In the movie Unfaithful, Diane Lane’s character seems to have it all: a nice house, kids, and a hunky husband to boot (played by Richard Gere). Yet, following a chance encounter with an attractive younger man, she finds herself being, well, unfaithful. Why would she risk all of the nice things in her life by cheating? There are several reasons why she would take such a risk. It could be something about her (her personality or self-esteem), something about her relationship (not satisfying or unfulfilling), or something about the situation (she just had the chance). However, infidelity or cheating could also result from, at least partially, underlying biological and hormonal influences.
For example, men with higher testosterone have more interest in having sex outside of their relationships, which is basically the same thing as cheating (assuming his partner does not condone it).1 Similarly, women with higher levels of estrogen are more likely to cheat.2 Even though we don’t carry around testosterone and estrogen testing kits to use on our partners (that would be cool, though, wouldn’t it?), we can determine levels of these hormones without realizing. How? By listening to our partners’ voices.3 Men with greater testosterone have deeper voices (e.g., Barry White, George Clooney and others), while women with more estrogen have higher voices (e.g., Mariah Carey or Katy Perry). In fact, it seems we may have some inherent knowledge of this link between infidelity and voice pitch. In one study, participants listened to audio clips of male and female voices that had been digitally altered to be higher or lower in pitch and then indicated how likely each person would be to cheat based on the voice. Participants rated men with masculine deep voices and females with feminine high voices as more likely to cheat than men with high voices, or women with deep voices.3
For women, their ovulatory cycle in another biological factor that may also influence her likelihood of cheating.4 Specifically, women are more likely to cheat when they are most likely to get pregnant (i.e., when they are ovulating). Whoa…this seems like an absolutely terrible idea, so why would this be? Evolutionarily speaking, women should desire to obtain the best genes possible (think Channing Tatum) for their offspring. But the super sexy mate may not stick around to raise the child, so she needs to have a more stable partner who will provide security (think Phil, the dad with three kids, from Modern Family)—which is why a woman may decide to cheat rather than abandoning her primary partner altogether. As a result, if a woman finds herself in a relationship with a lesser quality partner (think Napoleon Dynamite), she’ll cheat when she is most fertile so that her offspring will have the benefit of better genes. Of course, the hope here would be that old Napoleon wouldn’t figure it out.
These biological influences might make it sound like a person can’t help cheating because he or she is at the mercy of their hormones. However, that is not what the research shows. If biology were destiny, then every high-testosterone male and high-estrogen female would be a serial cheater, which clearly isn’t the case. Rather, hormones may make resisting harder, but people have the ability to be self-aware and self-reflective and thus should be held accountable for their own choices.
1. McIntyre, M., Gangestad, S. W., Gray, P. B., Chapman, J., Burnham, T. C., O’Rourke, M. T., & Thornhill, R. (2006). Romantic involvement often reduces men’s testosterone levels–but not always: The moderating role of extrapair sexual interest. Journal of Personality and Social Psychology, 91(4), 642-651.
2. Durante, K. M., and Li, N. P. (2009). Oestradiol level and opportunistic mating in women. Biology Letters, 5, 179-182.
3. O’Connor, J., Re, D., & Feinberg, D. (2011). Voice pitch influences perceptions of sexual infidelity. Evolutionary Psychology, 9, 64-78.
4. Pillsworth, E. G., & Haselton, M. G. (2006). Male sexual attractiveness predicts differential ovulatory shifts in female extra-pair attraction and male mate retention. Evolution and Human Behavior, 27(4), 247-258.