Research on the role of heredity in temperament indicates that
◦ heritability estimates derived from twin studies suggest a major role for genetic factors in temperament and personality.
◦ identical twins are more similar than fraternal twins across a wide range of temperamental traits and personality measures.
◦ only 5 to 10 percent of individual differences in temperament have been attributed to differences in genetic makeup.
◦ heritability estimates are much higher for expressions of positive emotion than for negative emotion.