Menopause and its side effects can all be blamed on men, Canadian experts suggest.
Evolutionary geneticists from McMaster University say men’s tendency to choose younger mates meant fertility became pointless for older women.
According to a PLOS Computational Biology article, experts say men’s preferences eventually led to the menopause.
However, a UK expert said that was the “wrong way round” and men chose younger women because older women were less fertile.
Researchers have long been puzzled as to why it appears that human are the only species where females cannot reproduce throughout their lives.
Previous theories had proposed a “grandmother effect”. This suggests 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.
The menopause was therefore seen as the block to older women from continuing to reproduce.
But this latest theory suggests things work the other way around, and that it is the lack of reproduction that has given rise to menopause.
Using computer modelling, the team from McMaster’s concluded “preferential mating” was the evolutionary answer – men of all ages choosing younger women as partners.
That meant there was “no purpose” in older women continuing to be fertile.
Prof. Rama Singh, an evolutionary geneticist who led the study, said men choosing younger mates were “stacking the odds” against continued fertility.
He said: “There is evidence in human history; there was always a preference for younger women.”
Prof. Rama Singh stressed they were looking at human development many thousands of years ago – rather than current social patterns,
He said this extended longevity – plus later childbirth – could potentially alter the timing of the menopause, over a significant period of time.
“The social system is changing. There are women who are starting families later, because of education or a career.”
Prof. Rama Singh suggested this trend would mean those women would have a later menopause, and those genes would be passed on to their daughters “with the possibility of menopausal age being delayed”.
However, Dr. Maxwell Burton-Chellew, an evolutionary biologist in the department of zoology at the University of Oxford, challenged the theory.
“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. Maxwell Burton-Chellew added: “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.”