effects may also arise through the environmental influences of other biological relatives (e.g., older siblings) or, less obviously, through selective friendship or mate selection effects (Jacob et al. 2001). For example, impulsive people might have a tendency to select other impulsive people as peers or partners. Because evidence suggests that genetic factors influence impulsive personality traits (e.g., Martin et al. 1979), such a “selective mating” process can create a positive genotype–environment correlation if the impulsiveness of such peers or partners in turn has environmental effects on the person’s behavior (e.g., alcohol use).
