evolution: a darwinian explanation for grandma

In contrast to most other animals, who reproduce until they die, human females live long after their childbearing years are over. Researchers offer proof in the March 11 Nature why this anomaly makes evolutionary sense: grandmothers, by helping their own children bring up children, ensure that more of their genes are passed on to future generations. Mirkka Lahdenpera of the University of Turku in Finland and her colleagues studied multigenerational demographic records of Finnish and Canadian women during the 18th and 19th centuries. According to their study, the longer a woman lived past menopause, the more successfully her children reproduced, breeding earlier and more frequently, and raising more offspring to adulthood. The researchers discovered that women gained, on average, two extra grandchildren for every 10 years they survived past age 50. A grandmother can pass on her child-care knowledge and also help care for her grandchildren, team member Virpi Lummaa stated in a press release, “making it more likely that her children will have more children more quickly.”

This news brief appeared in the Discoveries column of the Boston Globe’s Health/Science section on 3/16/2004.