Personality similarity in unrelated look-alike pairs: Addressing a twin study challenge

Numerous twin studies have demonstrated genetic influence on personality traits, yet twin methods continue to be challenged. A common misconception is that monozygotic co-twins’ personality resemblance results from similar treatment by others, due to their matched physical appearance. The present study brings unique evidence to this question by assessing the similarities in personality and self-esteem of 23 pairs of unrelated look-alike individuals. Intraclass correlations for the Big Five personality traits (r_is = −.27 to .29) and the Rosenberg Self-Esteem Scale (r_i = −. 03) demonstrated little within-pair resemblance. It is concluded that (1) MZ co-twins’ personality similarity mostly reflects their shared genes, and (2) reactive gene-environment correlation best explains MZ co-twins’ similar treatment by others.