双生児の環境に関する研究

抄録

This paper aims to scrutinize the differences in environment which are produced by the hereditary factors, by studying certain phases of the environment of twins in repect to intra-pair differences.
The subjects studied consisted of 25 identical, 23 like-sex fraternal and 9 oppositesex twin pairs enrolled from the 5th grade in elementary school to the 2nd grade in senior high school. The data were obtained by a combination of interview and questionnaire. The differences in environment were considered from the following two phases ; the one is the difference of life-situation such as the length, the frequency and the causes of their separation from each other, and the other is the difference of social relation such as their relation with their parents at home and with their friends.
In most of the phases of environment studied, intra-pair differences of fraternal pairs were on the average greater than those of identical pairs, and still greater differences were found among the twin pairs of opposite-sex than among those like-sex. (Table 1. 2.)
The differences in the environments of the fraternal pairs may be attributed to the influence of their different hereditary predisposition upon the individual's choice of environment.
The assumption that intra-pair differences in the environment of identical pairs are, on the average, equal to those of fraternal pairs has been made in many previous studies of twins. The author's study indicates that this assumption is not necessarily justified and some modifications should be made in those conclusions based upon the previous assumption.