Until now it has been unknown why female humans, unlike most other animals, stop reproducing so early in life. Researchers from various universities have collaborated to solve this great mystery of nature. Their study explains that the menopause evolved, in part, to prevent competition between a mother and her new daughter-in-law.
“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. So why are women so different?,” said co-author Dr Andy Russell when interviewed for a press release. “Our study shows for the first time that the answer could lie in the relationship between a mother-in-law and daughter-in-law.”
The researchers analyzed data from church registers of Finland from 1700 to 1900, which included information on birth and death rates, before the advent of modern contraception or healthcare.
They found that women had more grandchildren if they stopped reproducing around the age of 50. Furthermore the data showed that 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. Remarkably, this was not the case when mother and daughter gave birth at the same time.
The benefits of menopause for posterity, may help explain why menopause evolved. The present study indicates that mothers and daughters don’t compete with each other, while mothers and daughters-in-law do.
Why? The ultimate evolutionary purpose of humanity is to pass and maintain their own DNA. Mothers and daughters share 50 percent of their DNA and therefore being in competition for food and other resources makes little sense. For mothers and daughters-in-law it’s different: they are not related, so it’s logical they should compete to increase their chances of spreading their genes.
In general, the findings adds weight to the theory that the menopause evolved to allow women to focus on their grandchildren. “The research adds weight to the argument that menopause evolved because of the vital role that grandmothers played in rearing grandchildren in traditional societies,” said author Dr Virpi Lummaa when interviewed for a press release.
“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. 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.”
The paper will be published in the journal Ecology Letters.