Day 2: Evolutionary Explanation of Menopause

Every species, including we humans, evolves over time. This ensure we adapt to our ever-changing environments and continue surviving as a species. 

If you remember your biology 101, we are mammals and part of the animal kingdom, species homo sapien – human. And, in the animal world, we are somewhat of an anomaly. Unlike most of our mammalian kin, we are one of the very few species that has a limited time for reproduction. Along with a couple of whale species, we lose our reproductive capabilities long before our lives end. 

Everyone else seems to have fertility throughout their lifespans. Even our closest primate relatives have the capability of reproducing most of their adult lives. They stop having babies around 30 years old, but their life span is not much longer than that. So they essentially reproduce over their adult lifespan. 

Other mammals with longer life spans seem to retain this ability too. Elephants commonly have calves when they are in their 60’s. And did you know that whales can have babies well into their 80’s? Let that sink in for a second. A newborn baby to care for…in your 80’s. Wow. 

So, what’s going on here? We have longer life spans than our closest animal relatives but we lose our ability to reproduce relatively early in comparison. Evolution has a reason for everything. What is its reason for menopause? 

The fact is, science doesn’t really know for sure. There are two schools of thought though. Adaptive theories for menopause suggest that menopause evolved as an adaptation to the environment that gives us an advantage as a species. These theories are based on the positive reasons for menopause. 

There are lots of adaptive theories. They suggest that evolution favors early fertility over late fertility not just biologically, but socially. Given the roles that women take as they age, it is seen as advantageous to support younger descendants so that they can continue to take full advantage of their child-bearing years while receiving help to ensure the well-being of their other children. 

One of the most commonly cited adaptive theories is the “grandmother hypothesis”. This theory says that menopause is protective for a woman of a certain age. Menopause shields an older woman from the increased risks of child-birth. By avoiding the risk of death in childbirth, the mature woman remains available to raise her own children to maturity, and also care for grandchildren, supporting the survival of the genetic line. Makes sense, right? 

Another adaptive is the “mother hypothesis”. It suggests that menopause avoids the risks of dying in childbirth that older women face.  As women get older, they are more likely to experience complications in childbirth and less likely to survive long enough to raise a child to maturity.

And then, there’s the “reproductive conflict hypothesis”. This theory is based on the long-standing hunter-gatherer tradition of multigenerational living. Mothers and daughters-in-law generally lived under the same roof and had to share what were often scarce resources. Daughters usually married and went to live with their in-laws. This theory asserts that menopause occurs because when older mothers and younger daughters had children at the same time, they were competing for resources. That competition was likely to result in poor outcomes for the kids. And there are actually some interesting facts to support this idea. Researchers in Finland found that 50 percent of children born to older women who were pregnant at the same time their daughter-in-law did not survive to age 15. Children born to younger women pregnant at the same time as their mother-in-law, were 66 percent less likely to survive to adolescence.¹ So this theory seems to suggest that child-bearing risk and competition for resources with younger females might explain menopause. 

Non-adaptive theory, on the other hand, is based on the idea that menopause is simply the result of evolutionary changes in the human lifespan. There’s no distinct “purpose” to it. Human females were simply designed to reproduce for about as long as they were likely to live based on their evolutionary history. The fact is, our lifespan is MUCH longer than even our recent ancestors. We just live longer and our reproductive system gives out long before the rest of the body does. And, thanks to medical advances, we can remain relatively healthy well into our 80’s and 90’s. But, we’ve seen menopause mentioned even back as far as ancient Greece when lifespans were still fairly short. It may not be this simple. 

So, what do we really know about the evolution of menopause? Some but not much. What we do know is that mature women play crucial roles. Our mothers, aunts, grandmothers, even great-grandmothers, are the sages in our family. They hold the knowledge and history of who we are and where we came from. Not just the facts. They know the tales and the nuances. Before there were books and TV’s and the internet, there were the matriarchs. They were and still are the holders of the real history of our families and culture. We need them when we’re younger, we become them when we’re older. Whether we women choose to reproduce or not, there’s no denying that we are crucial to our species and our society.

As we come to the end of this evolutionary tale, think about the mature women who have been in your life – your mother, grandmother, maybe a mentor in your career, or even celebrities you admire. Think about the role you want to play in your family and society as you enter a new phase of your life. Keep that in mind as we progress to the next lesson.