The Science of Religion Part IV: Sex

The deep link between religiosity and restricted sexual ethics

One of the big American stories of recent decades is the ongoing, spectacularly dramatic collapse in religious belief. Secularization is nothing new, of course. Already back in the mid-19th century, the English poet Matthew Arnold lamented the “melancholy, long, withdrawing roar” of faith receding from the modern world like an ebbing tide. It was an apt metaphor, because secularization has proceeded in waves ever since. Religion even picked up again for a while after World War II, as the baby boom coincided with renewed churchgoing.

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But when the 1960s hit and young, longhaired people began seriously challenging traditional values in a culture-wide way — especially in the sexual domain, where old norms about marriage and monogamy gave way to newer acceptance of no-strings-attached sex — the tide seemed to recede anew, this time maybe for good. American Christianity pitched into a steeper decline that’s mostly continued ever since.

Why did the counterculture’s sexual revolution seem to knock the legs out from under religious authority? The answer is simple and, for most people, pretty intuitive: there really just is a deep connection between religiosity and sexual conservatism. Traditional religions actually do place a “sex premium” on moral questions. Religious adherents see violations of sexual norms as especially egregious in comparison with other forms of misbehavior. Loosen those restrictive sexual mores, and take the wind out of religion’s sails.

In this fourth essay in my series about the 21st-century scientific study of religion (SSR), we’re turning to this thorny question of religion and sex. In the previous essays, my aim was to cover recent research that falsifies 2000s-era macho atheist predictions that religion would turn out to be just a bundle of harmful cognitive errors. SSR doesn’t have much to say about the truth or falsity of religious beliefs, but as the data rolled in over the past two decades, it became pretty clear that religion is no mere pernicious byproduct of human cognition. In fact, data shows¹ that religion seems to do things for us: it helps us cooperate, improves mental health, helps us regulate our emotions and behavior.

Putting it in biological terms, religiosity helps individuals achieve things like health and cooperation that benefit fitness: the ability to survive, find mates, and have families.² Joining a church can therefore be a very canny move. Smart strategy.

(A quick aside: this is reductionistic language. Talking about fitness and biology might make humans sound like bags of atoms mindlessly trying to reproduce themselves, which is in fact exactly what evolutionary science argues. It might be helpful to keep in mind physicist John Polkinghorne’s concept of the “binocular vision”: science is reductionistic and mechanistic, a perspective we need in order to understand the world — but it’s only looking through one eye, so to speak. Through the other “eye” we view the personal universe, where purpose and meaning aren’t just present, but intrinsic. Reality itself is a weaving together of these two, just as normal human vision integrates perspectives from both eyes. In this essay, we’ll be mostly looking through the scientific eye, so humans are going to come out looking more like entropy-resisting organisms trying to reproduce themselves than like persons made in the image of God. But this is an interpretive strategy for the sake of knowledge, not a comprehensive statement about human reality.)

In fact, as we’ll see below, people’s decisions about religion seem strongly influenced by their strategic choices when it comes to pursuing fitness — but particularly in the realm of mating, or sex and romance.

According to what one group of researchers (not very lyrically) calls the “reproductive religiosity model,” religion has three ways of improving adherents’ fitness vis-à-vis the mating game: it promotes a high-investment sexual strategy, increases paternity certainty, and encourages cooperative (group) childcare, also called alloparenting.

Again, this is not exactly poetic language. So let’s explain what these biological and social-science terms mean to find out what scientists are learning about religion and sex.

Sex and Strategy

they play chess or cribbage,

games that call for patience, foresight, manoeuvre,

like war, like marriage.

— W.H. Auden

In life, every organism, every animal, has to make a choice. It’s a difficult tradeoff, and it goes like this: do you have lots and lots of offspring, spread them on the wind (literally or figuratively), and dust off your hands, hoping that some of them turn out all right? Or do you invest your time and efforts and soul into just a few offspring, nurturing them with oodles of parental care so that they turn out really well and someday give you adoring grandkids?

