Hair and evolution

[00:00.36] Compared to other large mammals on Earth, we humans have relatively little hair. 与地球上其他大型哺乳动物相比，我们人类的头发相对较少。

[00:05.63] This obvious fact is not so strange until we look at our closest living relatives in the animal kingdom – chimpanzees and other great apes. 这个显而易见的事实并不奇怪，直到我们看看我们在动物王国中最亲近的亲戚——黑猩猩和其他类人猿。

[00:13.90] Why, might we ask, have we evolved to be almost hairless when all other primates are still covered in fur? 为什么，我们可能会问，当所有其他灵长类动物仍然被毛皮覆盖时，我们进化到几乎没有毛了？

[00:21.43] In fact, bizarre as it may seem, our lack of hair has been the key to our evolutionary success as a species.事实上，尽管看起来很奇怪，但我们没有头发一直是我们作为一个物种进化成功的关键。

[00:28.70] The question why our earliest ancestors lost their hair when fur would have been beneficial to them – for keeping warm on cold nights, 为什么我们最早的祖先在毛皮对他们有益时会掉头发——在寒冷的夜晚保暖，

[00:37.23] 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." 例如——著名进化论者查尔斯·达尔文曾深思：“没有人认为皮肤的裸露对人类有任何直接的好处。”

[00:46.76] He concluded that the reason hominins lost their hair was sexual selection. In other words, we prefer our partners to have little hair. 他得出的结论是，人类失去头发的原因是性选择。换句话说，我们更喜欢我们的伴侣头发少。

[00:54.55] But what caused our ancestors to start losing their hair before this preference set in?但是是什么导致我们的祖先在这种偏好出现之前就开始脱发呢？

[00:59.57] 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.最有可能解释脱发的假设是，大约 2 到 300 万年前，当早期原始人开始捕猎大型猎物时，当早期原始人迁移到更开放的稀树草原栖息地时，脱发就变得很有必要了。

[01:12.37] 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. 在开阔的大草原上狩猎意味着一天要暴露在强烈的阳光下几个小时，并且有过热的危险。

[01:21.15] Being covered in hair prevented our ancestors from losing heat fast enough. 被头发覆盖会阻止我们的祖先足够快地散热。

[01:25.67] 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. 因此，正如英国利物浦约翰摩尔斯大学的彼得惠勒所解释的那样，脱发使他们能够发展出汗并因此降温的能力。

[01:36.21] Early humans could, as a consequence, be out at midday hunting and foraging. 因此，早期人类可能会在中午外出狩猎和觅食。

[01:40.73] "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.牛津大学的 Tamás Dávid-Barrett 说：“能够在整个中午觅食、寻找配偶或与敌人作战，这将是一个巨大的优势。”

[01:51.26] "Sweating allows that, and for sweat to be efficient you need to be mostly hairless". “出汗可以做到这一点，为了让汗水有效，你需要大部分时间都没有毛”。

[01:56.28] The meat from hunting animals gave early humans the energy to fuel their growing brain.狩猎动物的肉为早期人类提供了能量来为他们不断增长的大脑提供燃料。

[02:02.55] Humans are the sweatiest primates on Earth. They have up to 5 million sweat glands,which produce about 12 litres of sweat per day. 人类是地球上出汗最多的灵长类动物。它们有多达 500 万个汗腺，每天产生约 12 升汗水。

[02:11.09] It's this propensity to sweat that accounts for our hairlessness and has allowed us to thrive. 正是这种出汗的倾向导致了我们的无毛并让我们茁壮成长。

[02:16.86] It might help to remember this next time you're surrounded by sweaty hairless torsos in the gym!下次你在健身房被汗流浃背的无毛躯干包围时，记住这一点可能会有所帮助！