This post is in response to Does Oral Sex Have an Evolutionary Purpose? by Scott A. McGreal

In the study of human sexuality, the psychological factors associated with interest in oral sex have been understudied. In a previous article, I discussed a recent paper that proposed an evolutionary explanation for interest in oral sex, namely that performing oral sex is performed to detect partner infidelity. That paper focused on men’s interest in cunnilingus. The authors have more recently published a new companion paper focusing on women’s interest in fellatio. Contrary to the authors’ expectations, a woman’s interest in fellatio was unrelated to how attractive she considered her partner, unlike men’s interest in cunnilingus. The authors make a rather convoluted and puzzling attempt to fit the findings of this paper to their theory, but the actual reasons for the considerable variation in women’s interest in oral sex remain unclear. Future research could more profitably explore how female interest in oral sex might be connected to personality traits known to be related to variations in sexual attitudes and behaviour.

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The rationale behind the two recent studies discussed here (Pham & Shackelford, 2013; Pham, Shackelford, & Sela, 2013) is that human interest in performing oral sex evolved as a way to test if one’s partner had recently been unfaithful. This notion, initially proposed in a 2006 book, is based on the idea that if one’s partner has recently had sexual contact with someone else, a detectable smell or taste would be left behind on their genitals. Additionally, the authors argue that having a highly attractive partner puts one at increased risk of partner infidelity. Therefore the authors reason, if the infidelity detection hypothesis is correct, then the more attractive one’s partner is, the more interested a person will be in performing oral sex on them. As discussed in detail in my previous article, Pham and Shackelford initially tested this hypothesis in relation to men, and found, as anticipated, that among men in committed heterosexual relationships, those who rated their partners as more attractive also showed more interest in performing oral sex. They considered this as evidence for their infidelity detection hypothesis, although they did discuss two alternative hypotheses, i.e. that oral sex increases partner satisfaction, and that inducing orgasm through oral sex may increase sperm retention (this last one I consider unlikely). Personally, I found it puzzling that they did not consider the more mundane possibility that men who find their partners highly attractive might be more interested in sexual acts generally, including oral sex.

In a more recent article, Pham et al. applied the same methodology to women. In this study, women in committed heterosexual relationships of at least one year’s duration were asked about how attractive they considered their partner, their most recent sexual experience, and their satisfaction with the relationship. Contrary to expectations, women’s ratings of their partner’s attractiveness (to themselves and to other women) was not significantly related to their own interest in performing fellatio. Women’s satisfaction with the relationship did have a small significant positive association with their interest in oral sex. However, in a statistical analysis controlling for duration of intercourse and relationship length, neither attractiveness nor relationship satisfaction were significant predictors of the woman’s interest in oral sex. Additionally, when they compared the results of this study to those of the one on men, they found, not surprisingly, that the relationship between partner attractiveness and interest in performing oral sex was stronger in men than in women.

Based on these results, I would think that a reasonable conclusion is that women appear to have different reasons than men for being interested in oral sex, at least in committed relationships. Their motivations (unlike those of men) would seem to be largely unrelated to their partner’s attractiveness and so the infidelity detection hypothesis does not apply to women. I therefore found the way the authors expressed their own conclusion somewhat convoluted:

The current results provide support for the infidelity detection hypothesis of oral sex; the differences in fluid quantity left behind by a rival (i.e., semen from a rival male vs. vaginal fluids from a rival female), may influence the effectiveness of, and motivation to, use oral sex as a means to detect infidelity.

To me, this sounds like a roundabout way of saying that "fellatio is ineffective compared to cunnilingus for detecting infidelity and therefore our theory cannot explain why women are interested in fellatio at all." The purpose of the study was to test the predictions of a theory, not to make excuses for it. Therefore, their statement that “the current results provide support” for their hypothesis, is a misleading one.

The authors do raise the reasonable consideration that fellatio involves a greater risk of transmitting an STD to the recipient compared to cunnilingus. However, if a woman was concerned that her highly attractive partner was seeing other women and putting her at risk of an infection, then I suspect that she would show reduced interest in performing oral sex to protect herself. If this were true, then one would expect a negative correlation between partner attractiveness (and the greater risk of infidelity) and the woman’s interest in oral sex, and this was not found either.

As noted earlier, Pham and Shackelford considered that the results in the study on men might be explained by the sperm retention hypothesis. Common sense would seem to suggest that this does not apply to women’s interest in oral sex, yet Pham et al. go on to make the following bizarre statement:

The current results also support the sperm retention hypothesis of oral sex; men but not women are concerned with their sperm being retained in their partner’s reproductive tract.

 I find this statement simply baffling, defying explanation. Why would women be concerned with (their?) sperm being retained in their male partner’s non-existent reproductive tract? What does this even mean? Even if they only meant to refer to the woman’s reproductive tract, I still don’t see how the sperm retention hypothesis has any relevance to this particular study at all.

The authors attempt to address the satisfaction hypothesis, but in a strange way:

The current results do not support the sexual satiation (sic) hypothesis of oral sex because the occurrence of oral sex is positively associated with both men’s and women’s relationship satisfaction.

 This statement appears to contradict itself: surely if oral sex was related to relationship satisfaction in both sexes, this would support the notion that people do it to increase said satisfaction. Furthermore, prior research findings have focused on the satisfaction of the recipient of oral sex, something which the current pair of studies did not address. In another paper they do discuss in detail the theory that men may use cunnilingus to keep their partner happy and dissuade her from straying from the relationship. I do not see why they did not devote space in the new paper to discuss the possibility that women might employ fellatio for the same purpose, instead of wasting time going on about sperm retention.

