Ever wondered why many religious people seem to be especially passionate about traditions concerning sexual mores and family? Somewhat ironically, this turns out to be a product of the finer workings of biological and cultural evolution.

After all, the gold standard of fitness in evolutionary biology is the number of offspring throughout the generations. And as has been discussed here on TVOL: regularly praying people tend to have far more children than their secular neighbors, even after controlling for other factors such as education, income, and urbanization. Nevertheless, after the empirical rejection of religion-as-harmful-virus-theories, most adaptationist theories of religiosity emphasized religion’s potential in enforcing cooperative morals. Among other things, this approach resonated with classic secularization theories pointing out that as secular institutions increase in strength they tend to replace religious ones, thereby leading to an inevitable decline in religious activities and experiences. As Ara Norenzayan recently put it in his groundbreaking book “Big Gods” (2013): “Secular societies climbed the ladder of religion, and then kicked it away.”

But in the same book, the social psychologist acknowledged “the secularists’ Achilles’ heel”: religious demography. It’s no longer only about the religious having some more kids, it’s about future generations in general. While numerous religious groups such as the Old Order Amish, Hutterites, Mormons or Haredim have been able to retain high fertility rates throughout the centuries, historical research reaching back to Roman, Greek, and Indian classic antiquity has not turned out a single example of a non-praying population featuring at least two children per woman (that is, demographic replacement level) for just a century. It seems that secular institutions might replace cooperative functions more easily than reproductive ones.

Now, Jason Weeden and Robert Kuzban set out to directly test the conflicting theories empirically in “What predicts religiosity? A multinational analysis of reproductive and cooperative behaviors”, Evolution and Human Behavior (2013).

Using data from no less than 296,959 individuals in around 90 countries from the World Values Survey & European Values Study (survey waves 1989 to 2008), they tested the relative strength of cooperative versus reproductive morals in predicting individual differences in religiosity. Their results clearly strengthened the reproductive perspective (p. 6):

“Our results provide virtually no support to the position that the primary current function of religiosity involves the expression of cooperative morals. Clearly, support for stricter cooperative morals is often statistically significantly associated with increased levels of religiosity. Indeed, consistent with the findings of Atkinson and Bourrat (2011), we find a modest correlation (r = .090) between religiosity and cooperative morals. But, as shown in the analyses here, this small relationship often does not survive when controlling for the substantially larger relationship between religiosity and reproductive morals.”

In fact, the relationship between religion and reproduction turned out to be even stronger among the wealthy and partially secularized milieus of our planet (p. 5):

“Around the world, people in poorer regions tend simultaneously to have high average levels of restrictive reproductive morals, high levels of religiosity, and a weak individual-level relationship between religiosity and reproductive morals. Wealthier regions, in contrast, tend simultaneously to contain wide variance in reproductive morals, wide variance in religiosity, and a strong individual-level relationship between religiosity and reproductive morals.”

Nevertheless, Weeden and Kurzban are careful enough to point out that their study explored individual differences – not the ways they were transmitted. And here, of course, social networks and groups could be of paramount importance in shaping and educating moral traditions and in forming and offering family-supporting institutions such as kindergartens, schools, hospitals and the like. Religious groups emphasizing the cooperative but not tapping the demographic potentials of religiosity – such as the communal, all-celibate Shakers – would tend to decline inevitably, whereas highly fertile groups such as the Old Order Amish or the Haredim would transmit their moral teachings to more and more offspring. Future studies and debates might decide whether cooperative and reproductive theories of religion are competing or complementary theories. As evolutionary studies of human beings repeatedly produce multi-layered results (for example, linking biological roots and sociocultural products in the evolution of speech or music), I would place my bet on future complementary models in the evolutionary studies of religion.

Published On: December 19, 2013

Michael Blume

Michael Blume

Michael Blume was born in 1976 in Filderstadt, Germany. He lectured Religious Studies at the universities of Tübingen, Heidelberg, Leipzig and currently in Jena. His doctoral thesis focused on theories on religion in the brain sciences (the so-called “neurotheologies”). Dr. Blume then specialized on the reproductive potentials of religiosity – the complex workings of religious communities augmenting cooperation, birth and survival rates (and thus: evolutionary success) of religious people in comparison to their (more) secular neighbors.


  • Empedocles says:

    It not just fertility, it is subscribing to an external, non-negotiable, moral order that holds one to sexual morality. Compare with the secular ideal of autonomy which demands to accept no outside rules and self-rule instead.  The set of moral principles must be seen as binding in the strongest sense (God’s will).  If they are just seen as rules of Darwinian fertility maximization they will be discarded as restrictions on utility.

  • Tim Tyler says:

    Is there a reference for the “religion-as-harmful-virus-theories”?

    Did anyone claim that religions typically reduced host reproductive output?

  • Dave says:

    Thank you for this —- interesting stuff!!

    Tim, Professor Blume may be able to elaborate on this, but I think the ‘religion as virus’ is mostly a product of the ‘New Atheist’ camp (especially Daniel Dennett), who are often and justly criticized for confusing their descriptions of the spread of religious ideas with their condemnation of them. That is… they see religion as intellectually stunting and oppressive, so the ‘virus’ that spreads it is ‘harmful’.

    I was not aware of Weeden and Kurzban’s research, but will check it out now. I am particularly interested in this rather tricky element of ‘fitness’ here. It seems like a rather narrow view… almost as if the authors see nothing more happening with religious sexual and reproductive codes than staunch heterosexuals making as many babies as they can.  Couldn’t we also presume the health and survivorship of children in strongly religious families (and communities) likely benefit from religions’ emphases on enduring marriage, discipline, close-knit extended families, and so on? Why base fitness on the number of babies that come out per family… we know that it’s not number of offspring that matters, but the number of offspring that survive to reproduce themselves!

    Anyway, thanks smile

  • Michael Blume says:

    @Empedocles, Tim Tyler & Dave

    Thanks for your insightful comments.

    After the Explaining Religion-conference in Bristol 2010, Susan Blackmore wrote a courageous essay about her former “religion as a virus of the mind”-assumptions and the impact of the empirical and especially demographic data. I think this text adressed your topics quite directly and would love to read about your opinions.

  • John V. Patrick says:

    Dogma – the deconstruction of our mental evolution and psyche advocates that self-actualization and its opposing counterpart denied self- actualization are the prime driving forces of our mental evolution. Every thing else is a product of our god given ability to think, learn and pass information between generations.  The connection between these premises is complicated but explained in enough detail in the book and documented by a critical look at our history.

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