Putting the [men] in [menopause] New study challenges grandmother theory

14 Jun

man-checking-out-other-woman

It’s no secret that men find youthful-looking women attractive.

We see it in countless movie plots. A well-to-do married man gets bored of his wife, and his young 20-something secretary who is always wearing some sort of low-cut blouse catches his eye. It’s human nature right? He can’t fight the temptation.

And then sometimes the plot continues to lead into an affair, and then later a divorce. The divorced woman tries speed dating, but finds herself tirelessly competing with the younger generation and therefore finds it tough to reign in another mate.

Yes, I know that is a depressing thought and it’s not typically the norm–but it is the basic reasoning behind a new theory of why women go through menopause.

A study published this week in PLOS Computational Biology is is challenging a previous theory as to why women outlive their ability to reproduce. Evolutionary biologists have tried to find the logic behind menopause for more than 50 years, and are still somewhat puzzled.

The previous and most popular theory was called “the grandmother theory.” Scientists explained that perhaps the reason women stop reproducing in their 40s and 50s is so that they can use their experience and nurturing abilities to help take care of their grandkids and improve survival of their kin and therefore, their genes.

Critics say the theory does not really fit with the theory of evolution as a whole. Logically, a woman would benefit more from having another child than giving up that chance to help her grandchildren who do not carry as many of her genes, they say.

But, the new study is taking a different approach to looking at the menopause puzzle. The authors suggest that menopause may simply be an outcome of natural selection prompted by a man’s desire for younger women.

Rama Singh, Ph.D. from the department of biology at McMaster University in Canada and one of the lead authors in the study, suggests that since men of all ages compete for younger women, older females are left in the dust and therefore have less of a chance of…um…getting some action?

Therefore in an attempt to protect the human species through individual fitness, natural selection may simply protect the women who are more likely to reproduce (the young ones) and sort of “give up” on the older ones.

In response to the grandmother theory, Singh suggests he is unconvinced.

“How do you evolve infertility? It is contrary to the whole notion of natural selection. Natural selection selects for fertility, for reproduction — not for stopping it,” he said.

His theory on the other hand suggests that menopause was not a change that was meant to help the survival of a species as the grandmother theory suggests.

“This theory 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,” Singh said.

He suggests menopause is simply a change that occurs because over the course of our evolutionary history women have less of a chance of reproducing as they age due to the competition of the younger generation and their youthful “assets.”

Since the hormonal changes caused by menopause can cause serious risks, Singh said further research should be conducted to see whether menopause may reverse itself one day if the risks begin to outweigh the benefits.

Citation: Morton RA, Stone JR, Singh RS (2013) Mate Choice and the Origin of Menopause. PLoS Comput Biol 9(6): e1003092. doi:10.1371/journal.pcbi.1003092

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One Response to “Putting the [men] in [menopause] New study challenges grandmother theory”

  1. Erik Andrulis June 15, 2013 at 5:06 pm #

    I like to hear about studies that challenge existing ad hoc theories. Thanks for sharing.

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