Genealogical Data Supports the 'Grandmother Hypothesis'

Source: https://www.facebook.com/KompotIsLife/

The so-called grandmother hypothesis suggests that as humans started to live longer, grandparents began to play a crucial role in reproductive success. With the appearance of grandparents more human babies were born, and they were more likely to live longer.

Earlier this year, two new studies, published in Current Biology, were reported to add evidence for this theory. Interestingly, in these studies biologists and anthropologists used the kind of documents that genealogists normally work with: population censuses and church records. Specifically, they analyzed these records in terms of the effect grandmothers had on their grandchildren’s number and survival.

Canadian researchers analyzed the data of the pre-industrial French settlers in the St. Lawrence Valley during the 17th and 18th centuries. Their study confirmed that reproductive success was higher when grandmothers were alive. Grandmothers who were alive allowed their daughters to increase their number of offspring born by 2.1 and to increase their number of offspring surviving to 15 years of age by 1.1 compared to when grandmothers were dead.

This effect decreased with grandmothers living far away from their daughters. As geographic distance increased, the number of offspring born and lifetime reproductive success decreased.

A team of researchers from Finland worked with birth and death records from the Finnish church books from 1731-1895. They found that having a maternal grandmother aged 50–75 improved grandchild survival. Women, whose mothers were not living nearby, had higher chances of death.

However, there were age limitations to the grandmothers' ability to provide help to young grandchildren. Researchers found that co-residence with paternal grandmothers aged 75+ decreased grandchild survival. It is not clear from the summary, however, whether or not the paternal lineage was a factor in this case. Maternal vs. paternal grandmother roles is subject to a whole scientific discussion. But in this case it might be simply because of the pre-industrial family structure: co-residing with paternal grandparents was more common.

In any case, it looks like genealogical data provides support to the "grandmother hypothesis". Children who were cared for by older women in the family had better chances of survival. The biggest positive effect on the grandchildren fitness and survival was from the maternal grandmothers aged 50–75, who lived in vicinity with their grandchildren.

I have not found similar research with Eastern European records, but it would be interesting to have more of such cross-disciplinary studies. As Eastern European genealogists, we could call it "the Babushka effect".