The next time your wellness is affected by the hot flushes, night sweats and mood swings of menopause, blame the nearest male. According to evolutionary geneticists from Canada’s McMaster University, who published their findings in PLOS Computational Biology, men’s tendency to choose younger mates meant fertility became pointless for older women over the years, which eventually led to the menopause.
Human beings are the only species in which females cannot reproduce throughout their lives, and this has long puzzled researchers. It has been surmised that women lose their fertility at an age where they might not live to see a child grow, and instead are available to care for younger women’s children. This is known as “the grandmother effect” and put menopause in the light of a block to older women from continuing to reproduce. Yet this new study suggests just the opposite; the lack of reproduction has given rise to menopause.
Study leader Professor Rama Singh, an evolutionary geneticist, commented that men choosing younger mates were “stacking the odds” against continued fertility. ‘There is evidence in human history; there was always a preference for younger women,’ he said, adding that they were looking at human development many thousands of years ago – rather than current social patterns. ‘The social system is changing. There are women who are starting families later, because of education or a career.’ Professor Singh noted that this, plus later childbirth, could potentially alter the timing of the menopause, over a significant period of time. Women may have later menopause, and those genes could be passed on to their daughters ‘with the possibility of menopausal age being delayed.’
However this theory has been challenged by Dr Maxwell Burton-Chellew, an evolutionary biologist in the department of zoology at the University of Oxford. According to Dr Burton-Chellew, ‘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.’
‘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,’ Dr Burton-Chellew explained. ‘Evolutionarily-speaking, older females faced an interesting “choice”: have a child that may not reach adulthood before your own death, or stop reproducing and instead focus on helping your younger relatives reproduce.’
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