Why did nature give men and some women beards?

Civilization is at war with nature. That is true at least with regard to facial hair. In the heat of this centuries-long battle, on which billions of dollars are spent each year, few have paused to consider how the war began in the first place. Why did nature give men—and some women—beards? How did they end up with a band of hair on their cheeks and chins that society requires they scrape off every day? If one hopes to discover the meaning of beards, it makes sense to start with these basic questions. And that will require us to peer into the mists of the evolutionary past.

It is tempting to think that beards are a holdover from our much hairier progenitors, that for whatever reason this trait survived as we developed into the naked ape. Yet bonobos, our closest relative in the animal kingdom, lack hair around their mouths—precisely where the human beard grows. It would seem that, if anything, human beings have added hair to their faces, even as they lost it most other places. Even if our ape ancestors had had hairy faces, a question would remain: Why did women lose this hair while men retained it? As it is, a hairy chin and upper lip are virtually unique to the human male.

The beard is also distinctive as the last of the sexual traits to manifest itself in a man’s development, other than baldness. Biologists have determined that both beard growth and baldness are stimulated by androgens, such as testosterone, and that the rate of growth varies according to naturally occurring cycles of hormone secretion. One scientist reported in the journal Nature in 1970 that he had measured an increased rate of beard growth (by weighing the clippings from his shaver) on days before he traveled to visit his distant lover. 1 He surmised that his androgen levels spiked as he anticipated sexual activity, causing his beard to grow faster. Later studies found that androgen production followed a five- or six-day cycle, as well as a daily cycle, with facial hair growth reflecting its variation.

A California scientist reported in 1986 that both illness and jet lag affected the rate of his beard growth, apparently by disrupting these hormonal rhythms. 2 More recently, biologists have mapped some of the endocrine pathways that link androgens with hair follicles in the face and scalp. It is clear that male hormones are part of the mechanism of beard growth and hair loss, but this does not explain why these androgens have evolved this function.

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