By: Stephanie Pappas, LiveScience Senior Writer
Published: 10/09/2012 09:56 AM EDT on LiveScience
Humans are not nearly as furry as our closest primate relatives, a fact that has puzzled evolutionary biologists for more than a century. One common theory for our relative hairlessness suggests that women long ago adopted a preference for less hairy guys as a way to avoid lice and other nasty bloodsuckers that might call a pelt home.
But new research suggests that this so-called "ectoparasite avoidance hypothesis" may not explain the evolution of human hairlessness. In fact, women prefer relatively hair-free guys across the board, according to new research published online Sept. 13 in the journal Archives of Sexual Behavior. This preference for smooth skin holds whether or not parasite risk is high.
"According to evolutionary view, hairless men should be preferred, particularly in areas (or cultures) with high parasite threat, which means close to the equator, where parasite richness is highest," study researcher Pavol Prokop, a professor of biology at Trnava University in Slovakia, wrote in an email to LiveScience. "We compared only two countries that differ in parasite threat, but we found no differences in women's preferences."
Prokop and his colleagues asked 161 Turkish and 183 Slovakian women to rate the attractiveness of men with hairy and hairless chests. To keep the men's appearance as consistent as possible, the researchers had men photographed from the neck to the waist with hairy chests, and then asked them to shave before posing for an identical photograph.
Turkey was chosen because the country has a higher rate of parasite-transmitted diseases, such as malaria and dengue fever, than Slovakia and has long had more instances of these illnesses, the researchers wrote. The researchers expected to find, then, that Turkish women would be more sensitive to parasite concerns and prefer less-hairy men than their northerly counterparts in Slovakia, where parasites are less of an issue. [Top 10 Disgusting Parasites]
Instead, the researchers found that very few women in either country prefer a hairy chest. Only about 20 percent of women rated the more hirsute versions of the men as more attractive.
Before the ectoparasite hypothesis for hairlessness is ruled out, researchers need to test a broader range of countries, Prokop said. Earlier studies suggested women's hair preferences do differ by country and even U.S. state, with women in the African nation of Cameroon, for example, preferring hairier guys, while women in China, New Zealand and California went for a bare look. Some research even suggests women in fertile phases of their menstrual cycles are attracted to less hair on men than women in less-fertile phases, who prefer a slightly hairier look.
"Clearly, more cross-cultural comparison is needed to solve this question," Prokop said.