Behavioural genetics and temperament.

Three recent developments in behavioural genetics are relevant to temperament research. First, the search for genetic influences on temperament has been frustrated by the finding that twin studies using self-report and parental rating instruments detect a genetic influence for all personality traits whereas twin studies using objective assessments rarely find a genetic influence. Secondly, environmental influences salient to temperament appear to operate in such a way as to make members of a family (siblings, for example) as different from one another as are individuals in different families. The importance of such 'E1', or non-shared, environmental influences suggests the need for studies of more than one child per family. Thirdly, adoption studies are needed to complement the extensive research on temperament in twins. In addition to its usefulness in isolating genetic influences, the adoption design can study environmental influence devoid of the confounding effects of hereditary influences; it can also isolate interactions between genotypes and environments. Preliminary results from the Colorado Adoption Project show little relationship between the temperaments of adopted and non-adopted one-year-olds and the personality characteristics of thier parents. Measures of the home and family environment did not relate to infant temperament, and no genotype-environment interaction was detected.