A nuclear twin family study of cognitive abilities: Results from the German TwinLife study

Numerous studies of the etiology of cognitive abilities have shown that genetic influences account for approximately 50% of the variance in cognitive abilities. Research has also shown that shared environmental factors appear... [ view full abstract ]

Numerous studies of the etiology of cognitive abilities have shown that genetic influences account for approximately 50% of the variance in cognitive abilities. Research has also shown that shared environmental factors appear to be more important early in life and in childhood, whereas nonshared environmental influences as well as genetic influences become more important in early adulthood and later in life. However, most studies on the heritability of cognitive abilities relied on the classical twin model which assumes random mating (i.e., uncorrelated phenotypes of the parents), as well as the absence of gene-environment interaction and correlation, and therefore only display broad estimates of heritability. When these assumptions are not met, estimates of the heritability may be biased and potentially misinterpreted.

To contribute to a deeper understanding of the sources of inter-individual differences in cognitive abilities, we leveraged a nuclear-twin family design to assess the presence of assortative mating and the presence of cultural transmission between the parent and offspring generation independent of the heritability of cognitive abilities in a sample of 4,010 twin families. Analyses were based on data from 1,837 MZ twins, 2,173 DZ twin pairs comprising four different age groups (5, 11, 17, and 23 years of age), 3,802 biological mothers and 2,456 biological fathers. Results are discussed with respect to developmental trajectories in the various age groups and the role of the family environment.