A DEVELOPMENTAL GENETIC-ANALYSIS OF ADULT PERSONALITY - EXTROVERSION AND NEUROTICISM FROM 18 TO 59 YEARS OF AGE

Developmental genetic analyses were conducted on Extraversion (E) and Neuroticism (N) scale scores from nearly 15,000 male and female Finnis h twins, ages 18-53 at baseline, who were tested on 2 occasions, 6 yea rs apart. Significant genetic effects on both traits were found, at al l ages, in men and women, on each measurement occasion. For E, heritab ility was invariant across sex but decreased from late adolescence to the late 20s, with a smaller additional decrease at about 50 years of age. Heritability for N also decreased from late adolescence to late 2 0s and remained stable thereafter. For all ages after the early 20s, h eritability of N was significantly higher among women. Means for E and N were sex-dependent and, apparently, influenced by cohort and time o f assessment, as well as by age. There was little evidence of new gene tic contributions to individual differences after age 30; in contrast, significant new environmental effects emerged at every age.