Who falls asleep first?

After the climax: New science offers tantalizing insights into the meaning of what we do post-sex, from sleeping to cuddling by Katie Ryder

We’ve learned in sultry old romances and indie films about ill-advised affairs that we like to smoke between the sheets. People like to fix late night sandwiches, cuddle, talk about the future, take a shower. Every sitcom ever made posits that men don’t want women to talk after sex. And everyone seems to think it matters who falls asleep first.

But does it really? In recent years, a small number of researchers have been working to develop the science of post-coitus — a field that’s barely been touched.

I spoke with Daniel Kruger and Susan Hughes, evolutionary psychologists at the University of Michigan and Albright College in Pennsylvania who have been working on uncovering the secrets of post-sex behavior. “There is so much attention, in the popular literature in psychology and even in evolutionary research, looking at everything leading up to the act of sex,” said Kruger. “But then there isn’t anything about what happens after. It’s as if the attitude is, ‘oh, of course sex is the end goal, right?’ We’re making the point that the time that couples spend together after sex is an important part of healthy sexual relationships.”


Counter to popular opinion, a dated study, and the great wisdom of many lady mags, researchers have not found that men fall asleep faster than women after sex. In fact, according to a recent study of heterosexual pairings by Kruger and Hughes, a woman is just as likely as a man to be out first. But — and here’s the interesting part — regardless of gender, the partner who stayed awake longer reported that they weren’t getting enough post-sex hugging, kissing or talking – what evolutionary psychologists call “pair bonding” activities. (Somehow, Marie Claire got this exactly, 100 percent wrong.)

Both Kruger and Hughes are interested in what the post-sex sleep study says about male behavior. “This shows that men are concerned about partner bonding too,” said Kruger. “Human males are notable among primates for their high levels of paternal investment, so men may have a lot to lose as well if their partner leaves them.”

And what about the other activities people move on to after sex, like hanging out in bed, ordering Chinese food, or smoking a cigarette? Earlier in 2011 Kruger and Hughes published a report in the Journal of Sex Research, considering a wider range of after-sex impulses. In that case they found that our post-coital behaviors – again considering only heterosexual sex – tend to split along gender lines. Eating, fixing yourself a drink, smoking and asking your partner for favors – all activities that sound pretty good to me – were more likely to be taken on by the men. The women, in this case, placed greater importance on behaviors related to intimacy, like cuddling and “professing their love.”

The researchers interpret these results as related to the women’s need for “pair bonding.” Men in the survey were said to be more interested in gaining “extrinsic rewards” after sex – getting a new high from food, alcohol, cigarettes or some other non-sexual activity – or, in trying to have more sex.

These findings may suggest that men are better “adapted” to manage casual sex – not exactly a challenge to cultural lore. But there is a possible explanation for the men’s “hasty post-copulatory departure” that this research doesn’t address.

Our bodies release a mix of hormones following orgasm, including oxytocin, prolactin and endorphins. While contributing to feelings of contentment, high levels of oxytocin can put you to sleep. Post-orgasmic prolactin seems to be an even more critical factor in our post-sex behavior. It’s been shown to decrease sexual arousal and offset the dopamine effects of an orgasm. Essentially, prolactin brings your body and your brain back to baseline “Stop petting me I’m reading” mode. It has even been shown to make you temporarily less attracted to your partner.

Putting aside hormones, it seems intuitive that a so-called orgasm discrepancy could affect how we interact with our partners and could leave one person reaching for more attention. According to the Kinsey Institute, 75 percent of men always have orgasms in heterosexual sex, while only 29 percent of women can say the same. This would seem to have real bearing on studies that find gender differences in our post-sex impulses.

Kruger theorized, “For people who don’t orgasm during sex, maybe having their partner fall asleep first or move on to a new activity will be even more adversive.” Hughes agreed and said that orgasm differences might be “like adding salt to the wound.” (Of course, the orgasm discrepancy could be a sources of people’s divergent feelings and behavior in the first place.) The physiological effects of a prolactin reset, the pleasant influence of feeling like you’ve had harmonious or equitable sex, and the contentment of intense physical pleasure all seem rather critical to our post-sex impulses, and these are variables that should be squared away before we can jump to conclusions about gender differences and post-coitus.

After-sex research raises a number of questions. Wanting more attention after sex could very well be an expression of unresolved arousal, for example. And while the men in the post-sex activities study said they continue to “grope” their partner when they want a rematch, some women might ask for more sex in less obvious ways. Other women might reach out for some good-old fashioned togetherness as an alternative. Rather than cuddling because they want to shore up the evolutionary “protection” of their partner, or because they are naturally more prone to cling, partners who want to loll around in bed after sex might just be working up a dopamine fix – or contentment – of a different kind.