What’s that famous quote, by Edna St. Vincent Millay? Oh, yes: "I love humanity but I hate people." It’s a sentiment that captures my normal misanthropically tinged type of humanitarianism well, but it roars apropos on some particular occasions. For example, making conversation at the pizza shop in my small village in Northern Ireland one recent evening, the topic turned to what I do for a living. Now, this simple query is usually a hard question for me to answer; when I say I’m a professor, inevitably I’m asked what I teach. When I say psychology, they giggle uncomfortably about their problems or say—as if it’s the most original line—that I’m in the right town for that. When I correct them and say I’m not a clinical psychologist, but a researcher, I have to explain what exactly I research. "Evolutionary psychology" tends to conjure up some bizarre ideas in the non-academic. And so it did on this occasion, as I struggled to articulate the nature of my profession in a cramped pizza parlor with about a half dozen locals eavesdropping on as I did so. Somehow or another, as conversations with me so often do, homosexuality came up as an example of a complex human behavior which evolutionary psychologists try to understand.

I wish I’d had a notebook in hand to scribble down the young employee’s comments word-for-word, so as to provide you with a proper ethnographic account. But here, in a nutshell, is what he very confidently said to me, flavored with the peculiar vernacular flourish found in this part of the world: "Aye. Don’t get me wrong, I’ve got nothin’ against gay people. But what I don’t get is why they’d choose to be selfish and not &lslsquo;ave a family and kids-like which is what we’re here for, how’s you’s go against evolution by not continuin’ the line cause you’s can’t help the species without having kids. Just seems selfish-like to me." I replied that, as a gay man myself, it’s not quite as simple as ‘choosing’ not to breed; since women are as arousing to me as that half-eaten pepperoni pizza sitting on that table over there, I said, I couldn’t get an erection to inseminate a woman for the life of me. I do, however, I continued, get a mighty erection by seeing other men’s erections, so therein—I pointed my finger to the heavens for emphasis—lies the true Darwinian mystery! I then took my pizza and left. In haste. And now I’m writing this from Ohio.

But in any event, the exchange reminded me of my German colleague Michael Blume’s research on reproduction and religiosity. And it occurred to me that religiously motivated homophobia may be at least partially rooted in this assumption that gay people are shirking their human reproductive obligations. I detected a strong whiff of religious residue in the employee’s comments about homosexuality, which given the churchliness of Northern Ireland probably wasn’t my imagination.

In evolutionary biological terms, where natural selection occurs at the level of the gene, not at the species level, there are serious flaws in his conjecture about lineal reproduction. Modern technological methods helping gays to be parents aside, there are many ways that childless individuals can still be genetically successful, in some cases more so than simply being a biological parent, such as investing heavily in biological kin who share their genes. (In scientific parlance, this is known as kin selection or inclusive genetic fitness.) Having said that, he was not entirely wrong about the prime evolutionary significance of reproduction either. People really do need to reproduce, either directly or indirectly, for nature to continue operating on their genes. This is not the "reason" or "purpose" we’re here, as that would insinuate some form of intelligent design for human existence, rather it’s just a mechanical fact.

But where all of this gets really interesting, says Blume, an evolutionary theorist and religion researcher at the University of Heidelberg, is where the illusion of intelligent design intersects with a reproductive imperative—essentially the commonplace idea that God "wants" or "intends" or "demands" us, as faithful members of our communities, to have a litter of similarly believing children. You’ve been blessed with your pleasure-giving loins for a reason, so the unspoken logic goes, and that’s to get married to the opposite sex and to breed. By God, just look at the Old Testament. "Be fruitful and multiply" is the very first of 661 direct commandments. God doesn’t seem to be merely making a suggestion here but instead issuing a no-nonsense order.

Blume has found that those religions that actually put this issue front and center in their teachings are—for rather obvious reasons—at a selective group advantage over those that fail to endorse this stern commandment. He reviews several religions that are either already extinct or presently disappearing because they strayed too far from this reproductive principle. The Shakers, for example, hindered and even forbade reproduction among their own followers, instead placing their emphasis on missionary work, proselytizing and the conversion of outsiders. But this turned out to be a foolish strategy, evolutionarily speaking. "In the long run," Blume points out, "mass conversions happen to be the historic exception, not the rule. Most of the time, only fractions of populations tend to convert from the religious mythology handed to them vertically by their parents and they convert into different directions. [C]ommunities who start to lack young members also tend to lose their missionary appeal to other young people. Therefore, the Shakers overaged and deteriorated."

Some religious splinter groups have also tinkered a bit too much with God’s reproductive imperative, even exploring eugenics by attempting to "perfect" communal offspring. Such a calculated, deliberate scheme of human breeding may backfire, however, if it also means preventing couples from reproducing at their own personal discretion. This was part of the downfall of the Oneida Community of upstate New York, a 19th-century Christian commune that had a very practical—almost too practical—view of human sexuality. Reproduction was tightly regulated by a eugenics system known as stirpiculture. Over several generations, Oneida community physicians mated men and women that were carefully selected for their genetic health (I saw some of the handwritten medical records while going through the archives at the Kinsey Institute this past summer, and I can assure you that the breeding system was real and meticulous). Children born through this process of artificial selection were raised communally and maternal bonding was discouraged.

