“Men go to sleep because women don’t turn into a pizza”
there would have also been evolutionary selection pressures favoring males with the tendency to fall asleep with the person with whom they just had sex… those who got up and leave increase the likelihood that the partner would have a subsequent sexual encounter decreasing chances of assured paternity. even the shape of the head of the male penis increases the likelihood of removing competitor sperm that may be present in a partner…says Dave Zinczenko, the author of “Men, Love and Sex: The Complete User Guide For Women,” as to why men fall asleep after sex.
Research using positron emission tomography (PET) scans has shown that in order for a person to reach orgasm, a primary requirement is to let go of “all fear and anxiety.” Doing so also tends to be relaxing and might explain the tendency to snooze.
Then there is the biochemistry of the orgasm itself. Research shows that during ejaculation, men release a cocktail of brain chemicals, including norepinephrine, serotonin, oxytocin, vasopressin, nitric oxide (NO), and the hormone prolactin. The release of prolactin is linked to the feeling of sexual satisfaction, and it also mediates the “recovery time” that men are well aware of—the time a guy must wait before “giving it another go.” Studies have also shown that men deficient in prolactin have faster recovery times.
Prolactin levels are naturally higher during sleep, and animals injected with the chemical become tired immediately. This suggests a strong link between prolactin and sleep, so it’s likely that the hormone’s release during orgasm causes men to feel sleepy.
(Side note: prolactin also explains why men are sleepier after intercourse than after masturbation. For unknown reasons, intercourse orgasms release four times more prolactin than masturbatory orgasms, according to a recent study.)
Oxytocin and vasopressin, two other chemicals released during orgasm, are also associated with sleep.
It’s also possible that sleepiness is just a “side effect” associated with a more evolutionarily important reason for the release of oxytocin and vasopressin. In addition to being associated with sleep, both chemicals are also intimately involved in what is called “pair bonding,” the social attachment human mates commonly share. The release of these brain chemicals during orgasm heightens feelings of bonding and trust between sexual partners, which may partially explain the link between sex and emotional attachment.
(via livescience)
I thought the section in bold was really interesting. I wonder why that is true..
