Author: Sujata Gupta / Source: Science News
Grandmothers are great — generally speaking. But evolutionarily speaking, it’s puzzling why women past their reproductive years live so long.
Grandma’s age and how close she lives to her grandchildren can affect those children’s survival, suggest two new studies published February 7 in Current Biology. One found that, among Finnish families in the 1700s–1800s, the survival rate of young grandchildren increased 30 percent when their maternal grandmothers lived nearby and were 50 to 75 years old. The second study looked at whether that benefit to survival persists even when grandma lives far away. (Spoiler: It doesn’t.)
The studies are part of a broader effort to explain the existence of menopause, a rarity in the animal kingdom. The so-called “grandmother hypothesis” stipulates that, from an evolution standpoint, women’s longevity is due to their contributions to their grandkids’ survival, thus extending their own lineage (SN: 3/20/04, p. 188).
In the Finnish study, researchers wanted to know if grandmas eventually age out of that beneficial role. The team used records collected on the country’s churchgoers born from 1731 to 1895, including 5,815 children. Women at that time had large families, averaging almost six children, with about a third of kids dying before age 5.
The team found that when maternal grandmothers living nearby were aged 50 to 75, their 2- to 5-year-old grandchildren had a 30 percent higher likelihood of survival than children whose maternal grandmothers were deceased. Similarly aged paternal grandmothers and maternal grandmothers aged past 75 did not affect children’s overall survival.
But when paternal grandmothers lived past age 75, their grandchildren’s odds of dying before age 2 was 37 percent higher than a child with a deceased…
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