Links for Keyword: Evolution

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Sid Perkins The two-million-year-old remains of a novel hominin discovered in August 2008 are an odd blend of features seen both in early humans and in the australopithecines presumed to have preceded them. A battery of six studies1–6 published today in Science scrutinizes the fossils of Australopithecus sediba from head to heel and yields unprecedented insight into how the creature walked, chewed and moved. Together, the studies suggest that this hominin was close to the family tree of early humans — although it remains controversial whether it was one of our direct ancestors. “We see evolution in action across this skeleton,” says Lee Berger, a palaeoanthropologist at the University of the Witwatersrand in Johannesburg, South Africa. For instance, whereas the creature’s arms are ape-like, its hands and wrists are remarkably like those of humans. And although the hominin’s pelvis is shaped like a modern human's, its torso included a narrow upper rib cage like those found in apes. One of the six studies focused on Au. sediba’s teeth1, comparing 22 different aspects across hundreds of teeth from several other species of australopithecines and thousands of early human teeth. Tooth similarities among the species are more likely to signify common ancestry than independent evolution towards a beneficial design, says Debbie Guatelli-Steinberg, an anthropologist at Ohio State University in Columbus. That's because most of the characteristics the team chose to study, such as the subtle curvature of a portion of the tooth’s surface, are not likely to be evolutionarily useful. © 2013 Nature Publishing Group

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:None
Link ID: 18027 - Posted: 04.13.2013

by Michael Marshall Neanderthals may have had bigger eyes than modern humans, but while this helped them see better, it may have meant that they did not have brainpower to spare for complex social lives. If true, this may have been a disadvantage when the ice age reduced access to food, as they would not have had the skills to procure help from beyond their normal social group, speculates Robin Dunbar at the University of Oxford. Neanderthals' brains were roughly the same size as modern humans, but may have been organised differently. To find out, a team led by Dunbar studied the skulls of 13 Neanderthals and 32 anatomically modern humans. The Neanderthals had larger eye sockets. There are no Neanderthal brains to examine, but primates with larger eyes tend to have larger visual systems in their brains, suggesting Neanderthals did too. Their large bodies would also have required extra brain power to manage. Together, their larger eyes and bodies would have left them with less grey matter to dedicate to other tasks. Neanderthals may have evolved enhanced visual systems to help them see in the gloom of the northern hemisphere, Dunbar says. "It makes them better at detecting things in grim, grey conditions." As a by-product of larger eyes, they may not have been able to expand their frontal lobes – a brain area vital for social interaction – as much as modern humans. As a result, Dunbar estimates they could only maintain a social group size of around 115 individuals, rather than the 150 that we manage. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 7: Vision: From Eye to Brain
Link ID: 17896 - Posted: 03.13.2013

by Michael Marshall Humans aren't built for giving birth. Babies' heads are big to accommodate their big brains, but the mother's hips are small because they walk upright. As a result, birth takes hours and is extremely painful – and midwives almost always help out. Other animals may find birth difficult, particularly if the babies have been gestating for a long time and have grown large. Nevertheless, most mammals have it easier than humans. Monkeys give birth in less than ten minutes. So it is a surprise that female black snub-nosed monkeys may be assisted by "midwives" when they give birth. This behaviour has only been seen once in this species, but it suggests that it's not just human mothers that need help giving birth. Black snub-nosed monkeys live in societies called bands, which can be over 400 strong. Each is divided into smaller groups of around 10 monkeys. Most groups contain one male and several females plus offspring, but there are also all-male groups. Wen Xiao of Dali University in Yunnan, China, and colleagues have been observing black snub-nosed monkeys in the province for years, but had never seen one give birth: the monkeys normally deliver at night. Then on 18 March last year, they got lucky. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior; Chapter 1: Biological Psychology: Scope and Outlook
Related chapters from MM:Chapter 1: An Introduction to Brain and Behavior
Link ID: 17781 - Posted: 02.11.2013

