Why women go through menopause
Menopause partly evolved to prevent competition between mothers and their daughter-in-laws, researchers say.
According to a study, when a grandmother had a baby later in life, and at the same time as her daughter-in-law, both newborns were 50 percent less likely to survive to adulthood.
The researchers, from the University of Sheffield and Turku University in Finland among others, said it could explain why women stop reproducing so early in life unlike most other animals.
It 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.
For the new study, scientists analysed 200-years' worth of data collected by Dr Virpi Lummaa of the University of Sheffield and her student Mirkka Lahdenpera of Turku University, Finland, 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 revealed that women had more grandchildren if they stopped reproducing around the age of 50.
The research team believes 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 conflictually.
However, 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.
"Although family roles have changed, many grandmothers still play a vital role in caring for their grandchildren and in western society a large number provide daycare," the Daily mail quoted Dr Lummaa as saying.
"It is interesting that even today, mothers rarely choose to have children at the same time as their offspring: even if they have not yet been through the menopause," Dr Lummaa added.