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  • Young adults often stray from religion, especially when they hope to be sexually adventurous, while parenting motivations tend to lead to greater religiosity.    Tweet This
  • Religions seem to persist partly because of their very real implications for reproduction.  Tweet This
  • Religious people generally have more children than their nonreligious counterparts, perhaps in part because of cultural norms that encourage children. Tweet This
Category: Religion

People often have very strong intuitions about what religions do, but are these intuitions correct? Not always: one study found that people most frequently selected “fear of death” as the main attraction to religion, even though the link between death anxiety and religion is actually quite small and inconsistent.  

Similarly, people often assume religion is a prime mover in the sexual realm—religions breed puritanical views of sex, judgmental toward those who are less prudish, etc. And there is certainly something to this idea—being raised in a culture that tells you that sexual sins are among the most serious is bound to make one a little less sexually adventurous. For example, there is some evidence that the more Muslims live in a country, the less likely people (both Muslim and non-Muslim) are to report engaging in premarital sex. 

But religion is not some ephemeral force causing us to act in unpredictable ways; indeed, religions can’t survive if they don’t appeal to individuals. Based on a recent review of the research, I’ll suggest that religions are concerned about sexual behavior largely because that is what adherents want. 

People are often able to choose whether or not to engage in religion, and there is usually a bit of logic behind these decisions. People are more drawn toward religion when it can fulfill some important function in their lives. That is, if religions are supremely concerned with people’s sexual behavior, it might be because (at least some) people are concerned with others’ sexual behavior. And it’s not just some elite class controlling everyone else—if people preferred sexually liberal religions, there would be more sexually liberal religions.  

Thus, rather than religion arbitrarily instilling conservative sexual values in adherents, people might be attracted to religion precisely because it upholds such lifestyles and creates costs for opposing these lifestyles. If this is the case, we might expect people to become more or less religious during their lives, depending on their reproductive interests or their family goals. Indeed, young adults often stray from religion, especially when they hope to be sexually adventurous, while parenting motivations tend to lead to greater religiosity.   

What Does Religion Do For People?

People’s lifestyle choices might partly drive them to religion, but does religion actually do anything for them? Let’s take an evolutionary view and consider how religion might help people pass on their genes more effectively. Here, I’ll list several ways this might happen. 

Number of Children

The first—and most straightforward—is that religions simply encourage people to have more children. Naturally, the Shakers—who famously practice celibacy—have very few members, while Islam is projected to become the world’s largest religion by the year 2075. 

Fertility rates, of course, vary by religion, but religious people generally have more children than their nonreligious counterparts, perhaps in part because of cultural norms that encourage people to have children. What’s more, people who marry within their religious tradition (religion “homogamy”) tend to have more children than those who marry outside of their religion.

Paternal Certainty

But religion might help people reproduce in some different ways, too. For example, men often face paternity uncertainty—the possibility that they are not the biological father of their child(ren). This can create an adaptive problem for men, resulting in the loss of valuable resources. Because of this, men are willing to invest more resources into their children when paternity uncertainty is low—for example, if the children resemble their father. That is, pouring one’s resources into a child is less of a risk (in evolutionary terms) if a father can be confident that it is his biological child.  

Religion might help bolster paternal certainty in a few ways. Just by virtue of religious people being less likely to report being unfaithful, or the fact that religious cultures make infidelity more costly, we might expect religious men to have fewer suspicions about their mates. Some experimental evidence suggests that reminding people of religious concepts makes them especially likely to condemn behaviors they view as sexually immoral. A society with frequent religious reminders, then, might make people more vigilant in policing others’ sexual behavior. 

But in some cases, there are rituals that seem specifically designed to limit women’s ability to find additional sexual partners. For example, the indigenous religion of the Dogon (West Mali) includes menstrual taboos, in which women are restricted to uncomfortable menstrual huts. This ritual allows men and their families to keep a close eye on them during and after their time in these huts. One study found that Dogon men who practice the indigenous religion have a significantly lower probability of facing cuckoldry, perhaps because of these rituals. Some have suggested that practices such as veiling in Islam similarly serve to restrict sexual behavior, and it isn’t hard to think of analogous modesty norms in other religions. 

To the extent these practices actually do increase paternal certainty, they are beneficial both to men—who can more safely invest resources into their children—and women—who are more likely to have help raising their children. Yet you may have noticed that many of these practices seem to restrict women’s behavior at the benefit of men. There is some evidence that these kinds of practices benefit men more than women—for example, people who have sons (vs. daughters) are more likely to support veiling. Assuming people are sensitive to the interests of their children, this would suggest that veiling is, on the whole, more advantageous for men than women. Considering how religion might benefit men and women differently may have implications for patterns of cultural differences in religious attendance.  

Pooling Parenting Resources

One fundamental tradeoff in biology is “quality vs. quantity” (quality here is not a judgment that the offspring are better, only that they are more likely to survive). That is, the more offspring an organism has, the higher the mortality rate of the offspring tends to be. However, this tradeoff appears to be less steep among religious communities: religious people have more children, but these children are not dying at higher rates. 

Some recent research suggests that this is because religious people are more likely to engage in alloparenting—that is, they tend to pool their resources together, ultimately making more efficient use of their resources. These practices allow religious individuals to have the best of both worlds—higher fertility, but also high “quality” offspring. 

So Why Do So Many Religions Place Emphasis on Sexual Behavior? 

We can think of religion as a tool that people use that, in part, helps them advance their family-related goals. But how did religions come to look this way? 

Cultures change through the process of cultural evolution—pieces of culture are more likely to spread when they appeal to people’s biases (e.g., following what is popular or what the more prestigious members of a society do), or when they provide an advantage over other cultures. For example, one prominent theory of the cultural evolution of religion suggests that societies that believed in punishing, morally-concerned deities had an advantage over societies with deities that were less interested in enforcing people’s behavior. 

Similarly, we can think about how religions might, over time, develop a strong concern with sexual behavior. As we have seen, religion seems to provide some reproductive benefits. Even some of the more puzzling aspects of religion, like celibacy, fit nicely within this perspective. Put simply, religions seem to persist partly because of their very real implications for reproduction. 

None of this is to say religion is either good or bad—it certainly has both desirable and undesirable effects, and the ways it promotes reproduction are not always good for the well-being of adherents: consider the Dogon women who spend time in menstrual huts, or those who face extreme shame because of their failures to live up to religious norms, and many others whose human rights have been violated because they are incongruent with religious norms. 

This perspective simply seeks to explain why—even though religion often asks so much of its adherents—religions continue to be so popular and to take the forms they take. Simply put, the answer seems to be that one reason people often engage with religion is because it fulfills some of their mundane goals in life. In contrast, when people can fulfill these goals in other ways, or when religion becomes less useful as a tool to achieve these goals, we should expect people to become less religious. 

Jordan W. Moon is a social scientist who studies religion. He received his PhD from Arizona State University.

Editor's Note: The opinions expressed in this article are those of the author and do not necessarily reflect the official policy or views of the Institute for Family Studies.