Maybe women outlive their fertility to ensure that their grandchildren thrive.

Most female primates never stop having babies. Why are women different?

Some scientists think we undergo menopause to benefit our families: in our 50s and beyond, unencumbered by young of our own, we can make sure our grandchildren thrive.

Maybe we outlive our fertility to ensure that our grandchildren thrive.

Until about 10,000 years ago, humans didn’t farm. Instead, we eked out a living by hunting and gathering.

Often, when mothers came up short, kids starved.

In hard times, grandmas might have made all the difference by finding kids extra food, scientists say.

What’s more, mothers who got help from their own mothers could wean their babies sooner and bear more of them.

Under these circumstances, natural selection may have favored the evolution of both mid-life menopause and a long period of subsequent vigor: in other words, grandmotherhood as we now know it.

The so-called “grandmother hypothesis” was developed in the 1990s by anthropologist Kristen Hawkes, who spent years living among the Hadza, an African tribe that still hunted and gathered. Older Hadza women, she noticed, often foraged tubers and other hard-to-find foods for their grandkids.

A Hazda couple and their baby in 1985. Anthropologist Kristen Hawkes formulated the "grandmother hypothesis" after observing that post-menopausal Hazda women played an important role in nourishing their grandchildren. Photo by James F. O'Connell.
A Hadza couple and their baby in 1985. Anthropologist Kristen Hawkes formulated the “grandmother hypothesis” after observing that post-menopausal Hadza women supplied a significant amount of food to their grandchildren. Photo by James F. O’Connell.

“Unlike other primates, including chimpanzees, human children are unable to feed themselves when they reach weaning age,” Hawkes writes. “The foods we rely on are too difficult for young children to handle.”

“This gives women whose fertility is ending (so they have no newborns of their own) an opportunity to influence the reproductive success of their daughters and survival of their grandchildren through assistance in food provisioning.

The boost that prehistoric grandmothers might have given their grandkids has been dubbed the “grandmother effect,” and scientists have been hotly debating its existence for nearly 20 years. Some scholars agree with Hawkes that grandmas mattered enough to make mid-life menopause an evolutionary imperative; others aren’t convinced.

I’m not qualified to weigh in on Hawkes’ theory, but I like the questions it raises, and this site’s name is a nod to it.

My guess is that grandparents have always been important to their children and grandchildren, but that the degree of their importance has ebbed and flowed.

Maybe grandparents were crucial to their grandchildren’s survival when humans were hunter-gatherers struggling to make it in the wild.

Maybe they weren’t so crucial in the United States of the mid-twentieth century, when children were raised in two-parent homes, mothers stayed home with them, and fathers earned enough money to support the whole crew.

And maybe they’re once again crucial today.