Child Development, November/December 2002, Volume 73, Number 6, Pages 1761–1774 Adolescent Twins and Emotional Distress: The Interrelated Influence of Nonshared Environment and Social Structure Robert Crosnoe and Glen H. Elder, Jr. This study examined the power of nonshared environment to differentiate the development of adolescent monozygotic twins, and the extent to which this power varied across social structural contexts (e.g., ethnicity, socioeconomic status). Estimation of difference score models on 289 same-sex monozygotic twin pairs from the National Longitudinal Study of Adolescent Health revealed that differences in maternal closeness, teacher bonding, and religious participation differentiated monozygotic twins on emotional distress, with the more distressed twin typically lower on all three. Family income was the strongest structural moderator of these re- lations, with parental autonomy granting more important in higher income families and religious participation more important in lower income families. Finally, in some groups, one monozygotic twin’s emotional distress was also associated with the other twin’s familial and extrafamilial relationships. The results of this study demonstrate that interpersonal contexts can shape monozygotic twins’ individual experiences within the structure of the larger society. INTRODUCTION In recent years, behavioral genetic research on the so- cioemotional similarities of siblings and twins has sparked a new wave of developmental research that focuses on the differences among these pairs (Hether- ington, Reiss, & Plomin, 1994). Such differences offer key insight into the nature of development. Siblings, especially monozygotic twins, are born into the same family and share genetic material, but they do not necessarily lead similar lives. By choice, chance, or constraint, they enter into different groups in differ- ent settings, and, in the process, form different social ties. These nonshared aspects of environment may lead to divergence in adjustment, such as differences in emotional health (Reiss, Neiderhiser, Hethering- ton, & Plomin, 2000). Moreover, the impact of these nonshared environmental elements may differ by structural location, with such factors as ethnicity and family socioeconomic status (SES) moderating the differentiating power of microcontexts (Gutman & Eccles, 1999). The present study explored two general avenues: (1) the power of nonshared environment, within and outside the family, to differentiate same-sex monozy- gotic twins on emotional distress; and (2) the varia- tion of this differentiating power by social structural context. The National Longitudinal Study of Adoles- cent Health (AddHealth) was uniquely suited to the task, because it is an ongoing study that contains a subsample of siblings, including a sizable portion of monozygotic twins; provides extensive information on micro- and macrocontexts; and is diverse enough to study processes across diverse groups. Such research adds to the developmental literature in key ways. Unlike most studies in this area, the present study moved beyond the family to explore other important microcontexts such as the school and church, and how the developmental influences of these more proximate contexts were related to structural contexts (e.g., ethnicity, gender). By focusing exclu- sively on monozygotic twins, this study controlled for the important role of genetic relatedness in the link- age between nonshared environment and siblings’ emotional health (O’Connor, Hetherington, & Reiss, 1998). Examining the individual trajectories of ado- lescent monozygotic twins and bringing together multiple levels of influence offers insight into adoles- cent development by focusing on the complex inter- dependence of lives (in and out of the home) and the embeddedness of lives in the larger structure of society. The Study of Twins and Nonshared Environment Twin research has mostly been the domain of be- havioral geneticists, who use quantitative methods to partition phenotypic variance into environmental and genetic components. The sibling cascade, in which similarity in some factor varies as a function of ge- netic relatedness (e.g., between monozygotic twins and full siblings), illustrates the general principle of such research. The techniques of this field provide one method for developmentalists to study the com- plex role of genetics (Reiss et al., 2000). © 2002 by the Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2002/7306-0010