Waiting to have children may add years to a woman’s life, says Jenni Pettay of the University of Turku in Finland. The evolutionary biologist analyzed 5,000 birth records from four generations of 17th- and 18th-century Finns and found that women who waited the longest before having their first child were statistically more likely to live longer. The delay in childbirth seems to be inherited: Late mothers’ daughters also tended to become late mothers themselves. (Late was defined as after 30.)
Previous research has suggested that women who delay having children live longer. But none of these studies was able to determine if the longevity was due to cultural factors, such as a higher socioeconomic class or better living conditions. Pettay got around those issues by studying women from a homogeneous population who did not have access to contraception or advanced medical care.
Still, Pettay says, it’s culture, not genes, that explains why Westerners delay parenthood: “In modern society there tends to be a low number of offspring per couple, so natural selection isn’t at work. But this study does suggest there may be benefits to later motherhood that evolved to counteract the decrease in total fertility years, such as living longer to provide care to grandchildren.”