Connie K. Ho for redOrbit.com — Your Universe Online
A new study by investigators from the University of Turku in Finland, the University of Exeter in the United Kingdom, University of Sheffield in United Kingdom, and Stanford University finds that menopause evolved as a way to limit competition between a mother-in-law and her new daughter-in-law.
Women normally experience menopause around 45 to 55 years of age and researchers have yet to understand its purpose. With a review of previous research, the team of investigators proposed that menopause was due to the interactions between the mother-in-law and daughter-in-law.
The researchers studied 200 years of data taken from church records between 1700 and 1900 regarding births and deaths in pre-industrialized Finland. The findings were recently published in the journal Ecology Letters.
“The research adds weight to the argument that menopause evolved because of the vital role that grandmothers played in rearing grandchildren in traditional societies. 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,” Dr. Virpi Lummaa, researcher at the University of Sheffield’s Department of Animal and Plant Sciences, told Medical Daily.
According to Medical Daily, the study discovered a statistic that stated that a child could die before 15 years of age if he or she who was born to a family that had a mother-in-law and daughter-in-law reproducing simultaneously. The scientists believe that, if the two are reproducing at the same time, there is increased animosity. The competition is intensified even more if they are not related.
“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? Our study shows for the first time that the answer could lie in the relationship between a mother-in-law and daughter-in-law,” commented co-author Dr. Andy Russell, a researcher at the University of Exeter´s Centre for Ecology and Conservation, in a Science Blog article.
The investigators also determined that women who stopped reproducing after 50 years of age had a higher likelihood of having more grandchildren. They believe that a grandmother who was not reproducing was more likely to help in supporting and caring for the grandchildren and daughter-in-law. On the other hand, when the grandmother had another child, the percentage of her child and the daughter-in-law´s child surviving was decreased by 50 percent.
The research strengthens the argument that menopause evolved because of the vital role that grandmothers played in rearing grandchildren in traditional societies. 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,” noted Lummaa in the Science Blog article.
The study concludes that women in modern society avoid having children once they take up the role of mother-in-law. This topic has not been analyzed prior as it was difficult to analyze data from successive generations of females along with tracking information on whom the females lived with and when they lived them.