I recently came across a journal article entitled Is Cunnilingus-Assisted Orgasm a Male Sperm-Retention Strategy? Naturally, I dropped everything I was doing and read it immediately--how could I not with a title like that? The researchers sought to test the novel hypothesis that, after ejaculation during intercourse, heterosexual men try to get their female partners to reach orgasm via oral sex in order to help them retain as much sperm as possible. To the extent that the female orgasm produces uterine contractions that draw sperm further into the reproductive tract, this would theoretically facilitate conception. However, in order for the cunnilingus-assisted orgasm to serve this purpose, it would need to occur right around the man’s ejaculation (specifically, anywhere from one minute before to about 45 minutes after)—if her orgasm occurs sooner or later than that, it will not have a sperm-retaining effect.

To test this idea, researchers recruited a sample of 243 young men who were in committed, heterosexual relationships. The men were asked to report on when they ejaculated relative to their female partner’s cunnilingus-assisted orgasm (if it occurred) during their most recent sexual event. Results indicated that in cases where the female partner had a cunnilingus-assisted orgasm, most of the men (58%) did not ejaculate during the potential sperm-retention time window. Thus, it did not appear to be the case that these oral sex orgasms were timed to facilitate conception.

So is there perhaps a different evolutionary purpose of the cunnilingus-assisted orgasm? The researchers speculate that it may instead be a “mate retention” strategy designed to increase a woman's satisfaction with her relationship, thereby decreasing the likelihood that she will go off and potentially become pregnant by another man. As some support for this idea, this study revealed that the men who were most likely to produce a cunnilingus-assisted orgasm felt that their partners were the most desired and sought after by other men. Thus, men may try harder to get their partners to orgasm via oral sex when they know their partners have other desirable options.

That said, this study has a lot of limitations and, in my view, it is far from clear what it tells us about the evolutionary significance of oral sex and orgasms. For one thing, as far as I can tell, participants were not asked if they wore condoms or if their female partners were using any form of contraception (e.g., birth control pills). Likewise, the men were not asked whether their ejaculation actually occurred intra-vaginally, and we have no verification from the female partners that they actually reached orgasm (we know that women sometimes fake it and men aren’t particularly adept at determining which orgasms are fake and which are not). Thus, for a study designed to look at the link between orgasm and sperm-retention, all of these variables seem like important things that should have been taken into account.

Also, perhaps cunnilingus doesn’t have any evolutionary significance. We know that most women do not reach orgasm through vaginal penetration alone, so perhaps cunnilingus is just a way that men try to enhance women’s opportunity to orgasm during sexual activity because it’s the decent thing to do (i.e., perhaps cunnilingus is a social convention rather than an evolutionary imperative). Furthermore, if oral sex were truly an adaptive behavior, then we should see similarly high prevalence and acceptability of this behavior cross-culturally. However, in certain cultures, oral sex (and any other sexual activity that involves the mouth, such as kissing) is seen as disgusting.

On a final note, I find it interesting that fellatio is not mentioned at all in this research, but we know that fellatio is an even more frequent activity in heterosexual relationships than cunnilingus. So why are we only focusing on one of these oral behaviors, but not the other? To the extent that cunnilingus is a mate retention strategy employed by men, isn't fellatio just as much of a mate retention strategy employed by women? Furthermore, if oral sex is a mate retention strategy, isn't almost every other sexual behavior designed to help your partner reach orgasm serving a similar purpose (e.g., clitoral and nipple stimulation)?

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To read more about this research, see: Pham, M. N., Shackelford, T. K., Sela, Y., & Welling, L. L. (2012). Is cunnilingus-assisted orgasm a male sperm-retention strategy? Evolutionary Psychology, 11, 405-414

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