Twins' responses to pleasant, unpleasant, and life events.

Pairs of monozygotic (n = 41) and same-sex dizygotic (n = 29) twins were administered the Pleasant Events Schedule, the Unpleasant Events Schedule (Lewinsohn & Amenson, 1978), and the Life Experiences Survey (Sarason, Johnson, & Siegel, 1978). These provided indices of both the frequency of and the emotional response to mood-related events. Monozygotic twins resembled one another more than dizygotic twins on all subscales of these measures, and the greater similarity was statistically significant for most of the subscales. This suggests that there may be a genetic influence on affect, which is expressed through both the frequency of engagement in and the emotional response to mood-related events. The results are discussed in the context of studies of genetic influences on subclinical levels of depression and other emotions.