Several attributes of human women are routinely posited as evolutionary enigmas because they tend to be placed in the “not really necessary” and/or “inconvenient” bins: hidden ovulation (How’s a guy to know a kid is his?? Ergo, chastity belts and purdahs!); orgasms (Who cares, as long as the kids come out?); and living past menopause (Done with heir production and no longer eye candy — discard!).
However, it turns out these attributes are not that enigmatic unless you believe that teleology drives evolution. It looks increasingly like the bright red buttocks of our primate relatives are actually a recent acquisition, and hidden ovulation is the earlier default. Some cultures have solved the kinship problem: brothers act as fathers to their sisters’ children, to whom they are unequivocally related. Orgasms are equally explicable once you accept the simple fact that the clitoris is the equivalent of the penis, including the associated excitability and sensitivity (which is why female genital mutilation is identical to a penectomy, not to foreskin circumcision). As for living longer than the contents of one’s ovaries, which is a third of women’s lifespan once they’re past the risky childbirth years, it may have to do with what made us human in the first place. So says the grandmother hypothesis, first intimated by George C. Williams of antagonistic pleiotropy fame and later elaborated by Kristen Hawkes and her colleagues in the late nineties, after observations of the Hadza people in Tanzania.
Back in the fifties and in today’s evo-psycho groves, the fashion has been to posit the nuclear family as the kernel unit of primordial humanity. If you take the crucial details of humans into account (unique birth risks, extended neoteny, unusual nutritional requirements, necessity for higher-order skill acquisition), you realize that the possibility of such a unit seeing offspring reach adulthood is close to nil. Not surprisingly, when anthropologists look carefully and past their own cultural blinders at less technologically endowed human groups, the scaffolding they see is always communal. As Sarah Blaffer Hrdy said, it really does take a village to raise a child.
Such a configuration is not problem-free: it’s vulnerable to tyranny of conformity as well as the devastation that can be wrought by charismatic sociopaths. Nevertheless, it allows distribution of infant care, overlap of skills, quasi-fair apportioning of resources and monitoring of emerging imbalances. And grandmothers, maternal ones in particular, play a crucial role in all of these.
The grandmother hypothesis postulates that the presence of grandmothers allowed more children to reach adulthood, because grandmothers not only foraged for their daughters’ older offspring but also socialized them, taught them important skills and transmitted knowledge and experience. It also postulates that older children had to develop ways to compel caretaker attention, giving rise to the enlarged frontal lobe unique to humans. So the hypothesis argues that female longevity is essentially a “quality over quantity” fitness adaptation that in turn favored descendants of women who fit this profile.
There is, of course, a competing hypothesis far more beloved of Tarzanists. The hunting hypothesis, demolished by Sally Slocum, postulates that hunting became better than foraging as a means of sustenance when resources became scarcer in Africa; and that coordinating the hunt (versus, say, figuring out which berries weren’t poisonous) led to natural selection for bigger brains as well as ushering in the female adoration of “alpha males” who brought home the only protein that supposedly counts.
Kristen Hawkes recently published the results of a mathematical simulation of the grandmother hypothesis. The algorithms did not include brain size, hunting or pair bonding. The model showed that grandmother effects alone are sufficient to double life spans in less than sixty thousand years. Not surprisingly, one requirement is natal homing: living close enough to the maternal grandparents that grandmothers can exert their humanizing effects. This fits with the observation that rigidly patrilocal and patrilineal societies which completely obliterate female kinship networks have often gone for quantity over quality, essentially reducing women to incubators that can always be exchanged for newer models – and that some of these societies used to discard infant girls and older women literally like garbage. Other societies went the opposite route, treating older women like honorary almost-men (allowing them to keep sacred objects, for example, though few were made council heads) once they were no longer “tainted” by menstruation.
Those who had grandmothers almost certainly remember the stories they told and the moderating influence they exerted on the family. I never met either of mine. Both died young; tuberculosis hollowed one, fire consumed the other. I did get to know my father’s stepmother, a gentle too-religious soul who was one of the first Greek women to become a teacher. She tried her best, but was not strong enough to counteract my mother’s fierceness, which I have internalized by now. I wonder if I would have been more adjusted to social expectations had my other grandmothers been around, wielding the authority of blood kinship. Given my other non-adaptive core attributes, I suspect the answer is no.
Slocum, Sally. (1975, reissued 2012). Woman the Gatherer: Male Bias in Anthropology. In Anthropological Theory: An Introductory History. R. Jon McGee and Richard L. Warms, eds. Pp. 399-407. New York: McGraw-Hill.
Hawkes, Kristen. (2003). Grandmothers and the evolution of human longevity. American Journal of Human Biology 15 (3): 380–400.