Investigating additive genetic, maternal, and paternal (co-)variation in fertility and educational level in the Netherlands. An application of the ‘animal model’.

Low levels of fertility in Western countries are often attributed to men and women pursuing careers first and babies later. Research has shown considerable similarity between parents-children and siblings in completed fertility and education. This raises the possibility that the effect of education on fertility is not causal, but has a genetic basis and/or arises due to non-genetic factors of the family of origin. Relatively little research investigates the (common) genetic origin of these outcomes. Most of the existing bio-demographic research on fertility uses the Danish Twin Study (cf. Kohler and Rodgers). It is crucial to extend this line of research to other contexts to generalize findings and gain insight into possible environmental variability. Unfortunately, twin data are not readily available for most contexts, but genetic origins can also be investigated using information from multi-generation surveys using the so-called ‘animal model’. This is a mixed model that takes advantage of information on the relatedness of all individuals in a pedigree to estimate the genetic merit of an individual. We apply this model to the Netherlands Kinship Panel Study (8,200 families and 56,000 individuals) to investigate the role of additive genetic effects, maternal and paternal effects on (the co-variation of) fertility and education.