The results of the Pham et al. paper fail to provide an adequate theory of why women might be interested in performing oral sex. The results indicate that women might have different reasons than men for being interested in oral sex, but they do not indicate what these reasons might be. Individual differences in women’s motivations for performing fellatio do not seem to have been researched in great depth, but I get the impression from the literature I have seen that women may vary more than men in how much they enjoy performing oral sex. For example, one study of college students found that men and women were about equally likely to say that their most typical reason for performing oral sex was for the pleasure of the recipient (about 80% of men and women gave this as their main reason). No big surprise there. More interesting though, was that the second most common typical reason was for the pleasure of the giver, and this reason was more frequently given by men than women (26.8% vs. 16.9%). That is, men were more likely than women to say that they gave oral sex primarily for their own enjoyment (Chambers, 2007).

Another study, this one on married couples, found that about 55% of women said they found fellatio satisfying overall, while the remainder found it unsatisfying (Apt, Hurlbert, Sarmiento, & Hurlbert, 1996). The most common reasons women gave for finding it unsatisfying were disliking the taste of semen, fear of ejaculation, and to a lesser extent regarding it a “personal turn-off.” Interestingly in the light of earlier remarks about fellatio and STDs, over a third of women who found it unsatisfying cited concern about germs/cleanliness. The authors of this study suggested that women who find fellatio satisfying may be those who have more liberal and experimental attitudes towards sex, and who are free of psychological blocks about sex, such as disgust at the male genitals and semen in particular.

From the foregoing, it seems plausible that individual differences in women’s liking of oral sex might be related to stable personality traits. A number of personality traits have been linked to sexual attitudes. High openness to experience in women, for example, is related to greater marital satisfaction in couples, perhaps because such women are more open to exploring their sexuality (McCrae & Sutin, 2009). Openness to experience is also associated with a wider range of sexual fantasies and more accurate knowledge about sex. High openness to experience in women (but not men) has also been found to correlate positively with a trait called sexual sensation seeking, which refers to the desire to seek optimal levels of sexual excitement and to engage in novel sexual experiences (Gaither & Sellbom, 2003). Research rooted in evolutionary psychology has also identified a number of sexual dimensions of personality previously overlooked by personality theorists (Schmitt & Buss, 2000). These include a trait called “sexual attractiveness”, which includes such descriptors as ‘sensual’, ‘erotic’, and ‘sexy.’ Whether this trait is related to variation in interest in oral sex does not seem to have been studied, but it seems like a good candidate. Furthermore, “sexual attractiveness” is positively correlated with extraversion in both sexes, and with openness to experience in women only. I am not aware of any studies that have tested this, but it seems likely that women’s interest in fellatio is probably related to high openness to experience, and to relevant sexual dimensions of personality.

The studies on interest in oral sex by Pham and colleagues attempted to link this behaviour with a particular theory rooted in evolutionary psychology. Attempting to link human behaviours to a broader theory is a worthwhile endeavour, but in this case I think the attempt has been unsuccessful, particularly in the study on women. I think that a more potentially fruitful approach would be to study this behaviour in the context of personality traits that already have known linkages with human sexuality. Influences of personality traits could also be assessed in the context of more situational motivational factors, such as the desire to please one’s partner. It may also be interesting to compare motivations to perform oral sex in a wider variety of relational contexts, e.g. comparing its occurrence in committed relationships versus more casual contexts.


Michael Pham, the lead author of the target article discussed in this post, has kindly taken the time to address issues that I have raised, in the comments section here

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© Scott McGreal. Please do not reproduce without permission. Brief excerpts may be quoted as long as a link to the original article is provided. 

Other posts about sex and psychology

Porn Stars and Evolutionary Psychology

The Personalities of Porn Stars

Are Sex and Religion Natural Enemies?

Does Oral Sex have an Evolutionary Purpose?

The Pseudoscience of Race Differences in Penis Size

Semen an Antidepressant? Think Again

BDSM, Personality and Mental Health

Personality Traits of BDSM Practitioners: Another Look

Further reading on Evolutionary Psychology

Evolutionary Psychology: A Primer by Leda Cosmides and John Tooby. This is an essential read for anyone interested in understanding the scientific basis of the subject. 

Tooby and Cosmides response to Gould - debunks widely believed misinformation about the subject that originated with biologist Stephen Jay Gould, e.g. the false notion that evolutionary psychologists think that "every behavior is an adaptation." 


Apt, C., Hurlbert, D. F., Sarmiento, G. R., & Hurlbert, M. K. (1996). The role of fellatio in marital sexuality: An examination of sexual compatibility and sexual desire. Sexual and Marital Therapy, 11(4), 383-392. doi: 10.1080/02674659608404452

Chambers, W. C. (2007). Oral Sex: Varied Behaviors and Perceptions in a College Population. Journal of Sex Research, 44(1), 28-42. doi: 10.1080/00224490709336790

Gaither, G. A., & Sellbom, M. (2003). The Sexual Sensation Seeking Scale: Reliablity and Validity Within a Heterosexual College Student Sample. Journal of Personality Assessment, 81(2), 157-167. doi: 10.1207/s15327752jpa8102_07

McCrae, R., & Sutin, A. R. (2009). Openness to Experience. In R. H. H. Mark R. Leary (Ed.), Handbook of Individual Differences in Social Behavior (pp. 257-273). New York/London: The Guildford Press.

Pham, M. N., & Shackelford, T. K. (2013). Oral sex as infidelity-detection. Personality and Individual Differences, 54(6), 792-795. doi:

Pham, M. N., Shackelford, T. K., & Sela, Y. (2013). Women’s oral sex behaviors and risk of partner infidelity. Personality and Individual Differences, 55(4), 446-449. doi:

Schmitt, D. P., & Buss, D. M. (2000). Sexual Dimensions of Person Description: Beyond or Subsumed by the Big Five? Journal of Research in Personality, 34(2), 141-177. doi:

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