By Erin Wayman The story of the Neandertals may need a new ending, a controversial study suggests. Using improved radiocarbon methods, scientists redated two of the youngest known Neandertal cave sites and concluded that they are at least 10,000 years older than previous studies have found. The findings cast doubt on the reliability of radiocarbon dates from other recent Neandertal sites, the researchers suggest online February 4 in the Proceedings of the National Academy of Sciences. This means the last Neandertals might have died out much earlier than previously thought, which could cause anthropologists to rethink how and why these hominids vanished. Researchers have long debated whether the harsh Ice Age climate, the appearance of modern humans migrating out of Africa, or some other factor drove Neandertals to extinction. “The paper is simply excellent,” says archaeologist Olaf Jöris of the Romano-Germanic Central Museum in Mainz, Germany. The new research supports Jöris’ own review of Neandertal dates, in which he concluded that the most-recent Neandertals probably lived around 42,000 years ago. The standard view suggests that the last of these hominids occupied Europe as recently as about 28,000 years ago. But other archaeologists are not convinced by the new work. “We shouldn’t get too carried away over results that amount to a few radiocarbon dates from two sites,” says Paul Pettitt, an archaeologist at Durham University in England. © Society for Science & the Public 2000 - 2013

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:None
Link ID: 17758 - Posted: 02.05.2013

By Christie Wilcox There’s a lot to be said for smarts—at least we humans, with some of the biggest brains in relation to our bodies in the animal kingdom, certainly seem to think so. The size of animal brains is extravagantly well-studied, as scientists have long sought to understand why our ancestors developed such complex and energetically costly neural circuitry. One of the most interesting evolutionary hypotheses about brain size is The Expensive Tissue Hypothesis. Back in the early 1990s, scientists were looking to explain how brain size evolves. Brains are exceedingly useful organs; more brain cells allows for more behavioral flexibility, better control of larger bodies, and, of course, intelligence. But if bigger brains were always better, every animal would have them. Thus, scientists reasoned, there must be a downside. The hypothesis suggests that while brains are great and all, their extreme energetic cost limits their size and tempers their growth. When it comes to humans, for example, though our brains are only 2% of our bodies, they take up a whopping 20% of our energy requirements. And you have to wonder: with all that energy being used by our brains, what body parts have paid the price? The hypothesis suggested our guts took the hit, but that intelligence made for more efficient foraging and hunting, thus overcoming the obstacle. This makes sense, but despite over a century of research on the evolution of brain size, there is still controversy, largely stemming from the fact that evidence for the expensive tissue hypothesis is based entirely on between species comparisons and correlations, with no empirical tests. © 2013 Scientific American

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior; Chapter 13: Homeostasis: Active Regulation of the Internal Environment
Related chapters from MM:Chapter 9: Homeostasis: Active Regulation of the Internal Environment
Link ID: 17649 - Posted: 01.05.2013

By GRETCHEN REYNOLDS Anyone whose resolve to exercise in 2013 is a bit shaky might want to consider an emerging scientific view of human evolution. It suggests that we are clever today in part because a million years ago, we could outrun and outwalk most other mammals over long distances. Our brains were shaped and sharpened by movement, the idea goes, and we continue to require regular physical activity in order for our brains to function optimally. The role of physical endurance in shaping humankind has intrigued anthropologists and gripped the popular imagination for some time. In 2004, the evolutionary biologists Daniel E. Lieberman of Harvard and Dennis M. Bramble of the University of Utah published a seminal article in the journal Nature titled “Endurance Running and the Evolution of Homo,” in which they posited that our bipedal ancestors survived by becoming endurance athletes, able to bring down swifter prey through sheer doggedness, jogging and plodding along behind them until the animals dropped. Endurance produced meals, which provided energy for mating, which meant that adept early joggers passed along their genes. In this way, natural selection drove early humans to become even more athletic, Dr. Lieberman and other scientists have written, their bodies developing longer legs, shorter toes, less hair and complicated inner-ear mechanisms to maintain balance and stability during upright ambulation. Movement shaped the human body. But simultaneously, in a development that until recently many scientists viewed as unrelated, humans were becoming smarter. Their brains were increasing rapidly in size. Copyright 2012 The New York Times Company

Related chapters from BP7e: Chapter 11: Motor Control and Plasticity; Chapter 17: Learning and Memory
Related chapters from MM:Chapter 5: The Sensorimotor System; Chapter 13: Memory, Learning, and Development
Link ID: 17635 - Posted: 12.27.2012

