Women socially punish promiscuous women, and men prefer not to have relationships with promiscuous women. It is evolutionary psych:

Women have uteruses, men do not. Therefore, sex is a relatively low reward, high risk endeavor for women when compared to men: - Opportunity cost of pregnancy (high risk) - More likely to catch STD's because of shorter urethra (high risk) - Physically weaker than the man she is being vulnerable with (high risk) - Possibility only of having one pregnancy at any given time, as opposed to dozens (low reward) Obviously the reverse is true for men; it is relatively high reward, low risk. Thus, women are much more selective about who they have sex with. When one sex is much more selective, one sex becomes relatively desperate. This leads to competition. This leads to men being more competitive and organizing themselves into dominance hierarchies, partially in competition for mating opportunities. Since women are much more selective and men are more competitive and desperate, women, practically speaking, can demand things in return for sex. Women, de facto, demand protections and provisions from men. Naturally, in a paleolithic tribal setting, men and women will typically pair bond, and women will exchange sex for men's protections and provisions. Now, if you take a paleolithic tribe of 100 men and 100 women, and you introduce a handful of very promiscuous women, this upsets the entire marketplace, since it saturates the marketplace with very easy-to-obtain sex, for the men. This decreases the value of sex, so it makes it much more difficult for the women to use sex to get protections and provisions from men. That is why women socially punish promiscuous women. Promiscuity hurts all of the women of the tribe. Further, the willingness of a man to invest protections and provisions into a woman is inversely proportional to his perceived promiscuity of the woman, since increased promiscuity indicates a decreased likelihood that any child she has will be his own.