| Abstract: | Genetic and environmental sources of continuity and change in aggression were studied in a sample of 1,041 twin pairs (364 monozygotic; 348 same‐sex dizygotic; and 329 opposite‐sex dizygotic) as part of an ongoing, population‐based Finnish twin‐family study. At ages 12 and 14, the twins' aggression was assessed by their classroom teachers, using a rating form of the Multidimensional Peer Nomination Inventory. Genetic and environmental sources of continuity and change were studied by fitting a longitudinal bivariate Cholesky decomposition model. Longitudinal model‐fitting results indicated that both genetic and environmental factors influenced continuity in aggression during this 2‐year period, but the age‐to‐age correlation of these factors differed by sex. Continuity in boys' aggression was mediated by genes and common environmental factors; in girls, in contrast, continuity was due primarily to common environmental, and to a lesser degree, unique environmental factors. Genes and unique environments contributed to change in aggression in both sexes. Aggr. Behav. 31:1–13, 2006. © 2006 Wiley‐Liss, Inc. |
