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随身英语Hair and evolution 毛发和进化论 Play audio file为什么进化后的人类毛发稀疏？而和我们人类最近似的动物王国里的亲戚则仍全身匹着毛发？在物种进化过程中，毛发稀疏的人类是如何确保自己能成功生存下来？本期《随身英语》谈论毛发和人类进化的关系。 课文内容 词汇: Evolution 进化 Compared to other large mammals on Earth, we humans have relatively little hair. This obvious fact is not so strange until we look at our closest living relatives in the animal kingdom – chimpanzees and other great apes. Why, might we ask, have we evolved to be almost hairless when all other primates are still covered in fur? In fact, bizarre as it may seem, our lack of hair has been the key to our evolutionary success as a species. The question why our earliest ancestors lost their hair when fur would have been beneficial to them – for keeping warm on cold nights, for example – was pondered by Charles Darwin, the famous evolutionist: "No one supposes that the nakedness of the skin is any direct advantage to man." He concluded that the reason hominins lost their hair was sexual selection. In other words, we prefer our partners to have little hair. But what caused our ancestors to start losing their hair before this preference set in? The most likely hypothesis to explain the loss of hair is that it became necessary when early hominids moved to a more open savannah habitat around 2 to 3 million years ago, when they started to hunt big game.Hunting in open savannah meant being exposed to the strong heat of the sun for several hours in the day and being in danger of overheating. Being covered in hair prevented our ancestors from losing heat fast enough. So, as Peter Wheeler, of Liverpool John Moores University in the UK, explained, losing hair allowed them to develop the ability to sweat and therefore to cool down. Early humans could, as a consequence, be out at midday hunting and foraging. "It would be [an] enormous advantage to be able to spend the entire midday foraging, finding mates or fighting enemies", Tamás Dávid-Barrett of Oxford University says. "Sweating allows that, and for sweat to be efficient you need to be mostly hairless". The meat from hunting animals gave early humans the energy to fuel their growing brain. | 
