To put it another way, our ancestors found a way to pre-digest food outside the body. Biologically, we only have one stomach; prosthetically, we have two. And the authors tentatively suggest that this shift is what allowed us to develop more complex cognition:
For a long time, we were pretty dumb. Humans did little but make "the same very boring stone tools for almost 2 million years," he said. Then, only about 150,000 years ago, a different type of spurt happened — our big brains suddenly got smart. We started innovating. We tried different materials, such as bone, and invented many new tools, including needles for beadwork. Responding to, presumably, our first abstract thoughts, we started creating art and maybe even religion.
To understand what caused the cognitive spurt, Khaitovich and colleagues examined chemical brain processes known to have changed in the past 200,000 years. Comparing apes and humans, they found the most robust differences were for processes involved in energy metabolism.
The finding suggests that increased access to calories spurred our cognitive advances, said Khaitovich, carefully adding that definitive claims of causation are premature.
The research is detailed in the August 2008 issue of Genome Biology.
The extra calories may not have come from more food, but rather from the emergence of pre-historic "Iron Chefs;" the first hearths also arose about 200,000 years ago.
In most animals, the gut needs a lot of energy to grind out nourishment from food sources. But cooking, by breaking down fibers and making nutrients more readily available, is a way of processing food outside the body. Eating (mostly) cooked meals would have lessened the energy needs of our digestion systems, Khaitovich explained, thereby freeing up calories for our brains.
Instead of growing even larger (which would have made birth even more problematic), the human brain most likely used the additional calories to grease the wheels of its internal functioning.
The raw food movement and other health food movements tend to focus on "natural" foods and diets. But if we were cyborgs before we were human, does the idea of a "natural" diet even make sense? Second question: is there anything more natural to human beings than a good cookbook?
Today, humans have relatively small digestive systems and burn 20-25 percent of their calories running their brains. For comparison, other vertebrate brains use as little as 2 percent of the animal's caloric intake.
Does this mean renewing our subscriptions to Bon Appetit will make our brains more efficient? No, but we probably should avoid diving into the raw food movement. Devoted followers end up, said Khaitovich, "with very severe health problems."