The Relationship Code is the report of a longitudinal study, conducted over a ten-year period, of the influence of family relationships and genetic factors on competence and psychopathology in adolescent development. The sample for this landmark study included 720 pairs of same-sex adolescent siblings-including twins, half siblings, and genetically unrelated siblings-and their parents.

Using a clear expressive style, David Reiss and his coinvestigators identify specific mechanisms that link genetic factors and the social environment in psychological development. They propose a striking hypothesis: family relationships are crucial to the expression of genetic influences on a broad array of complex behaviors in adolescents. Moreover, this role of family relationships may be very specific: some genetic factors are linked to mother-child relationships, others to father-child relations, some to relationship warmth, while others are linked to relationship conflict or control. The specificity of these links suggests that family relationships may constitute a code for translating genetic influences into the ontogeny of behaviors, a code every bit as important for behavior as DNA-RNA.