June 14, 2013
Blame Menopause On Men, Says One Evolutionary Biologist
Michael Harper for redOrbit.com — Your Universe Online
Menopause has always been a stage of life experienced exclusively by women, but a new study finds that its existence could be blamed entirely on men. A professor from McMaster University in Canada made waves this week when he presented evidence that from an evolutionary point of view, women only stopped reproducing at an older age because men always chose younger mates. Once outside of the mating pool, women become victims of natural selection and enter menopause. The study also finds that if women had historically chosen younger mates, menopause might have been experienced exclusively by men instead.
The study was published in this week´s PLOS Computational Biology.
Evolutionary geneticist Rama Singh authored this report and claims menopause isn´t something that was evolutionarily developed but rather an act of natural selection gone wrong.
“In a sense it is like aging, but it is different because it is an all-or-nothing process that has been accelerated because of preferential mating,” said Singh in a statement. “Menopause is believed to be unique to humans, but no one had yet been able to offer a satisfactory explanation for why it occurs.”
As women get older, they generally stop reproducing. Historically, this can be traced to our earliest of ancestors who were concerned about peopling the species and moving humanity forward. Natural selection noticed men were choosing younger women with whom to reproduce instead of older women and began to favor the younger of the species. The fitness of these younger women was then protected by natural selection to keep them in peak reproductive capacity. However, once a woman grows past this period, natural selection allows a wave of mutations and hormones that kick start menopause and leads to a host of other health problems.
If it weren´t for this slow down in reproduction, Singh says menopause would never take effect in women.
Using a computer model and simulations, Singh and team showed how a male´s preference to mate with younger females can actually build up these mutations which are later responsible for the decrease in female fertility and ultimately, menopause.
“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.”
Yet, this study is concerned with the historical reproductive choices of men to determine why menopause developed in females. Social structure have changed dramatically since the days when Homo sapiens roamed the plains of northern Africa, and nowadays women have far more of a choice in deciding when they start their families. As such, women are giving birth later than ever, and this, says Singh, could mean that menopause may be pushed back even further into a woman´s life.
This is a bold theory, and with any new idea there will be those who disagree. Dr. Maxwell Burton-Chellew, an evolutionary biologist in the department of zoology at the University of Oxford, spoke with the BBC and said Singh may be looking at the problem of menopause from the wrong angle.
“The human male preference for younger females is likely to be because older females are less fertile,” explained Dr. Burton-Chellew in an interview with BBC.
"I think it makes more sense to see the human male preference for younger females largely as an evolved response to the menopause, and to assume that ancestral males would have been wise to mate with any females that could produce offspring."