The evolutionary history of menopause in humans has been one of the longest-standing areas of research interest in life history evolution. One of the big ideas has been the “grandmother hypothesis”, the idea that the assistance given by grandmothers to their grandchildren has a larger fitness benefit to women than any additional children that the grandmothers might otherwise carry to term. The anthropologist Kristen Hawkes has been the largest contributor to developing this idea.
This week, Smithsonian magazine has an article from Elizabeth Landau that provides a review of the grandmother hypothesis and other current thinking on the evolution of menopause: “How Much Did Grandmothers Influence Human Evolution?”.
The article reviews some of the reasons supporting the idea that menopause was a product of adaptive evolution. Landau also spoke with scientists who have doubts about the adaptive value of menopause, or who argue that longer lifespans are mostly a recent aspect of human history.
The following passage presents a nice point, that when scientists look for differences between populations in their experience of menopause today, they must consider whether reported differences are cultural or genetic in origin.
But Lynette Sievert, biological anthropologist at the University of Massachusetts, Amherst, is skeptical. She has done fieldwork on menopause in many communities worldwide, from Bangladesh to Mexico to Hawaii. Her work has found that while women in some cultures may say that they do not experience hot flashes, monitoring devices on volunteers in those groups show that actually hot flashes are common—these women just don’t talk about them. Sievert says the universalities of the menopausal experience across the world suggest a shared experience of estrogen decline at midlife. Hot flashes may have ancient roots.
While no one can observe the hot flashes of Homo erectus, Sievert and others say humans and their ancestors have gone through menopause for at least 1 million, even up to 1.8 million years—even before anatomically modern Homo sapiens.
This is a difficult part of human biology to come to clear answers. I think there is a lot of potential in work that adds a stronger cross-cultural understanding of the way people structure their post-reproductive lives, as well as better documentation of the variability of menopause in today’s people. It is such an important aspect of women’s health that it’s disappointing there is not stronger scientific data on the causes of variability within and between populations.