From his free monthly nutrition e-mail news letter ( also readable on veganmd.com):http://www.drgreger.org/november2003.html
G. Raw versus Cooked: Which is More Natural?
"Raw foodist" lifestyle advocates tend to argue that cooking is unnatural. They often argue that since we evolved eating raw foods like the rest of the animal kingdom, we are better adapted to eat that way. In a landmark article just published in the journal of Comparative Biology and Physiology, however, two Harvard anthropologists argue just the opposite.[10}
First, they note that other than the new deliberate "raw foodists," there do not seem to be any current or historical populations, small groups or even individuals living for more than a few days without access to cooked foods. Then they take on the belief that cooking is a recent phenomenon for our species.
Mammalian species like ourselves can evolve adaptations in as few as 5000 years. Human beings have been cooking for at least 250,000 years, and maybe as long as 1.9 million years, long before we were even Homo sapiens. They argue that not only have humans adapted to eating cooked foods, they argue that human beings have adapted so much that eating cooked food now seems obligatory for optimum health. And indeed the medical literature backs them up.
The only study I know of 100% raw foodists followed for years was published in 1999. It showed that a third of the raw foodists were suffering from Chronic Energy Deficiency. Many were just wasting away. Most of the women suffered menstrual irregularities and half of the women lost their menstrual periods altogether, which could lead to devastating osteoporosis. And this was in modern urban people with relatively low activity levels who had access to high-quality high-calorie produce from around the world year-round. How might our nontropical gatherer/hunter ancestors lived through a single winter without cooking, especially with their extreme energy expenditure?
There have been major changes in our digestive biology over the past few hundred thousand years, and the researchers argue that these changes may have been due to the availability of cooked foods. 100,000 years ago, for example, the size of our jaws and molar teeth started to shrink, perhaps as an adaptation to softer, easier-chewed cooked foods. They also posit that perhaps other differences between our digestive systems and those of the great apes may also have been because of our adaptation to cooked foods--our smaller gut volume, longer small intestine, smaller colon, and faster gut passage rate.
They conclude that while well-supported individuals in an urban environment with a relatively sedentary lifestyle may be able to thrive on a raw food diet, it is neither natural nor necessarily desirable for optimal health.