Answer to Question 1
D
Answer to Question 2
Is there a hereditary basis for mental illness? Might some people be genetically predisposed to commit deviant or antisocial acts? Although these ideas seemed absurd 30 years ago, it now appears that the answer to both questions is a qualified yes.
Consider the evidence for schizophreniaa serious mental illness, characterized by severe disturbances in logical thinking, emotional expression, and social behavior that typically emerges in late adolescence or early adulthood. A survey of several twin studies of schizophrenia suggests an average concordance rate of .48 for identical twins but only .17 for fraternal twins (Gottesman, 1991). In addition, children who have a biological parent who is schizophrenic are at increased risk of becoming schizophrenic themselves, even if they are adopted by another family early in life (Loehlin, 1992). These are strong indications that schizophrenia is genetically influenced.
Because identical twins are usually discordant (that is, not alike) with respect to mental illnesses and behavior disorders, environment must be a very important contributor to these conditions. In other words, people do not inherit behavioral disorders; instead, they inherit predispositions to develop certain illnesses or deviant patterns of behavior. And even when a child's family history suggests that such a genetic predisposition may exist, it usually takes a number of very stressful experiences (for example, rejecting parents, a failure or series of failures at school, or a family breakup due to divorce) to trigger a mental illness (Plomin & Rende, 1991; Rutter, 1979). Clearly, these findings provide some basis for optimism, for it may be possible someday to prevent the onset of most genetically infl uenced disorders should we (1) learn more about the environmental triggers that precipitate these disturbances while (2) striving to develop interventions or therapeutic techniques that will help high-risk individuals to maintain their emotional stability in the face of environmental stress (Plomin & Rutter, 1998).