Cynical hostility in adult male twins.

The heritability of hostility as measured by the Cook and Medley Ho scale was assessed in an adult male sample of 60 monozygotic and 61 dizygotic twin pairs. For the total Ho scale, as well as its health predictive component, the results were consistent with a moderate genetic effect. Results are discussed in terms of genetic and environmental influences on the development of this trait, and possible genetic contributions to the association between hostility and subsequent health.