the behaviors of the MZ twin pairs are likely due to environmental influences. A second type of human study extends the twins reared apart design by incorporating non-twin siblings who were placed in separate adoptive homes. One existing study examined siblings’ criminal behavior and found that conviction rates of siblings were similar despite the fact that they were reared apart, especially when their biological father had a court conviction (Mednick, Gabrielli, & Hutchings, 1984).
