Scientists unravel the mystery of man's hair loss (down to the short and curlies)

Early humans shed their coats of fur as a result of being plagued by disease-carrying parasites, a new theory of evolution claims.

The new hypothesis challenges the long-held view that our early ancestors become almost hairless in order to control their body temperatures in the heat of the African savannah.

Instead, claim two scientists from Reading and Oxford universities, Professor Mark Pagel and Professor Walter Bodmer, our ancestors' hair loss was a consequence of their natural intelligence.

These hominids were smart enough to use fire, clothing and shelter to regulate body temperatures. And - unlike the dense fur that still covers apes and monkeys, forcing them constantly to groom each other for lice - clothing and bedding could be cleaned if they became infested.

This is the latest in a series of theories about why humans, unlike their ape relatives, lost their hair. The temperature hypothesis is the best known, but some biologists have linked hairlessness to our phase as aquatic animals six to eight million years ago.

This explanation, claim Professors Pagel and Bodmer, is let downby a complete absence of physical evidence. The temperature theory, they also argue, has a serious flaw, in that being hairless is a great disadvantage at very hot or very cold periods.

Professor Pagel, from Reading's School of Animal and Microbial Sciences, argues that being less hairy than the next prehistoric man became an evolutionary advantage - a theory advanced by the father of evolution, Charles Darwin.

"Hairlessness would have allowed humans to 'advertise' their reduced susceptibility to parasitic infection, and this trait therefore became desirable in a mate," he said.

Our heads of hair, and men's beards, were kept because they were potent ways of displaying sexuality.

What still puzzles the experts, however, is why we kept our pubic hair. One theory is that pubic hair helps store and send out sexual odours.

"Facial and head hair can be explained by their importance in sexual attraction, although pubic hair does pose a challenge for our theory. There is some evidence, however, that pubic hair enhances pheromonal signals involved in mate choice," said Professor Pagel.