Dan Vergano, USA TODAY

A study finds women rated better-endowed men as more attractive

The effect mattered more for taller men than others

The finding adds to suggestions that female mating preferences may play a role in human evolution

So much for that nice smile and neat haircut -- women are indeed looking for a well-endowed guy, suggests an Australian study of male attractiveness.

Since Darwin, biologists have studied the role of female "mate choice" in species ranging from fruit flies to people, generally finding a fondness among women for taller guys with broader shoulders. Evolutionary biologists have also pointed to the relatively-larger size of human male genitalia compared to our ape cousins to suggest a link there as well.

On the question of whether "size matters" to human women, however, the results have been mixed. Until now, suggests a team led by biologist Brian Mautz, of the University of Ottawa, Canada, in a study published Monday in the Proceedings of the National Academy of Science.

"The big message is that that penis size does matter for attractiveness," Mautz says. "It does interact with height and shoulders though, so it matters more to taller guys that to shorter ones."

In the study, the researchers showed a series of life-size cut-out images of variously-sized men viewed by 105 heterosexual Australian women ages 18 to 53. The women, who stood about 20 feet away from a movie screen to watch and rate videos depicting 343 varied male outlines in a non-aroused state, were told only that the study was measuring "male attractiveness." They also rated taller and more broad-shouldered men as more attractive, as in past studies, but being well-endowed mattered almost as much as height in the new study.

"It is a pretty unusual study, but sex and behavior are important parts of evolution for any species, so the results are worth noting," says evolutionary biologist Wyatt Anderson of the University of Georgia in Athens, who led the review of the study for the journal. "It was a well-controlled study and the reviewers all agreed with the conclusions they reported."

The attractiveness results, however, stopped increasing as fast past a certain length, about 3 inches, the study reports, supporting the idea that the results may have been more a matter of pleasing proportional size in the most attractive masculine shapes, Mautz says. "This is a first-time study, so we should be cautious."

"Another possibility is that females use previous sexual experiences to infer a link between penis size and (an orgasm)," the study added. However they didn't see a connection between a woman's age and the preference, which would argue against that conclusion.

The study authors acknowledge that modern culture may have played a role in what the women rated as attractive, but they also suggest that a preference for the well-endowed may have played a role in the evolution of the human male in prehistory. People have been wearing clothing for about 170,000 years, studies suggest.

One option for a future study would be to run the cut-outs by women from non-Western cultures, to see if they rate men the same, Mautz says.

"It's true that people have culture and it is very difficult to disentangle the effects of culture from evolution, but that doesn't mean that evolution isn't happening," says University of Minnesota professor Marlene Zuk, author of Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live. "Absolutely there are limitations on the study, it isn't the final word, but it does point to evolution having an effect on humans."

"It certainly is a weakness of the study that we can't go back in time and see how it all played out," Mautz says. "The study also doesn't say anything about what women would find attractive in the future either."