Author: Sujata Gupta / Source: Science News for Students
Grandmothers can be great for many reasons. In terms of evolution, however, it’s puzzling why women might live long past their child-bearing years.
Having them around may help later generations survive, find two new studies. But gran’s benefit seems to depend on her age and where she lives.The studies are part of a broader effort to explain why menopause exists. This is the time at which a woman stops being able to have a baby. Throughout the animal world, females in few species live much beyond their reproductive age.
So what’s different about humans?
One idea is that long-living women may help their grandkids survive to adulthood. That would up the chance that gran’s genes would be passed on to future generations. Scientists sometimes refer to this as the “grandmother hypothesis.”
Today, especially in richer countries, relatively few people die in childhood. So it would be hard to tell in modern families whether grandmas affect kids’ survival. Instead, researchers have turned to data from past centuries, when people had larger families and more children died young.
One research team used church records. It reviewed those for 5,815 children born in Finland between 1731 and 1895. (Many churches kept detailed records about members, including births and deaths.) Back then, families had an average of almost six children. About one-third of those kids died before age 5.
Kids between two and five years old were 30 percent more likely to survive if their mom’s mom lived nearby, the data showed — but only if she was 50 to 75 years old. Living near dad’s mom, even if she was the same age,did not aid a child’s survival. Neither did mom’s mother if she was over age 75.
And when a dad’s mom lived past age 75? She might actually hurt her grandkids’ chances of survival, the team found. A child was 37 percent more…
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