A great example of the former strategy is our friend the salmon. Salmon hatch, swim out to sea, live their little salmon lives, and then swim back upstream to try desperately to spawn. Most of them fail, eaten by bears or caught in fish nets or devoured by eagles or whatever. It’s a real bloodbath. And the tiny fraction of them that do make it back to their spawning grounds do nothing but basically emit a gazillion eggs into the water, then promptly die.

Nature is a cruel harlot.

But those gazillion eggs will hatch into a gazillion baby salmon, many of which (about 99%) will be slurped up immediately by hungry kingfishers and pike. None of these doomed fries ever meets their parents, and if they’re in the ludicrously minuscule percentage of hatchlings that survive long enough to spawn, they won’t meet their offspring, either.

Investment in offspring: zero.

Near the opposite side of the spectrum we find elephants. These fine animals typically give birth to a single extremely cute calf at a time, with births spaced out by around four years. Mothers pour a ton of attention into those calves, suckling them for two years or more, so they enjoy excellent chances of survival into adulthood. Grandmothers and other females also help care for the young, who remain immature for up to two decades and need lots of parenting and attention (sound familiar?). This kind of shared care for offspring is what scientists mean when they say alloparenting.

Investment in offspring: very, very high.

“Why yes, I will put my life on hold to take care of you for approximately the next decade! You’re damned lucky you’re cute.”

Some biologists describe this tradeoff in terms of a “fast” versus a “slow” life history. “Fast” animals like salmon are thought to mature rapidly, spray out offspring like confetti, and die. “Slow” ones like elephants mature slowly, carefully nurture a few offspring, and live long lives.³

This theory is complex, and not everyone agrees on the usefulness of the fast-slow distinction. But assuming that it is useful, we humans hang out somewhere near the slow end of the spectrum. Our adolescence lasts forever. (There’s fossil evidence of Neanderthal guys playing primitive stone Playstations in their parents’s basements well into their thirties.⁴) We’re born so helpless that, in many cultures, mothers and other caretakers maintain almost continuous contact with their infants for months. We need absolutely stupid amounts of parental investment and care, including alloparenting by grandparents and extended kin.

But we’re also very, very flexible. We can alter our reproductive strategies based on context. In some environments, it might make more sense, offspring-wise, to go for quantity over quality. This would mean putting more effort into finding new sexual partners, but potentially investing less in the offspring that result. Acting more like salmon than like elephants.

Psychologists call this way of doing things “unrestricted sociosexuality.” People with unrestricted sociosexuality have little interest in monogamous commitment to one partner. They’re pursuing short-term sexual pleasure.

People with restricted sociosexuality, on the other hand, pursue a long-term strategy. They prefer commitment to one partner (or, in conservative polygamous cultures, sometimes a handful of women for one man) and take a dim view of casual hanky-panky.

Tradeoffs and Sex

At this point, you might be getting worried. Is this essay veering toward the sort of judgmental and chauvinistic outlook that sees uncontrolled sexuality as somehow a moral problem? Is this a back-to-the-50s post? Am I Dwight Eisenhower?

Well, let me put it this way: the children of short-term strategists often have rough lives. If your dad is out three nights a week philandering, that’s three nights a week he isn’t spending with you, teaching you to fish or reading bedtime stories or going camping or telling you lies about how the earth’s rotation works. If your mom keeps bringing home boyfriends, that’s a hefty amount of energy and time she isn’t spending cuddling you up and singing lullabies as she tucks you tenderly into bed.

That’s why this question of sexual strategy is couched in terms of tradeoffs. No one can be in two places at the same time. Every hour you spend chasing new sexual partners is an hour you can’t spend with the kids you’ve got.

Unsurprisingly, if you grow up with short-term strategists as parents, you’ll be more likely to go on and pursue a short-term mating strategy yourself. Doing so might even make biological sense, because the takeaway message from your own childhood will be that people are unreliable, relationships are unpredictable, and you should jump on any opportunities you get. (Pun intended?)

Long-term strategists, by contrast, invest those extra hours in their kids or in securing resources for the family. They’re directing their time, money, and energy into building a nest of high-quality kids. If it works out, those kids will probably go on to pursue long-term strategies with their own mates.

