The American Psychiatric Association (APA) has updated its Privacy Policy and Terms of Use, including with new information specifically addressed to individuals in the European Economic Area. As described in the Privacy Policy and Terms of Use, this website utilizes cookies, including for the purpose of offering an optimal online experience and services tailored to your preferences.

Please read the entire Privacy Policy and Terms of Use. By closing this message, browsing this website, continuing the navigation, or otherwise continuing to use the APA's websites, you confirm that you understand and accept the terms of the Privacy Policy and Terms of Use, including the utilization of cookies.

×
Published Online:https://doi.org/10.1176/ajp.127.12.1597

This report, part of a longitudinal study of ten pairs of twins, delineates personality differences that appear in the first year of life, especially in the areas of dependence-independence, emotionality, sociability, curiosity, and activity-passivity. Other variables that differentiate twins include: birth order, birth size, neurological competence, occurrence of a significant traumatic experience, parental "linkage," and physical development. The findings are discussed in relation to studies of normal development and studies of adult twins discordant for schizophrenia. Although twinship is a special circumstance, the authors believe that the observations of this study are probably valid for personality development in general—more obviously with siblings or dizygotic twins, more subtly with the only or firstborn child.

Access content

To read the fulltext, please use one of the options below to sign in or purchase access.