This introductory chapter examines the sizes of human brains in the prehistoric era to emphasize the important aspect of human brain evolution. The Australopithecus, considered as the forebears of the human species (Homo), had a brain weighing only 400 grams. They inhabited the earth at the end of the Tertiary period. During the ice age, the Homo habilis and Homo erectus appeared in Africa and Europe respectively. Their brains weighed some 900 grams. Last to arrive during the Prehistoric era were the Homo sapiens or modern man with a brain weighing approximately 1,600 grams. The growth of the modern brain has two important characteristics not found in other mammals, not even in primates. First, the brain needs two decades to complete, which allows for a long period of education. Second is the late development of the brain in newborns. During this slow-growth period the child receives signals from the outside world, interacts with social groups and aquires articulate speech. Nonhuman primates develop according to different modalities.
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