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Passage Backgrounds S1. ?年轻一代的存在（社会类） ?S1250302
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A Our ancestor, Homo erectus, may not have had culture or even language, but did they have teenagers? That question has been contested in the past few years, with some anthropologists claiming evidence of an adolescent phase in human fossil. This is not merely an academic debate. Humans today are the only animals on Earth to have a teenage phase, yet we have very little idea why. Establishing exactly when adolescence first evolved and finding out what sorts of changes in our bodies and lifestyles it was associated with could help us understand its purpose. Why do we, uniquely' have a growth spurt so late in life?
B Until recently, the dominant explanation was that physical growth is delayed by our need to grow large brains and to learn all the behavior patterns associated with humanity - speaking, social interaction and so on. While such behaviour is still developing, humans cannot easily fend for themselves, so it is best to stay small and look youthful. That way your parents and other members of the social group are motivated to continue looking after you. What's more, studies of mammals show a strong relationship between brain size and the rate of development, with larger-brained animals taking longer to reach adulthood. Humans are at the far end of this spectrum. If this theory is correct, and the development of large brains accounts for the teenage growth spurt, the origin of adolescence should have been with the evolution of our* own species (Homo sapiens) and Neanderthals,