On personality difference and interdependent relationship in identical twins

Abstract

Purpose: To grasp personality differences in identical twins who have been growing up in the so-called “same environment” (with no organic defect) in connection with their interdependent relationship. Subjects: 18 pairs of twins, aged about 12 years, all were pupils of the Middle School attached to TokyoUni-versity. They consisted of 12 pairs of identical twins, 4 pairs of fraternal twins of the same sex and 2 pairs of fraternal twins of uni ike-sex. Procedure: 1) The behavioral characteristics and the differences between the twins (A and B) of each pair and the behavioral characteristics of the whole were outlined by observing their behavior at school for about half a year and during summer camp for a week. 2) Various personality tests were given. The children were asked to rate both themselves and their twins. The ratings given by each pair of twins were compared to determine the degree of agreement in their responses. 3) Three series of problem-solving experiments were conducted with both twins, participating conditions were changed and frustrating situations were presented so that the author could observe the response patterns, attitudes toward the goals and interdependent relationships. Results and Conclusions: 1) Though the high degree of personality resemblance of identical twins has been emphasized, from the bio-social point of view, considerable differences in fundamental behavioral characteri- sties were found. 2) The results obtained from various personality tests indicated that there were some differences between the identical twins but these were not so large as the differences found in fraternal twins. 3) In thinking about the causes of differences, the influence of their physical and physiological conditions must be considered. The writer observed that where large physical differences existed -there were also greater personality differences. 4) Identical twins who have been assigned definite roles of elder brother (A) or younger brother (B) within the family show greater fraternal personality differences. 5) The results of the problem-solving experiments indicated that generally speaking A was more independent and showed leädership, while B inclined to be dependent and submissive. In addition, the author was able to get some data on the co-operation competition relationships between A & B in frustrating situations. © 1969, The Japanese Association of Educational Psychology. All rights reserved.