Wednesday, May 25, 2005

The Case of the Female Orgasm, part 4

Below the fold is my response to the NYT article on Lloyd and a link to Pharyngula

(No really, honey, this is work. I am not slacking off at the office blogging. This is academic work. At the very least, the book review that will come out in Metapsychology Online will be listed on my CV)

(Note expandable posts have been hinky of late. If anyone actually tries to click through, and can't see the full post, let me know.)

(Expandable post removed, for the benefit of the anxious masses. Hopefully you won't be dissappointed by the fact that this is really just a post about biology. At least I use the phrase "spree fucking" in it.)

The NY Times Article

For those of you who are new to the story, Lisa Lloyd's new book argues that research into the evolution of the human female orgasm has been marred by androcentric and adaptationist biases. The Times' Dinitia Smith interviewed Lloyd and got replies from four of the people she criticized, Alcock, Thornhill, Baker and Hrdy. (The article is now behind the pay wall.) In this post I simply want to reply to these four on behalf of Lloyd.

The article does a nice job of explaining Lloyd's on prefered, developmental explanation of female orgasm, from Donald Symons.

That theory holds that female orgasms are simply artifacts -- a byproduct of the parallel development of male and female embryos in the first eight or nine weeks of life.

In that early period, the nerve and tissue pathways are laid down for various reflexes, including the orgasm, Dr. Lloyd said. As development progresses, male hormones saturate the embryo, and sexuality is defined.

In boys, the penis develops, along with the potential to have orgasms and ejaculate, while ''females get the nerve pathways for orgasm by initially having the same body plan.''

Nipples in men are similarly vestigial, Dr. Lloyd pointed out.


However, Smith oversimplifies her account of Lloyd's criticisms of the adaptationist accounts, and as a result, screws up the communication between Lloyd and her critics.

Central to her thesis is the fact that women do not routinely have orgasms during sexual intercourse.

She analyzed 32 studies, conducted over 74 years, of the frequency of female orgasm during intercourse.

When intercourse was ''unassisted,'' that is not accompanied by stimulation of the clitoris, just a quarter of the women studied experienced orgasms often or very often during intercourse, she found.

Five to 10 percent never had orgasms. Yet many of the women became pregnant.

...

Dr. Lloyd said there was no doubt in her mind that the clitoris was an evolutionary adaptation, selected to create excitement, leading to sexual intercourse and then reproduction.

But, ''without a link to fertility or reproduction,'' Dr. Lloyd said, ''orgasm cannot be an adaptation.''


Lloyd's argument does hinge on the fact that women rarely orgasm from vaginal intercourse, but you need to (1) explain why this is a problem for the competing accounts and (2) emphasize that Lloyd is not demanding a perfect correlation of orgasm with intercourse . Otherwise, the adaptationists will simply say "my account does not require that orgasm always occur with intercourse," which is exactly what Thornhil and Alcock did.

Here's Alcock's response: "orgasm doesn't occur every time a woman has intercourse is not evidence that it's not adaptive...I'm flabbergasted by the notion that orgasm has to happen every time to be adaptive."

Thornhill: In a phone interview, Dr. Thornhill said that he had not read Dr. Lloyd's book but the fact that not all women have orgasms during intercourse supports his theory. There will be patterns in orgasm with preferred and not preferred men," he said.


Both Alcock and Thornhill advocate mate-choice explanations of the human female orgasm. Basically, the idea is that women use orgasm to judge whether their partners would make good mates. Men who give women more orgasms will be mated with more often. According to Alcock, women are judging whether the man will be a good caregiver for their children. Thornhill's picture is more unconscious. He and his colleagues speculate that the main variables in determining whether a woman orgasms are markers for genetic fitness, like facial symmetry. They further claim that in orgasm, the uterus "sucks up" sperm, making fertilization more likely. In fact, they imagine that this would occur in situations where the female has had sex with two different males in a short period of time, and that the increased facial symmetry of the more genetically fit male will cause more of his sperm to be sucked up into the uterus.

