, 1992). Their findings make is wonder anew about the sources of our own individuality. Probably the best way to assess the relative contributions of heredity and environment to personality is to study identical twins that have been separated at birth and reared apart. When identical twins that were reared apart have strikingly similar traits, as in the case of Oskar and Jack, it is assumed that heredity has been a major contributor.In the Minnesota twin study, Tellegen and others (1988) found that the identical twins are quite similar on several personality factors regardless of whether they are raised together or apart. Heritability refers to the degree to which a characteristic is estimated to be influenced by hereditary. After studying heritability of trait in 573 adult twin pairs, Rushton and colleagues (1986) found that nurturance, empathy, and assertiveness are substantially influenced by heredity. Even altruism upbringing, were actually more heavily influenced by heredity. A meta-analysis by Miles and Carey (1997) revealed that the heritability of aggressiveness might be as high as .50 (or 50%).Twin studies have also revealed a genetic influence on social attitudes such as traditionalism-whether a person endorses traditional moral values and follows rules and authority (Finkel & McGue, 1997). The risk of divorce appears to have a heritability of .55 for women and .59 for men. This is not to say that there is a gene for divorce; rather, the risk derives from a genetic influence on certain personality factors (Jocklin et al., 1996). Genes also influence personality factors that correlate with psychological disorders as measured by the Minnesota Multiphasic Personality Inventory (DiLalla et al., 1996). There even seems to be a genetic influence on people’s sense of well-being (Lykken & Tellegen, 1996), their interests (Lykken et al., 1993), how they tend to view their environment (Chipuer et al., 1993), and how they perceive ...
