The Evolutionary Role of Cookery

Dr Wrangham thus believes that cooking and humanity are coeval. In fact, as he outlined to the American Association for the Advancement of Science (AAAS), in Chicago, he thinks that cooking and other forms of preparing food are humanity’s “killer app”: the evolutionary change that underpins all of the other—and subsequent—changes that have made people such unusual animals.

Humans became human, as it were, with the emergence 1.8m years ago of a species called Homo erectus. This had a skeleton much like modern man’s—a big, brain-filled skull and a narrow pelvis and rib cage, which imply a small abdomen and thus a small gut. Hitherto, the explanation for this shift from the smaller skulls and wider pelvises of man’s apelike ancestors has been a shift from a vegetable-based diet to a meat-based one. Meat has more calories than plant matter, the theory went. A smaller gut could therefore support a larger brain.

Dr Wrangham disagrees. When you do the sums, he argues, raw meat is still insufficient to bridge the gap. He points out that even modern “raw foodists”, members of a town-dwelling, back-to-nature social movement, struggle to maintain their weight—and they have access to animals and plants that have been bred for the table. Pre-agricultural man confined to raw food would have starved.

Interesting. It was cooking rather than meat that allowed humans to prosper.

How big of a difference does cooking make?

Cooking alters food in three important ways. It breaks starch molecules into more digestible fragments. It “denatures” protein molecules, so that their amino-acid chains unfold and digestive enzymes can attack them more easily. And heat physically softens food. That makes it easier to digest, so even though the stuff is no more calorific, the body uses fewer calories dealing with it.

Cooking increases the share of food digested in the stomach and small intestine, where it can be absorbed, from 50% to 95% according to work done on people fitted for medical reasons with collection bags at the ends of their small intestines. Previous studies had suggested raw food was digested equally well as cooked food because they looked at faeces as being the end product. These, however, have been exposed to the digestive mercies of bacteria in the large intestine, and any residual goodies have been removed from them that way.

Another telling experiment, conducted on rats, did not rely on cooking. Rather the experimenters ground up food pellets and then recompacted them to make them softer. Rats fed on the softer pellets weighed 30% more after 26 weeks than those fed the same weight of standard pellets. The difference was because of the lower cost of digestion. Indeed, Dr Wrangham suspects the main cause of the modern epidemic of obesity is not overeating (which the evidence suggests—in America, at least—is a myth) but the rise of processed foods. These are softer, because that is what people prefer. Indeed, the nerves from the taste buds meet in a part of the brain called the amygdala with nerves that convey information on the softness of food. It is only after these two qualities have been compared that the brain assesses how pleasant a mouthful actually is.

I was aware that cooking makes food easier to digest, but I was not aware the extent to which cooking increases absorption of nutrients.

This makes me wonder how accurate nutritional labels are. It appears that raw foods should show only 1/2 the calories that cooked foods do. Calorie counting just got a whole lot more complicated.

In a way, cooking allowed humans to "eat" woods and grasses that we couldn't digest. A portion of the calories in these biofuels was transferred to raw foods via cooking. It has been estimated that our current agricultural system uses seven to ten calories of input energy to produce one calorie of food. I wonder how the calories in the biofuels used to cook compared to the calories in the raw food eaten? Was more land (or net primary productivity) needed to support one human who cooked his food than one who ate it raw? Hopefully his upcoming book Catching Fire: How Cooking Made Us Human will answer these questions.

via The Economist and Wired