Half a million years ago, our ancestors found themselves with very big brains. Yet, they were not particularly intelligent. To what do we owe their rapid transformation into highly intelligent modern humans? It seems that we have been touched not so much with celestial fire, as poet William Blake would say, but with metabolic fire. Recent genetic research finds that our brains started to use energy much more rapidly. We ascended into sublime realms of thought and creativity but also incurred greater risk of mental illness.
The human brain increased in size for different evolutionary reasons (see earlier posts). We had a boost from being primates, and therefore highly social. We also adjusted to a diet high in meat and refined foods that shrank the intestines and fueled a rapid increase in brain size.
After all this brain enlargement, our ancestors were still comparatively dimwitted brutes. They lacked originality in tool construction, were pre-linguistic, and left behind no evidence whatever of any introspective thought. This was a somnolent Frankenstein monster waiting for the electric current to get switched on.
According to Chinese biologist Philipp Khaitovich (1), our big brains suddenly became smart about 200,000 to 150,000 years ago which is but a blink of the eye in terms of evolutionary time. His genetic research indicates that during this period our brains began to burn extra calories.
So what earth-shattering transition accounted for this development in cerebral energetics? We began using fire to prepare our meals. The earliest hearths date to about 200,000 years ago.
Why is cooking so critical? The key point is that cooking partially breaks down food making it easier to digest. Thanks to the culinary arts, the human gut had less work to do and shrank even further. With the further decline in our intestines, yet more energy was freed up for the brain.
Yet, our brains did not expand further. If you want to understand why the brain did not get any more enlarged, ask any woman who has recently given birth whether this would be a good idea. Instead of getting bigger, the brain underwent metabolic change allowing it to burn through more energy without increasing its volume.
This increased energy use meant that we got suddenly, and dramatically, smarter. Before long, humans were refining their toolkit into the efficient technology for killing at a distance that drove many large prey species into extinction around the globe (an event known as the Pleistocene overkill).
If the culinary theory of intelligence has any merit, there are at least two important practical implications, in no particular order. First, our brains are adapted to a diet that is cooked. This means that one should be wary of the raw food movement. According to Khaitovich, this may lead to severe health problems (2). Second, the metabolic changes in brain tissue that allowed us to use more energy, and to think more elaborate thoughts, pushed our brains to an extreme performance where they are more likely to break down. We became more vulnerable to schizophrenia and other mental illnesses.
The flavor of this risk is captured by poet John Dryden's line that "Great wits [meaning intelligence] are sure to madness near allied" Very brainy people, such as novelists, and other highly creative folk do suffer more from a variety of brain disorders including migraine, depression, and mania. When pushed to its limits, the brain, like any other system, is vulnerable to failure. That is why so few race cars can last through an entire race without a pit stop.
By controlling fire and using it to prepare their food, our ancestors could rev their cognitive engines in a manner previously unknown on Earth. Hence the explosion of new technologies through which we have come to dominate, and endanger, this planet.
Cooking gave our brains more fuel and genetic change allowed us to exploit it through speeded-up cerebral metabolism. The consequences have been interesting. Or, as William Blake would say, "energy is eternal delight."
1. Khaitovich, P., et al. (2008). Metabolic changes in schizophrenia and human brain evolution. Genome Biology, 9: R124, 1-11.
2. Nixon, R. (2008, 11 August). Cooking and cognition: How humans got so smart. LiveScience.
