In general, genetic studies of twins, including adoption and cross-fostering studies, suggest that the disposition to behave in a delinquent or criminal fashion is at least partly a function of biological inheritance. Research into the relationship between genetic abnormalities and delinquency has not produced consistent results. Despite evidence for a genetic contribution, information about the characteristics transmitted is vague and confounded by environmental variables. Attempts to demonstrate that delinquents are poor learners or are resistant to conditioning have generally not been successful. However, there is some evidence to suggest deficits in their aversive inhibitory conditioning. Additional research into autonomic nervous system functioning of delinquent populations suggests that slowed electrodermal recovery may play a role in individual difficulty in acquiring conditioned inhibitory responses. Approximately 120 references.