Characteristics of adolescents' groups are especially highly heritable, such as the peer group's academic orientation or their delinquency. The reason for this high heritability may be that you can choose your friends but you cannot choose your family, as Harper Lee wrote in 'To Kill a Mockingbird.' You passively share genes with your parents and siblings, which leads to correlations between genes and your family experiences. With friends, you can select individuals similar to you genetically, actively creating correlation between your genes and your experiences with friends. 'Blueprint. How DNA makes us who we are' - Robert Plomin