Naked ape evolved 'to avoid biting insects'
Humans became hairless to avoid biting insects rather than stay cool in hot climates, scientists claimed today.
A new theory says the “naked ape” lost its fur in order to deprive fleas, ticks and other blood sucking insects of a home.
In time, hairlessness became a sexually attractive trait, ensuring that it was passed down through the generations.
The theory from two senior British academics challenges the widely accepted view that hairlessness evolved to control body temperature in the heat.
Humans are virtually alone among mammals in lacking a dense layer of protective fur or hair.
Our closest cousins, chimpanzees, are hairy. Why humans uniquely lost their hair has been a long standing mystery.
Until now it was generally believed that humans became naked to keep cool.
But there is a serious flaw in that theory. Hairless skin increases the rates of energy gain and loss during the hottest or coldest periods.
As a result, more heat is lost at night, and during the day more has to be dissipated.
Another theory, that humans are hairless because they are descended from aquatic apes, lacks supportive evidence.
The new proposal from Professor Sir Walter Bodmer, from Oxford University, and Professor Mark Pagel, from the University of Reading, links hair loss with the development of clothing and protection from parasites.
Writing in the Royal Society journal Biology Letters, they said: “Hairlessness is made possible in humans owing to their unique abilities to regulate their environment via fire, shelter and clothing.
“Clothes and shelters allow a more flexible response to the external environment than a permanent layer of fur, and can be changed or cleaned if infested with parasites.”
Hairlessness would have allowed humans to advertise their reduced susceptibility to parasitic infection, making it desirable in a mate. A selection pressure was therefore created that ensured humans remained hairless.
The retention of hair on the face, head and pubic regions may also be linked to sexual selection, said the professors.
Pubic hair posed a challenge to the theory because it could harbour parasites while offering no obvious advantage, such as protecting the head from the sun.
But there was some evidence that pubic hair helped to concentrate pheromones used for sexual signalling.
The theory could be tested, it was claimed. Humans who evolved in parts of the world with large numbers of parasites, such as the tropics, would be expected to have less hair than those in other regions.
