Cooking Up Bigger Brains

One of the latest podcasts from The Economist had a fascinating interview with Harvard biological anthropologist Richard Wrangham. He maintains that the leap from the big chest cavities of H. habilis to the big brain pans of H. erectus may have been facilitated or even made possible by cooking:

Richard Wrangham has tasted chimp food, and he doesn’t like it. “The typical fruit is very unpleasant. . . . Fibrous, quite bitter. Not a tremendous amount of sugar. Some make your stomach heave.” After a few tastings in western Uganda, where he works part of the year on his 20-year-old project studying wild chimpanzees, Wrangham came to the conclusion that no human could survive long on such a diet. Besides the unpalatable taste, our weak jaws, tiny teeth and small guts would never be able to chomp and process enough calories from the fruits to support our large bodies.

Then, one cool fall evening in 1997, while gazing into his fireplace in Cambridge, Mass., and contemplating a completely different question — “What stimulated human evolution?” — he remembered the chimp food. “I realized what a ridiculously large difference cooking would make,” Wrangham says. Cooking could have made the fibrous fruits, along with the tubers and tough, raw meat that chimps also eat, much more easily digestible, he thought—they could be consumed quickly and digested with less energy. This innovation could have enabled our chimp­like ancestors’ gut size to shrink over evolutionary time; the energy that would have gone to support a larger gut might have instead sparked the evolution of our bigger-brained, larger-bodied, humanlike forebears.

The podcast interview continued this thread, noting that the current rise in obesity corresponds with the rise in eating ever more processed foods, essentially softer and hotter meals. Wrangham notes that heat from cooking changes the available energy content of food in three main ways:

Heat gelatinizes starches and collagens, allowing the glucose molecules to dissolve and become available to digestive enzymes;

Heat denatures proteins, opening them and likewise exposing them to digestive enzymes; and

Heat softens food.

Don't discount that last point! The less work the digestive tract has to do to free the nutrients from a meal, the more nutrient doesn't have to be converted into energy to allow the tract to do that work. For an analogy, imagine running into a steady headwind. Cooking food can put the wind to your back, helping you rather than hampering and allowing you more energy to make more speed or distance. Comparing a day's worth of meals identical in caloric value but differing in whether or not they were cooked, Wrangham estimates raw meals require extra energy "probably about the equivalent of running a mile." To support this last claim, he cited a study by Oka in which rats eat meals similar in caloric intake, but different in texture. Even with the same exercise regimen, the rats eating the softer diet gain more weight.

We digest with both physical and chemical processes, but for decades now, he notes, diet has been the domain of those concentrating almost solely on biochemistry. Hopefully more emphasis can be placed on the biophysics.


Note: I'm tagging this one in the Worms! category, because though no worms were mentioned, much of what he said reminded me of The Wife's digestive symptoms.