Now both Alcock and Thornhill's accounts predict that there will be variability in rates of orgasm with intercourse. Lloyd acknolwedges this and even praises Alcock's for getting that part right. However, neither can account for the way in which orgasm and intercourse are partially linked. On their accounts, we should expect most women to sometimes have orgasm sometimes with intercourse--specifically those times when they have a good mate. But this is only 42% of women at best. It says nothing about all the women out there who *never* have orgasm with intercourse or all the women out there who *always* have orgasm with intercourse. (Unless, for some reason, there are women out there who have *never* chosen a fit partner and other women who *always* choose them.) And this is exactly the point Lloyd makes. She makes it on page 75 in responding to Alcock and 212 in responding to Thornhill et al. The idea the Lloyd was insisting on 100% correlation between orgasm and intercourse seems to be a flaw in the way Smith represented Lloyd's work to Alcock and Thornhill. There are other problems with Alcock and Thornhill's accounts as well. For instance, why does Alcock assume that men who are good lovers will also be good with children? Thornhill's work has an even bigger problem huge problem, because it is based on the sperm upsuck hypothesis from Baker and Bellis, which brings us to Baker's reply to Lloyd.

Baker, together with Mark Bellis, proposed the sperm upsuck theory. Their argument was marred by use of really small sample sizes (like one), screwy reasoning around the timing of orgams, and a generally watering down of the hypothesis to the point where it could explain anything. By the time Lloyd is finished with Baker and Bellis, she is wondering "how the Baker and Bellis paper ever got published in Animal Behavior the flagship journal in the field" (232). In light of that remark, Baker's defense to the Times seems quite weak

In an e-mail message recently, Dr. Baker wrote that his and Dr. Bellis's manuscript had ''received intense peer review appraisal'' before publication. Statisticians were among the reviewers, he said, and they noted that some sample sizes were small, ''but considered that none of these were fatal to our paper.''


The most adaptive hypothesis on the evolution of the human female orgasm comes from Hrdy. While every other evolutionary psychologist studying sexuality is obsessed with male jealousy and the mechanisms males use to confirm the paternity of their children, Hrdy emphasizes the methods females have used to confuse paternity. In other primates like chimps, the most common cause of infant death is infanticide by newly dominant males killing the offspring of their rivals and sending the females into heat. Hrdy points out that females can save their children if they can keep males in the dark about parentage.

Hence, spree fucking. Hrdy imagines that in some point in hominid evolution, females would have bouts where they mate with large numbers of adult males in rapid succession, as some contemporary primates do. (I much prefer the term "spree fucking" here to the porno term "gang bang".) Orgasm might facilitate such behavior if females required long periods of penetration to achieve orgasm, durations that could only be achieved by mating with many males in rapid succession.

The problem with this theory is that in fact most human women do not increase their chance of orgasm by increasing duration of vaginal penetration. Certainly after 15 minutes, if you haven't arrived yet, you aren't going to. This is due to a simple fact known to any sensitive lover: the clitoris is king. Women orgasm as quickly as men given clitoral stimulation, and vaginal stimulation, no matter how sustained, simply won't do the trick.

In the Times, Hrdy replies that she is not talking about human sexuality. She is imagining that one of our common primate ancestors, perhaps seven million years ago, engaged in this kind of spree fucking. But now the account has become totally speculative. If you are ruling out evidence from current sexuality as relevant, you really have left the realm of testable hypotheses.

Alright, that's all for now. I've got more thoughts on Lloyd to post, and then it will all be assembled into my review. Perhaps I should also get a paper out of this. For the PSA, perhaps? If I push the Bonobo line from my first post I might have an interesting thesis.

In other news
PZ Myers demonlishes a writer who tries to use Lloyd's book to push the "teach the controversy" approach to creationism in the schools.

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