Having Too Many Sons May Shorten Mothers Lives Compared to Daughters: Study

A new Finnish study say that women who have numerous boys don't live as long after the last birth of their son, compared to women who have many daughters.

Before the study may sound off alarms among mothers of several boys, it's important to note that the Finnish study is a bit dated. Researchers reviewed 300 years of parish data before the industrialization took place and most of the 11,000 women involved were born before 1960.

"Adult sons may be beneficial for their parental well-being and thus survival in some countries, but girls may be beneficial in other countries," study co-author Samuli Helle, an evolutionary ecologist at the University of Turku in Finland, wrote in an email to LiveScience.

The study, published Feb. 26 at the journal Biology Letters, suggests that cultural differences in how sons and daughters have historically been raised could be a cause for why these mothers didn't live as long when they had many sons.

"Girls in many traditional societies are, as we know, much more helpful to mothers than boys," says an expert who didn't work on the study. "They may help with child care; they may help with many tasks."

Also, boys' tendency to be heavier babies could mean they require more nutrients from their mothers during pregnancy and breast-feeding. On the other hand, in societies like China, sons appear to be linked to longer maternal lives. Either way, in a post-industrial society with birth control and more food availability, things may be different today, an author says.

Helle also noted that since food was scarcer and woman had no birth control, this may have affected the outcome.

"One could speculate that owing to modern medical care, smaller family size and more abundant resources, the biological costs of reproduction might not play that important role in modern societies anymore," Helle wrote.