This report deals with the nature-nurture problem in relation to some primary aspects of character in normal twins and siblings; namely, on 12 primary impulses, or propensities, whereon reports of detailed study are rare. These factors form the energetic side of any human being's behavior and thereby the native equipment in anybody's character: its units of composition. In agreement with Galton's dichotomy of intellect and character, the latter actually makes up the second half of our personality's organization: its motor area.

In the search for character roots through the interaction of heredity and environment, Galton was the first to bring out, through pedigree studies, the existence of noticeable hereditary components. However, as to inquiries by twin method, character is in a far less satisfactory status than any of the other heritable traits of personality. So far, we know neither the possible genetic stability of those primary impulses which in clinical experience passed for the most forcible, nor the degree of peristatic plasticity of those which might admittedly be the most docile.

A sample of 44 MZ and 41 same-sexed DZ twin pairs and 39 pairs of siblings were administered a standard battery of 120 questions of the Self-Rating Questionnaire type. For each pair, individual scores, as well as intrageminal differences, were worked out.