ABSTRACT
Throughout evolution, vital energy resources are channelled into body organs which will enhance an animal’s chance of survival. In hominins this was the brain rather than muscle. The human brain accounts for 2% of the body weight, but 20-25% of its energy, An increase of 350% in size of the hominin neocortex over the last 2 million years was associated with a 600% increase in blood flow. This energy supply had to be diverted from other body organs (heart, liver, kidney and gut). The gut was the only possible option as the other 3 were working at optimum efficiency. This diversion of blood and energy resources to the brain was only made possible because of a significant change in hominin diet when fire was discovered and hominins started to cook, allowing far quicker digestion of previously tough food.
In early hominins, the intestinal tract was geared to slow digestion of plant foods and later a more omniverous diet. Like chimpanzees, they spent 5-6 hours a day chewing raw food. Use of fire meant that the gut was shortened and required much less energy, allowing redirection of blood and energy resources to the developing brain. Increasing intelligence led to the cognitive revolution, several aspects of which are discussed. More recent genetic evidence has implicated two genes which control brain development. (208 words)
