Tables 8.1 and 8.2, respectively, summarize a large selection of twin and sibling adoption studies which have specifically examined the genetic and environmental influences on aggressive behavior in child, adolescent, and adult samples. Several studies use prospective, longitudinal designs, and large samples, and three of the twin studies were designed, in particular, to study aggressive and antisocial outcomes. All three of these studies are ongoing. One of these is the University of Southern California Twin Study of Risk Factors for Antisocial Behavior (RFAB), which is a prospective study of the interplay of genetic, environmental, social, and biological (psychophysiological) factors on the development of antisocial and aggressive behavior from childhood to emerging adulthood. The project includes more than 750 twin pairs studied on several occasions, at ages 9–10, 11–13, 14–16, and 17–18 years (Baker et al., 2006). A second major twin study is the Environmental Risk Longitudinal Twin Study (E-risk study) in the United Kingdom. The E-risk study involves data on more than 1000 twin pairs at ages 5, 7, and 12 with the special focus on what factors in the
