Trading Descendants for Persistence? – Cost-Benefit-Ratios of Consanguineous Marriages among the Swedish Nobility [1600-1900] and the Economic Elite of the Krummhörn Region, Germany [1720-1874]

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

Kin marriages are widespread around the globe and are found in historical as well as contemporary populations. Consanguinity has benefits and disadvantages for families that take part in this practice. Advantages include an increased intergenerational transmission of landholdings and political power through the patriline, which we showed in previous research. The concentration of wealth and power hereby might contribute to the maintenance of high family socioeconomic status as well as its ability to find good matches for offspring, have and raise children. Yet the tradeoff is that there might be fewer kin in the following generations. Consanguinity is associated with fewer descendants due to an offspring collapse and due to inbreeding depression. However, a reduction of descendants might be a welcome side-effect in a saturated population or among families of higher social strata where cutthroat competition calls for offspring quality rather than quantity. We develop a theoretical model to estimate the population- and niche-specific thresholds where the benefits of consanguineous marriages compensate for the costs. We use family reconstitution data from the Krummhörn region (Germany, 1720-1874) as well as pedigrees of the Swedish Nobility (1600-1900). In a first step we use generalized linear mixed models to investigate the role of consanguineous marriage for lineage extinction and having no male heir, respectively. In a second step, the transition and reproduction rates in both populations are used as templates for simulated populations. Using simulated populations, we can estimate the role of population-specific contextual parameters such as offspring mortality for the risk of extinction of the consanguineous lineages.

No extended abstract or paper available

 Presented in Session 33. Marriage Patterns and Practices: New Historical Evidence