The Evolution of the Human Female Orgasm

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So I just finished reading Lisa Lloyd's new book The Case of the Female Orgasm: Bias in the Science of Evolution. It's a facinating case study in the way bias, particularly androcentric bias, can ruin a scientific investigation. It’s not out officially yet, but I want to blog about it, both to encourage you, the internet, to buy it when it does come out, and because I want to sort out my thoughts.

Mostly the thoughts I want to sort out revolve around my continuing belief that the human female orgasm is an adaptation. It’s not like the male nipple, which is just there as a byproduct of female nipples. Moreover, I think the human female orgasm was selected for because it facilitated social relations in one or more ways, including preventing conflicts and aiding reconciliation after conflicts, regulating tension, solidifying same sex and different sex alliances, and expressing social status. These are the functions that sexual pleasure seems in general to serve in everyone’s favorite super-sexy-love-primate, the bonobo (see Huhmann and Fruth 2000), and the bonobo strikes me as the right super-sexy-love-primate on which to model human evolution.

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So this is the deal. Lloyd surveys all of the available evolutionary accounts of the human female orgasm, 20 in all. (She misses the one in my tiny little head, which on the one hand is understandable, since I've never told anyone about it, but on the other hand is kinda odd, because it seems to be in a lot of other people's tiny little heads that I've talked to, so you'd think it was actually written up somewhere, especially since everyone is all into bonobos these days.)

So where was I, oh yes, Lloyd surveys all of the available evolutionary accounts and finds all sorts of gross mistakes in reasoning and handling of data in all but one of them. She then argues that these mistakes come from two biases, one purely methodological and one with serious political overtones. On purely methodological side, she identifies adaptationism, the persistent belief that any important trait must be somehow adaptive. This bias is most in evidence in the bizarre fealty people feel to failed adaptive accounts, even when far more natural nonadaptive accounts are available. On the more political side, she identifies the problem as coming from androcentrism, specifically, the assumption that female sexuality is like male sexuality. This comes out, for instance, in models that assume females become sleepy after orgasm, as males do.

All this is clearly right, and her case is well made. The problem is that in making the case, Lloyd herself makes some androcentric assumptions. A big one is her almost Clintonesque definition of sex. An important point in almost all of her arguments is that women orgasm more readily in masturbation than in sex, a fact which she refers to as the orgasm/intercourse discrepancy. The root of this discrepincy, according to Lloyd, is that in masturbation, the clitoris is stimulated directly, where intercourse--defined as vaginal penetration--only stimulates the clitoris indirectly.

The orgasm/intercourse discrepancy is what allows her to dismiss all the evolutionary models that revolve around social bonding. All of the social bonding models Lloyd finds in the literature are actually pair-bond models--they assume that if orgasm helped social bonding, it must have helped lifetime monogamous pairings. All of these models are ultimately decended from the ur-nonsense on human evolution from Desmond Morris. According to Lloyd, the root problem with all these models is the orgasm/intercourse discrepancy. If women orgasm more easily solo, how could orgasm have helped the pair bond?

Now, I'm not a fan of the Desmond Morris models either, but Lloyd's objection to them is flawed. The orgasm/intercourse discrepancy only exists if you assume that sex is vaginal penetration. Now I know this definition of sex is popular among ex-presidents and Christian teens who wish to maintain that they are virgins, but it never made much sense to me. I mean, the word “sex” is right there in the name “oral sex.” Once you count oral sex as sex, the orgasm/intercourse discrepancy disappears. Really, the orgasm/intercourse discrepancy is a discrepancy between clitoral and vaginal stimulation. But clitoral stimulation has no special tie to masturbation, and vaginal stimulation has no special tie to intercourse.

The real problem with the Morris pair bond models is the "pair" part of social bonding. There's no reason to assume that our ancestors used our odd mating system. Moreover, we already know that sexual pleasure in general is adaptive in Bonobos, who are flagrantly nonmonogamous. So why isn't there a model out there which tells the story of the evolution of the human female orgasm based on an analogy to the currant adaptive of sexual pleasure in general in bonobos? Shouldn't Frans de Waal be on this?

Reference

Hohmann, G, and B. Fruth. 2000. Use and function fo genital contacts among female bonobos. Animal Behavior 60:107-120.