There's actually some decent evidence that women are biologically more interested in having multiple sexual partners than men are, at least prior to fertilisation. The logic goes like this:
Sorry, but this kind of backward logic concerning genetics has always annoyed me. No one, neither snake, bird or human, has even thought "Hmm, how can I produce the strongest offspring to help advance the species?"
People (and presumably animals) deal with physical attraction. Sure, a couple here and there might be attracted to some monkey's mind, but that doesn't occur often enough to be statistically relevant. Genetics doesn't work through the force of logic, instead it works on a primal level and the species either survives or it doesn't, not due to any plan by the animals in question.
That said, they've done studies of many animal species, and 'cheating' in almost universal in the animal kingdom, with females cheating as much, if not more, than males. By the way, rape and homosexuality are perfectly natural and occurs throughout the animal kingdom, as anyone who's ever spent much time on a farm can attest. (My family raised hunting dogs, and we had more than our share of lesbian bitches!) Again, those dogs don't care whether it'll produce strong and rich children, they act on instinct.
As for increasing the quality of the human race, I only have on suggestion: ban all politicians (and bureaucrats) from ever having sex! (There's no need to stop nerds or authors, nerds don't get the chance, while authors are too busy writing in their basements to ever encounter other human beings for long.) 'D