Genetic and environmental mechanisms determining intelligence, neuroticism, extraversion and psychoticism: an analysis of Irish siblings

Traditional theories of psychology have held that a child's personality is greatly influenced by the parents' child-rearing style. However, recent studies have suggested the opposite, indicating an absence of effect on the long-term personality of the child, regardless of whether the parents are authoritarian or liberal, punitive or permissive, and sociable or withdrawn. Whatever effects are exerted by child-rearing practices, they appear to occur before puberty. Another issue is the effect of upbringing on intelligence; research suggests that child-rearing style has more influence on intelligence than on personality. This study was designed to test the theory that the family environment does affect intelligence more than personality. The subjects were 386 pairs of young adolescent (ages 11 to 16) Irish siblings. They were given a vocabulary test and a personality inventory. The correlations between siblings were as follows: 0.48 for intelligence, 0.31 for extraversion, 0.14 for psychoticism, and 0.06 for neuroticism. This indicates that the correlations for the three personality traits were considerably lower than the correlation for intelligence. Since the three personality-trait correlations vary in magnitude, they may result from different combinations of genetic and environmental factors. Based on the low correlations, it was concluded that neuroticism and psychoticism were not influenced by the shared family environment. The authors concluded that environment does appear to influence extraversion, and even more strongly, intelligence, but genetic factors probably contribute to the correlations between siblings as well. (Consumer Summary produced by Reliance Medical Information, Inc.)