Grandmas are badasses
That shouldn’t come as a surprise to you if you think back to your own grandmothers. Yes, grandmas are badasses and so are great-grandmothers (mine sure were) but we’ll get to them later. Recent research on the evolutionary power of menopause in Orcas (aka killer whales) suggests that post-menopausal grandmothers improve the survival and reproduction of her grandchildren and her own genes. It seems that grandma Orcas not only help raise and share their food with their grandchildren but also teach them how to find the best areas to look for food. After all, the grandma Orcas have many decades of hard-won experience that greatly benefit their offspring’s offspring. But the core issue here is not so much about menopause, but why do women long outlive their fertility?
Fertility and menopause
At some point in a woman’s life – usually, around 50 – her ovaries stop producing eggs. She no longer menstruates, gets pregnant and nurses. She may no longer be reproductive, but she becomes amazingly productive in a variety of ways besides bearing children. Post-menopausal women continue to live for decades, which is not only interesting from an evolutionary point of few, it also suggests that they play a critical role in the survival of our species. The Grandmother Hypothesis, one of the most popular explanations around, posits that a longer post-reproductive life span makes sense “if a grandmother improves the survival and reproduction of her grandchildren, thus ensuring continuation of her own genes—including genes that contribute to longevity.” Not everyone is on board, however.
Skeptics contend that from an evolutionary perspective, it doesn’t make much sense for a woman to forego having additional children of her own to improve the survival of her grandchildren, who carry only a quarter of her genes. Doing so would mean she only passes on a quarter of her genes instead of half her genes. Anthropologist Kirsten Hawkes of the University of Utah and mother of the grandmother hypothesis says, other researchers are right to focus on intergenerational conflict. “Elephants have babies in their 60s, and some whales give birth in their 80s. It’s clearly something selection can adjust,” she says. “So explaining why it hasn’t in us has to be part of the story.”
Survival of the grand offspring
A new paper recently published in Proceedings of the National Academy of Sciences (PNAS) examined the “powerful benefits of having post-reproductive grandmothers in Orca communities.” The study, which looked at whether post-reproductive Orcas helped their offspring better than grandmothers who continued to reproduce, discovered that “not only did grandmothers significantly increase the survival of their grand offspring, but grandmothers were even more beneficial to their grand calves when they were no longer reproducing,” according to the study’s authors. Another interesting finding was that if a whale lost its grandmother, its chances of dying increased dramatically over the following two years, even in whales up to 20 years old. The grandma whale’s extensive ecological knowledge accumulated over many decades was instrumental in the survival of entire families. And the benefits were even more significant if the grandmother whale was no longer bearing offspring, thus allowing her to devote her time, energy and resources to help her grand offspring survive.
Previous studies believe that menopause might be beneficial because there is less competition for resources between generations of females. This could also explain why in humans, females generally stop reproducing at about the same time when their offspring start. The findings also help explain why Orcas have the longest post-reproductive life span of all nonhuman animals. According to the authors of the study, “natural selection has decided that post-reproductive grandmas are precious resources. Perhaps this is why humans have a longer post-reproductive life span than other primates.” I guess this proves what we already knew: Grandmas are badasses, thank goodness. Otherwise, we wouldn’t be around.