A new study that sought to uncover what factors predict women’s likelihood of committing infidelity has been making a lot of headlines . Although this study identified several variables linked to women’s cheating behaviors, most media reports have focused exclusively on one: women were statistically more likely to cheat on men with longer penises. Most of the headlines said something along the lines of “The Larger Your Penis, The More Likely Your Wife Will Cheat.” Others went as far as claiming that penis size is “a leading cause of marital infidelity.” The message is clear: large penises are destroying the institution of marriage! But why? According to media reports, it’s because bigger penises cause painful and uncomfortable sex, which leads women to look for partners who are packing less heat. So are these claims warranted by the data? A closer look at the research suggests that the headlines have been wildly exaggerated.
For starters, it is important to note that this study focused on a sample of 545 fishermen and their wives from Kenya. Although I think it’s great that these scientists conducted research in Kenya, we must keep in mind that these data come from a very specific cultural and ethnic context. Why? Because the meaning and structure of marriage differs dramatically across cultures. For instance, consider that polygamy is actually quite common in Kenya and other parts of Africa. As a result, it is not wise to assume that the factors that predict infidelity in one culture would necessarily be the same in other cultures.
In addition, some research suggests that there are racial differences in penis size, with men of African descent tending to have larger penises than men of European descent. This is especially noteworthy in light of the fact that female genital cutting (FGC) remains common in Kenya. Given that some versions of FGC actually restrict the size of the vaginal opening, it is quite possible that sex might feel different for women in Kenya compared to women in other parts of the world. As you can see, there are many reasons to be cautious about taking findings from one culture and assuming that they apply more broadly.
It’s also worth mentioning that of the 545 women surveyed, just 6.2% reported having sex outside of their marriage—that translates to a total of 34 women who actually committed infidelity. That seems like a pretty small number to use as the basis for making sweeping claims about why women in Kenya (or anywhere else for that matter) cheat, don’t you think?
As for the link researchers identified between penis size and female infidelity, the journalists who reported on this study made the erroneous assumption that larger penis size therefore causes women to cheat. Given that these are correlational data, we cannot assume that penis size has any type of cause-and-effect relationship with infidelity. One alternative possibility is that penis size is statistically linked to some other factor that actually causes cheating. For instance, some research has found that men with larger penises are more narcissistic . In light of this, it might be the case that larger penises do not directly cause cheating; rather, it might be that men with larger penises have personalities that lead them to treat their partners in ways that increase the odds of infidelity.
Most media reports also went too far in claiming that larger penises promote cheating because they contribute to painful sex. In all fairness, the journalists were simply quoting the study authors, who stated the following in their article: “Women associated large penises with pain and discomfort during sex which precludes the enjoyment and sexual satisfaction that women are supposed to feel.” How did the authors come to this conclusion? They cited what one (just one) woman that they interviewed said:
“Some penis may be large yet my vagina is small, when he tries to insert it inside, it hurts so much that I will have to look for another man who has a smaller one [penis] and can do it in a way I can enjoy.”
I’m not in any way discounting or invalidating this woman’s experience because she is certainly not alone, especially not in Africa, a continent where FGC is common. However, for the researchers to essentially claim that all of the women in their sample found larger penises painful based upon one quote from one woman, well, that’s just not good science. If you’re going to make a broad claim about the nature of your sample, you need to have more than one quote from one participant to back it up.
In short, while this study may have found a statistical link between penis size and female infidelity, we have to consider it within the cultural context in which the study was conducted and the limitations of the methods and data. And even if painful sex as a result of large penises truly is a “leading cause” of infidelity in Kenya, I would be hesitant to just assume that the same is true in other parts of the world, especially in light of the fact that a significant number of Western women report that longer than average penises make them more likely to orgasm .
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 Kwena, Z., Mwanzo, I., Shisanya, C., Camlin, C., Turan, J., Achiro, L., & Bukusi, E. (2014). Predictors of Extra-Marital Partnerships among Women Married to Fishermen along Lake Victoria in Kisumu County, Kenya. PLoS ONE, 9(4), e95298.
 Moskowitz, D.A., Rieger, G., & Seal, D.W. (2009). Narcissism, self-evaulations, and partner preferences among men who have sex with men. Personality and Individual Differences, 46, 725-728.
 Costa, R. M., Miller, G. F., & Brody, S. (2012). Women who prefer longer penises are more likely to have vaginal orgasms (but not clitoral orgasms): Implications for an evolutionary theory of vaginal orgasm. Journal of Sexual Medicine, 9, 3079-3088.
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