By Michael Balter “What would you do with a brain if you had one?” Dorothy’s question to the Scarecrow in The Wizard of Oz elicited one of the movie’s most delightful songs, in which her straw-filled friend assured her that, among other things, he could “think of things I’d never thunk before.” But the Scarecrow seemed to do quite well without one, thus avoiding the high energy costs of fueling and cooling a human brain—which, with an average volume of about 1,400 cubic centimeters, is humongous relative to our body size. How did our brains get so big? Researchers have put forward a number of possible explanations over the years, but the one with the most staying power is an idea known as the social brain hypothesis. Its chief proponent, psychologist Robin Dunbar of Oxford University, has argued for the past two decades that the evolution of the human brain was driven by our increasingly complex social relationships. We required greater neural processing power so that we could keep track of who was doing what to whom. Our expanded brains could have been practical for other things, of course, such as innovations in tool use and food gathering. Most researchers, including Dunbar, agree that these hypotheses are not mutually exclusive. Whatever the reasons for the very large human noggin, there is a lot of explaining to do, because big brains have a lot going against them. The oversized Homo sapiens brain let us take over the planet, build cities, send space probes to Mars, and do all the other marvelous things that we humans are so proud of. But none of these things makes us much better at reproducing, and in terms of evolution, that’s really all that matters. © 2012 The Slate Group, LLC.

Related chapters from BP7e: Chapter 7: Life-Span Development of the Brain and Behavior; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 13: Memory, Learning, and Development
Link ID: 17423 - Posted: 10.26.2012

By Rachel Ehrenberg Chimps, gibbons and other primates are not just humans’ evolutionary cousins; a new analysis suggests they are also our blood brothers. The A, B and O blood types in people evolved at least 20 million years ago in a common ancestor of humans and other primates, new research suggests. The analysis deepens a mystery surrounding the evolutionary history of the ABO blood system, and should prompt further research into why the different blood groups have persisted over time, Laure Ségurel of the University of Chicago and colleagues report online October 22 in the Proceedings of the National Academy of Sciences. “Their evidence is rather convincing that this is a shared, very old capability that has remained throughout the divergence of the species,” says doctor and transfusion specialist Martin Olsson of Lund University in Sweden. Different forms of a single blood type gene determine what types of molecules sit on your red blood cells: type A molecules, type B molecules, A and B together, or no intact surface molecules in the case of type O (O was originally called type C, then was changed to O for the German “ohne,” meaning “without”). The A, B and O versions of the gene differ only slightly, and scientists have debated two scenarios to explain their evolution. One posits that the A version of the gene existed long ago, and the B and/or O versions later cropped up independently in several species (including humans, gorillas, baboons and chimps). Alternatively, all of those species may have inherited the A and B types from a single ancestor. © Society for Science & the Public 2000 - 2012

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:None
Link ID: 17418 - Posted: 10.25.2012

By Erin Wayman Rusty red stains on the head of a fossilized segmented creature found in southwestern China are a paleontological record-breaker: They are the remains of the oldest arthropod brain ever found. The imprint of the 520-million-year-old critter’s three-part brain indicates that complex nervous systems evolved fairly early in animal evolution, among the ancestors of insects, centipedes and crustaceans. The roughly 7-centimeter-long specimen includes the entire body of Fuxianhuia protensa. The species lived during the Cambrian period, before modern arthropod lineages evolved. The fossil shows F. protensa had a brain composed of three sections that sat in front of the animal’s gut. That’s the same setup seen today in insects, crabs, lobsters and many other arthropods, researchers report in the Oct. 11 Nature. “It was very fascinating and very exciting,” says study coauthor Nicholas Strausfeld, a neuroscientist at the University of Arizona. “It suggests that the organization we see in the modern [arthropod] brains is very ancient.” Scientists had thought early arthropods had simpler brains like those of modern water fleas, fairy shrimp and other tiny freshwater crustaceans called branchiopods. The branchiopod brain consists of two connected parts with a third mass of nervous tissue sitting behind the stomach. Sometime after the branchiopod lineage split from the other arthropods, scientists had assumed, the nervous tissue behind the gut migrated up and connected with the other parts of the brain, Strausfeld says. © Society for Science & the Public 2000 - 2012

