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Friday, September 21, 2007

Human evolution files: Menopause explained! - or maybe not

Recently, an article appeared in New Scientist, a magazine for all things Darwin, wherein we are assured that "Caring grandmas explain the evolutionary role of menopause."

The article argues, based on research in Gambia prior to the introduction of modern medicine, that children were more likely to survive their mother's death if their maternal grandmother was alive (and presumably looked after the child):
... Daryl Shanley and colleagues at Newcastle University, UK, analysed the births and deaths of 5500 people in Gambia between 1950 and 1975 – before a modern medical clinic arrived. They believe this provides an approximation to the situation experienced by females during the evolution of humans.

Interesting idea - that life in Africa has not changed at all since the Old Stone Age.

It's an interesting article, all the more because menopause may not even require an "evolutionary" explanation.

The article explains,
Human female reproductive functions stop around age 50, and start tapering off even earlier. In other mammals, female reproduction simply stops because of ageing, at a variety of ages. But in humans the shutdown is deliberate and early. And it is genetically controlled, meaning the genes responsible were selected by evolution.

Wait a minute ... do we have any good reason to believe that in earliest human history most women even lived to be fifty years of age? How many people over 35 years of age, never mind 50, were the subjects of natural selection (which is what New Scientist means by "evolution")? Also, I wonder how many animals living in nature really outlive their fertility or die of old age.

Doesn't a woman develop all her eggs while a fetus herself, start to release them at menarche and go through them at a rate of about one a month? When the monthly release of eggs stops, that’s menopause.So, why bother with an evolutionary purpose for menopause? Isn’t menopause just the state of outliving one’s fertility?

Of course, in some cultures, mom's mom would raise the child of a dead mother, and in other cultures she might only raise a boy (not a girl). In others, maybe a child whose mother died is bad luck. Indeed, in some cultures I suspect that dad's mom would shove mom's mom out of the way and grab a BOY immediately.

In the cafeteria at Biola University in October 2005, I recall an eager young Darwinist proclaiming to me (rightly, I believe), "Evolution doesn't care about you when you are old." I may have been the only "old" person within 500 metres, but I was hardly alarmed to learn that "evolution" didn't care about me.

(I only wish that the Toronto snow shovelling compliance inspector had the same view ... Unhappily, he knows that I exist, and that I am a few years short of free shovelling, no matter how big the mountain of snow is.)

Hat tip to the first reader to spot an article in New Scientist explaining the evolutionary adaptation of living to be over eighty years of age and being no darn use to anyone who does not want to listen to extended yarns of ye good old days...

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