@Jim Eshelman said
"The net effect is (as a generalization across the species, varying with age and other consideration), men are "one peak wonders" and women are "distance runners." The most natural consequence of this mix is that (1) men are done for the moment and may tend to fall asleep, and (2) women are wired to keep going, socially and communicatively engage, and exhibit behaviors that move toward having another orgasm. On a pure biologically functioning level, it makes more sense for her to pursue further orgasms - and not necessarily with the same partner. (Five orgasms. Line up five guys. "Next!")
In thinking about how nature could have benefitted from this (why it would have sorted out that way in evolution), I came to a quick answer. Nature benefits from expanded genetic diversification - the opportunity for more and varied genetic mixes. Historically, it has been held that men accomplish this for the species by being able to wander about (even across large expanses of geography) impregnating a lot of women. It's often argued that one man could theoretically have hundreds of children in the time it takes a woman to have one. (270 days for a typical gestation, three seed-plantings a day, a fourth of them "take seed" - that's 200 births right there.) But it would be highly inefficient of nature to have let only half of a species contribute to this vitally important point of genetic diversification. On learning the above biochemical facts and their implications, I suddenly understood that women contribute to the same thing by having sex with many men in a short term (under a day) so that a wider variety of sperm are "competing: for the same egg."
Interesting stuff. From the other direction, there is the Coolidge Effect:
"Human males experience a post-ejaculatory refractory period after sex. They are temporarily incapable of engaging in sex with the same female after ejaculation and require time to recover full sexual function. In popular reference, the Coolidge effect is the well-documented phenomenon that the post-ejaculatory refractory period is reduced or eliminated if a novel female becomes available."
en.wikipedia.org/wiki/Coolidge_effec