An interesting topic, isn’t it? Unfortunately, the authors, probably not wanting to attract attention of the IgNobel Prize Committee, obscured their findings in an impenetrable academic jargon (See below).
I provide a translation to (hopefully ) human-readable language:
In many animals male genitala (MG) is a trait, which is selected post-copulation, e.g. if the male genitalia work better during copulation, fertilisation is more probable. However, in humans MG can be selected before copulation through the female’s choice. This was easy before the clothes and there is hypothesis that human penis is larger than in the other apes and lacks a penile bone as a result of sexual selection: women like bigger penises.
The authors have shown (105) females videos of men with different bodies and penises. They discovered that women preferred bigger penises, but after MG reached a certain size, their attractiveness started to decline. Size mattered more for selection of shorter men and men with more masculine bodies – wide shoulders, narrow hips (professional swimmers must be very popular with the ladies): a short man with a larger penis is more attractive than the same height man with a smaller penis, but less attractive than a taller man.
The most interesting finding was that larger penis and greater height have almost equal attractiveness. I think this may explain gradual evolution of average human height from petite to inching above 2 meters. Which in turn increases chances of cancer. Also it would be interesting to see a symmetrical study: boobs vs female height.
Compelling evidence from many animal taxa indicates that male genitalia are often under postcopulatory sexual selection for characteristics that increase a male’s relative fertilization success. There could, however, also be direct precopulatory female mate choice based on male genital traits. Before clothing, the nonretractable human penis would have been conspicuous to potential mates. This observation has generated suggestions that human penis size partly evolved because of female choice. Here we show, based upon female assessment of digitally projected life-size, computer-generated images, that penis size interacts with body shape and height to determine male sexual attractiveness. Positive linear selection was detected for penis size, but the marginal increase in attractiveness eventually declined with greater penis size (i.e., quadratic selection). Penis size had a stronger effect on attractiveness in taller men than in shorter men. There was a similar increase in the positive effect of penis size on attractiveness with a more masculine body shape (i.e., greater shoulder-to-hip ratio). Surprisingly, larger penis size and greater height had almost equivalent positive effects on male attractiveness. Our results support the hypothesis that female mate choice could have driven the evolution of larger penises in humans. More broadly, our results show that precopulatory sexual selection can play a role in the evolution of genital traits.Proc Natl Acad Sci U S A. 2013 Apr 23;110(17):6925-30. doi: 10.1073/pnas.1219361110.