Ressemblances et dissemblances au sein de couples gemmellaires

This study belongs to the current of research using the method of twins. It aims at assessing the relative importance of genetic factors and nosological influences in the determination of personality components, and the fluctuations of their interaction as a function of the chronological variable. Besides an intelligence test (Raven's Progressive Matrices, two personality tests were used. The latter were projective techniques, one verbal (Rorschach's test) and one kinesigraphic (Mira y Lopez's MPK test). They were given to 28 pairs of monozygotic twins (MZ) and to 27 pairs of dizygotic twins (DZ) with equal proportion of both sexes. The subjects were grouped into two age classes : 14 to 22 and 25 to 65 years. It is at level of intellectual processes that the character of inneity appears at best : for the Progressive Matrix, the differences between raw scores for MZ partners are significant less of intelligence than those for DZ partners. However, with aging the type important is increasingly submitted to environmental factors. Intratension and extratension, as evaluated by the MKP test, as well as introversivity and extraversivity, as evaluated by the Rorschach test, also constitute dimensions of personality the innate character of which appears obvious : deviations for young MZ partners are significanttly less important than those existing for their homologous DZ partners. A certain amount of other dimensions of personality such as aggressivity emotional control, inhibition, possesses on the contrary a genetic determinism that is overshadowed by other intervening factors : significant differences are found for MZ adults only. These results are discussed with reference to the opinion that at the adolescence - a period of crisis - the twin bond especially of the MZ kine would constitute a powerful nosological force leading to differentiation from the partner.