OK, OK, I know: Both Mother’s Day and Father’s Day are cultural inventions, full stop. But I’m nonetheless gonna lay a bit of biology on this, for the same reason famously given for why climb Everest … because it’s there.
The reality is that there is no human society, anywhere, in which men do more fathering than women do mothering. This doesn’t deny the existence of many “mothering men” and of maternally indifferent women, but exceptions don’t disqualify generalizations, which are, after all, statements that are generally true. In addition to the above cross-cultural universal, there’s a parallel cross-species universal: There is no species of mammal, anywhere, in which males do more fathering than females do mothering. (There are close calls, to be sure, such as pygmy marmosets, California mice and one of my favorites, the Malagasay giant jumping rat, but once again, the generalization nonetheless stands.) Biologists have asked why, and the answer is pretty clear-cut, leading to yet another generalization.
Here it is: Confidence of genetic relatedness. Not conscious confidence, to be sure, but rather, a situation that is consistently valid and which has therefore selected for a comparably consistent suite of adaptive biological responses. If a baby comes out of your very own body, it’s a pretty good bet that it shares your very own genes; more precisely, there’s a 50-percent probability that any genetically influenced propensity for parental care-taking present in you will also be present in your offspring, who is guaranteed to be, in fact, yours.
Not so for males.
In short, “Mommy’s babies, Daddy’s maybes,” which summarizes one of those undeniable male-female biological asymmetries. No natural way around it (except these days with DNA fingerprinting … which is, as they say in my rural part of Washington State, “a whole ‘nother thing”). John Maynard Smith, a towering figure of late 20th century evolutionary biology, pointed out that this also explains what might otherwise be an unacknowledged puzzle, one of those questions that typically don’t even arise, because they require looking askance at something that seems so, well, natural: Why don’t male mammals lactate? After all, given that the female has gone through all the hassles of pregnancy, nourishing the unborn offspring, followed by the risks and rigors of childbirth, wouldn’t it be only fair if the male pitched in at this point?
But natural selection doesn’t care about fairness, only about success in projecting one’s genes into the future (as good a definition as any of “fitness”). I’d bet that if those male “maybes” were instead “definites,” there would be at least as many Pater Lactans as Madonna Lactans.
Interestingly, among fish in which fertilization is external (unlike the internally fertilizing mammals), and in which males and females are therefore equally entitled to confidence of genetic relatedness with their offspring, males and females are about equally likely to assume parental duties.
If at this point, you’re wondering about adoption, my hat is off to you. But if you’re also hoping for some sort of anti-biological triumphalism based on this human capacity (maybe even penchant), I’m sorry—actually, not sorry at all!—to say that in fact, there’s a cogent evolutionary explanation for this, too. And I’ll write about it very soon; I promise.
(Image from wikimedia.commons)
