The argument that post-menopausal women help to produce more offspring has been around for long time. But a study of 18th and 19th century Finnish and Canadian farm families (stable populations with excellent record-keeping) puts numbers behind this aren’t we helpful idea.
Women whose mothers were alive began having children 2.4 years earlier than women whose mothers had died. (Was this because their mothers were nagging them about getting married? The records don’t say.)
Both men and women who had a post-reproductive mother living with them, produced more children and experienced fewer childhood mortalities. Interestingly, this difference in childhood mortality connected to Grandma’s presence only kicks in after the age of two, which implies that, for the first two years, a child is the responsibility of its mother.
It also helps more if Grandma is relatively young. “Grandchild survival to adulthood is enhanced by 12% when grandmothers are under 60 at their birth, but by only 3% when grandmothers are over this age.”