Why Humans are Hairless

Gets Rid of Parasites, Improves Sexual Attraction

Medically Reviewed by Michael W. Smith, MD on June 11, 2003

June 11, 2003 - Apparently, lack of parasites is an attractive quality in a mate. A new study suggests that humans became hairless to reduce the risk of biting flies and other parasites that live in fur and to enhance their sexual attractiveness.

Humans are rare among mammals for their lack of a dense layer of protective fur or hair. And the new theory challenges widely accepted theories that humans became hairless to provide better temperature control in varied climates. This conventional view argues that hair was no longer necessary because humans could regulate their environment with the use of shelter, fire, and clothing.

But a study, published in the June 9 issue of Biology Letters, suggests an alternative explanation for humans' lack of hair.

Researchers propose that because humans could effectively alter their environment by producing clothing, shelter, and fire, they could also reduce their risk of parasitic diseases. Bug-infested clothing and shelter could be cleaned and changed more easily and faster than a permanent layer of fur.

Naked Apes are Sexy

Researchers suggest that the difference in hair distribution between men and women is also more easily explained by this new hypothesis.

"Hairlessness would have allowed humans to convincingly 'advertise' their reduced susceptibility to parasitic infection and this trait therefore became desirable in a mate," write researcher Mark Pagel of the University of Reading in Reading, England, and colleagues.

They say the greater loss of body hair among women follows the stronger pattern of sexual selection from men to women. But the evolutionary survival of facial and head hair among men is proof of its continued importance in sexual attraction and selection.

The researchers admit that the presence of pubic hair does pose a challenge to their theory of hairless human evolution. The warm, humid environment provided by pubic hair provided an ideal breeding ground for parasites.

However, researchers say pubic hair also plays an important role in sexual attraction by enhancing the exchange of pheromonal signals. Pheromones are scentless chemicals released by men and women that are thought to play a role in sexual attraction.

Researchers say their theory can be tested in future studies by checking to see if humans whose evolutionary history is in tropical areas with higher rates of parasitic diseases have less body hair than others.