Mixed blessings for middle-aged mothers

Abstract

There are several explanations for the evolution of human longevity and senescence^1,2, a recent example being the suggestion by Perls et al.³ of a relationship between longevity in women and the age at which they bore children. Perls et al. showed that women surviving to at least age 100 were four times more likely to have had children while in their 40s than women who survived to age 73. But it is not possible to argue from these data that “the driving selective force of human lifespan is maximizing the period of time during which women can bear children” without a comparison of the total number of offspring produced (lifetime repro- duction, LR) of the two groups of women.

Main

Natural selection favours genes that increase LR^2,4, and consequently analyses must be based on LR if they are to conclude that the length of the reproductive period in women is a driving force in the evolution of human lifespan. The interpretation of Perls et al. would be supported if women in the centenarian group had a larger LR than those who died at 73. Alternatively, if women in the second group had equal or larger LR than those in the other, the shorter lifespan is probably an expression of costs associated with child care at an earlier age.