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:None
Link ID: 17357 - Posted: 10.11.2012

By Bruce Bower A new study suggests that present-day Europeans share more genes with now-extinct Neandertals than do living Africans, at least partly because of interbreeding that took place between 37,000 and 86,000 years ago. Cross-species mating occurred when Stone Age humans left Africa and encountered Neandertals, or possibly a close Neandertal relative, upon reaching the Middle East and Europe in the latter part of the Stone Age, says a team led by geneticist Sriram Sankararaman of Harvard Medical School. The new study, published online October 4 in PLOS Genetics, indicates that at least some interbreeding must have occurred between Homo sapiens and Neandertals, Sankararaman says. But it’s not yet possible to estimate how much of the Neandertal DNA found in modern humans comes from that interbreeding and how much derives from ancient African hominid populations ancestral to both groups. A separate analysis of gene variants in Neandertals and in people from different parts of the world also found signs of Stone Age interbreeding outside Africa. That study, published online April 18 in Molecular Biology and Evolution, was led by evolutionary geneticist Melinda Yang of the University of California, Berkeley. Results from Sankararaman and Yang’s groups “convincingly show that the finding of a higher proportion of Neandertal DNA in non-Africans compared to Africans can be best explained by gene flow from Neandertals into modern humans,” says evolutionary geneticist Johannes Krause of the University of Tübingen in Germany. © Society for Science & the Public 2000 - 2012

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 17336 - Posted: 10.06.2012

by Elizabeth Norton Baboons, like people, really do get by with a little help from their friends. Humans with strong social ties live longer, healthier lives, whereas hostility and "loner" tendencies can set the stage for disease and early death. In animals, too, strong social networks contribute to longer lives and healthier offspring—and now it seems that personality may be just as big a factor in other primates' longevity status. A new study found that female baboons that had the most stable relationships with other females weren't always the highest up in the dominance hierarchy or the ones with close kin around—but they were the nicest. Scientists are increasingly seeing personality as a key factor in an animal's ability to survive, adapt, and thrive in its environment. But this topic isn't an easy one to study scientifically, says primatologist Dorothy Cheney of the University of Pennsylvania. "Research in mammals, birds, fish, and insects shows individual patterns of behavior that can't be easily explained. But the many studies of personality are based on human traits like conscientiousness, agreeableness, or neuroticism. It isn't clear how to apply those traits to animals," Cheney says. Along with a group of scientists—including co-authors Robert Seyfarth, also at the University of Pennsylvania, and primatologist Joan Silk of Arizona State University, Tempe—Cheney has studied wild baboons at the Moremi Game Reserve in Botswana for almost 20 years. Besides providing detailed, long-term observations of behavior in several generations of baboons, the research has yielded a wealth of biological and genetic information. © 2010 American Association for the Advancement of Science.

Related chapters from BP7e: Chapter 15: Emotions, Aggression, and Stress; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 1: An Introduction to Brain and Behavior
Link ID: 17323 - Posted: 10.02.2012

By Gary Stix Evolutionary psychology has typically tried to identify the piece parts of human cognition shaped by the rigors of natural selection. New questions have arisen in this contentious discipline about what exactly is on that parts list—or whether the list itself really exists. One of the foremost debating points centers on whether the brain consists of a series of Lego-like modules, each one produced from evolutionary adaptations that resulted in mental tools for things like going after Mastodons, forming clans and communicating the daily incidentals related to food, shelter and mating. Another way to think about all this is to invoke the metaphor of a Swiss-Army knife, with each adaptive module the equivalent of a corkscrew, nail clipper or a myriad of cutting implements. The revisionist viewpoint rejects this neat tailoring of mental functioning championed by psychologists like Leda Cosmides and John Tooby. Instead, upstarts trot out the human hand as a replacement analogy for the pocket knife, a single all-purpose implement that can poke, prod, pull and push. A walk through the new thinking on evolutionary psychology appears in the Aug. 5 edition of the Philosophical Transactions of the Royal Society of London B. (The original journal, founded in 1665, was the first anywhere to deal solely with science—and this issue is open to everyone for a download.) The metaphor of the hand, notes Cecilia Heyes of Oxford in an introductory article, alludes to the ability of a limb extension that can “strip the defensive spines from a piece of fruit, making it safe to eat, but in Thai dancing it can also signal the smallest nuances of emotion. The human hand performs with equal facility a vast array of tasks that natural selection did and did not ‘foresee’.” © 2012 Scientific American,

