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.

    為什么人們在下身有一叢毛發仍然成為一個新的話題

    我們可能是裸體的類人猿演變而來，但從多毛的的標準來衡量的話，人類勝過了所有其他的靈長類動物。盡管大多數靈長類動物在生殖器周圍的毛發也要比身體其他地方來得細軟，可是成年人會炫耀他們的令人印象深刻的一大叢厚實的陰毛。

    長期以來一直認為，陰毛是人類進化史上有皮毛階段的殘余物，而真正的問題在于為什么我們身體的其他地方所留下過多的毛發卻已經不見了。今年早些時候，倫敦大學學院的羅賓·威斯指出，人們的陰毛是在人類進化到的某個時刻時才明顯地變得比身體上其他地方的毛發更為濃密。（《生物學雜志》第8卷，第20頁 ）.當然，這種變化的發生必須有一個原因。所以我們要問，是什么原因促使陰毛的演變呢？

    這個問題至今還沒有公認的解釋，但許多潛在有利條件已經提出了好幾年。也許其中最為流行的是，既然有濃厚的毛發集中生長在頂漿分泌（香味）汗腺和外分泌（冷卻）汗腺的部位，它可能有助于飄送性成熟信號的氣味。隨著女孩乳房的日益增大和臀部的加寬以及男孩胸部的加深和胡須的長出，陰毛也可能作為成年人的一種視覺信號。還有各種各樣的其他好處可以說明陰毛值得保留。陰部厚厚的、越來越多的毛發不僅可以保護人們在性生活時和在另外一些場合下的生殖器--減少在走路時的擦傷，例如-它也有助于保持人們最敏感的地區的溫暖，使它免受風寒。

    至于陰毛是什么時代演變而成的呢？基于在美國蓋恩斯維爾的佛羅里達自然歷史博物館的大衛·里德對陰毛虱子演變的研究，威斯認為陰毛大概是在3.3百萬年以前形成的。就是在這個時候，人類陰毛上的虱子已經與發現在大猩猩的上厚厚體毛上的相關虱子的品種存在著差別。威斯認為，這可能表示那時人們的其余部分是赤裸無毛的，由此說明，人類已經演變出相當厚實的陰毛可以使虱子在不同生物之間跳來跳去，并成為把虱子扎根（take hold）在那里的東西。