By Randy Dotinga

HealthDay Reporter

MONDAY, April 8 (HealthDay News) -- Rekindling the old debate on whether size matters, new research finds that women may take a man's penile endowment as a key factor in "mate selection," ranking it as important as his height.

Besides making some men insecure, the research might offer insight into evolution and the fact that humans have especially large penises for their size.

The research, which has limitations, isn't definitive. The women were only asked to consider the attractiveness of hairless, mannequin-like depictions of men with flaccid penises. None of the women lived outside the Western world. And other research has shown that human females, contrary to popular belief, aren't especially interested in penis size.

Still, the findings suggest that "penis size matters," said study lead author Brian Mautz, currently a postdoctoral research fellow at the University of Ottawa, in Canada. However, he added, "It's relative. Other traits like height and body shape are important too. And they all seem to interact to contribute to attractiveness."

Mautz, then at the Australian National University, and colleagues launched their study in an attempt to better understand how evolution affected the development of the human penis. Unlike some other mammals, the size of a human penis is obvious at first glance -- at least when men are naked -- and evolution may have favored men with larger ones.

The researchers gathered 105 Australian heterosexual women whose average age was 26 and asked them to rank the attractiveness of 53 images of computer-generated naked "men" of various heights and body shapes and with various flaccid penis lengths.

The apparent measurements of the computerized "men" were based on a study of more than 1,000 Italian men. The longest flaccid penis length in the images was the equivalent of 5.1 inches in real life.

The researchers found that greater penis size made the "men" more attractive, even the shorter ones who were considered the least attractive overall. But the boost in attractiveness was "not in a fashion where a 1-centimeter increase equals a 1-percent increase in attractiveness," Mautz said. "It's more complex."

It's not necessarily surprising that women were more attracted to men with larger penises, Mautz said. What is surprising is that it had an equal effect on attractiveness as greater height, he said. And larger penises made more of a difference in a man's attractiveness if he was taller.

The study appeared online April 8 in the journal Proceedings of the National Academy of Sciences.

Previous research linked greater height to positive differences in men's lives. Taller men have a greater chance of attaining leadership positions and having more sexual partners, Mautz noted.

The new study didn't consider the wide variety of factors that could affect a modern woman's choice in a mate, from personality to wealth to his level of attraction toward her.

Even so, the researchers speculated that women's preference for larger penises could have played a role in the evolution of the human body. Men with larger penises may have had more children and passed on the trait because they were more likely to attract women.

Sai Gaddam, a neuroscientist who has written about the psychology and biology of human sexuality, said the study introduces "a useful method to tease apart the factors that make us attractive. But do the aesthetic judgments of computer-generated male mannequins by 105 Australian women reveal a factor in mate attractiveness? Not yet," he said.

"I am guessing you would find similar results if the study was done with men," Gaddam suggested. "That is, men passing aesthetic judgment on computer-generated male models. What conclusions would we derive from that?"

It is clear that women aren't especially drawn to penises, he said, although heterosexual men often think the opposite is true: "Our own analysis of male and female erotica revealed that men are far more interested in penises than women are."

More information

For more about evolution, try the University of California, Berkeley.