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17218 - Posted: 08.30.2012

By SEAN B. CARROLL Early one evening a few years ago, I took a short hike with my wife, Jamie, in the Cockscomb Basin Wildlife Sanctuary in Belize. The large, lush reserve is known for its healthy population of jaguars, so, following closely behind our guide, we kept our eyes peeled for the elusive cats. We saw a few tracks and some claw marks on trees, but elected to leave the jungle before nightfall. We were very near the end of the trail when we were surprised by a large snake, about six feet long, crossing directly in front of us. Belize has lots of snakes, more than 50 species. Some can get pretty large, like the boa constrictor, which is impressive but harmless. This one was not harmless. Even in the darkening jungle, the triangular pattern on its back allowed me to identify it quickly as a fer-de-lance, the most dangerous snake in Belize. Excited, and comfortable that I was well out of striking range, I reached into my backpack for my video camera and flipped on its “night shot” feature. I now saw the magnificent snake clearly on my LCD screen. As I tried to creep in for a closer shot, however, I felt something holding me back. It was Jamie. She had a grip on my backpack and was concerned that my enthusiasm for snakes had overtaken my judgment. She was not convinced that we were out of range, nor that the snake would not move quickly toward us. I used the zoom and filmed from where I stood. For me to film the snake in the dark, I had to rely on Sony’s innovation and engineering. The camera’s infrared LED source generated light with a longer wavelength than the human eye can detect; those photons then bounced off the snake and were detected by the camera’s infrared sensors and converted into an image. © 2012 The New York Times Company

Related chapters from BP7e: Chapter 8: General Principles of Sensory Processing, Touch, and Pain; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 5: The Sensorimotor System
Link ID: 17210 - Posted: 08.28.2012

by Hannah Krakauer Kanzi the bonobo continues to impress. Not content with learning sign language or making up "words" for things like banana or juice, he now seems capable of making stone tools on a par with the efforts of early humans. Eviatar Nevo of the University of Haifa in Israel and his colleagues sealed food inside a log to mimic marrow locked inside long bones, and watched Kanzi, a 30-year-old male bonobo chimp, try to extract it. While a companion bonobo attempted the problem a handful of times, and succeeded only by smashing the log on the ground, Kanzi took a longer and arguably more sophisticated approach. Both had been taught to knap flint flakes in the 1990s, holding a stone core in one hand and using another as a hammer. Kanzi used the tools he created to come at the log in a variety of ways: inserting sticks into seams in the log, throwing projectiles at it, and employing stone flints as choppers, drills, and scrapers. In the end, he got food out of 24 logs, while his companion managed just two. Perhaps most remarkable about the tools Kanzi created is their resemblance to early hominid tools. Both bonobos made and used tools to obtain food – either by extracting it from logs or by digging it out of the ground. But only Kanzi's met the criteria for both tool groups made by early Homo: wedges and choppers, and scrapers and drills. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: 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: 17191 - Posted: 08.22.2012

By Jason G. Goldman The largest fish in the ocean is the whale shark (Rhincodon typus). This massive, migratory fish can grow up to twelve meters in length, but its enormous mouth is designed to eat the smallest of critters: plankton. While the biggest, the whale shark isn’t the only gigantic filter-feeding shark out there: the basking shark and the megamouth shark also sieve enormous amounts of the tiny organisms from the sea in order to survive. While scientists like Al Dove and Craig McClain (of Deep Sea News) are learning more and more about the basic biology and behavior of these magnificent creatures, other scientists are busy investigating their neuroanatomy. A few years ago, Kara E. Yopak and Lawrence R. Frank from the University of California in San Diego got their hands on two whale shark brains from an aquarium, and put them into an MRI scanner. But they weren’t just interested in imaging the brains of the whale sharks. What they wanted to know was how the organization of whale shark brains compared to the brains of other shark species for which scientists had previously obtained neuroanatomical data. Would the brains of two species be more similar if they shared a recent evolutionary ancestor, and were therefore more genetically related? Or would shark brains be more similar among species that shared a similar lifestyle, such as those that patrol the middle and surface of the water column (pelagic sharks, such as the great white, oceanic whitetip, blue, mako, and whale sharks) versus those that live along the sea floor (benthic sharks, such as the nurse and cat sharks). Or perhaps the brains of sharks would be grouped according to their habitat, such as those that live in coastal waters, around reefs, or in the open ocean. Maybe sharks brains ought to be grouped according to behavioral specialization, such as hunting methods. Answers to these questions could shed some important light on brain evolution, both in sharks as well as more generally. © 2012 Scientific American

