In an attempt to break away from the problem of similar environments affecting the results of these studies, some psychologists have advocated the use of adoption studies which, it is believed, may offer the opportunity of comparing the individual with both their biological and adopted parents. An answer to the problem of causation may come from the diathesis-stress model, which attempts to provide an interactionist explanation for crime with the biological factor providing the diathesis or predisposition towards crime and a social or psychological factor providing the stressful event that could act as the trigger for the predisposition to become exposed. Even in modern times, similar arguments about the use of eugenics have tended to focus on minority ethnic groups due to their supposed heavier involvement with crime and have led some to argue for licences to allow some to reproduce while excluding others.