The Evolutionary Increase in the Size of the Main Areas of the Brain

The crucial change in the human brain in this million years or so has not been so much the increase in size by a factor of three, but the concentration of that increase in three or four main areas. The visual area has increased considerably, and, compared with the chimpanzee, the actual density of human brain cells is at least 50 percent greater.

A second increase has taken place in the area of manipulation of the hand, which is natural since we are much more hand-driven animals than monkeys and apes. Another main increase has taken place in the temporal lobe, in which visual memory, integration, and speech all lie fairly close together. And the fourth great increase has taken place in the frontal lobes. Their function is extremely difficult to understand ...; but it is clear that they're largely responsible for the ability to initiate a task, to be attentive while it is being done, and to persevere with it. (Bron-owski, 1978, pp. 23-24)

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