Two camps within evolutionary psychology have conflicting hypotheses on what has led to people’s diversity when it comes to how religious they are. One camp believes religion’s essence is in promoting behaviors related to cooperation, while another believes that the attraction of religion has to do with sex and reproduction.

In a new study, senior researcher Jason Weeden and professor Robert Kurzban of the Department of the Psychology in the School of Arts & Sciences have used a massive global survey to show that people’s attitudes toward sexual behaviors is far more predictive of their religiosity than their attitudes toward cooperation.

Data from the World Values Survey and European Values Study comes from nearly 300,000 people from more than 90 countries and contains responses to questions on a wide variety of subjects. One section asked respondents how much they felt certain behaviors could be justified. The researchers categorized some of these behaviors, such as “lying in your own interest,” “stealing property,” and “cheating on taxes if you have a chance,” as having to do with “cooperative” morals. They selected others, including “abortion,” “sex before marriage,” and “homosexuality,” as representing “reproductive” morals. The researchers compared respondents’ answers in these two categories with answers to questions about their religiosity, such as their belief in God and the frequency with which they attended religious services.  

“When you make this comparison, it turns out that reproductive morals are the big, clear winner,” Weeden said. “Once you know the difference between how people think about things like abortion, premarital sex, and divorce, you don’t learn anything else about how religious they are by asking what they think about lying and stealing.”

“It’s clear that people in religious groups cooperate,” Kurzban said, “but it’s never been clear that religious groups are more cooperative than other kinds of groups. In fact, you can learn a whole lot more about who is religious by asking them about their reproductive morals than about their cooperative morals.”

This new study builds upon research Weeden and Kurzban have been conducting over the last several years on the way people make decisions about religion. The overwhelming correlation between religion and attitudes about reproductive issues is further evidence toward their hypothesis that those issues are at the core of religion's utility.

“We think of being involved in a religious group as a social tool—it’s either useful or not,” Weeden says. “What churches do, in developed countries in particular, is provide an environment that helps out people who want committed relationships and more children. If you live a lifestyle where a stable marriage and lots of children is important to you, belonging to a church mitigates some of the risks that go along with that lifestyle. But if you're not planning to get married or have kids for a long time, all you’re getting from a religion is a bunch of hassles. So in the real world, what happens is that those people stop going to church, even if they were raised religious.”