A new study of women suggests size truly does matter when it comes to choosing a man.

Australian researchers showed female university students images of naked men, and determined that penis size is a predictor of male attractiveness. The researchers explained the attractiveness might be rooted in evolution.

"We found that flaccid penis size had a significant influence on male attractiveness," wrote the researchers, lead by Dr. Brian S. Mautz, a biologist at Australian National University in Canberra. "Males with a larger penis were rated as being relatively more attractive."

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The study was published April 8 in Proceedings of the National Academy of Sciences.

Previous studies that looked at the link between penis length and male attractiveness involved modifying length in a single image of the same naked man five times and asking women to rate them for attractiveness, according to the researchers. For the new study, however, they wanted to see what happened when other, different male traits were factored in, including different heights and body shapes.



For example, they wanted to find out whether increases in penis length have the same effect on perceived attractiveness in both short and tall men.

To find out, researchers enlisted 105 heterosexual women, average age of 26, who were enrolled at Australian universities. Women were shown projected, life-sized computer generated images of nude men which rotated 30 degrees, to allow participants to see all the males' features. Specifically, researchers developed figures with seven possible values of each trait, which included flaccid penis size, body shape (as determined by shoulder-to-hip ratio), and height.

The women were shown a randomly selected set of 53 of these images, and were not told which traits varied. They were asked to rate sexual attractiveness of the images on a scale of one to seven, and did so anonymously out of sight from the researchers.

The study found that penis size was positively associated with attractiveness, but the linear relationship gradually slowed when men measured three inches and above flaccid.

Body shape was also a big factor, with changes in shoulder-to-hip ratio accounting for 80 percent of variation in attractiveness scores. After controlling for body shape, the researchers determined greater penis size elevated attractiveness far more strongly for taller men than it did for shorter men. The same was true for penis size increasing attractiveness in men with more masculine body shapes (or greater shoulder-to-hip ratios), when height was removed from the equation.

The researchers were also surprised to find that greater height and larger penis size had the same positive effects on attractiveness scores.

"Height and penis size had the same effect, and to me, that's surprising," Mautz told Bloomberg. "We know taller men make more money, are more likely to have leadership positions and have more children. To have penis size have the equivalent effect was just, wow."

The researchers say their findings show that penis size interacts with body shape and height to determine male sexual attractiveness.

Mautz told National Geographic early humans did not wear clothes, therefore it's possible that women chose mates based on genitalia size, and that influenced the evolution of larger penises.

"We can't say for sure that female choice is what drove the evolution of penis size," he said. But, "at this point in time, penis size has an effect on attractiveness."

The editor who led the review of the study before publication told USA Today the findings are noteworthy.

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

Nature reported that the findings add to a debate that started in 1966 when sexuality researchers concluded penis size to be unimportant to females.

"This research will allow an uncomfortable subject to become a legitimate topic of discussion," Dr. Geoffrey Miller, an evolutionary psychologist at New York University, told Nature. He was not involved in the study.

