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HARVARD GAZETTE ARCHIVES

Cooking up quite a story:

Ape, human theory causes evolutionary indigestion

By William J. Cromie
Gazette Staff

Think about this the next time you're waiting for your burgers to cook on the grill: How was cooking "invented"? Today, all societies depend on cooked food, but when and how did cooking begin?

It's an important question. Cooking played a major role in the development of smaller jaws and teeth, bigger brains, smaller guts, shorter arms, and longer legs, according to Richard Wrangham, professor of biological anthropology at Harvard University. He also believes that cooking is associated with females getting heavier and more fertile. That, in turn, changed mating and social behaviors. Instead of large males beating each other with clubs for the relatively rare privilege of mating, smaller guys mated more regularly and began to dine with the family more often.

There's a lot of agreement among anthropologists that human ancestors were cooking their food as long ago as 250,000 to 500,000 years, but Wrangham and a few of his colleagues see evidence that cooks spoiled the broth as long ago as 2 million years. That's about the time when our ancestors became less like apes and more like humans.

There's more agreement on how cooking started than when. Most anthropologists think bush fires, started by lightning, baked or singed exposed tubers and other roots. Human ancestors tried the fired food and the rest, as they say, is history.

One of the big unknowns in this scenario is when our ancestors started to build their own fires. Many clues point to the conclusion that pre-people lit their own fires about 300,000 years ago, but much less positive evidence hints that they controlled fire a million and a half years earlier. Either way, use of fire for warmth, or to keep away large animals with sharp teeth, would have hastened the origin of roast roots and meat.

The joy of cooking

Whenever its origin, cooking had an enormous impact. Heating food makes it safer, more digestible, and better tasting. Even Charles Darwin thought about this. Cooking, he wrote, provides a means "by which hard and stringy roots can be rendered digestible, and poisonous roots or herbs innocuous." Cooking allows a diner to extract many more calories from a root or thigh than eating it raw.

Wrangham was staring at a fire one evening in his backyard when thoughts about the difficulty of eating raw food ignited the embers of his theory. "I've studied chimps for many years in East Africa," he notes. "To get insight into how they live, I have eaten the same food they do. Chewing raw food requires a lot of work."

Wrangham first reported his theory of fire control in a 1999 scientific paper co-authored with several colleagues, including David Pilbeam, Curator of Paleoanthropology in Harvard's Peabody Museum of Archaeology and Ethnology. They and a few others have continued to expand on the idea of cooking as a much more ancient art than generally believed. They have gathered evidence both from ancient ape-people and modern humans.

Studies of modern food faddists who eat only raw food indicate that it's not a very healthy diet. About a third of such people have chronic energy deficits, according to one study. Half of the women stop menstruating. "And this is under the best possible conditions," Wrangham notes, "when the food is abundant and of good quality."

Less chewing and gnawing would gradually lead to less massive jaws and smaller, rounder teeth. It can also account for reduction of gut and rib-cage size. "You don't need large body chambers to break down stringy carbohydrates," Wrangham says. "And more readily digested food can account for the increased energy needed for fueling a larger brain."

When researchers look for such body and brain changes, they find them in skulls and bones as old as 1.9 million years. This is the time when ape-persons were evolving into Homo erectus, an immediate ancestor of modern humans. As the name implies, H. erectus walked upright. His and her arms were no longer adapted for hanging in trees and their legs were longer. The size of their brain cases almost doubled that of apes.

A most curious and dramatic change also developed in the relative size of males and females. Females became a full 60 percent heavier, drastically reducing the size difference between them and males. "Ape males are 50 to 100 percent larger than ape females," Wrangham points out. But the size difference in Homo erectus was essentially the same as that of modern humans, or about 15-20 percent."

Critics who say the early-cooking theory is half-baked attribute such changes to eating more raw meat. Those who preceded H. erectus, referred to as australopithecines, learned to make better stone weapons and to hunt bigger game. That living style, they insist, could have changed brain and body size.

Ah, but what about the teeth and jaws? Eating raw meat, even when sliced up by a keen stone knife, would result in sharp, spiky dentures, not smaller rounded teeth sculpted by eating softer food.

Then there's the big time gap. Australopithecines scavenged or hunted big game 2.5 million years ago, a half million years or more before H. erectus came on the scene. What happened during the gap? After the dramatic changes of 1.9 million years B.C., no remarkable body shifts took place until roughly 100,000 years ago. If cooking didn't begin until 500,000-250,000 years ago, why are there no prominent changes in face and shape like those that occurred 1.9 million years ago?

Hearth times

All of that is just circumstantial evidence, Wrangham admits. There is no "smoking skewer" to prove H. erectus families gathered around hearths so far back in time.

Evidence most anthropologists feel comfortable with shows that our ancestors in Europe dug oven pits 300,000 years ago. In Africa, small patches of reddened, heavily oxidized soil date from 1.5 million years. Even Wrangham agrees that these spots could be caused by natural changes. However, he notes that "Africans don't use cooking pits today. They cook over campfires, traces of which soon disappear."

Studies now under way may resolve the controversy. Microbits of wood and plant material around the reddened areas could show if these particles came from one kind of bush or tree, which would indicate in-place burning by lightning. If the particles come from diverse sources, that would support the idea of wood being brought from different places to build a campfire. Close examination of "microwear" on fossil teeth might also reveal when our ancestors switched to food softened by cooking.

"The evidence in favor of our theory will get stronger," Wrangham believes.

Cooking heats up mating

Reduction in size difference between early H. erectus males and females resulted in profound differences in mating and social behavior that helped to distinguish humans from their more ape-like predecessors, Wrangham maintains. Among apes, the largest males win battles to impregnate females. That doesn't lead to very frequent mating. Gorillas, for example, have fewer than 20 copulations per birth.

When size is more equal, smaller males get to mate more frequently. For chimpanzees and humans, the mating rate rises to 100 or more copulations per birth. This leads Wrangham to postulate that an important turn toward the current human system of mating took place with the evolution of H. erectus some 2 million years ago, the only known time during evolution when the relative body size of males dropped so markedly.

Cooking meant that food would be brought "home," instead of being eaten on the spot. That must have created the problem of large, lazy males raiding the larders attended only by females. They, in turn, would have reacted by trying to form closer relationships with males who would protect their food stores. One way to do this was to increase their sexual attractiveness, which would have increased the number of matings per pregnancy, reduced competition between males, and led to more pair bonding.

If all this is true, then cooking had a major impact on humanization. As Wrangham puts it: "If the foraging and mating systems of humans were indeed shaped powerfully by cooking, the ancient Greek myth that attributes humanity to the gift of fire may be close to the truth."









Copyright 2002 by the President and Fellows of Harvard College