There is a new theory to answer the question of why humans are largely hairless, unlike their furry close relatives, the apes.
The generally accepted theory until now has been that hairlessness evolved to control body temperature in hot climates.
Would he be sexier without all that hair?
But Professor Mark Pagel, of the University of Reading, UK, and Professor Sir Walter Bodmer, of Oxford University, UK, argue that humans became hairless to evade biting flies and parasites and to increase their sexual attractiveness.
The heat control theory runs into problems when scientists look at situations where it is very hot or very cold, they argue.
All about sex
Professors Pagel and Bodmer write in the Royal Society journal Biology Letters that past humans were able to respond flexibly and effectively to their environment by producing fire, shelter and clothing.
So hairlessness became possible and desirable as clothes and shelter could be cleaned or changed if infected with parasites.
The pair say their theory also has a better answer to why there are differences between hair covering in men and women.
"Hairlessness would have allowed humans to convincingly 'advertise' their reduced susceptibility to parasitic infection and this trait therefore became desirable in a mate and the greater loss of hair in women follows to stronger sexual selection from men to women.
"Facial and head hair can be explained by their continued importance in sexual attraction and selection, 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," they write.
The two say that their theory could be tested.
"One expects to find that humans whose evolutionary history has been in regions with higher concentrations of disease-carrying parasites such as in the tropics will have less body hair than others," they say.