Why humans have clumps of hair in private places is still open for debate

    We may be the naked ape, but on one measure of hairiness humans trump all other primates. While most of them have finer hair around their genitals than on the rest of their body, adult humans sport an impressively thick bush of pubic hair.

    It has long been assumed that pubic hair is a remnant of a furrier period in our evolutionary history, and that the real question is why the rest of the body lost its hirsuteness. Earlier this year, though, Robin Weiss of University College London pointed out that our pubic hair clearly became thicker than that on the rest of our bodies at some point in our evolution （Journal of Biology, vol 8, p 20）. And this must have happened for a reason. So what drove the evolution of pubic hair?

    There's no accepted explanation, but many potential advantages have been suggested over the years. Perhaps the most popular is that since thicker hair gathers in regions where we have apocrine （scent） sweat glands as well as eccrine （cooling） ones, it may serve to waft odours that signal sexual maturity. It may also act as a visual signal of adulthood, along with growing breasts and widening hips in girls and deeper chests and beards in boys. Various other benefits could have made it worth keeping. A thick bush not only protects the genitals during sex and at other times - reducing chaffing while walking, for example - it also helps keep our most sensitive regions warm and free of draughts.

    So when did it evolve? Based on studies of the evolution of pubic lice by David Reed at the Florida Museum of Natural History in Gainesville, Weiss suggests some time around 3.3 million years ago. This is when human lice diverged from a closely related species found on the thick body hair of gorillas. This, Weiss suggests, could signal that while the rest of our bodies were naked by that time, we had evolved thick enough pubic hair for the lice to jump species and take hold.

    为什么人们在下身有一丛毛发仍然成为一个新的话题

    我们可能是裸体的类人猿演变而来，但从多毛的的标准来衡量的话，人类胜过了所有其他的灵长类动物。尽管大多数灵长类动物在生殖器周围的毛发也要比身体其他地方来得细软，可是成年人会炫耀他们的令人印象深刻的一大丛厚实的阴毛。

    长期以来一直认为，阴毛是人类进化史上有皮毛阶段的残余物，而真正的问题在于为什么我们身体的其他地方所留下过多的毛发却已经不见了。今年早些时候，伦敦大学学院的罗宾·威斯指出，人们的阴毛是在人类进化到的某个时刻时才明显地变得比身体上其他地方的毛发更为浓密。（《生物学杂志》第8卷，第20页 ）.当然，这种变化的发生必须有一个原因。所以我们要问，是什么原因促使阴毛的演变呢？

    这个问题至今还没有公认的解释，但许多潜在有利条件已经提出了好几年。也许其中最为流行的是，既然有浓厚的毛发集中生长在顶浆分泌（香味）汗腺和外分泌（冷却）汗腺的部位，它可能有助于飘送性成熟信号的气味。随着女孩乳房的日益增大和臀部的加宽以及男孩胸部的加深和胡须的长出，阴毛也可能作为成年人的一种视觉信号。还有各种各样的其他好处可以说明阴毛值得保留。阴部厚厚的、越来越多的毛发不仅可以保护人们在性生活时和在另外一些场合下的生殖器--减少在走路时的擦伤，例如-它也有助于保持人们最敏感的地区的温暖，使它免受风寒。

    至于阴毛是什么时代演变而成的呢？基于在美国盖恩斯维尔的佛罗里达自然历史博物馆的大卫·里德对阴毛虱子演变的研究，威斯认为阴毛大概是在3.3百万年以前形成的。就是在这个时候，人类阴毛上的虱子已经与发现在大猩猩的上厚厚体毛上的相关虱子的品种存在着差别。威斯认为，这可能表示那时人们的其余部分是赤裸无毛的，由此说明，人类已经演变出相当厚实的阴毛可以使虱子在不同生物之间跳来跳去，并成为把虱子扎根（take hold）在那里的东西。