Biosocial Models of Low-Fertility Societies

THIS ARTICLE SUGGESTS how theoretical biosocial models may give insight into fertility-related processes in modern, permissive societies. I do not allow the absence of data to constrain my thoughts. Biosocial models explain behavior by jointly considering sociological or psychological determinants and biological determinants. The jointness of the model may involve additive, interactive, or indirect effects of biological and sociological characteristics on behavior. The models may be microlevel or multilevel. The relationship between biological variables and demographic processes has long been a subject area for demography. Subtopics in this field now include the reproductive biology of fecundability, reproductive ecology, the biology of aging, health/disease and demographic process, and the effects of demographic events on biological processes. This article focuses on a specific corner of the biology-demography interface. It concerns only how biological processes affect voluntary behavior choices that are demographically consequential. Biological variance refers here only to the variance that arises from biological influences on behavior choices. Biosocial models include both biological sources and social sources of variance in behavior choices as independent variables. The most widely known biosocial models that explore this area are behavior-genetic models (Plomin, 1994). Because behavior-genetic models compare the behavior of individuals with known genetic similarities and differences, and with known environmental similarities and differences, they allow the separation of environmental and genetic variance. These models have been in use for decades. Since genetic designs are not always available, I provide here some propositions that illustrate various biosocial relationships without using genetic models. First, let me posit three biosocial relationships using a microlevel model. Additive: Androgenic hormones and religious participation independently affect the sexual behavior of adolescent boys, but in opposite directions.