Evolutionary psychologists have long asserted that the menopause evolved in humans to prevent older women from competing with their daughters-in-law over whose children to protect.
Now, scientists at Exeter University have reinforced the theory that might help explain why sometimes there’s tension between you and your mother-in-law.
In a study of Finnish birth and death rates between 1700 and 1900, research found that children born to families where a mother and daughter-in-law were both reproducing at the same time were twice as likely to die before reaching 15.
This was not the case, however, when biological mothers and daughters were both having children at the same time.
Dr Andy Russell, co-author of the report at Exeter University, said: "This was almost certainly to do with the way food was shared in the household – when families were related they did not compete.”
In evolutionary terms, mothers are more likely to share resources with their biological daughters but to compete with women to whom they are not related, even at a cost to their son's child, Dr Russell said.
The research reinforces the theory that women stop producing children in middle age in order to help provide for their grandchildren.
Dr Virpi Lummaa, from the University of Sheffield's Department of Animal and Plant Sciences told the Telegraph, “Although family roles have changed, many grandmothers still play a vital role in caring for their grandchildren.
“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.”