2. We have a surfeit of facts. What we do not have, and most of us in the quiet of our nights know it, is an overarching conception of context in which we can put these facts and, having done so, the truth then stands a chance of emerging. Seymour B. Sarason (1989, p. 279)
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Editor's Notes
http://www.npr.org/templates/story/story.php?storyId=128849908 Our earliest ancestors ate their food raw — fruit, leaves, maybe some nuts. When they ventured down onto land, they added things like underground tubers, roots and berries. It wasn't a very high-calorie diet, so to get the energy you needed, you had to eat a lot and have a big gut to digest it all. But having a big gut has its drawbacks. "You can't have a large brain and big guts at the same time," explains Leslie Aiello, an anthropologist and director of the Wenner-Gren Foundation in New York City, which funds research on evolution. Digestion, she says, was the energy-hog of our primate ancestor's body. The brain was the poor stepsister who got the leftovers. More From The Human Edge The Human Edge Mrs. Charles Darwin's Advice For Walking Upright The lovely Emma Darwin has graciously volunteered to show the differences between humans and chimps. The Human Edge Until, that is, we discovered meat. "What we think is that this dietary change around 2.3 million years ago was one of the major significant factors in the evolution of our own species," Aiello says. That period is when cut marks on animal bones appeared — not a predator's tooth marks, but incisions that could have been made only by a sharp tool. That's one sign of our carnivorous conversion. But Aiello's favorite clue is somewhat ickier — it's a tapeworm. "The closest relative of human tapeworms are tapeworms that affect African hyenas and wild dogs," she says. So sometime in our evolutionary history, she explains, "we actually shared saliva with wild dogs and hyenas." That would have happened if, say, we were scavenging on the same carcass that hyenas were. But dining with dogs was worth it. Meat is packed with lots of calories and fat. Our brain — which uses about 20 times as much energy as the equivalent amount of muscle — piped up and said, "Please, sir, I want some more." Carving Up The Diet As we got more, our guts shrank because we didn't need a giant vegetable processor any more. Our bodies could spend more energy on other things like building a bigger brain. Sorry, vegetarians, but eating meat apparently made our ancestors smarter — smart enough to make better tools, which in turn led to other changes, says Aiello. "If you look in your dog's mouth and cat's mouth, and open up your own mouth, our teeth are quite different," she says. "What allows us to do what a cat or dog can do are tools." Tools meant we didn't need big sharp teeth like other predators. Tools even made vegetable matter easier to deal with. As anthropologist Shara Bailey at New York University says, they were like "external" teeth. "Your teeth are really for processing food, of course, but if you do all the food processing out here," she says, gesturing with her hands, "if you are grinding things, then there is less pressure for your teeth to pick up the slack." Our teeth, jaws and mouth changed as well as our gut. Enlarge Jung Yeon-Je/AFP/Getty Images Meat is packed with lots of calories and fat. Jung Yeon-Je/AFP/Getty Images Meat is packed with lots of calories and fat. A Tough Bite To Swallow But adding raw meat to our diet doesn't tell the whole food story, according to anthropologist Richard Wrangham. Wrangham invited me to his apartment at Harvard University to explain what he believes is the real secret to being human. All I had to do was bring the groceries, which meant a steak — which I thought could fill in for wildebeest or antelope — and a turnip, a mango, some peanuts and potatoes. As we slice up the turnip and put the potatoes in a pot, Wrangham explains that even after we started eating meat, raw food just didn't pack the energy to build the big-brained, small-toothed modern human. He cites research that showed that people on a raw food diet, including meat and oil, lost a lot of weight. Many said they felt better, but also experienced chronic energy deficiency. And half the women in the experiment stopped menstruating. It's not as if raw food isn't nutritious; it's just harder for the body to get at the nutrition. Wrangham urges me to try some raw turnip. Not too bad, but hardly enough to get the juices flowing. "They've got a tremendous amount of caloric energy in them," he says. "The problem is that it's in the form of starch, which unless you cook it, does not give you very much." Then there's all the chewing that raw food requires. Chimps, for example, sometimes chew for six hours a day. That actually consumes a lot of energy. "Plato said if we were regular animals, you know, we wouldn't have time to write poetry," Wrangham jokes. "You know, he was right."
