Catching Fire

by Richard Wrangham

How many times have you read a book and been so struck by the cogency of its thesis that you slapped yourself on the forehead and exclaimed, “Why didn’t I think of that?” I had that experience recently when I read In the Blink of an Eye, which explained the Cambrian Explosion half a billion years ago as the direct result of the development of vision.

Well, I had that experience again when I read this book. It starts with an idea that everybody knows, then develops it to surprising results. That idea is that cooking was an important step in the development of
Homo Sapiens. Sure, everybody knows that. But Mr. Wrangham takes that concept much further than you would expect. His starting point is the observation that cooking saves us enormous amounts of effort. For example, gorillas, who are vegetarians, spend many hours each day chewing their food. Humans, by contrast, spend perhaps an hour a day masticating their food. This frees their time up for all sorts of other activities, such as playing videogames or hunting gazelles. An even more surprising fact is the cost of digesting food. Converting all that mangled food into usable nutrients is a complicated chemical process that requires a considerable amount of metabolic energy. In other words, it takes energy to digest food. With many low-quality foods, especially vegetable matter, the digestive cost of the food is almost as great as the energy derived from the food. That in turn means that a vegetarian must spend a great deal of time gathering, eating, and digesting food just to stay ahead of the game.

Here’s where cooking comes in: cooking food breaks down many of the complex molecules that are so difficult to digest. Viewed this way, cooking is a kind of “external pre-digestion” that permits humans to make the food both easier to chew and easier to digest. By cooking their food, humans magnified its nutritive value. Mr. Wrangham offers a great deal of evidence from nutrition science to show that we cannot derive much nutrition from raw food. Our digestive systems have evolved to take advantage of the benefits of cooking. Our teeth are smaller than those of our ancestors, because we don’t have to do as much chewing. Our intestinal tracts are shorter, because we don’t have to subject our food to as much digestive chemistry to obtain its nutrients. In effect, by moving a portion of our digestive process out of the body and into the cooking pot, we were able to prosper with leaner, less encumbered bodies. It is theoretically possible for a human to survive on purely raw food -- there is a movement of food purists who insist on eating raw food. But such people must carefully manage their diets if they are to avoid malnutrition. Did you know that you obtain less nutrition from a raw egg than a cooked one?

Inasmuch as the distinctive changes in our dentition and digestive tracts are first evidence nearly two million years ago, Mr. Wrangham concludes that hominids began cooking their food roughly two million years ago. His conclusion is not supported by any direct evidence; the oldest example we have of a fireplace or campfire known to be associated with human detritus is only 750,000 years old. Still, the evidence from fossils clearly shows hominid teeth becoming smaller almost two million years ago. That reduction in size was no accident; something caused it, and cooking is easily the best hypothesis to explain it.

Thus, cooking wasn’t merely a side element in the evolution of humanity – it was absolutely fundamental to our progress. Had we not stumbled upon cooking, it is inconceivable that we would have developed the other accoutrements of humanness. Cooking must be added to language as one of the fundamental defining components of the human behavioral set.