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior; Chapter 2: Functional Neuroanatomy: The Nervous System and Behavior
Related chapters from MM:Chapter 0: ; Chapter 2: Cells and Structures: The Anatomy of the Nervous System
Link ID: 17180 - Posted: 08.18.2012

By Bruce Bower An ancient finger bone recently landed a genetic sucker punch on scientists studying human evolution. DNA extracted from this tiny fossil, unearthed in Siberia’s Denisova Cave, unveiled a humanlike population that interbred with people in East Asia at least 44,000 years ago. Denisovans supplied nearly 5 percent of the genes of native groups now living in Australia, New Guinea and on several nearby islands. That molecular shocker followed a revelation that the genetic instruction books of people from Australia to the Americas contain a roughly 2.5 percent contribution from Neandertals, modern humans’ evolutionary cousins that died out around 30,000 years ago. Pulling the DNA shades up on ancient human dalliances with Neandertals and closely related Denisovans has sparked a scientific consensus that members of mobile human groups interbred with closely related populations in the Homo genus during the Stone Age. “The question is no longer ‘When did ancient populations such as Neandertals go extinct?’ but ‘What happened to those populations and to modern humans as a result of interbreeding?’ ” says anthropologist John Hawks of the University of Wisconsin–Madison. Clear signs of interbreeding have left archaeologists and other students of the Stone Age scrambling to revisit existing ideas about Homo sapiens’ evolutionary past. A dominant theory holding that humans evolved in Africa and left on neat one-way routes to Asia and Europe has to be revised. Instead, these ancient people must have followed a tangled web of paths taking them to other continents and sometimes reversing course. During these travels, humans encountered Neandertals, Denisovans and probably other humanlike populations that were already traipsing interconnected avenues through Asia and Europe. © Society for Science & the Public 2000 - 2012

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17161 - Posted: 08.14.2012

By Michael Harré As humans, we aren't born with formidable armaments or defenses, nor are we the strongest, fastest, or biggest species, yet despite this we are amazingly successful. For a long time it was thought that this success was because our enlarged brains allows each of us to be smarter than our competitors: better at abstract thinking, better with tools and better at adapting our behavior to those of our prey and predators. But are these really the most significant skills our brains provide us with? Another possibility is that we are successful because we can form long-lasting relationships with many others in diverse and flexible ways, and that this, combined with our native intelligence, explains why homo sapiens came to dominate the planet. In every way from teaching our young to the industrial division of labour we are a massively co-operative species that relies on larger and more diverse networks of relationships than any other species. In 1992 British anthropologist Robin Dunbar published an article showing that, in primates, the ratio of the size of the neo-cortex to that of the rest of the brain consistently increases with increasing social group size. For example, the Tamarin monkey has a brain size ratio of about 2.3 and an average social group of size of about 5 members. On the other hand, a Macaque monkey has a brain size ratio of around 3.8 but a very large average group size of about 40 members. From this work Dunbar put forward what is now known as the “social brain hypothesis.” The relative size of the neo-cortex rose as social groups became larger in order to maintain the complex set of relationships necessary for stable co-existence. Most famously, Dunbar suggested that given the human brain ratio we have an expected social group size of around 150 people, about the size of what Dunbar called a “clan.” © 2012 Scientific American,

