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Unformatted text preview: INSIGHTS PALEOANTHROPOLOGY Cooking Up Bigger Brains
Our hominid ancestors could never have eaten enough raw food to support our large, calorie-hungry brains, Richard Wrangham claims. The secret to our evolution, he says, is cooking BY RACHAEL MOELLER GORMAN
ichard Wrangham has tasted chimp In the 10 years since coming on his the- evolution. He is out of his league. Furtherfood, and he doesn't like it. "The ory, Wrangham has stacked up consider- more, archaeological data does not suptypical fruit is very unpleasant," able evidence to support it, yet many port the use of controlled fire during the the Harvard University biological anthro- archaeologists, paleontologists and anthro- period Wrangham's theory requires it to. pologist says of the hard, strangely shaped pologists argue that he is just plain wrong. Wrangham, who first encountered fruits endemic to the chimp diet, some of Wrangham is a chimp researcher, the skep- chimps as a student of Jane Goodall's in which look like cherries, others like cock- tics point out, not a specialist in human 1970, began his career looking at the way tail sausages. "Fibrous, quite bitter. ecological pressures, especially food Not a tremendous amount of sugar. distribution, affect chimp society. He Some make your stomach heave." famously conducted research into After a few tastings in western Uganchimp violence, leading to his 1996 da, where he works part of the year on book Demonic Males. But ever since his 20-year-old project studying wild staring into that fire 10 years ago, he chimpanzees, Wrangham came to the has been plagued with thoughts of conclusion that no human could surhow humans evolved. "I tend to think vive long on such a diet. Besides the about human evolution through the unpalatable taste, our weak jaws, tiny lens of chimps," he remarks. "What teeth and small guts would never be would it take to convert a chimpanable to chomp and process enough zeelike ancestor into a human?" Fire calories from the fruits to support our to cook food, he reasoned, which led large bodies. to bigger bodies and brains. Then, one cool fall evening in And that is exactly what he found 1997, while gazing into his fireplace in Homo erectus, our ancestor that in Cambridge, Mass., and contemfirst appeared 1.6 million to 1.9 milplating a completely different queslion years ago. H. erectus's brain was tion--"What stimulated human evo50 percent larger than that of its prelution?"-- he remembered the chimp decessor, H. habilis, and it experifood. "I realized what a ridiculously enced the biggest drop in tooth size in large difference cooking would human evolution. "There's no other RICHARD WRANGHAM make," Wrangham says. Cooking time that satisfies expectations that could have made the fibrous fruits, we would have for changes in the FLAME ON : Argues that the practice of cooking along with the tubers and tough, raw body that would be accompanied by food, beginning with Homo erectus, ultimately meat that chimps also eat, much cooking," Wrangham says. enabled the human brain to evolve to its current more easily digestible, he thought-- The problem with his idea: proof is large size. they could be consumed quickly and slim that any human could control INTO THE FRYING PAN : His theory has many digested with less energy. This innofire that far back. Other researchers skeptics because only scattered signs of fire use vation could have enabled our chimpbelieve cooking did not occur until by H. erectus exist. One example: a Chinese site like ancestors' gut size to shrink over perhaps only 500,000 years ago. Conwhere H. erectus may have spat hackberry seeds into evolutionary time; the energy that sistent signs of cooking came even latearly campfires (producing spectacular sparks). would have gone to support a larger er, when Neandertals were coping gut might have instead sparked the with an ice age. "They developed earth ON THE IMPORTANCE OF THE STOVE: "Everywhere, evolution of our bigger-brained, largoven cookery," says C. Loring Brace, everyone expects a cooked meal every evening." er-bodied, humanlike forebears. an anthropologist at the University of R 102 SCIENTIFIC AMERICAN 20 07 SCIENTIFIC AMERIC AN, INC. January 2008 KATHLEEN DOOHER INSIGHTS INSIGHTS Michigan at Ann Arbor. "And that only goes back a couple hundred thousand years." He and others postulate that the introduction of energy-rich, softer animal products, not cooking, was what led to H. erectus's bigger brain and smaller teeth. So Wrangham did more research. He examined groups of modern hunter-gatherers all over the world and found that no human group currently eats all their food raw. Humans seem to be well adapted to eating cooked food: modern humans need a lot of high-quality calories (brain tissue requires 22 times the energy of skeletal muscle); tough, fibrous fruits and tubers cannot provide enough. Wrangham and his colleagues calculated that H. erectus (which was in H. sapiens's size range) would have to eat roughly 12 pounds of raw plant food a day, or six pounds of raw plants plus raw meat, to get enough calories to survive. Studies on modern women show that those on a raw vegetarian diet often miss their menstrual periods because of lack of energy. Adding high-energy raw meat does not help much, either-- Wrangham found data showing that even at chimps' chewing rate, which can deliver them 400 food calories per hour, H. erectus would have needed to chew raw meat for 5.7 to 6.2 hours a day to fulfill its daily energy needs. When it was not gathering food, it would literally be chewing that food for the rest of the day. To prove that cooking actually does save energy, Wrangham partnered with Stephen Secor, a University of Alabama biologist who studies the evolutionary design of the digestive system. They found that the python -- an animal model with easily studied gut responses -- expends less effort breaking down cooked food than raw. Heat alters the physical structure of proteins and starches, thereby making enzymatic breakdown easier. Wrangham's theory would fit together nicely if not for that pesky problem of controlled fire. Wrangham points to some data of early fires that may indicate that H. erectus did indeed tame fire. At Koobi Fora in Kenya, anthropologist Ralph Rowlett of the University of Missouri Columbia has found evidence of scorched earth from 1.6 million years ago that contains a mixture of burned wood types, indicating purposely made fire and no In contemplating the question of what stimulated human evolution, "I realized what a ridiculously large difference cooking would make," Richard Wrangham says.
signs of roots having burned underground (a tree struck by lightning would show only one wood type and burned roots). The discoveries are consistent with humancontrolled fire. Rowlett plans next to study the starch granules found in the area to see if food could have been cooked there. Still, most researchers state that unless evidence of controlled fire can be regularly confirmed at most H. erectus sites, they will remain skeptical of Wrangham's theory. Moreover, other food-based theories can explain the body and brain expansion without flames. One is the expensive tissue hypothesis, proposed in 1995 by Leslie C. Aiello, professor emeritus of biological
January 2008 104 SCIENTIFIC AMERICAN 20 07 SCIENTIFIC AMERIC AN, INC. C. LYTTLE zefa/Corbis INSIGHTS anthropology at University College London, and physiologist Peter Wheeler of Liverpool John Moores University in England. The main idea of the hypothesis -- that smaller guts correlate with bigger brains in primates -- fits with Wrangham's theory, but Aiello and Wheeler think that energy-dense animal-derived foods, such as soft bone marrow and brain matter, were the reason humans developed these characteristics, not cooking. Lacking the proof for widespread fire use by H. erectus, Wrangham hopes that DNA data may one day help his cause. "It would be very interesting to compare the human and Homo erectus genetics data to see when certain characteristics arose, such as, When did humans evolve improved defenses against Maillard reaction products?" he says, referring to the chemical products of cooking certain foods that can lead to carcinogens. Even without such evidence yet, some think Wrangham's theory is just the thing to shake up the field of human evolution. "It doesn't matter who develops these ideas," says Aiello, who is also president of the Wenner-Gren Foundation, which supports anthropological research. "You have to listen to what Richard is saying because he has some very interesting, original data. Sometimes the most creative ideas come from unexpected places." She points to Goodall, who surprised the world by proving that humans were not the only toolmakers. "It's one of the best illustrations I know of the value of primate research informing our knowledge of human evolution and adaptation," Aiello says. If Wrangham's strange ideas turn out to be true, we can thank an early hominid Emeril Lagasse who picked a charred tuber out of a campfire and swallowed it. Without that person, we might never have been able to examine our origins -- or enjoy a good grilled steak-- in the first place. g Rachael Moeller Gorman is a writer based in Boston. A Q&A version of her interview with Wrangham is at www.SciAm.com/ontheweb
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This note was uploaded on 04/16/2008 for the course BIO 131 taught by Professor Paz y mino during the Fall '08 term at UMass Dartmouth.
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