2019.02.13: Grandmother Hypothesis
Published by DB,
Humans are one of the rare species where females outlive their reproductive age. Killer whales and Japanese aphids are two others. This fact has long befuddled biologists since it isn't explained by the golden rule of evolution: all organisms are optimized to survive so they can reproduce. In the 1960s, scientists came up with the grandmother hypothesis to explain this mystery. It posits that grandmother homo sapiens enable mothers to have more children. So women with a genetic proclivity to live longer would ultimately have more offspring carrying their genes in the form of grandchildren and great-grandchildren. But there has been scant research to back up the grandmother hypothesis—until now! This month, a study appeared in Current Biology examining a detailed record of all marriages, births, and deaths in the Saint Lawrence River Valley near Quebec since 1608. The extremely rich dataset allowed the researchers to follow women as they had children who either stayed close to home or moved away before having more children. It turned out that staying close to grandma paid off big time in family size. Women who lived 200 miles or further from mom had, on average, 1.75 fewer children than their sisters who lived in the same parish as their mother. One grandma whose kids stayed close to home had 195 grandchildren! It's a first step in proving that grandmas are useful for more than just providing unconditional love—they are walking survival guides!