Why Do Grandmas (Post-Menopausal Women) Exist?

Judith Shulevitz at The New Republic homes in on two theories: the “stopping-early hypothesis” and the “grandmother hypothesis”:

In 1957, the evolutionary biologist George Williams proposed what is called the “stopping-early” hypothesis: Middle-age women need baby-free time to usher their youngest children into adulthood. In the 1980s, an American anthropologist named Kristen Hawkes and two colleagues came up with a different explanation. They had gone to northern Tanzania to study the foraging habits of the Hadza, the last known hunter-gatherers in Africa. While there, the scholars were struck by how strong the tribe’s old women were and how, rather than live off the fruits of others’ labor, they worked hard digging up the tribe’s main starch staple, a deeply-buried tuber. “Their acquisition rates were similar to the rates of younger women,” Hawkes told me, “but these old ladies were spending even more time” than their daughters gathering food, leaving camp earlier, coming back later, and bringing back more than they needed. The anthropologists also noticed that many children with grandmothers or great-aunts had faster growth rates than their counterparts.

From these slim clues, Hawkes and her colleagues developed the “grandmother hypothesis,” which holds that women past childbearing age helped not just their children, but their children’s children, and lengthened the human lifespan in the process. Without babies of their own to lug around, grandmothers had both time and a very good reason to be useful. When they eked out food for their daughters’ children, they reduced the chance that those children would die. That gave the grandmothers a better chance of passing on their own predisposition to longevity. […]

Two decades later, the grandmother hypothesis has gone from oddball conjecture to one of the dominant theories of why we live so long, breed so fast, and are so smart. The extra calories and care supplied by women in their long post-fertile period subsidized the long pre-fertile period that is childhood. And that’s what made us fully human.

I’ll add a few guesses to these hypotheses (which is what we’re basically doing absent hard evidence):

  • Group selection. If group selection plays a role in human evolution–and there are evolutionary biologists like David Sloan Wilson who argue that it does, then giving care to grandmas (and not just exploiting their labor) adds dignity and value to the tribe as a whole. It says: Healthy or unhealthy, we don’t leave our wounded and elderly on the battlefield of life to die. We are all ‘in’ with one another. We rise and fall together. This bonding gesture between young and old makes every individual more willing to take risks on behalf of the others in the tribe, and to expect similar gestures in return. This could certainly be an evolved group trait that raises the fitness of the group as a whole.
  • Grandmas raise courage. The existence of grandmas may add spine to warriors. Men fight for the women and children back at the home base, not for themselves. This gives men a righteous cause born of love (for mothers, for mates, for children) and probably makes them more effective and less self-absorbed fighters.
  • Grandmas inspire love. Grandmas may have brought selective pressure to the evolution of love. We love our mothers and grandmothers. Their bond with us runs deep. And the emotion of love makes for a stronger collective group. When you love somebody so much that you will not let them die or be abandoned no matter what, you demonstrate traits that work in more adaptive contexts as well. (Who wants a mate that dishonors and abandons his or her parents? If you’re in the mating game, you want to have a reputation for loving your parents.)
  • Grandmas carry cultural memory and know-how. This one seems almost too obvious to point out.

These guesses broadly fit within the “grandma hypothesis” generally. The extension of the lives of post-menopausal women have all sorts of benefits to group survival (some obvious, others less so). 

If anybody can think of other evolutionary advantages conferred from extending the lives of grandmas (and grandpas as well), I’d be curious to know your thoughts. It’s an important issue going forward, obviously. Social policy in the United States seems to be favoring the idea that the elderly are, on balance, a burden. And we worship youth and fear growing old.

About Santi Tafarella

I teach writing and literature at Antelope Valley College in California.
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6 Responses to Why Do Grandmas (Post-Menopausal Women) Exist?

  1. I’ll add one. Grandmas are from a different world … and they KNOW you. I guess you got that in the last point but you didn’t quite cover the fact that grandmas train young warriors when their own parents are too busy with other children. Grandmas increase the efficacy of training of young children by the family unit. It’s not just food and love but an additional source of knowledge and skills learning, not that they have it, but that they add to the available pool of knowledge and skills.

  2. I have another reason besides “were not animals, we’re human beings”: Because Christian morality keeps euthanasia for the elderly at bay. Evolutionists always fail to ask why Grandpa is also still allowed to live. (Hint: For the same reason that Grandma’s allowed to live.)

    • Santi Tafarella says:

      I agree that religious taboo is involved in contemporary treatment of the elderly when they are near death, but the evolutionary psychologist is raising a different issue. Why, long before the traditional religions were even in existence, did women outlive their fertility? Most animals don’t. It must confer some survival benefit for our particular species or the trait would not persist.

      As for grandpas, it is an interesting fact that old men can still get young women pregnant, but it is also true that their DNA is compromised. So their contribution to the gene pool late in life is probably trivial. If it’s not a fluke, there must be other evolutionary benefits to having male oldsters as part of the tribe.

      Another interesting fact is that women outlive men on average by about a decade. Again, why?

      If Christianity and other religions went away tomorrow, societies that treated their elderly badly would become less competitive, not more so. And, of course, societies that treated their elderly well would enhance their collective survival in ways perhaps not obvious, but nevertheless real. So it’s not really religion, but evolution that is protecting the elderly. Religion puts its stamp of approval on something evolution was already doing (keeping the elderly alive and giving younger people personality traits of love for one’s parents and grandparents). These aren’t going away just because religion goes away.


      • “Why, long before the traditional religions were even in existence, did women outlive their fertility? Most animals don’t.”

        Simple; most animals don’t have the advantage that comes with having a human brain. Thus, in the animal kingdom, the weakest perish first: the sick, the very young, the old (with females being more vulnerable because they tend to be smaller, weaker, and less aggressive), and so on. Humans, on the other hand, can use the experience and knowledge that comes with age to their advantage in order to survive the “cold, cruel world.” And, BTW, animals living under the protection of human beings as pets have no problem with living well into their animal Golden Years–just like their human counterparts.

        “So it’s not really religion, but evolution that is protecting the elderly.”

        No…why make it more complicated than it is? It’s our uniqueness as human beings that protects the elderly (who by the way play an active role in their own survival and longevity). It’s our humanity. Our intelligence. Our compassion and empathy. Our foresight. These are our “survival mechanisms.”

      • Santi Tafarella says:

        You make good points, but it’s not an either-or to my mind. There are a lot of complex factors at work and you’ve put into the mix some additional interesting ones.

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