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The idea of women having sex outside of marriage drives some people crazy, to the point that in certain parts of the world women are regularly murdered as a result of accusations of promiscuity. What accounts for this profound discomfort, and the (usually) more restrained version we see in the United States? It’s obviously complicated, but a new paper suggests it can be traced back in part to the outdated idea that since women have to rely on men, they can’t afford to be sleeping around.

In the paper, which consisted of two studies and was published in Archives of Sexual Behavior, researchers from Brunel University asked a large group of Americans to rate their level of agreement with statements like “It is wrong for women to engage in promiscuous sex” and “It is fine for a woman to have sex with a man she has just met, if they both want to.” They also had them respond to statements gauging to what extent they viewed women as economically reliant on men — “Of the women I know who are in long-term heterosexual relationships, most do not depend very heavily on money contributed by their male partner,” and so on.

Overall, the more likely a given respondent believed women were economically dependent on men, the more likely they were to view female promiscuity as immoral. These were modest to medium effects, but they were statistically significant, even controlling for factors like religiosity and political conservatism.

What accounts for this connection? The researchers explain:

Results of both studies were consistent with the theory that opposition to promiscuity arises in circumstances where paternity certainty is particularly important and suggest that such opposition will more likely emerge in environments in which women are more dependent economically on a male mate. Attempts to replicate these results in other cultures will be necessary in order to determine the robustness of this model under diverse social conditions. Further research will also be necessary to illuminate the psychological mechanisms that underlie the observed association between female economic dependence and opposition to promiscuity (e.g., the cues which shape individual perceptions of the local environment). One plausible mechanism is that people living in environments characterized by higher female dependence are more likely to learn about negative consequences associated with promiscuity (e.g., difﬁculties faced by parents and offspring in situations of high paternity uncertainty), a process which could generate a cultural opposition to promiscuity that is founded on biological concerns.

In other words, the more dependent on men women are, the higher the reproductive stakes: If you get pregnant and can’t make a strong case that a given man was the father, you (and your child) could be in serious trouble.

This is a pretty old-school way of looking at things, of course, but that’s the point: Not all aspects of human culture are caught up to modern life. As the researchers write, these “beliefs may persist due to cultural evolutionary adaptive lag … that is, because the environment has changed faster than the moral system.” Today, thanks to modern contraception, when we want to separate sex and reproduction, we can do so with a very high success rate. Many of our older and more conservative ideas of morality may have developed before this was the case.