Genetic Aspects of Temperamental Differences in Infants: A Study of Same-Sexed Twins, by Anne Marie Torgersen, Ph.D, and Einer Kringlen, M.D

Abstract

A sample of 53 same-sexed twin pairs has been studied at 2 and 9 months with regard to the temperamental attributes of activity level, rhythmicity, approach/withdrawal, adaptability, intensity, threshold, mood, distractibility, and attention span/persistence. By comparing the MZ and DZ groups, we found that genetic factors play an important role in the development of temperamental characteristics. In all the temperamental variables measured, MZ twins were more similar than DZ twins, statistically significant with regard to three temperamental categories at 2 months, and significant for all temperamental variables at 9 months.