be an entirely selfless action. “If there’s any kind of selfish interest at stake, like secretly hoping for a return favour or even doing it deliberately because you know it will make you feel good, then that doesn’t really count at all,” says psychologist Michael Platt of the Center for Cognitive Neuroscience at Duke University, North Carolina.

Keyword: Aggression; Intelligence
Link ID: 20522 - Posted: 01.27.2015

by Catherine Brahic Move over Homo habilis, you're being dethroned. A growing body of evidence – the latest published this week – suggests that our "handy" ancestor was not the first to use stone tools. In fact, the ape-like Australopithecus may have figured out how to be clever with stones before modern humans even evolved. Humans have a way with flint. Sure, other animals use tools. Chimps smash nuts and dip sticks into ant nests to pull out prey. But humans are unique in their ability to apply both precision and strength to their tools. It all began hundreds of thousands of years ago when a distant ancestor began using sharp stone flakes to scrape meat off skin and bones. So who were those first toolmakers? In 2010, German researchers working in Ethiopia discovered markings on two animal bones that were about 3.4 million years old. The cut marks had clearly been made using a sharp stone, and they were at a site that was used by Lucy's species, Australopithecus afarensis. The study, led by Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, was controversial. The bones were 800,000 years older than the oldest uncontested stone tools, and at the time few seriously thought that australopithecines had been tool users. Plus, McPherron hadn't found the tool itself. The problem, says McPherron, is that if we just go on tools that have been found, we must conclude that one day somebody made a beautifully flaked Oldowan hand axe, completely out of the blue. That seems unlikely. © Copyright Reed Business Information Ltd.

Keyword: Evolution
Link ID: 20512 - Posted: 01.23.2015

By Christie Aschwanden Maybe it’s their famously protruding brow ridge or perhaps it’s the now-discredited notion that they were primitive scavengers too dumb to use language or symbolism, but somehow Neanderthals picked up a reputation as brutish, dim and mannerless cretins. Yet the latest research on the history and habits of Neanderthals suggests that such portrayals of them are entirely undeserved. It turns out that Neanderthals were capable hunters who used tools and probably had some semblance of culture, and the DNA record shows that if you trace your ancestry to Europe or Asia, chances are very good that you have some Neanderthal DNA in your own genome. The bad rap began when the first Neanderthal skull was discovered around 1850 in Germany, says Paola Villa, an archaeologist at the University of Colorado. “The morphological features of these skulls — big eyebrows, no chin — led to the idea that they were very different from us, and therefore inferior,” she says. While the majority of archaeologists no longer believe this, she says, the idea that Neanderthals were inferior, brutish or stupid remains in popular culture. Neanderthals first appeared in Europe and western Asia between 300,000 and 400,000 years ago. They are our closest (extinct) relative, and their species survived until 30,000 to 40,000 years ago, when they vanish from the fossil record, says Svante Paabo, director of the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany, and author of “Neanderthal Man: In Search of Lost Genomes.” Why these relatives of ours thrived for so long and then ended their long, successful run about the same time that modern humans began to spread remains a point of debate and speculation.

Keyword: Evolution
Link ID: 20498 - Posted: 01.20.2015

// by Jennifer Viegas Researchers eavesdropping on wild chimpanzees determined that the primates communicate about at least two things: their favorite yummy fruits, and the trees where these fruits can be found. Of particular interest to the chimps is the size of trees bearing the fruits that they relish most, such that the chimps yell out that information, according to a new study published in the journal Animal Behaviour. The study is the first to find that information about tree size and available fruit amounts are included in chimp calls, in addition to assessments about food quality. "Chimpanzees definitely have a very complex communication system that includes a variety of vocalizations, but also facial expressions and gestures," project leader Ammie Kalan of the Max Planck Institute for Evolutionary Anthropology told Discovery News. "How much it resembles human language is still a matter of debate," she added, "but at the very least, research shows that chimpanzees use vocalizations in a sophisticated manner, taking into account their social and environmental surroundings." Kalan and colleagues Roger Mundry and Christophe Boesch spent over 750 hours observing chimps and analyzing their food calls in the Ivory Coast's Taï Forest. The Wild Chimpanzee Foundation in West Africa is working hard to try and protect this population of chimps, which is one of the last wild populations of our primate cousins. © 2015 Discovery Communications, LLC

Keyword: Language; Evolution
Link ID: 20497 - Posted: 01.20.2015

Helen Fisher, a biological anthropologist at Rutgers University responds: Several years ago I embarked on a project to see if the seven-year itch really exists. I began by studying worldwide data on marriage and divorce and noticed that although the median duration of marriage was seven years, of the couples who divorced, most did so around their fourth year together (the “mode”). I also found that divorce occurred most frequently among couples at the height of their reproductive and parenting years—for men, ages 25 to 29, and for women, ages 20 to 24 and 25 to 29—and among those with one dependent child. To try to explain these findings, I began looking at patterns of pair bonding in birds and mammals. Although only about 3 percent of mammals form a monogamous bond to rear their young, about 90 percent of avian species team up. The reason: the individual that sits on the eggs until they hatch will starve unless fed by a mate. A few mammals are in the same predicament. Take the female fox: the vixen produces very thin milk and must feed her young almost constantly, so she relies on her partner to bring her food while she stays in the den to nurse. But here's the key: although some species of birds and mammals bond for life, more often they stay together only long enough to rear their young through infancy and early toddlerhood. When juvenile robins fly away from the nest or maturing foxes leave the den for the last time, their parents part ways as well. Humans retain traces of this natural reproductive pattern. In more contemporary hunter-gatherer societies, women tend to bear their children about four years apart. Moreover, in these societies after a child is weaned at around age four, the child often joins a playgroup and is cared for by older siblings and relatives. This care structure allows unhappy couples to break up and find a more suitable partner with whom to have more young. © 2015 Scientific American