To prevent unplanned, non-engineered children, the Oneida members implemented a variety of controls, including encouraging teenage boys to have sex with postmenopausal women. This simultaneously stemmed both parties’ libidos and also, in forging personal alliances between the two, provided important ecumenical tutelage to the youth by the very devout older women. Adult men practiced male continence, a sexual "technique" in which males do not ejaculate during intercourse; given that Oneida also had polyamorous relationships, this was key for stirpiculture purposes. All of this may sound logical in theory, even unusually rational as far as religions go, but the tight regulations meant a quick death for the Oneida Community. After only about 30 years and peaking at just a couple of hundred members, the religious commune officially dissolved in 1881. Its members, presumably of good genetic stock but scanty in ranks, went into the silverware trade instead; today the Oneida Community is known as the hugely successful company Oneida Limited.

By contrast, similarly insulated, non-proselytizing religions that encourage their members to proliferate alleles the old-fashioned way—such as Orthodox Jews, Mormons, the Hutterites and Amish—and also emphasize "home-grown" faith in which members are born into the group and indoctrinated, are thriving. The story of the Amish is particularly impressive, having seen an exponential explosion in their numbers over a very short span of time. Emerging as a branch of the Anabaptist movement in the aftermath of the Protestant Reformation in Europe, about 4000 Amish fled Germany to avoid persecution and found refuge in the US and Canada during the 18th- and early 19th-centuries. Most people know that the Amish are extremely insular, shunning almost all contact with the non-Amish world—except during the brief "Rumschipringa" (transl. "jumping around") period, in which not-yet-baptized Amish youth flirt with the devilish goods outside before deciding whether or not to return to their family and faith. For boys, one incentive for retuning to the community is that if you want to have sex with (i.e., marry) a local Amish girl, you have to first be baptized, which is only for those who come home. Eighty percent do.

What you may not know is that the Amish population has been swelling since its New World inception. With growth rates hovering between 4 to 6 percent per year, their numbers double every 20 years or so. In 2008 they numbered 231,000; the year before, it was 218,000. Having children is a heavenly blessing but it’s also an official duty. With an average of 6 to 8 children born to each Amish woman, and with 80 percent of those returning to the group after Rumschipringa, this extraordinary growth rate—which continues to soar—is easy to understand. What’s especially ironic, points out Blume, is that like many increasingly secularized countries, the original Amish countenance of Germany has been succumbing to sharp population declines for decades. "The closing of churches has been followed by that of playgrounds, kindergartens, schools and whole settlements." At least in sheer numbers, then, it seems that the Amish—long-ridiculed by their European countrymen as the "dumb Germans" who wouldn’t give up their silly archaic beliefs—are getting the last laugh.

In fact, Blume’s research also shows quite vividly that secular, nonreligious people are being dramatically out-reproduced by religious people of any faith. Across a broad swath of demographic data relating to religiosity, the godly are gaining traction in offspring produced. For example, there’s a global-level positive correlation between frequency of parental worship attendance and number of offspring. Those who "never" attend religious services bear, on a worldwide average, 1.67 children per lifetime; "once per month," and the average goes up to 2.01 children; "more than once a week," 2.5 children. Those numbers add up—and quickly. Some of the strongest data from Blume’s analyses, however, come from a Swiss Statistic Office poll conducted in the year 2000. These data are especially valuable because nearly the entire Swiss population answered this questionnaire—6,972,244 individuals, amounting to 95.67% of the population—which included a question about religious denomination. "The results are highly significant," writes Blume:

… women among all denominational categories give birth to far more children than the non-affiliated. And this remains true even among those (Jewish and Christian) communities who combine nearly double as much births with higher percentages of academics and higher income classes as their non-affiliated Swiss contemporaries.

In other words, it’s not just that "educated" or "upper class" people have fewer children and tend also to be less religious, but even when you control for such things statistically, religiosity independently predicts number of offspring born to mothers. Even flailing religious denominations placing their emphasis on converting outsiders, such as Yehova’s witnesses, are out-reproducing nonreligious mothers. Hindus (2.79 births per woman), Muslims (2.44), and Jews (2.06), meanwhile, are prolific producers of human beings. Nonreligious Swiss mothers bear a measly 1.11 children.

Blume recognizes, of course, that these are correlational data. It’s not entirely clear whether being religious literally causes people to have more children, or whether—somewhat less plausibly but also possible—the link is being driven in the opposite direction (with people who have more children becoming more religious). Most likely it’s both. Nevertheless, Blume speculates on some intriguing evolutionary factors that could have resulted—and are still occurring through selection today—from the fact that religious people have more children. Since religiosity is to some degree a heritable trait, offspring born to religious parents are not only dyed in the wool of their faith through their culture, but Blume believes that they may also be genetically more susceptible to indoctrination than children born to nonreligious parents.

The whole situation doesn’t bode well for the "New Atheism" movement, in any event. Evolutionary biology works by a law of numbers, not moralistic sentiments. Blume, who doesn’t try to hide his own religious beliefs, sees the cruel irony in this as well:

Some naturalists are trying to get rid of our evolved abilities of religiosity by quoting biology. But from an evolutionary as well as philosophic perspective, it may seem rather odd to try to defeat nature with naturalistic arguments.

As a childless gay atheistic soul born to a limply interfaith couple, I suspect, perhaps for the better, that my own genes have a very mortal future ahead. As for the rest of you godless hetero-couples reading this, toss your contraceptives and get busy in the bedroom. Either that or, perish the thought, God isn’t going anywhere anytime soon.