What’s Cooking?

Besides the use of written language, one of the most distinctive characteristics of humans, as a species, is that we cook our food.  Dr. Richard Wrangham, who is a Professor of Biological Anthropology at Harvard University, and is the director of the Kibale Chimpanzee Project in Uganda, has a theory that cooking is not only a distinctly human trait, but something that helped shaped human evolution in the first instance.

The NPR Web site has an interview with Dr. Wrangham [transcript and audio] in which he discusses his theory.  Although the origins of cooking are, as he says, lost in pre-history, there is some good evidence that people would have immediately liked cooked food, even if its discovery was accidental:

…  the reason for saying that is we have done tests on the great apes, and the great apes uniformly show a preference for cooked food over raw or sometimes have no preference for cooked over raw in the case of one or two things, but they never prefer raw to cooked.

The evolutionary question Dr. Wrangham is trying to answer is what happened that led to the development of modern humans, first Homo erectus and then Homo sapiens (us), distinct from our common ancestors with the great apes.  The most obvious biological difference is that we have very much larger brains; and this is an issue because, not to put too fine a point on it, the brain is a metabolic pig, using something like 20-25 % of the calories burned by the body.  Yet, despite the increased energy requirements of a big brain, humans have significantly smaller jaws, teeth, and digestive systems than our great ape relatives.

Dr. Wrangham’s theory is that cooking accounts for the difference.  Cooked food is more efficiently digested for several reasons:

• It makes the food softer, so that fewer calories need to be expended to mechanically break down the food in the gut.  (Interestingly, some chimpanzees will mash some foods before eating them, presumably for the same reason.)
• Cooking makes protein more available for digestion, by relaxing its molecular structure, making the amino acids more accessible to digestive enzymes.
• Cooking also makes some carbohydrates (starches) more accessible, by opening up the structure of amylose and amylopectin sugar chains to digestive action.

It’s estimated, for example, that if an egg is eaten raw, about 55-60 % of the protein can be digested; if the egg is cooked before eating, then about 95 % of the protein can be digested.  So, in essence, cooking increases the “rate of return” on eating, allowing us to get enough fuel to run our large, expensive brains with a reasonable expenditure of effort.  Confirming this, it’s observed that people who try to eat a diet composed entirely of raw “natural” foods have difficulty getting enough calories.

(This also points up a flaw in the way foods are currently labeled for their nutritional value.  The implicit assumption in this labeling is that the number of calories from, say, a carrot is the same whether it is eaten raw or cooked.  Some of this newer research indicates that assumption is false.  Interestingly, this may explain in part why the increased prevalence of highly-processed foods in our diet is correlated with excess weight.)

So the next time you grill a steak, or make some scrambled eggs, be reassured that you’re just doing what comes naturally.  Of course, if you want to be an evolutionary rebel, you could always have some sushi.