Why the females of some species undergo menopause while others do not has always been a conundrum despite our understanding of the biological mechanisms involved.
Now researchers in the UK are suggesting that the menopause could be nature's way of minimizing reproductive competition between generations of females in the same family unit which may explain why women, on average, stop having children a full ten years before the onset of menopause.
They say the hormonal change stops older women having children and competing for a larger share of an extended family's resources, leaving daughters-in-laws to concentrate on rearing any offspring instead.
The scientists from Cambridge and Exeter Universities say age-old tensions between wives and their mothers-in-law could be the reason for the menopause and women stop breeding when the next generation starts to breed.
Despite vast differences in wealth, resources, and access to medicine, women in all societies experience menopause which suggests that the human fertility schedule is genetic.
According to biologist Dr. Michael Cant, from Exeter University, when more than one female breeds the offspring have to compete for food and help for years and when it comes down to a choice between breeding and helping with other children, the younger women has nothing to gain; she is not related to anyone in the group, whereas the older female can help to rear her grandchildren.
He says this gives the younger female the advantage as she will breed no matter what.
Dr. Cant says women experience a rapid decline in fertility after the age of 40, culminating in the menopause around ten years later and the study helps to explain why the rapid ageing of the reproductive system starts when it does.
This is not the first research to suggest that the menopause evolved to ensure women care for their grandchildren and there are studies which show that having a grandmother at hand greatly increases a baby's chance of survival; the grandmother also benefits by safeguarding the survival of her genes.
The research is published in the latest edition of the journal, Proceedings of the National Academy of Sciences.