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The Surprising Source of Our Sexual Morals

New research uncovers an evolutionary basis for some sexual mores.

People often ask what kind of human sexual relationship is most evolutionarily "natural." Is human nature adapted for promiscuity or long-term relationships, for example? And if we're wired for long-term relationships, what kind—monogamy or some type of polygamy?

It turns out that people are probably adapted—biologically and psychologically—for all of the above. That is, people appear to be, sexually, "strategically pluralistic": We are adapted for various kinds of long-term and short-term relationships, and the mating strategy we choose depends on factors including our gender (on average and cross-culturally, men are more interested than women in short-term relationships), our attractiveness, and the specific characteristics of our sociocultural and ecological environments [1,2]. This evolved flexibility leads to considerable diversity across individuals and cultures in the mating strategies that people pursue.

However, being intensely social and moralistic creatures, people are often not content simply to choose the mating strategy that suits them best and just get on with it. They often also feel compelled to pass judgement about the sexual behavior of others.

Promiscuity, for example, has historically attracted harsh disapproval. Why? We could attribute it to the influence of organized religion, which has indeed been a historically powerful purveyor of anti-promiscuity morality. But explaining morality in terms of religion (or any other cultural force) seems superficial, as it just moves the question back one step, at which point any truly curious person must ask: Why has promiscuity been the target of so much religious reprobation? Instead of trying to explain culture in terms of more culture, it would be more satisfying to find an ultimate evolutionary explanation for anti-promiscuity morality.

In search of such an explanation, I collaborated with two other psychologists, Nicholas Pound and Isabel Scott, on a paper (free to download) that has just been published in the journal Archives of Sexual Behavior [3]. We hypothesized, based on the evolutionary concepts of paternity certainty and paternal investment, that in social environments in which women were more dependent economically on a male mate, people would be more opposed to promiscuity. When women depend more on men to provide resources for their children (paternal investment), then mothers and fathers both have greater interest in ensuring that fathers can identify their own children and thus deliver on this investment. Because promiscuity undermines paternity certainty, people object to it more in environments where there is higher female economic dependence.

We tested this hypothesis in two studies involving a sample of over 5,000 United States residents. We found that in states where women earn more money and are perceived as being less economically dependent on men, attitudes towards promiscuity are indeed more relaxed. We also found that individuals who reported knowing more economically-dependent women tended to be more opposed to promiscuity. These relationships between female economic dependence and anti-promiscuity morality persisted, even after controlling for other influences on sexual morality such as religiosity and political conservatism. That is, female economic dependence wasn’t correlated with anti-promiscuity morality merely because religious and conservative people tended to score highly on both female economic dependence and anti-promiscuity morality; instead, female economic dependence explained variance in anti-promiscuity morality above and beyond that explained by religiosity and conservatism. Moreover, attitudes towards promiscuity were specifically related to female income, rather than to male income or wealth in general.

These findings have potentially important implications for how people in different social environments judge the sexual behavior of others. In communities where women earn less, people may be more hostile towards behaviors that are perceived (rightly or wrongly) to entail promiscuity, such as open marriage or homosexuality. People in these environments may also be more likely to think that promiscuous individuals deserve any hardships that befall them. For example, if they perceive a pregnancy as having resulted from a woman’s promiscuity, they may see it as a justified "punishment" for her behavior, and even see abortion as an unfair attempt to escape this punishment.

Our results don’t suggest that female economic dependence is the only influence on moral attitudes about promiscuity; religion and conservatism were also highly related to such attitudes in our study. However, our results do imply a hypothesis for why religious and conservative ideologies themselves tend to be anti-promiscuity: because they emerged in environments characterized by high female economic dependence.


A version of this post was originally published at

To read Rob Brooks' great post at the Conversation about our Archives of Sexual Behavior article, click here.


  1. Gangestad, S. W., & Simpson, J. A. (2000). The evolution of human mating: Trade-offs and strategic pluralism. Behavioral and Brain Sciences 23: 573–644.
  2. Schmitt, D. P. (2005). Sociosexuality from Argentina to Zimbabwe: A 48-nation study of sex, culture, and strategies of human mating. Behavioral and Brain Sciences 28: 247–311.
  3. Price M. E., Pound N., Scott I. (2014). Female economic dependence and the morality of promiscuity. Archives of Sexual Behavior. DOI 10.1007/s10508-014-0320-4.

Copyright Michael E. Price 2014. All rights reserved.