Behavior Genetics

, Volume 18, Issue 3, pp 309-328

First online:

Frequency of social contact and intrapair resemblance of adult monozygotic cotwins—Or does shared experience influence personality after all?

  • Richard J. RoseAffiliated withDepartment of Psychology, Indiana University
  • , Jaakko KaprioAffiliated withDepartment of Public Health, University of Helsinki

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To establish effects of shared experience on adult personality resemblance, we evaluated intrapair resemblance for short-form Extraversion (E) and Neuroticism (N) scale scores in 2320 pairs of adult monozygotic (MZ) twins who were classified by the frequency of their social interactions with one another. Our analysis parallels MZ cotwin control designs, where environmental differences within pairs provide an incisive measure of idiosyncratic experience, unconfounded by genetic differences; here, experiential differences between MZ pairs yield a sensitive measure of shared experience, again free of genetic confounds. We found that MZ pairs in more frequent interaction were significantly more alike for both personality dimensions. Hierarchical multiple regressions evaluated effects of social contact on intrapair similarity after the influence of both age and gender were removed; results confirmed that social interaction significantly contributes to the prediction of a twin's E or N scores from those of the cotwin. Finally, for both these MZ twins and 4824 agematched DZ (dizygotic) twin pairs, adult resemblance was associated with the age at separation. These data, obtained from a nonselected, population-based cohort of twins, challenge the widespread assumption that experiences shared by siblings make little or no contribution to similarities in their adult personalities.

Key Words

monozygotic (MZ) twins intrapair resemblance extraversion neuroticism