Sleep: Depraved?

Scienceline.org attempts to lift the eyelids on a truism about sex: After it is over, men want to go to sleep.

Some women take the inclination personally, as though the man had come for a feast at someone’s house, engorged himself, and left without so much as taking time for a post-meal cup of coffee.

Research shows there’s no need for offense: After orgasm—particularly one where a partner is involved in helping bring it about (as opposed to one the fruit of masturbation)—the male brain releases a flood of chemicals a number of which even in isolation could make someone drowsy. Like eating a big meal of turkey and coasting to dreamland on a tide of L-tryptophan, a satisfying bout of lovemaking has chemical properties to send the man to dreamland.

But for what good in terms of natural selection?

One possibility is that the drowsiness is an insignificant byproduct of the chemical release. In other words, one of the chemicals (oxytocin) promotes bonding, but an incidental side-effect may be sleepiness.

More meaningful, however, is this possibility: A drowsy man is more likely to hang around with the his partner after sex. Should another male come along, the satisfied lover can keep the potential interloper away, giving the lover’s sperm time to fertilize the egg.

The Scienceline.org story wraps up with a pretty good line that should console women who are aggrieved when their partners fall asleep after sex. Worth a trip to the story by itself.