Size does matter, Nature reports, at least to some extent. A new paper published in the Proceedings of the National Academy of Sciences found that female preference likely helped shape the size and thickness of the human penis through natural selection.

Human penises are longer and wider than the penises of other primates. Biologists know that penises of other species reveal information about what shaped a particular animal’s evolution, and they figured humans should be no exception. To try and get at what drove human males to develop such comparatively long penises, the study authors created virtual images of males combining different heights, shoulder-to-hip ratios and penis lengths. They showed 53 of the life-size images to 105 women and asked them to rate the computer-generated men by their sexual attractiveness, Nature explains.

The ladies preferred taller men with larger shoulder-to-hip ratios and longer penises to be the most attractive—though, as Nature points out, that preference had its limits. Once the men exceeded a threshold for extreme size, the women ranked their attractiveness as only slightly above average.

Study leader Brian Mautz, a biologist now at the University of Ottawa in Canada, says that there seems to be a ceiling effect for each trait — a point of theoretical peak attractiveness, beyond which women’s ratings will begin to decline. The team’s model predicts that the most attractive penis would measure 12.8–14.2 centimetres in its flaccid state. Mautz notes that this ideal size is relatively closer to the population average (of 9 centimetres) than are the predicted ideals for the other traits, implying that women prefer more extreme shoulder-to-hip ratio and tallness but less extreme penis size.

But, as Nature writes, women’s preference for partners with larger penises doesn’t necessarily mean they can take credit for the evolution of men’s members. There’s still this question to answer: Do these men tend to father more children who carry those large penis genes?

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