Fertility and life span: late children enhance female longevity.

The relation between fertility and postmenopausal longevity is investigated for a sample of 1635 women from a historical (17th to 18th century) French-Canadian cohort who lived past the age of 50 years. We find that increased fertility is linked to increased rather than decreased postreproductive survival. Postreproductive life expectancy extension is found to be tied to late births. This finding sheds new light on the cost of reproduction and may be viewed as supporting a new paradigm that states that reproductive potential drives remaining longevity. The emerging reproductive potential concept complements the well-established cost of reproduction hypothesis. Alternative explanations for the observed association are also explored. A specific finding is that the degree to which mortality increases for 50-year-old mothers as a result of senescence is closely tied to the logarithm of the age of their youngest child. For example, 50-year-old mothers experience a mortality decrease of 38% and an increase of remaining lifetime of 3.93 years for every 10-fold decrease in the age of their youngest child. This amount of gain in remaining life expectancy would apply to a mother with a two-year-old child as compared with a mother with a 20-year-old offspring. We also find evidence for the existence of vulnerable periods in human life history that are characterized by phases of heightened mortality and are found to be tied to reproduction and senescence.