Washington, D.C. ? A pair of researchers, drawing on the experience of nearly 22,000 couples in the 19th century, have measured the “fitness cost” of human reproduction. This is the price that parents pay in their health and longevity for the privilege of having their genes live on. The findings were published last month in the Proceedings of the National Academy of Sciences.

Women paid a bigger price than men. Older mothers were four times as likely to die in the year after having a child than their mates. Having lots of children was especially risky: A mother of 12 had five times the risk of dying prematurely as a mother of three.

Despite avoiding the hazards of childbirth, fathering more children meant more risk of dying before their time, too.

And the later-born children in large families had less chance than their older brothers and sisters of surviving into adulthood and having children themselves. Losing a mother raised every child’s risk of dying young.