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.
和地球上其他大的哺乳动物比较，我们人类毛发相对来说比较少，这个明显的事实并不奇怪，知道我们看到动物王国里的最亲密亲属——猩猩和猿，为什么？我们可能会问，当所有其他灵长目动物浑身是毛，而我们进化得几乎无毛？事实上，看起来奇怪，我们缺少毛发正是我们进化成功的一个关键。
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?
为什么我们最早的祖先失去他们的毛发，而毛发有助于他们在寒冷的夜晚保暖这个问题，使得著名的进化学者查尔斯达尔文陷入深思，“没有人认为皮肤的裸露对人有直接的好处。”他认为人类失去毛发的主要原因是性选择。换句话说，我们宁愿要我们伴侣，而不想失去毛发。但是在这种偏好设置之前是什么导致我们的祖先开始失去他们的毛发？
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.
最可能解释毛发脱落的假说是大约2到300百万前早期的人类有必要转移到一个更广阔的草原栖息地，他们开始狩猎，在开放的草原上狩猎意味着每天暴露在强阳光下几个小时，处于过热的危险中。毛发遮盖身体使得我们的祖先散热慢，所以，英格兰利物浦摩尔大学的皮特解释说，脱发能使得他们更容易出汗，更容易散热。因此，早期人类可以在中午出去狩猎和觅食。“能够度过整个中午的觅食，寻找配偶或者与敌人战斗，这是一个巨大的优势。”牛津大学的大卫说，“出汗证明你大部分没有毛发对汗腺更有用。”捕猎动物的肉给早期人类大脑提供能量。
Humans are the sweatiest primates on Earth. They have up to 5 million sweat glands,which produce about 12 litres of sweat per day. It's this propensity to sweat that accounts for our hairlessness and has allowed us to thrive. It might help to remember this next time you're surrounded by sweaty hairless torsos in the gym!
人类是地球上出汗最多的灵长目动物。他们有多达500的汗腺，每天产生12L的汗水，正是这种出汗特点，使得我们脱发，让我们能很好的成长。要记住下一次你身边无毛躯干是在健身房！
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