Trading Descendants for Persistence? – Understanding the Cost-Benefit-Ratio of Consanguinity

Kai Willfuehr, University of Oldenburg
Johannes Johow, Independent Researcher
Eckart Voland, Justus Liebug Universitat

Consanguineous relationships are widespread around the globe and may be found in historical as well as contemporary populations. For agricultural societies, it has been shown that consanguinity is associated with an increased intergenerational transmission of landholdings through the patriline. The concentration of wealth hereby might contribute to the maintenance of high family socioeconomic status as well as its ability to have and raise children to adulthood. Marrying relatives is at the same time associated with fewer descendants due to a pedigree collapse and health issues due to inbreeding depression. In this paper, we develop a theoretical model to estimate the population- and niche-specific thresholds where the benefits of consanguineous marriages compensate the costs. The beneficial aspects of a consanguineous relationship are a function of the effectiveness and availability of hereditary resources; e.g. farmland. The costs are composed of a static biological component, e.g. deriving from inbreeding depression, and from a dynamic and environment-specific component which is basically the fitness detriment resulting from fewer descendants. However, a reduction of descendants and extensive kinship might be a welcome side-effect in high-K environments where cutthroat competition calls rather for offspring quality than quantity. We use historical family reconstitution data from the Krummhörn region in Germany (1720-1874) and the St. Lawrence Valley in Canada (1670-1799) as template for synthetic populations to test the explanatory power and the predictions of our model. Furthermore, we discuss the impact of socio-environmental constraints such as kin availability on the matrimonial market and cultural norms.

No extended abstract or paper available

 Presented in Session 245. Marriage and Partner Selection