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Why does menopause happen?

Summary. 

While preliminary research and hypothesis exist around drivers for menopause, there's certainly for more research. There are three primary theories around why humans experience menopause The Grandmother Theory, The Mother Hypothesis, and The Reproductive Conflict Hypothesis. The grandmother hypothesis appears to have the most data supporting it. Biologically women go through menses when their reserve of follicles is depleted. However, the decline in sex hormones and lived experiences of changes doesn't appear to be necessarily linear with the decline in follicles. It would be interesting to better understand parallel processes and complimentary drivers of menopause.

Theory

There are many theories as to why women go through menopause, but there does appear to be an evolutionary reason for women to go through menopause. From our earliest records and across the globe, women have been going through menopause around age 50 and for those women who reach menopause they often live a significant portion of their lives post menopause. Three of the leading theories are:

 

  1. The Grandmother Hypothesis seems to have originated in the 1950s, but who exactly started this theory is a bit unclear. More recently Kristen Hawkes' research on the Hadza people of Tanzania has continued to build on this hypothesis. The hypothesis suggests women's evolution is uniquely focused on altruism (Johnstone & Cant, 2019) and are best able to contribute to their communities by helping take care of grandkids as opposed to continuing to have and rear their own children. Data collected by Hawkes and her team found data supporting the theory that grandmothers help increase the wellbeing and survival of their grandchildren. Interestingly, humans and four types of whales are the only large mammals which not only experience menopause but also live a significant portion of their lives post menopause (Landau, 2021). The phenomena of post menopausal grandmothers helping the survival of their grandchildren has also been proven with resident killer whales (Nattrass et al, 2019) -

Further discussion: How does families being spread out today with children going away to college and living further away from their original families as they have their own children impact the longevity and wellbeing of children today?  How does this relate back to Ellen Langer's theory of kids living in old age the way they see their grandparents living?

 

  1. The Mother Hypothesis. This hypothesis proposed by George Williams in 1957, suggests women experience menopause for two reasons. First, pregnancies become riskier as women get older, so it becomes advantageous for survival to stop being able to reproduce. Second, human children have a long period of dependency on their parents at some point it becomes more beneficial to focus on supporting the children which have already been born than to add more children to the family. suggest this tipping point occurs when the next generation begins to reproduce. Assuming passing down genes is the motive for survival, it is more beneficial for women to allow their children to help by passing down their genes.

 

  1. The Reproductive Conflict Hypothesis. In this hypothesis Johnstone & Cant build on the work of George Williams in 1957 by suggesting  the tipping point between having kids and focusing on your existing children occurs when the next generation begins to reproduce. Assuming passing down genes is the motive for survival, it is more beneficial for women to allow their children to help them by passing down their genes.

 

Further discussion: This is a particularly prominent example of framing. Who is helping who? Are the grandmothers helping their own children or are their children helping them? How does biology align with how individuals consciously consider the impact their lives will have?

Biological Process

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Menses are driven in large part by the number of follicles carrying oocytes (immature eggs) which women are born with. The number of oocytes a woman has and the number of follicles she has should be approximately synonymous as each oocyte is held by a follicle. Follicles provide a protective environment for the oocyte before and during maturation. Once an oocyte matures, it breaks free of from the follicle and heads to the uterus where it might meet a sperm (Lumen Learning).

 

Throughout a normal menses FSH (follicle stimulating hormone) and LH (luteinizing hormone) stimulate the growth of follicles and their oocytes. This process also impacts the levels of estrogen, progesterone, and testosterone present for women and these hormones fluctuate regularly with the menstrual cycle.

 

Women are born with roughly 2 million follicles. This number is believed to peak in-utero and decline throughout the rest of a woman's life. As we approach age 50 it is believed very low follicle reserves signal the lack of a need for FSH and LH to continue to develop follicles. This lack of LH and FSH to develop follicles also means the levels of estrogen, progesterone, and testosterone eventually decline (Cox & Takov, 2025). As this process winds down, hormone levels may spike unexpectedly.

Further discussion: Why are there seemingly random spikes in hormone levels if menopause is driven entirely by the decline in follicle reserves? Why does progesterone decline at a different rate than estrogen? If the two are both linked to follicle reserves, wouldn't they both decline at the same rate?

 

 

Further discussion or research: What in particular sparks a woman's first period? How might this help us understand why and when periods stop?

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