Religious leaders and holy texts share deep preoccupations with sex and reproduction. From Islamic purdah to Jewish menstrual purity laws to Vatican neuroses about everything from contraception to masturbating nuns, it isn't difficult to see in all major religions a masculine obsession with reproductive control.
But how did religion and reproduction become so entangled? Perhaps it's just a hangover from a simpler time, near the genesis of religious beliefs, when sex and reproduction were more straitened. Or maybe societies do better with strong -- apparently divine -- rules and laws about marriage, fidelity and paternity.
Or perhaps religions arose as a way for the powerful and the anointed to control the reproductive lives of others -- particularly for men to control women's sexual behaviour and reproduction.
We may never get to the bottom of all these questions, but new research suggests religious practices can very effectively assure paternity -- the aspect of reproduction that undoubtedly causes men most anxiety (especially in the post-Viagra era).
For most of human history, as the old saying goes, maternity has been a matter of fact, whereas paternity has been a matter of opinion.
Women have also evolved a most remarkable capacity to conceal from men when they are ovulating. This keeps men guessing, and ensures they stay interested -- and working hard -- throughout the monthly cycle.
But it also means men have evolved a hair-trigger sensitivity to the chance of being cuckolded. Which is why new dads seldom find jokes about cuckoldry or paternity testing all that funny.
That need no longer be the case, of course. Cheap and reliable paternity testing can now erase paternal uncertainty. Paternity tests have become a weapon in sexual conflict. A double-edged sword.
Paternity tests give mothers the tool they need to pin down former partners and make them meet their child support obligations. Instead of a lengthy and humiliating interrogation of a mother's sexual past, DNA tests return the spotlight to the putative dad.
And men can resolve, one way or the other, if the children they are raising or supporting are really theirs. For many men -- including those who have been cuckolded -- no greater injustice can exist than a father raising or paying child support for a child who is not his genetic offspring.
How many children really are sired by somebody other than the guy they call Dad? Among men concerned enough to get paternity test, one men's rights groups claims the number is as high as 25percent. A sensationalist mid-'90s pop-science offering called "Sperm Wars" popularised the idea that up to 10 percent of children are the product of "extra-pair paternity."
In reality, the unbiased number is below 5 percent in most circumstances. But it isn't fixed. The proportion of babies conceived in cuckoldry varies in places and time because cultures differ in how tightly they regulate extra-marital activity, and especially in the power men (and their families) have to monitor and control women's behaviour.
Which is where religions come in.
It needn't be the doctrine of the religion, and the threat of divine punishment, that regulate paternity. The customs that build up around the religion are just as important. This is neatly illustrated by a study published this week in Proceedings of the National Academy of Sciences of the USA on paternity and religious customs among the Dogon people of Mali in West Africa.
Like many other religions, the traditional monotheistic faith of the Dogon includes menstrual taboos. Men fear they will lose their virility if they come into contact with a menstruating woman. And so their wives usually exile themselves to special huts when menstruating.
This conspicuous action allows a man and his relatives to keep regular tabs on where each woman is in her fertility cycle, making it substantially more difficult for a woman to conceive by another man when she subsequently ovulates. It also makes it hard for her to deceive her husband about a child's paternity.
According to the paper by Beverly Strassman and her colleagues, this custom keeps cuckoldry in check. Genetic tests indicate that children of women who used the huts conceived only 1.3 percent of their children by men other than the father. This is one of the lowest estimates on record, and significantly lower than the 2.9 percent among women who did not visit menstrual huts.
Intriguingly, Islam and Christianity have started to spread among the Dogon. Although these world religions include many features designed to assure men of their paternity, five times more children (about 4 percent) of Christian mothers were conceived in cuckoldry than among traditional-religion Dogon mothers who used the menstrual huts.
The recent transition to Christianity appears, in this case, to raise the level of extra-pair paternity, probably due to a release from the traditional ways in which men monitored women's fertility. This is not to say Christianity elsewhere isn't as effective in this role. Dogon Christians retain many other Dogon customs, including polygyny.
But Christian women neither attend menstrual huts, nor are they compelled to report the onset of their menstruation to their husbands. These women, freed from the old paternity-assurance customs, but not yet fully immersed in the traditional Catholic or Protestant customs appear freer to conceive by men other than their husbands.
Menstruating Muslim women also do not attend menstrual huts, but they are required to notify their husbands and they are not allowed to pray. Thus, Muslim husbands can track the fertility cycles of their wives and take closer interest in their behaviour. Interestingly, the level of extra-marital paternity in Muslim families was about twice that in the traditional religion but less than half of what it was in Christian families.
Follow Rob Brooks on Twitter: www.twitter.com/Brooks_Rob