Keyword: Sexual Behavior; Evolution
Link ID: 20496 - Posted: 01.20.2015

By Viviane Callier In the deep sea, where light is dim and blue, animals with bigger eyes see better—but bigger eyes are more conspicuous to predators. In response, the small (10 mm to 17 mm), transparent crustacean Paraphronima gracilis has evolved a unique eye structure. Researchers collected the animals from 200- to 500-meter deep waters in California’s Monterey Bay using a remote-operated vehicle. They then characterized the pair of compound eyes, discovering that each one was composed of a single row of 12 distinct red retinas. Reporting online on 15 January in Current Biology, the researchers hypothesize that each retina captures an image that is transmitted to the crustacean’s brain, which integrates the 12 images to increase brightness and contrast sensitivity, adapting to changing light levels. Future work will focus on how images are processed by the neural connections between the retinas and the brain. © 2015 American Association for the Advancement of Science.

Keyword: Vision; Evolution
Link ID: 20490 - Posted: 01.17.2015

By Michael Balter If there’s one thing that distinguishes humans from other animals, it’s our ability to use language. But when and why did this trait evolve? A new study concludes that the art of conversation may have arisen early in human evolution, because it made it easier for our ancestors to teach each other how to make stone tools—a skill that was crucial for the spectacular success of our lineage. Researchers have long debated when humans starting talking to each other. Estimates range wildly, from as late as 50,000 years ago to as early as the beginning of the human genus more than 2 million years ago. But words leave no traces in the archaeological record. So researchers have used proxy indicators for symbolic abilities, such as early art or sophisticated toolmaking skills. Yet these indirect approaches have failed to resolve arguments about language origins. Now, a team led by Thomas Morgan, a psychologist at the University of California, Berkeley, has attacked the problem in a very different way. Rather than considering toolmaking as a proxy for language ability, he and his colleagues explored the way that language may helps modern humans learn to make such tools. The researchers recruited 184 students from the University of St. Andrews in the United Kingdom, where some members of the team were based, and organized them into five groups. The first person in each group was taught by archaeologists how to make artifacts called Oldowan tools, which include fairly simple stone flakes that were manufactured by early humans beginning about 2.5 million years ago. This technology, named after the famous Olduvai Gorge in Tanzania where archaeologists Louis and Mary Leakey discovered the implements in the 1930s, consists of hitting a stone “core” with a stone “hammer” in such a way that a flake sharp enough to butcher an animal is struck off. Producing a useful flake requires hitting the core at just the right place and angle. © 2015 American Association for the Advancement of Science.

Keyword: Language; Evolution
Link ID: 20482 - Posted: 01.14.2015

by Clare Wilson Could a lopsided gap help set us apart from our primate cousins? Our brains and chimps' are built differently in the areas that give us our social skills and language. The human brain has a 4.5-centimetre-long groove running deeper along the right side than the left. Chimp brains lack this asymmetry, as François Leroy of the French National Institute of Health and Medical Research in Saclay, and colleagues, have discovered. The groove's function is unknown, but its location suggests it played a role in the evolution of our communication abilities. "One day this will help us understand what makes us tick," says Colin Renfrew of the University of Cambridge, who was not involved in the study. Although our brain is about three times the size of a chimp's, anatomical features that only the human brain possesses are surprisingly hard to find. One known difference is in a region called Broca's area, which is also involved in speech and is larger in humans than chimps. The asymmetrical groove in humans was also known, but the new study, in which 177 people and 73 chimps had brain scans, revealed it is almost completely absent in the other primates. In humans, the deeper groove in the right brain lies in the region that controls voice and face recognition and working out what other people are thinking – our so-called theory of mind. The shallower groove on the left is at the heart of the areas associated with language. The lack of symmetry could signify that tissue layers in the right brain have been reorganised, says Leroy. © Copyright Reed Business Information Ltd.

Keyword: Evolution; Laterality
Link ID: 20475 - Posted: 01.13.2015

By Virginia Morell Animals that live in larger societies tend to have larger brains. But why? Is it because a larger group size requires members to divide up the labor on tasks, thus causing some individuals to develop specialized brains and neural anatomy? (Compared with most humans, for instance, taxicab drivers have brains that have larger areas that are involved with spatial memory.) Or is it because the challenges of group living—needing to know all the foibles of your neighbors—cause the brains of all members to grow larger? Scientists tested the two hypotheses with wild colonies of acacia ants (Pseudomyrmex spinicola), which make their nests in the hollow spines of acacia trees in Panama. Ant workers at the base of the tree wait to attack intruders, while workers foraging on the leaves (as in the photo above), aren’t as aggressive but are faster at managing the colony’s brood. This division of labor is most marked in larger colonies (those found on larger trees), while workers in smaller colonies do both jobs. The scientists studied 17 colonies of ants and measured the brain volumes of 29 of the leaf ants and 34 of the trunk ants. As the colony size increased, the leaf ants showed a marked increase in the regions of the brain concerned with learning and memory, the scientists report today in the Proceedings of the Royal Society B. But the same neural areas decreased in the trunk ants. Thus, larger societies’ need for specialized workers, some strictly for defense, others for foraging and brood tending—rather than for social masters—seems to be the key to the expanding brain, at least in ants.

Keyword: Evolution
Link ID: 20457 - Posted: 01.08.2015