London: Menopause partly evolved to prevent competition between mothers and their daughters-in-law, explaining why women stop reproducing so early in life unlike most other animals, a new study has claimed.
The study by researchers from the University of Sheffield and Turku University in Finland also adds weight to the theory that menopause evolved to allow women to focus on their grandchildren.
Traditionally, this role included providing food for the family and protecting young children from accidents and disease.
Scientists analysed data collected by Dr Virpi Lummaa of the University of Sheffield and her student Mirkka Lahdenpera of Turku University, Finland, over 200-years from church registers of pre-industrial Finland.
They looked at information on birth and death rates from 1700 to 1900, before the advent of modern contraception or healthcare.
The study fund that women had more grandchildren if they stopped reproducing around the age of 50.
Researchers believe this was partly because of reduced competition between the older woman and her daughter-in-law and partly because of the support she could offer to her grandchildren.
A child born to families with a mother-in-law and daughter-in-law reproducing simultaneously was twice as likely to die before reaching the age of 15.
However, this was not the case in the instances when a mother and daughter had babies at the same time. This suggests that related women breed cooperatively and unrelated women breed in conflict.
This is not the case for a mother-in-law and daughter-in-law, since they are not related, it is logical they should compete to maximise on their chances of spreading their genes.
"We are so used to the fact that all women will experience menopause, that we forget it is seriously bizarre. Evolutionary theory expects animals to reproduce throughout their lifespan, and this is exactly what happens in almost every animal known, including human men," Co-author Dr Andy Russell from the University of Exeter said.
"The research adds weight to the argument that menopause evolved because of the vital role that grandmothers played in rearing grandchildren in traditional societies," Dr Virpi Lummaa, from the University of Sheffield`s Department of Animal and Plant Sciences, said.