Human body hair, once thought to be an evolutionary relic, has a real job to do
Dec 17th 2011 | from the print edition
Good night. Sleep tight. Mind the bugs don’t bite
MUCH ink and many electrons have been spilled on the question of human hairlessness: why, as Desmond Morris put it in the title of a book published in 1967, Homo sapiens is “The Naked Ape”. This lack of hair has been attributed to everything from a putative aquatic period in the species’s past to the advantages of displaying a healthy skin to members of the opposite sex.
Less attention has been paid, though, to the fact that humans are not really hairless at all. Per square centimetre, human skin has as many hair follicles as that of other great apes. The difference is not in the number, but in the fineness of the hair that grows from those follicles. These fine human hairs do not seem to be performing any of the functions of their counterparts in more hirsute species (insulation and, through colouration, either signalling or camouflage). So what are they for?
That is a question addressed by Isabelle Dean and Michael Siva-Jothy of Sheffield University, in Britain, in a paper inBiology Letters. Their conclusion is that humans have fine body hair to serve as an alarm system.
Ms Dean and Dr Siva-Jothy were testing the idea that fine body hairs (known, technically, as vellus and terminal hairs) are there to alert their owner to creepy crawlies such as bed bugs, which might be intent on biting them, and that the hair may also get in the way of such arthropods’ activities, giving the owner more time to react before he is bitten.