Sources of human psychological differences: The minnesota study of twins reared apart

Since: 1979, a continuing study of monozygotic and dizygotic twins, separated in infancy and reared apart, has subjected more than 100 sets of reared-apart twina or triplets to a week of intensive psrch0logical and physio logical assessment. Like the pnor, smaller studies of monozygotic twina reared apart, about 70% of the variance in IQ was found to be associated with genetic variation. On multiple measures of personality and temperament, occupational and leisure-time interests, and social attitudes, monozygotic twins reared apart are about as similar as are monozygotic twina reared together. These findinl!;s extend and support those from numerous other twin, family, and adoption studies. It is a plausible hypothesis that genetic diJferences a1fect psychological dilterenccs largely indirectly, by influencing the effi:ctive environment of the developing child. nus evidence for the strong heritability of most psychological traits, sensibly construed, does not detract from the value or importance of parenting, education, and other propaedeutic interVentions.