Religion Supports a Long-Term Strategy

Demographics and individual differences play heavily into whether particular people choose to become or remain religious. Women are (generally) more pious than men,⁵ older people are more religious than younger ones, and college-educated Americans attend church more often than their non–college-educated counterparts.

But in a 2008 paper, psychologist Jason Weeden and colleagues found that the single biggest predictor of religious service attendance was conservative sexual behaviors and attitudes, like valuing monogamy and commitment instead of free love.

That’s right: in a sample of more than 21,000 respondents to the US General Social Survey, preferring a long-term, high-investment-in-children mating strategy predicted whether someone went to church better than whether they were male or female, young or old, or any other demographic variable.

The authors argued that “one of the primary functions of religious groups in the United States is to help tip the balance…in favor of monogamous, high-fertility strategies.” And in another study, Weeden found a similar effect in a huge sample of nearly 300,000 respondents from 90 countries.

How exactly do traditional religions encourage monogamy and long-term investment in offspring? To begin with, they strongly discourage and moralize against promiscuity, and they often ostracize or punish those who break this rule. Negative social consequences for hooking up with strangers or sleeping around creates a selection effect: people who want a lot of casual sex tend to avoid religion, while those who want a long-term strategy gravitate toward it.

This selection effect is so strong that it outweighs so-called socialization effects. You might think that a conservative religious upbringing encourages a long-term mating strategy in adulthood, but in fact evidence shows that it’s the reverse: people who want a long-term mating strategy are the ones who become or stay religious.

Community support for long-term strategies is vital because, well, it takes two to tango. You need to find someone who wants to pursue a similarly monogamous strategy or you risk getting soaked. A long-termist guy with a short-termist wife might very well end up raising some other guy’s kids. A long-termist lady married to a short-termist cad will raise the kids alone while her guy is out chasing skirt. Short-term strategies are a kind of cooperative defection.

And as we already established in part 1, conservative religious groups are really good at weeding out uncooperative defectors. In the sexual domain, this means strongly sanctioning against promiscuity, increasing the social cost of sex by linking it to marriage, and ostracizing rule-breakers so that religious communities become places where the stable strategy at equilibrium becomes monogamy, or at least high investment in marriage and children.

Paternity Certainty

Marriage and anti-promiscuity norms serve another important purpose, which I just hinted at above: helping guys rest assured that they’re raising their own kids. I specify “guys” because women are very rarely uncertain whether they, personally, gave birth to a particular baby. (Ask your mom.) Fathers, on the other hand, can always doubt whether a kid they’re helping to raise is biologically theirs. Especially if the kid looks like the pool boy.

This discrepancy means that men and women face a bit of a conundrum.

Being pretty sure who their kids are, women tend to invest in them all about equally.

Having less inherent assurance about whose kids are whose, guys invest more in children they’re pretty confident are carrying their genes.⁶ So in a family where the husband entertains generalized doubts about his wife’s faithfulness, he will (all things being equal) invest less overall in the kids. This is a bad situation for the kids and for the family.

Now let’s scale this up. If an entire society is filled with guys who doubt that they’re raising their own kids, fathers will probably invest less in children generally. They’ll pivot their efforts more and more toward finding additional mates. Women will come to expect less investment from the men who father their children. They too will step up their mating efforts, which means less investing in kids.

Pretty soon, the entire society becomes geared for short-term mating strategies. It’s a vicious cycle.

This is why paternity certainty not only benefits men and their particular kids, but also helps stabilize high investment in children and families at the level of tribes, societies, or communities.

If a religious tradition or institution can help people, by which I mean fathers, enjoy greater confidence that the kids they’re raising are actually theirs, you can expect men to start investing more in kids and less in chasing new sexual opportunities. The local equilibrium — the dominant norm — will move toward high-investment strategies for everyone, men and women alike.

