Women generally live longer than men — on average by six to eight years, according to the World Health Organization. And while lifespan in most mammals can be viewed through an evolutionary lens (reproduction and the passing on of genes), female humans often live for decades past their childbearing years.
So why is this the case? Though researchers have long speculated — coming up with a myriad of explanations for women’s extended lifespans — there’s one hypothesis that’s especially intriguing.
The grandmother hypothesis
According to the grandmother hypothesis, the female human’s lifespan extends beyond fertility in order to help raise her grandchildren. Essentially, researchers are saying that after a woman’s body goes through menopause (around 45-55 years old), she is more effectively able to devote energy and resources to caring for her grandchildren.
Through an adaptationist lens, this ensures survival of a grandmother’s genes by increasing the fitness of her grandchildren. Through a nurturing grandmotherly lens, this is the perfect time to coddle and spoil your grandkids — and yes, even that is supported by science.
Research conducted in 1989 collected foraging data among the Hadza of Tanzania and found that post-menopausal women had high productivity in foraging, despite the challenging nature of gathering particularly valuable food. The researchers suggested that older females were preserving their family’s fitness by sharing their foraged food with their adult daughters. This would ensure the survival of both their daughters and their daughters’ offspring.
Further, the researchers suggested that grandmothers babysitting grandchildren while their adult daughters foraged could have the same effect on fitness and genealogy.
Anthropologists seem to prefer the grandmother hypothesis in comparison to other explanations for women’s extended lifespan. A 2010 paper, which studied Tsimane people of the Bolivian Amazon, showed that females in their 60s provided their grandchildren with a surplus of 500 calories per day. These researchers displayed that with grandmothers present, the number of grandchildren born increased, as did their healthiness through childhood.
So coddle, babysit, and offer your grandchildren as many treats as your heart desires. And remember: All of this isn’t to say that a grandmother’s love should be taken for granted. On the contrary: If you’re a grandma who yearns to spend a copious amount of time with her grandkids, know that anthropologists have your back. The grandmother hypothesis is yet another reason why grandmas are truly the best.