Updated February 2006

Whats New - Human Life History Project in Media

Having too many sons shortens mother’s life
Bruce Bower

HEALTH: Daily Times Report

ISLAMABAD: New research has indicated that having too many baby boys shortens the life span of the mother.

Scary as it sounds, the study even sets a specific price on the sex of a child: For every boy baby, there’s a 34-week reduction in the mother’s life span. The toll comes partly from the fact that boy babies are more demanding in the womb, but that age-old maternal complaint might be justified because boys didn’t ease their mothers’ burden by helping around the home, says a report in tomorrow’s issue of the journal Science.

The numbers come from information Finnish churches carefully recorded between 1640 and 1870 about a pre-industrial tribe, the Sami, which lived by reindeer herding, hunting and fishing. The information was so detailed that Samuli Helle was able to draw the boy-versus-girl baby comparison, which he used for his master’s degree thesis at the University of Turku. Helle now is working toward a doctorate there.

A mother’s life span was not affected by the total number of the children she bore and raised, Helle finds. However, the report shows a definite drop in a mother’s life span for every boy born and raised by her. And her life span increased for the number of daughters born and raised. That improvement was due to “the human family system in which the daughters help their mothers in everyday tasks,” the report says.

To show that it’s always the woman who pays, the study finds that “the number of sons or daughters born or raised to adulthood had no effect on paternal longevity.”

If there is any comfort to today’s mothers, it is that “I think the effect in modern society is not so great, because resources today are not as limited as they were 200 years ago,” Helle says. The burden of a boy starts with fertilization, he says.

The report cites studies indicating a male fetus makes more physical demands: It grows faster and becomes larger than a female fetus, and so a Sami woman who bore a boy baby took longer to achieve her next pregnancy than one who had a girl. There is also evidence that pregnancies with male fetuses are associated with higher testosterone levels that reduce the mother’s immune defenses, Helle says.

“But I think that social interactions may be even more important, because a daughter’s help could actually increase the mother’s survival,” he says.

It’s hard to say how much the Sami numbers can be applied to society today, says Virpi Lummaa, who worked with Helle in Finland and now is a postdoctoral fellow in the University of Cambridge zoology department.

“First, women have far fewer babies today,” she says. “Also, our food supplies are not as limited as they were then, so women can afford to have more sons. And also, with modern medical care people tend to live longer.”

But the grim statistics might still apply in less developed modern societies, Lummaa says, because they are up against many of the same restraints that faced the Sami.

When there are no limiting resources and you have as much as you need, you probably can afford to have sons,” she says. “But in developing societies, the numbers depend on various conditions in society.”