The human brain evolved its disproportionately large size more in response to ecological challenges–like finding food and shelter–than to the need to adapt to complex social situations, suggests a study in Nature. The proportion of brain size to body size is larger in humans than in other mammals. Due to its size and physiological activity, the human brain uses about 20 percent of the body’s energy. Researchers developed a mathematical model that used data about the metabolic costs of brain activity to simulate brain evolution. They found that the human brain attained its current size when the pressures our ancestors faced were 60 percent ecological, 30 percent cooperative/social and 10 percent competitive with other groups. (Monitor on Psychology)

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