modeled in mice (and presumably all other nonhuman animals). Similarly, some DSM-IV (American Psychiatric Association, 2000) criteria such as “ a persistent desire or unsuccessful efforts to cut down or control substance use” and “the substance use is continued despite knowledge [emphasis added] of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance” (p. 197) may not be practical phenotypes to model in animals and therefore environmental variables that rely upon uniquely (or largely) human abilities to affect the phenotype may be impossible to model fully in any animal model. Finally, most experimental designs employed in behavior genetic research with animals incorporates enough subjects to detect main effects of genotype or treatment, but not their interaction (Wahlsten, 1991).
