Scientific American Magazine - January, 2008
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
Richard Wrangham has tasted chimp food, and he doesn’t like it. "The typical
fruit is very unpleasant," the Harvard University biological anthropologist says
of the hard, strangely shaped fruits endemic to the chimp diet, some of which
look like cherries, others like cocktail sausages. "Fibrous, quite bitter. Not
a tremendous amount of sugar. Some make your stomach heave." After a few tastings
in western Uganda, where he works part of the year on his 20-year-old project
studying wild chimpanzees, Wrangham came to the conclusion that no human could
survive long on such a diet. Besides the unpalatable taste, our weak jaws, tiny
teeth and small guts would never be able to chomp and process enough calories from
the fruits to support our large bodies.
Then, one cool fall evening in 1997, while gazing into his fireplace in
Cambridge, Mass., and contemplating a completely different question — "What
stimulated human evolution?" — he remembered the chimp food. "I realized what a
ridiculously large difference cooking would make," Wrangham says. Cooking could
have made the fibrous fruits, along with the tubers and tough, raw meat that chimps
also eat, much more easily digestible, he thought—they could be consumed quickly
and digested with less energy. This innovation could have enabled our chimplike
ancestors’ gut size to shrink over evolutionary time; the energy that would have
gone to support a larger gut might have instead sparked the evolution of our
bigger-brained, larger-bodied, humanlike forebears.
...
Wrangham, who first encountered chimps as a student of Jane Goodall’s in 1970,
began his career looking at the way ecological pressures, especially food
distribution, affect chimp society. He famously conducted research into chimp
violence, leading to his 1996 book Demonic Males. But ever since staring into
that fire 10 years ago, he has been plagued with thoughts of how humans evolved.
"I tend to think about human evolution through the lens of chimps," he remarks.
"What would it take to convert a chimpanzeelike ancestor into a human?" Fire to
cook food, he reasoned, which led to bigger bodies and brains.
And that is exactly what he found in Homo erectus, our ancestor that first appeared
1.6 million to 1.9 million years ago. H. erectus’s brain was 50 percent larger than
that of its predecessor, H. habilis, and it experienced the biggest drop in tooth
size in human evolution. "There’s no other time that satisfies expectations that we
would have for changes in the body that would be accompanied by cooking," Wrangham
says.
...
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.
...
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
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 human-controlled
fire. Rowlett plans next to study the starch granules found in the area to see if
food
could have been cooked there.
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