And this is what we see in many religions. Those strong norms against promiscuity and casual sex make cuckoldry less frequent. Rules about modest dress can have an effect too, since revealing clothing can nudge men toward objectifying women and shorter-term thinking about sex.⁷

Many traditions also use other tools to make it easy for men to “guard” their mates. The local religion of the Dogon people of Africa, for example, traditionally required women to sequester themselves away in menstrual huts during their periods. Modern Dogon don’t always use menstrual huts, but one research team did genetic analyses and found that those who did use the huts were less likely to have children outside wedlock.

Indeed, many religious practices that seem oppressive to modern sensibilities may be lopsided methods of controlling female sexuality, just as feminists have always complained. In many societies, women are expected to be faithful to their husbands, but men can philander without consequence. In ancient Rome, for instance, it was part of religious piety for upper-class women to avoid affairs, but men could sleep with prostitutes and slaves with complete impunity.

These double standards might reflect the fact that, as we’ve been discussing, cuckoldry is a bigger risk for men than for women, biologically speaking. However, early Christianity distinguished itself in the ancient world by demanding that both men and women be faithful to their spouses. This teaching understandably was appealing to women who were sick of their husbands sleeping with everything that moved. Today, after centuries of Christian influence, we mostly understand that marriage means “forsaking all others” and being faithful to the person we married.⁸ And genetic records from Christian societies seem to show that the paternity certainty problem actually was solved.

I mentioned above that it can be creepy and weird talking about faith and human beings in this sort of reductionistic, biological way. But we are biological beings, and for biological beings choosing your investments wisely matters. For all the ways they can go wrong, religious means for encouraging paternity certainty often bring men’s and women’s incentives and motives into somewhat better alignment than they would be otherwise — especially when they’re applied fairly. (Which, admittedly, is rare.)

Alloparenting

But as any Democratic suburban lawn-sign lady will earnestly tell you, it takes a village to raise a child. Two parents really don’t have the resources and energy it takes to raise a gaggle of children all by themselves, so you need lots of alloparenting (help from others with parenting). This need for alloparenting probably helps explain the biological advent of menopause: by ceasing their own childbearing years, older women set themselves up to become grandmothers, who — just like elephants! — are a vital contributor to children’s well-being.

But even grandparents aren’t really enough. What if the grandparents are dead? What if they live in a retirement compound in Florida and spend all their time drinking margaritas and watching Fox News or MSNBC? You really do need a village. This is the final area where religious life has a serious leg up on secular existence. By encouraging shared childcare and parenting help, religious communities seem to not only make things easier on moms and dads, but they actually make it possible to have more children while still investing a lot in each one of them.

The tight cooperative networks that religions generate spread the load for childcare, with single congregants and fellow community members often helping look after kids, caring for them when parents are sick, or swapping babysitting aid. Following biological reasoning, this should drive down the overall burden of having kids, allowing parents to raise more kids with comparatively reasonable amounts of stress and challenge — but no drop-off in investment.

Testing this hypothesis, the anthropologist John Shaver (a friend of mine) found that New Zealanders who were religious and regularly practiced religious rituals not only had more children than those who didn’t, but they also cared more for other people’s kids. In another study in the UK, Shaver’s team found that this access to alloparenting helped explain why mothers in religious communities were able to have more kids than their secular counterparts.

This finding may help account for why, unlike in many other species, in humans offspring quantity and investment are positively correlated. Parents with more children tend also to pursue a sexually restrictive, high-commitment mating and parenting strategy, and the same behaviors that increase offspring quantity in other species — lots of mating effort, low-investment sex, and reduced offspring care — usually just lead to biological fizzling out in humans. With some notable exceptions, cads are reproductive duds.

But in modern, secular societies, the biological default sometimes seems to kick back in: offspring quality and quantity can become inversely correlated again, just like for salmon and elephants. Inhabitants of these “high-income, low-fertility” societies who pursue short-term mating strategies tend to churn out more kids but are able to invest less in them, while those who pursue long-term mating strategies tend to have just a couple (if any), but pour resources into them in the form of soccer camps, SAT coaches, and immense pressure to succeed.

It’s only religious communities within secular societies that seem to be able to resist this tradeoff. Alloparenting makes it possible for religious moms to garner help not only from committed mates, but also from a wide-flung network of kin, grandparents, and co-believers, which increases their overall fitness while contributing in kind to fitness for other members of their communities.

