Between nurture and nature: the shifting determinants of female fertility in Danish twin cohorts.
Behaviors related to fertility constitute primary candidates for investigating the relevance of evolutionary influences and biological dispositions on contemporary human behaviors. Using female Danish twin cohorts born 1870-1968, we document important transformations in the relative contributions of "nurture" and "nature" to within-cohort variations in early and complete fertility, and we point toward a systematic relation between the socioeconomic context of cohorts and the relevance of genetic and shared environmental factors. This transformation is most striking for early fertility where genetic factors strengthen over time and are consistent with up to 50 percent of the variation in early fertility in most recent cohorts. Understanding this emerging relevance of genetic factors is of central importance because early fertility constitutes an important determinant of complete fertility levels in low-fertility societies, and because teenage motherhood and early childbearing are often associated with negative life-cycle consequences. Moreover, our results emphasize the need for socially and contextually informed analyses of nature and nurture that allow both factors to influence human reproductive behavior over time.
Kohler
Hans-Peter
HP
Population Studies Center, University of Pennsylvania, 3718 Locust Walk, Philadelphia, PA 19104-6299, USA. hpkohler@pop.upenn.edu
Rodgers
Joseph Lee
JL
Christensen
Kaare
K
D000328:Adult; D001723:Birth Rate; D015331:Cohort Studies; D003710:Demography; D003718:Denmark / Q000453:epidemiology; D004777:Environment; D005260:Female; D005298:Fertility / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D008957:Models, Genetic; D011157:Population Dynamics; D012641:Selection, Genetic; D012959:Socioeconomic Factors; D018433:Twin Studies as Topic; D014427:Twins / Q000706:statistics & numerical data*