http://www.sciam.com/article.cfm?id=evolving-bigger-brains-th&page=1Your theory that cooking spurred the evolution of modern humans occurred to you while you were sitting in front of your own fireplace?
Yes, about 10 years ago, right after the start of the academic term, I was thinking about what stimulated human evolution. The fire just started drawing me in to the comparison with chimps, because I tend to think about human evolution through the lens of chimps: What would it take to convert a chimpanzeelike ancestor into a human? And as I thought about how long we have had fire, I realized what a ridiculously large difference cooking would make. It's a very simple thought; anyone who had ever taken an anthropology course should have had it long before this.
Just how would cooking make a difference? What's wrong with raw food that chimps eat?
I know chimpanzee foods fairly intimately, I've tasted the great majority of the things I've seen them eat, and I know what a huge difference there is between a chimpanzee diet and the human diet, because we cook. And that set me off thinking about whether or not humans really could ever survive on a raw diet. And my instant assumption was no, because of my experience with chimpanzee diets, which said to me we couldn't possibly do this?so that raises all these fascinating evolutionary questions. I'd had the experience of seeing a close relative eating all those foods and seeing how unpleasant they are and how difficult it would be for humans to survive on a diet like that. Maybe people assume that the kinds of places in which humans live would have apples and bananas dripping off the trees, but it's not like that.
What are the foods like, then?
The typical fruit is very unpleasant, very fibrous, quite bitter; the net effect is that you would not want to eat more than two or three of them before running for a big glass of water and saying, "That was not a pleasant experiment, I hope I don't get sick." They're not nice to eat. Not a tremendous amount of sugar in them. So there were very few fruits that I've tasted that I can actually imagine getting a stomach for because most of them are unpleasant to eat. Some make your stomach heave.
But maybe if we?or ancient humans?were accustomed to them, we would be able to eat them.
I recognize that I've got a palate softened by ease, and it may well be that if you're hungry in the bush you might be prepared to eat a lot of these nasty tasting things, but I've worked with Pygmies in eastern Congo in a forest where I knew a fair number of fruits were being eaten by chimps, and I would ask them, and they'd say there's no way I would ever eat this stuff. Chimpanzees eat, on average, 60 percent of their food as fruit. Humans couldn't do that. So one of the fascinating things for me as I ventured into this was really learning about what hunters and gatherers eat?and it turns out that there are no records of people having a large amount of their food come from raw food. Everywhere, everyone expects a cooked meal every evening.
What about the way our bodies are set up to digest food?besides not liking the taste, can we digest the foods chimps eat?
I think we can probably digest them?this is guesswork because we don't really know?but the point is they're very full of indigestible fiber. So the average human diet has, even in the more fibrous hunter-gatherer types, 5 to 10 percent, say, indigestible fiber. With our chimp studies, they eat 32 percent indigestible fiber. So that is something that the human body is not designed to handle. And the reason we can say that is that we have small colons and small stomachs which are adapted to food that has high caloric density. And food the chimps eat has low caloric density.
