Genetic and Environmental Influences on Aggression Across the Lifespan: A Longitudinal Twin Study

In this study, we investigated the genetic and environmental contributions to individual differences in aggression across the lifespan, in longitudinal data provided by 32,541 twin pairs aged 3 to over 60 years, from the Netherlands Twin Register. The dataset included participants with a varying number of repeated measures, and of different ages. We applied a genetic autoregressive simplex model to examine the continuity of genetic factors over time. Phenotypic correlations indicate substantial stability between aggression levels at different ages. Both genetic and environmental factors contribute to this stability in aggressive behavior throughout life. Specifically, genetic influences on aggression vary before age 25, with qualitative genetic differences as indicated by the emergence of new genetic factors, and quantitative differences as indicated by fluctuations in the heritability during this period. The heritability of aggressive behavior was highest around age 12 (.74) and then decreases to about .40 to .50 throughout life. After age 25, no new genetic factors contribute to individual differences in aggression, such that the genetic architecture of aggressive behavior does not change throughout the remainder of the lifespan. These findings have implications for understanding the etiology of aggressive behavior from a developmental perspective.