This week I've been wrestling with a particularly large writing project which has kept me away from posting in this column. But, staring into my Twitter feed in procrastination, I spotted much outrage about a paper on the adaptive basis of cunnilingus-assisted orgasm. I had to head over to the journal Evolutionary Psychology to take a look.
The authors, Michael N. Pham, Todd K. Shackelford, Yael Sela and Lisa L. M. Welling, all of Oakland University in Michigan report the results of a simple survey they administered to 243 men in committed, heterosexual relationships. They predicted that, in their own words:
among men who perform cunnilingus on their partner, those at greater risk of sperm competition are more likely to perform cunnilingus until their partner achieves orgasm (Prediction 1), and that, among men who ejaculate during penile-vaginal intercourse and whose partner experiences a cunnilingus-assisted orgasm, ejaculation will occur during the brief period in which female orgasm might function to retain sperm (Prediction 2).
It would be too easy to sneer at the rather joyless prose, here and throughout the paper, as some popular commentators have done. And it would also be wrong. We expect scientists working on other less sensitive questions to make clear predictions that avoid imputing value or emotion. And so should it be with predictions about oral sex.
This paper is part of a rich vein of research in Evolutionary Psychology on the function of the female orgasm. In particular, it tests an idea -- one enthusiastically championed by Todd Shackleford's group -- that orgasm functions to enhance the chance of conception.
One mechanism by which this could occur is by inducing uterine contractions which draw sperm toward the egg, shortening the distance sperm have to travel. This is one formulation of an old idea, colourfully called the "upsuck hypothesis." As Mary Roach points out in point six of the video below, evidence supporting "upsuck" is equivocal.
Legion studies provide circumstantial evidence consistent with the idea of orgasm as a form of after-the-fact mate choice ("use the sperm of the guy who made you come"). Women with wealthy partners report having more orgasms. More masculine and more attractive men tend to give their female partners more orgasms.
But when would women need to discriminate among men's ejaculates? When they mate with more than one man over a fertility cycle.
Studies on other animals, particularly insects, suggest that competition among males doesn't stop at copulation, but continues between the ejaculates when the female mates in reasonably close succession with two or more males. And that females can differentially use the sperm of some males over others.
Studying these questions in humans is, understandably, ethically fraught, and so the evidence for sperm competition is less direct. The size of men's testes and the volume of their ejaculate suggests that human sperm competition is important but by no means rampant.
That is consistent with the evidence that while humans show an intriguing capacity for monogamy, we are also often enthusiastically promiscuous.
So, returning to the paper in question, what do Pham and colleagues mean when they talk about "men at greater risk of sperm competition"? Did they secretly ask those men's partners if they had been furtively mating with somebody else? Nope. Turns out their measure, which they rather clinically name "recurrent risk of sperm competition" constitutes "the mean of four variables: how sexually and physically attractive the participant views his partner, and how sexually and physically attractive the participant believes other men view his partner."
So they asked men, four different ways, how attractive they thought their partners were. Attractive partners, by their logic, are at greater risk of having recently mated with other men.
And they found that men who rated their partners as highly attractive tended more often to have orally brought them to orgasm. Add this to another paper, recently published by Pham and Shackleford showing that men who rate their partners as attractive express greater interest in, and spend more time performing, oral sex on their partner.
Being a defender of evolutionary psychology isn't always easy. Most research in this field is conceptually interesting, well-replicated and generally robust science. But the stuff that breaks into the news cycle and infests the Twittersphere so often tends to come from the weakest science the field has to offer. And I have to confess I find these studies among the most underwhelming I have recently read.
We biologists tend to forget that talk about sperm competition and cunnilingus-assisted orgasm induces many folks to squirm. It isn't the squirm factor here that gets my goat.
It's the way in which the investigator's favoured hypotheses don't attract the sceptical self-scrutiny they deserve. And in which alternative ideas aren't duly considered.
And this includes considering the question from the woman's point of view. Perhaps gathering data from women. These weaknesses play helplessly into the worst stereotypes that critics of evolutionary psychology deploy to dismiss the biological study of human behaviour.
Have you asked the womenfolk?
Evolutionary explanations for the function of orgasm tend either to see orgasm as a form of mate choice or as a by-product of the male capacity to orgasm at ejaculation. A recent review of the evolutionary literature came down in greater favour of "mate choice" hypothesis than the by-product hypothesis.
The idea that men who view their partners positively might also be more interested in pleasuring them orally doesn't get the nuanced exploration is probably deserves. Giving and receiving of sexual pleasure is part of the complex social-biological interplay that defines relationships.
Kind men who care enough about their partners to please them sexually may also tend to view them as attractive. Men with attractive partners might work extra-hard to keep them sexually interested. Because those partners have better options should they leave.
My point is not that Pham et al are wrong. Their favoured explanation, cloaked here in the psuedo-objective language of a dry hypothesis, may well prove robust to more critical scrutiny. But there are a wealth of possible alternative explanations, some more likely than the favoured one. I trust the Conversation's busy commentators will, in typical fashion, identify them all.
One of the things that irritates me about this paper is the way in which the paper considers one explanation among hundreds, finds evidence in support of it, and then ignores the more complex context of the behaviour. Female orgasm and oral sex are indeed rich subjects for study. I would love to know more about why not all women orgasm, why those that do do so in different ways. And why oral sex practices vary so wildly among times, places and individuals.
It is this concession of the complex, social dimensions that concedes the most interesting aspects of behaviour to those who blur it in social constructionist and post-structural mumbo-jumbo.
I wish my evolutionary colleagues would get stuck in to the much more complex social aspects of orgasm and sexual pleasure.
Double standard, much?
Bizarrely, while the function of the female orgasm gets treated as a mystery, the male orgasm seldom gets an equal workout (cue whining from both sides of gender political spectrum). Because male orgasm so often accompanies ejaculation, should we think of it as a mere reward for depositing sperm, motivating men to become rampant sowers-of-oats?
Likewise, I don't see a lot of head-scratching about the functions of fellatio. And other practices that cause seed to be spilled in places other than a vagina connected to an ovulating uterus. We leave the ultraconservative nutbags to worry about these questions. So many of us stop uncritically at the assertion that sex, for men, is fun.
Why is sex fun? The answer, to so many of us, is obvious. But when Jared Diamond asked this question he exposed many far more intriguing questions that lurk beneath.
Anyone can conjure superficial answers to questions like "why do women have orgasms?", "why don't all women have orgasms?", "why do men orgasm when they ejaculate" and "what is the function of oral sex?" Good answers based on solid science are much, much harder to come by.
But that shouldn't stop us from trying.
Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
This article was originally published at The Conversation.
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