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17141 - Posted: 08.08.2012

By Tina Hesman Saey Expeditions to Africa may have brought back evidence of a hitherto unknown branch in the human family tree. But this time the evidence wasn’t unearthed by digging in the dirt. It was found in the DNA of hunter-gatherer people living in Cameroon and Tanzania. Buried in the genetic blueprints of 15 people, researchers found the genetic signature of a sister species that branched off the human family tree at about the same time that Neandertals did. This lineage probably remained isolated from the one that produced modern humans for a long time, but its DNA jumped into the Homo sapiens gene pool through interbreeding with modern humans during the same era that other modern humans and Neandertals were mixing in the Middle East, researchers report in the August 3 Cell. The evidence for ancient interbreeding is surprisingly convincing, says Richard “Ed” Green, a genome biologist at the University of California, Santa Cruz. “There is a signal that demands explanation, and archaic admixture seems to be the most reasonable one at this point,” he says. Scientists have discovered that some people with ancestry outside Africa have DNA inherited from Neandertals or Denisovans, a mysterious group known only through DNA derived from a fossil finger bone found in a Siberian cave (SN: 6/5/10, p. 5; SN: 1/15/11, p.10). But those researchers had DNA from fossils to guide their research. This time, researchers led by Sarah Tishkoff at the University of Pennsylvania in Philadelphia didn’t have fossil DNA, or even fossils. © Society for Science & the Public 2000 - 2012

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17112 - Posted: 08.01.2012

By JOHN NOBLE WILFORD In the widening search for the origins of modern human evolution, genes and fossils converge on Africa about 200,000 years ago as the where and when of the first skulls and bones that are strikingly similar to ours. So this appears to be the beginning of anatomically modern Homo sapiens. But evidence for the emergence of behaviorally modern humans is murkier — and controversial. Recent discoveries establish that the Homo sapiens groups who arrived in Europe some 45,000 years ago had already attained the self-awareness, creativity and technology of early modern people. Did this behavior come from Africa after gradual development, or was it an abrupt transition through some profound evolutionary transformation, perhaps caused by hard-to-prove changes in communication by language? Now, the two schools of thought are clashing again, over new research showing that occupants of Border Cave in southern Africa, who were ancestors of the San Bushmen hunter-gatherers in the area today, were already engaged in relatively modern behavior at least 44,000 years ago, twice as long ago as previously thought. Two teams of scientists reported these findings Monday in the journal Proceedings of the National Academy of Sciences. Since this early date for the San culture is close to when modern humans first left Africa and reached Europe, proponents of the abrupt-change hypothesis took the findings as good news. Richard G. Klein, a paleoanthropologist at Stanford University, said in an e-mail from South Africa that the new evidence “supports my view that fully modern hunter-gatherers emerged in Africa abruptly around 50,000 years ago, and I remain convinced that the behavior shift, or advance, underlies the successful expansion of modern Africans to Eurasia.” © 2012 The New York Times Company

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17108 - Posted: 07.31.2012

Matt Kaplan Neanderthals have long been viewed as meat-eaters. The vision of them as inflexible carnivores has even been used to suggest that they went extinct around 25,000 years ago as a result of food scarcity, whereas omnivorous humans were able to survive. But evidence is mounting that plants were important to Neanderthal diets — and now a study reveals that those plants were roasted, and may have been used medicinally. The finding comes from the El Sidrón Cave in northern Spain, where the roughly 50,000-year-old skeletal remains of at least 13 Neanderthals (Homo neanderthalensis) have been discovered. Many of these individuals had calcified layers of plaque on their teeth. Karen Hardy, an anthropologist at the Autonomous University of Barcelona in Spain, wondered whether it might be possible to use this plaque to take a closer look at the Neanderthal menu. Using plaque to work out the diets of ancient animals is not entirely new, but Hardy has gone further by looking for organic compounds in the plaque. To do this she and a team including Stephen Buckley, an archaeological chemist at the University of York, UK, used gas chromatography and mass spectrometry to analyse the plaque collected from ten teeth belonging to five Neanderthal individuals from the cave. The plaque contained a range of carbohydrates and starch granules, hinting that the Neanderthals had consumed a variety of plant species. By contrast, there were few lipids or proteins from meat. © 2012 Nature Publishing Group

Related chapters from BP7e: Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 0:
Link ID: 17067 - Posted: 07.19.2012