The gray, homogenous-looking men had different heights, shoulder-to-hip ratios (or body shapes), and flaccid-penis lengths. So his team set up an experiment in which 105 Australian women-averaging 26 years old-each looked at 53 life-size images of various computer-generated male silhouettes projected onto a screen. (Also see "Why Human Penises Lost Their Spines.")īut those women may have felt pressured to say the politically correct thing: That size doesn't matter, said study leader Brian Mautz, a biologist at the University of Ottawa, Canada. Past psychology studies that have asked women about their preferences for penis size have produced mixed opinions, with some saying they don't care about the size, while others say they prefer larger penises. The findings suggest that female choice may have driven the evolution of larger penises in humans. For the moment, let’s be content that we aren’t ducks.Bigger is better-at least when it comes to a woman's penis preferences, a new study says. Sex may be determining not just our actions, but our very form and our development as a species. There are many stereotypes about letting sex cloud the brain, but it may be worse than that. Remember, this hypothesis applies to any species with internal fertilization, not just waterfowl or lizards, so yes, humans may also be subject to this process. Nobody actually knew how duck copulation worked. Now that we have proof of rapid evolution in male genitalia in several species, evidence for sexual conflict is quite strong. The study showed that sexual conflict as an evolutionary driver is reflected in actual physiology, as prior to Brennan’s experiment it was all theoretical. Presumably, it would not be quite as difficult if the female consented to the mating. The results suggest that yes, female ducks do physiologically attempt to prevent forcible mating. The results? The drakes had the hardest time entering the tube that was actually shaped like female Muscovy genitalia (a clockwise spiral, in case you are interested). Before you cringe too much, the researchers also determined that duck penises become erect in less then a second and remain flexible when erect, so the procedure is actually quick and painless for the duck. The procedure is a fair approximation of a drake forcing itself on a female. This was possible because the drakes in question were practiced sperm donors-yes, sperm donors, trained to provide specimens for artificial insemination-who were allowed to get themselves in the mood with a female before quickly being transferred to the tube. In their outwardly bizarre but well-designed experiment, Brennan and colleagues tested the sexual conflict hypothesis by coaxing male Muscovy ducks (drakes) to mount differently shaped, oiled glass tubes. Many species of ducks are known for rather violent mating, in which one or more males will attempt to force themselves on a female. A lot of the classic research on sexual conflict has been done in waterfowl, which are known for oddly shaped and freakishly large penises relative to their body size (up to half the body length in some species). (A search in JSTOR for penis evolution returned 5000 results!) One important paper on the subject of sexual conflict was written by Patricia Brennan and colleagues in Proceedings: Biological Sciences. It’s tempting to make jokes, but there is a surprisingly large body of work regarding penis evolution. The rapid evolution fits in with a larger hypothesis known as sexual conflict, in which females try to evolve mechanisms in order to control copulation, and males evolve countermeasures. The study provides some confirmation for a long-standing assumption in evolutionary biology, that when fertilization is internal, male genitals will evolve rapidly to keep up with morphological changes in female genitalia. Lizard penises evolve much faster than the rest of the lizard, according to new research in the Caribbean.
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