An evolutionary approach to change of status-fertility relationship in human fertility transition

The change in benefits of high socioeconomic status to fertility in humans during the demographic transition from high to low fertility has interested both demographers and evolutionary biologists. Evolutionary analyses add to demographic analyses by considering also males and status-related differential in male mating success, but they have been limited to time cross-sections and have not linked this differential to differentials in other determinants of male fertility. We use life-history records of males (n = 3791) entering marriage market before (1810s-1880s) and during (1890s-1960s) the Finnish fertility transition to investigate associations between socioeconomic status and chance and timing of marriage, choice for spouse, and lifetime fertility. Low status invariantly brought a lower marriage chance throughout these 160 years, which partly explained why ever-married high-status men lost advantage at early marriage when the system of achieving a high status shifted from inheritance to self-effort. The loss, coupled with assortative mating by age, promoted disappearance of differential in wife's age at marriage and thus, disappearance of differential in fertility between ever-married high-and low-status men in the Finnish fertility transition. Consequently, among all men (married and unmarried), status-related differential in lifetime fertility-not selection coefficient-declined over the transition. This study is among the first to show the interrelated dynamics of status-related differentials in male mating and reproductive traits; by doing so, it contributes to an evolutionary understanding of change of status-fertility relationship in human fertility transition and confirms continuing phenotypic selection on male status/wealth in modern societies.