A History of Grandmothers?

By Jane Farrell

Did your grandmother ever encourage you to find a romantic partner? If so, she may be carrying out a tradition that reaches back to prehistoric times.

University of Utah anthropologist Kristen Hawkes is known for the “grandmother hypothesis,” which credits prehistoric grandmothering for our long human lifespan. Now, Hawkes has used computer simulations to link grandmothering and longevity to a surplus of older fertile men and, in turn, to the male tendency to guard a female mate from the competition and form a “pair bond” with her instead of mating with numerous partners.

“It looks like grandmothering was crucial to the development of pair bonds in humans,” said Hawkes, senior author of the new study published in Proceedings of the National Academy of Sciences.

“Pair bonds are universal in human societies and distinguish us from our closest living relatives,” Hawkes and colleagues wrote in the study. “Our hypothesis is that human pair bonds evolved with increasing payoffs for mate guarding, which resulted from the evolution of our grandmothering life history.”

That conclusion contradicts the traditional view that pair bonding “resulted from male hunters feeding females and their offspring in exchange for paternity of those kids so the males have descendants and pass on genes,” Hawkes said. The grandma hypothesis holds that “the key to why moms can have next babies sooner is not because of dad bringing home the bacon but because of grandma helping feed the weaned children. That favored increased longevity as longer-lived grandmothers helped more.”

In the late 1990s, Hawkes developed the “grandmother hypothesis” that humans developed lifespans longer than other apes because prehistoric grandmothers helped feed their grandchildren after weaning, allowing mothers to have more children sooner and increasing the prevalence of grandma’s longevity genes in the population.