2003-06-19 07:03:38 -- The theory, outlined in Royal Society Biology Letters this week, challenges the widespread view that humans lost most of their hair to promote body cooling when early hominids moved to open savannah regions.
Mark Pagel, professor of zoology at the University of Reading, and Sir Walter Bodmer, principal of Hertford College, Oxford, and a researcher in cancer and immunogenetics at John Radcliffe Hospital, instead propose that humans lost most of their hair when they developed the ability to control their environments using fire, shelter and clothing.
According to their paper, clothing, which can be cleaned and changed, provided humans with a much more flexible response to parasites and biting flies. Furry and hairy animals spend a lot of their day removing such bothersome insects from their coats.
Pagel told Discovery News that he and Bodmer were inspired by "the appreciation that parasitic infections exact very large tolls on human and other animal health, and that fur is a refuge for large numbers of biting flies and other insects that carry disease."
Since humans likely evolved in Africa, where parasites and flies are found in abundance, insects would have been a major problem for those living in close quarter hunter-gatherer groups, said Pagel and Bodmer.
The scientists further propose that relative hairlessness would have become a desirable trait. Sexual selection, they believe, helped us to evolve this feature, with some body hair remaining to enhance pheromone signals, and for other purposes mostly related to mating.
They also account for other creatures lacking fur and copious amounts of hair.
"Other 'hairless' mammals are either aquatic or have very thick hides, such as elephants," explained Pagel. "The exception is naked-mole rats, which live underground in temperature-controlled environments. We think they are hairless for the same reason as we are."
Robin Dunbar, professor of evolutionary psychology at the University of Liverpool, said Pagel and Bodmer's theory "is an interesting idea, but I'm not wholly convinced by it."
Dunbar said their ideas must rest on the notion that early humans built permanent shelters where parasites can breed. Previous research suggests humans evolved hairlessness just after they began walking upright on two legs, but shelters likely did not begin to appear until much later.
Dunbar also doubts that hairlessness became desirable for mating.
"You tend to like what you have to like," he said. "I'm sure that baboons find hairless baboons quite unattractive!"