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Pajiba Dirty Talk: Ribbed for Whose Pleasure?

By Dr. Pisaster | Pajiba Dirty Talk | March 15, 2011 | Comments ()

By Dr. Pisaster | Pajiba Dirty Talk | March 15, 2011 |


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A recent comparison of the human and chimpanzee genomes, published in this month's Nature, found two significant differences between our two species. The first is the loss of a growth-suppressing switch that may have allowed us to grow larger brains. Nobody cares about that though, because the second? Involves penises, and our species is nothing if not penis-obsessed. You may not know this, but the human penis is significantly different from those of our closest relatives, including chimps, because it lacks spines. Yes, you read that right. Many animals have spines made of keratin - the same stuff that makes up your fingernails - on the heads of their penises. The spines are tiny, hard bumps (about .35mm in chimps) which have been described as giving the penis a rough texture. Sort of like a cat's tongue (or a cat's penis, but I'm going to assume most of you have never felt one of those).

The loss is related to the disappearance from our genome of a regulatory factor that enhances the expression of a type of androgen gene receptor, androgens being hormones that control male characteristics. Like penis spines. That the spines are controlled by male hormones is not surprising; when you castrate a species with penile spines, the spines disappear, indicating that their growth is stimulated by hormones produced in the testes. The researchers also found that they could stimulate human cells to grow spines when transfected with the enhancer region, so the basic components for building the spines are all still there, we're just not using them. In the future, enterprising young men who feel that ribbed condoms or implanted beads aren't quite badass enough may be able to take a pill to stimulate spine growth. (Note, I actually hope that this does not happen, but I knew a guy in undergrad who was crazy enough to implant beads under the skin of his own dick so he could pleasure women more, so I'm pretty sure there is a market. And when I say he put the beads in, I don't mean he had someone else do it. I mean he did it to himself, in his dorm room, with his roommate looking on and taking pictures. I knew some crazy people in undergrad.)

Nobody is quite sure what the purpose of penis spines is. One theory is that it would increase female pleasure (as my old acquaintance believed), though a quick survey of reviews for ribbed condoms reveals that the extra stimulation is not to every woman's taste - just as many find it uncomfortable or even painful as find it pleasurable. A less pleasant theory is that the spines are to discourage females from mating with other males by abrading the vagina (though you'd think if that were the case they'd never want to mate at all). It's also been suggested that the spines are to draw out sperm of competing males. The spines are also related to whiskers, so it's possible their greatest impact is on male sensitivity. The main effect of the spines on men seems to be to increase their sensitivity and decrease their stamina.

Whatever their purpose, it's been noted before that these spines are most common in species in which females mate with multiple males. Primate species which lack the spines tend to favor monogamy, possible because the increased copulation time means the females don't need to mate with several males in succession to get off (I find it interesting that while the non-monogamy argument is most often used to support the idea that men need novelty, in our closest non-monogamous relatives it's the females that really get around). A point for the "monogamy is natural," types but of course we should be cautious about drawing too many conclusions about human social behavior from one genetic mutation. For one thing, paternity tests reveal that many so-called monogamous species are anything but. While they may pair bond and raise offspring together, it's pretty common for those offspring to have a different father. (If anybody has done any research to see if the males do much extra-pair mating, I haven't found it.) Sexual monogamy is complex and involves not just genetic factors but personal taste and choice as well. I get irritated when non-monogamous people use evolutionary arguments to claim that their way is the one true natural way, and I don't like the arguments that promote monogamy as the natural human state much either. Nature gives us competing goals and various strategies for achieving the all-important business of propagating the species. That said, our species does gravitate toward pair-bonds (though, again, not necessarily sexually monogamous ones), and the loss of penis spikes may have been one evolutionary step in that direction. I for one am grateful for the loss. I don't want anything resembling a tiny, sharp fingernail anywhere near my vagina.



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