This article was originally published on September 16, 2019, and has since been updated.
For many years, anthropologists and evolutionary biologists have not been able to explain the ‘why’ of menopause.
How could it be beneficial for women to no longer be able to have children when they still have decades left to live? Menopause is also a unique stage present only in human life; it is not shared with our primate relatives.
A 2012 study published in the journal Proceedings of the Royal Society B explains the role of how menopause and a woman’s need to be a grandmother has played a crucial part in human evolution.
The grandmother hypothesis explains that “grandmothering was the initial step toward making us who we are.”
Kristen Hawkes, an anthropologist at the University of Utah and the senior author of this published study, explains that grandmothering helped us to develop “a whole array of social capacities that are then the foundation for the evolution of other distinctly human traits, including pair bonding, bigger brains, learning new skills and our tendency for cooperation”.
Hawkes worked alongside Peter Kim, a mathematical biologist from the University of Sydney, and additionally James Coxworth, an anthropologist from Utah. Together, they prepared computer simulations to provide mathematical evidence for the grandmother hypothesis.
They simulated what would happen to the lifespan of a hypothetical primate species if they introduced menopause and grandmothers – as part of a social structure.
Chimpanzees typically live to be about 35 to 45 years old in their natural habitat. After their childbearing years, it is rare that they survive. For this simulation, researchers gave 1 percent of the female chimpanzee population a genetic predisposition for human-like life spans and menopause.
In this simulation, over 60,000 years went by, and the hypothetical primate species evolved the ability to live decades past their child-bearing years into their 60’s and 70’s. Eventually, 43 percent of the simulated female population were grandmothers.
How would grandmothers help us to live longer? There are many perks of having a grandmother and living in close proximity to her. She helps to collect and provide food, feeds the children, and enables mothers to have more children. Grandmothers are supplementary caregivers, and as this study suggests – they play a crucial role in human evolution.
Without menopause, older women could continue to mother children instead of acting as grandmothers. All children would be solely dependent on their mothers to survive. From an evolutionary perspective, grandmothers work to increase the survival rate of children instead of spending more energy on producing their own.
Hawkes also argues that social relations that go along with grandmothering could have contributed to the larger brains and other traits that distinguish humans: “If you are a chimpanzee, gorilla or orangutan baby, your mom is thinking about nothing but you,” she says.
“But if you are a human baby, your mom has other kids she is worrying about, and that means now there is selection on you—which was not on any other apes—to much more actively engage her: ‘Mom! Pay attention to me!’”
As Hawkes shares, “Grandmothering gave us the kind of upbringing that made us more dependent on each other socially and prone to engage each other’s attention.” This trend was also found to drive the increase in brain size, along with longer lifespans and menopause.
This may just be another reason to thank or think of your grandmother; while this simulation supports the idea that grandmothers help to evolve social skills and longer lives, anyone who has been close with their grandmother growing up may know this for themselves already.
There’s nothing quite like grandma’s love. She plays an essential role in our upbringing and helps families thrive, survive, and push through the hard times.
Keep Reading: Why We Shouldn’t Force Our Kids to Have Relationships With Emotionally Abusive Relatives
Sources:
- New Evidence That Grandmothers Were Crucial for Human Evolution. Smithsonian Magazine. October 2012.
- Increased longevity evolves from grandmothering. The Royal Society of Publishing. December 22, 20212
- The Perks of Living Near Grandma – THS