Conclusion

The reproductive religiosity model might seem controversial, possibly reactionary. But if so, that’s because you live in one of those high-income, low-fertility countries where everybody is supposed to be vaguely embarrassed by the intrinsic and obvious relationship between sex and children. This relationship necessarily points to certain differences between men and women that are politically inconvenient and intrinsically illiberal.

But traditional religions do not care one whit about this. They just keep organizing their social norms and practices to make it easier for people to find and commit to mates, and to receive social support for that commitment and for the kids that come out of it. Demographically, overall, the future therefore probably belongs to the religious.

Say what you want about the truth or falsity of religious beliefs. The picture this research paints is just not one in which religion is any kind of a maladaptive cognitive error. In fact, it looks adaptive in the strict biological sense, because it literally increases fitness for those who practice it.

It’s not just Christianity, either. Hinduism, Buddhism, Judaism, Islam, you name it —  they all seem to somehow intuit that norms that encourage successful long-term mating are a good thing. There is no major world religion that looks kindly on casual hookups or no-strings-attached sex. Anywhere. Even Islam, which allows men to have up to four wives, is famously conservative on promiscuity.

It’s no coincidence. Seen from a biological and social-psychological perspective, religions are essentially massive, unwieldy, but highly effective social technologies for pushing people away from “fast,” short-term mating strategies and toward “slow,” long-term ones. You could even make a good case that this is their single most important biological function.

Clinical language, I know. Yet I’m not saying that this function accounts for all that religion is, because I don’t think the biological (or psychological) perspective captures all that human life is. The numinous personal dimension that invariably slips out of the grasp of any reductionist theory, any scientific model, is also real. The intersection of the two is where reality, with all its colors and sound and fury, really exists. No faith or religious tradition, then, is just a means of getting people to fall in line on sex, or cooperate better, or self-regulate. It’s always also a way of orienting toward reality or, for Christians, a relationship with the living God.

But science operates within the frame of so-called “methodological reductionism”: the assumption that the universe is a closed system that operates according to fixed causal laws. Within this reductionist frame, no other scientific explanation for religion seems to account for quite so much⁹ of the data as the proposition that religion is really an über-complicated mechanism for getting people and communities to move away from short-term sex and toward long-term commitment and caring for children.

1. Yes, “data” is supposed to be plural, but please follow me carefully: I do not care. In my current day job in biomedical publishing, I’m constantly having to correct this in drug submissions and manuscripts. But outside that context, it’s pretty obvious that “data” has become a singular word in spoken English, and I think writers everywhere should just adapt. The almost total abandonment of the singular word “datum” supports my view; if “data” were really plural, then when there was only a single piece of data under discussion, we would say “datum.” But we don’t say this. We say “piece of data,” like we say glass of water or unit of weight. The obvious conclusion is that “data” is an uncountable singular noun.

2. Technically, fitness is the total proportional contribution an individual (or trait, or gene, depending on your level of analysis) makes to the population of the next generation. But maybe that’s a bit too reductionistic even for us.

3. This is a pretty egregious oversimplification. Life history is really more a bunch of different dimensions of possible strategies, from speed of maturation to number of and investment in offspring to longevity. Many species mix these up in different ways; for example, sea turtles mature slowly but lay bajillions of eggs, which they promptly abandon to their fates. No parenting investment at all, but very long lives. However, in general, the “fast” versus “slow” life history model works decently for this essay, so we’ll leave it at that.

4. This is of course a joke. Neanderthals weren’t that sophisticated. It was primitive Atari.

5. Although this may be changing in the youngest Gen-Z cohorts.

6. It’s unpleasant to dwell on, but this makes perfect sense biologically. Time and resources are, as we’ve established, limited. Males who put time and energy into some other guy’s offspring are hurting the chances that their own genes will make it into the next generation. What did I say about Nature being a harlot?

7. Although as the Taliban love to remind us, it’s very easy to push this too far.

8. Unless we write for the New Yorker, in which case we understand marriage to be polyamorous.

9. See?? Uncountable noun!