The stereotypical picture of a heterosexual couple post-coitus depicts a frustrated woman who wants to talk and cuddle staring at a sleeping (and usually snoring) man. Such tension between the sexes is just a natural part of life, right? I mean, this scenario has played out time and again in movies and television shows, and there’s even a book out there written by a physician entitled Why Do Men Fall Asleep After Sex?: More Questions You'd Only Ask a Doctor After Your Third Whiskey Sour. Despite how widespread this belief is, recent research does not back it up .
In a University of Michigan study, 456 college undergraduates completed a survey that inquired about whether they tend to fall asleep before or after their sexual partners. All participants were heterosexual and sexually active, and most were currently involved in some type of relationship. Contrary to researchers’ expectations, men and women reported that they were equally likely to be the first one to fall asleep after having sex. Thus, there was no apparent evidence of a widespread angry woman/tired man stereotype.
Where they did find a gender difference was in reports of who falls asleep first on occasions when sex does not occur. Specifically, when a heterosexual couple does not have sex, men actually report staying awake longer than their female partners. How do we explain this finding? We don’t know for sure, but the authors of the study suggest multiple possibilities. Perhaps men stay awake longer as a form of mate-guarding (i.e., making sure that their partner does not sneak away to have sex with someone else), or because men secretly hope to tempt their partners into some late-night lovemaking. Alternatively, perhaps women have evolved a tendency to fall asleep faster so as to limit opportunities for sex, given that the potential costs of sex (e.g., pregnancy) are higher to women than to men. It's also possible that none of these explanations are correct and that something entirely different is responsible.
Any way you look at it, sex and sleep have an intimate connection; however, our stereotypes about the nature of this association do not appear to match up with reality.
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 Kruger, D. J., & Hughes, S. M. (2011). Tendencies to fall asleep first after sex are associated with greater partner desires for bonding and affection. Journal of Social, Evolutionary, and Cultural Psychology, 5, 239-247.
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