Genetic and Environmental Influences on Temperament The Polish-German Twin Study, Based on Self-Report and Peer-Rating

Among the criteria for a personality paradigm the following three are the most crucial: biological basis (e.g., genetic contribution to the phenotypic variance), universality (existence of traits in different cultures) and reality (possibility to measure traits by different methods). The present study combines all three criteria to explore the impact of genetic and environmental factors on temperamental traits, as stipulated by Strelau's regulative theory of temperament, across two culturally different samples (Polish and German), and by means of two diagnostic methods (self-report and peer-rating). The analysis was conducted on data obtained from 1009 same-sex pairs of twins (German sample) and 546 same-sex pairs of twins (Polish sample). For each subject the self-report as well as rating from two independent peers was recorded by both the Polish and German versions of the Formal Characteristics of Behavior-Temperament Inventory. Results demonstrate substantial heritability of temperamental traits, although average peer-rating tends to provide lower heritability estimates than self-report (for six traits M = 33% and M = 46% of the total variance, respectively). After separating the error variance from the effect of nonshared environment for both methods (self-report and peer-rating) and both samples, joint analysis indicated a very high impact of genetic factors (the average raised up to 66% of the total variance). No significant "sample" effect was found, so that we may allows to conclude that temperamental traits are determined in both cultures to the same extent by genetic factors.