Genetic Influences
Though sometimes criticized, the evidence is pretty clear from studies of monozygotic
and dizygotic twins who were separated at birth and reared apart that many important psychological
variables are associated with genetic variation (Bouchard, Lykken, McGue,
Segal, & Tellegen, 1990). In summarizing the results of his research, Bouchard (2004)
reported that even vocational interests had a substantial genetic basis. The heritability coefficients
range from a low of .31 for the Enterprising interest to a high of .39 for the Artistic
interest. Schizophrenia has a heritability coefficient of .80, and the coefficient for intelligence
at age 26 is .88