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Archaic humans paid for their large brains in two ways.
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By comparison, the brains of other apes require only 8 per cent of rest-time energy. It accounts for about 2–3 per cent of total body weight, but it consumes 25 per cent of the body’s energy when the body is at rest. It’s not easy to carry around, especially when encased inside a massive skull. The fact is that a jumbo brain is a jumbo drain on the body. Most notably, humans have extraordinarily large brains compared to other animals.īut if giant brains are such a good idea, why are they so rare in the animal kingdom? The truth is that from about 2 million years ago until around 10,000 years ago, the world was home, at one and the same time, to several human species.ĭespite their many differences, all human species share several defining characteristics. This linear model gives the mistaken impression that at any particular moment only one type of human inhabited the earth, and that all earlier species were merely older models of ourselves. It’s a common fallacy to envision these species as arranged in a straight line of descent, with ergaster begetting erectus, erectus begetting the Neanderthals, and the Neanderthals evolving into us. Yet the real meaning of the word human is “an animal belonging to the genus Homo,” and there used to be many other species of this genus besides Homo sapiens. We are used to thinking about ourselves as the only humans, because for the last ten thousand years, our species has indeed been the only human species around. Not only do we possess an abundance of uncivilized cousins once upon a time we had quite a few brothers and sisters as well. Homo sapiens has kept hidden an even more disturbing secret.