Setting the second stage: the evolution of menopause & post-reproductive life

Published on February 28, 2017   32 min

Other Talks in the Series: Evolution and Medicine

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I'm Lynette Leidy Sievert. I'm a biological anthropologist. I'm currently a Professor of Anthropology at the Department of Anthropology at UMass Amherst. And I study human variation in age menopause, and human variation and symptoms during the menopausal transition. And I work all over the world, asking women who are 40 to 60 about their menopause, and the rest of their life. And I've become interested in the evolution of menopause and what makes us different from other animals. So today, I'm going to be talking about "Setting the Second Stage: the Evolution of Menopause, and Post-Reproductive Life."
So I'm going to be talking about the second stage of adulthood. And I'm using a quote here, from Mary Catherine Bateson from her book "Composing a Further Life: The Age of Active Wisdom." And the reason I like this quote is because I've always thought about the evolution of longevity as tacking on this extra piece on to the lifespan. But Mary Catherine Bateson points out that, "humans have inserted a new developmental stage into the life cycle." She calls it, "a second stage of adulthood, not an extension tacked on to old age." And this helped me to think about this age as being inserted and we're still healthy during the second stage of adulthood. So this is what I've become interested in thinking about.
The next slide is about menopause. We're gonna define menopause here two ways. First, by the WHO definition: "The permanent cessation of menstruation, due to the loss of ovarian follicular activity." And that is unique to humans, in the sense, that every human female is going to stop menstruating by at least the age of 60 or 62. I've never met a woman who is able to menstruate beyond the age of 62. I've never found in the literature any woman menstruating beyond the age of 62. This is a human universal among females. The reason we need a different definition for other mammals is because not all mammals menstruate. So Cohen suggested this definition: "The irreversible loss of the physiological capacity to produce offspring, due to intrinsic biological factors." So, it's a little more vague about what's going on. But the way you determine if an animal has been through menopause, is by looking to see what is their inter-birth interval. And so you see offspring, offspring, offspring. And then when you would expect another offspring, you wait another two standard deviations beyond the normal inter-birth interval. And if another offspring doesn't appear, you can say, "Oh, that female must be at menopause." And that gives us a nice definition that can be applied across species.

Setting the second stage: the evolution of menopause & post-reproductive life

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