This is cutting-edge research. We found it in the Telegraph, published in London: Men may be to blame for the menopause. Here are some excerpts, with bold font added by us:
Scientists claim that the menopause, which is thought to be unique to humans, may have evolved due to a preference among men to breed with younger women. A study using computer modelling to assess how such a preference would have driven evolution has now given some weight to the theory.
The cause and effect is not immediately obvious to us. Perhaps that will be explained as we read on:
Professor Rama Singh, from Canada’s McMaster University, said that competition between men for younger mates had left older females with less chance of reproducing. He said: “Menopause is believed to be unique to humans, but no one has yet been able to offer a satisfactory explanation for why it occurs. How do you evolve infertility? It is contrary to the whole notion of natural selection. Natural selection selects for fertility, for reproduction.”
If menopause couldn’t have evolved, perhaps — gasp! — it was intelligently designed. This is very confusing. Wait — they just posted about this at PhysOrg: Researchers conclude that what causes menopause is — wait for it — men. Let’s leave the Telegraph for a moment and see what PhysOrg says:
Singh, an evolutionary geneticist, backed by computer models developed by colleagues Jonathan Stone and Richard Morton, has determined that menopause is actually an unintended outcome of natural selection – the result of its effects having become relaxed in older women.
While conventional thinking has held that menopause prevents older women from continuing to reproduce, in fact, the researchers’ new theory says it is the lack of reproduction that has given rise to menopause.
We still don’t get it. Here’s a link to Singh’s paper, published in PLoS Computational Biology: Mate Choice and the Origin of Menopause. You can read it online without a subscription. Let’s stay with PhysOrg:
The prevailing “grandmother theory” holds that women have evolved to become infertile after a certain age to allow them to assist with rearing grandchildren, thus improving the survival of kin. Singh says that does not add up from an evolutionary perspective.
We never thought much of the grandmother theory. Natural selection seems unlikely to produce infertile nannies. Maybe in an anthill, but mammals aren’t that specialized. Aha — at last, here comes the proposed explanation:
The new theory holds that, over time, competition among men of all ages for younger mates has left older females with much less chance of reproducing. The forces of natural selection, Singh says, are concerned only with the survival of the species through individual fitness, so they protect fertility in women while they are most likely to reproduce. After that period, natural selection ceases to quell the genetic mutations that ultimately bring on menopause, leaving women not only infertile, but also vulnerable to a host of health problems.
Hmmmm. So even when a women had that oddball menopause mutation, she wasn’t selected out of the breeding pool because her reproductive days were already behind her. Okay, that makes sense — but how did that mutation become the common inheritance of all women? The differential breeding success of women with lifelong fertility should have kept menopause a rarity. The article continues:
“This theory says that natural selection doesn’t have to do anything,” Singh says. “If women were reproducing all along, and there were no preference against older women, women would be reproducing like men are for their whole lives.” The development of menopause, then, was not a change that improved the survival of the species, but one that merely recognized that fertility did not serve any ongoing purpose beyond a certain age.
We’re still not persuaded. Here’s one more excerpt:
The consequence of menopause, however, is not only lost fertility for women, but an increased risk of illness and death that arises with hormonal changes that occur with menopause. Singh says a benefit of the new research could be to suggest that if menopause developed over time, that ultimately it could also be reversed.
We wonder if that would cause men to change their ways. Somehow, we doubt it. Meanwhile, back at the Telegraph, we learn this:
Dr Maxwell Burton-Chellew, evolutionary biologist at the University of Oxford, said the study did not explain why the menopause is so rare in the animal kingdom. He said: “The authors argue that the menopause exists in humans because males have a strong preference for younger females. However, this is probably the wrong way round – the human male preference for younger females is likely to be because older females are less fertile.”
It still seems unsettled to us, and we can imagine the creationists making sport of this. We’ll end with a tantalizing incongruity — the extreme opposite of menopause. This is also from PhysOrg: Research shows male guppies reproduce even after death. Maybe there’s an afterlife after all.
After you’ve figured it all out, please explain it to us.
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