Historical Birth Cohort Trends

Fertility decreased across birth cohorts in the full database. Longevity increased across birth cohorts in the full database. The strongest patterns in the database were historical trends in longevity and fertility. The shorter lives of the highest-fertility women were attributed to their earlier birth cohort rather than necessarily to a biological cost of reproduction. Unadjusted analyses could make historical change appear as a negative fertility-longevity relationship.