prominence of family systems theory, with its focus on different sub-systems of the family, and to the interest in behavioral genetics. Studying siblings offers an ideal opportunity to examine the aspects of the environment that family members share in common (e.g., shared environmental influences) and the aspects that are not shared (e.g., non shared environmental influences). Moreover, sibling relationships are highly salient to adolescents; early adolescents have more conflicts with siblings than with anyone else (e.g., fathers, grandparents, friends, or teachers) except maybe mothers, but relationships with brothers and sisters are also important sources of companionship, affection, and intimacy. The quality of the relationship has been found to vary by birth order. Older siblings are perceived as more domineering and more nurturing than are later-born siblings, while later-born siblings admire and feel closer to their older brothers and sisters than their brothers or sisters feel toward them. Like relationships with parents, relationships with siblings are transformed during adolescence to become more egalitarian, less asymmetrical, less conflictive, and less close, most likely because siblings spend less time together as they get older.
The research has shown that better relationships with brothers and sisters lead to better adjustment during adolescence. Even after controlling for level of parental and peer support, greater support from brothers and sisters has been associated longitudinally with lower levels of internalizing problems for both younger and older adolescents and with less externalizing behavior, particularly when girls perceive more support from an older brother. At the other extreme, however, sibling similarity in problem behavior, early sexual activity, and drug use suggests that older siblings’ involvement in these behaviors is a risk factor for younger siblings.
Much attention has focused on parents’ differential treatment of their offspring as an example of non-shared environmental influences. Both parents and siblings perceive parents as treating siblings differently, although it is found that the majority of early adolescents in their sample perceived their parents’ differential treatment as fair and justified on the basis of age, personality, and need. Nevertheless, parents’ differential treatment has been found to affect siblings’ development and adjustment. The effects of parents’ differential treatment persist even after controlling for the effects of parenting, particularly when parenting is low in warmth or high in negativity. Parents’ (and particularly fathers’) differential treatment has been associated with higher levels of negative behavior between siblings.
Similarities and differences in siblings’ behavior and relationships with parents also have been of interest and have been explained within two competing theoretical frameworks. According to social learning theory, older siblings may serve as models for younger siblings; the research indicates that older siblings are seen as more effective models only if younger siblings perceive their older siblings as likable and nurturing, so that the younger sibling wants to be around and learn from them. In contrast, sibling deidentification theory posits that adolescents respond to parents’ differential treatment by defining themselves as different from each other, pursuing different domains of competence and interest to avoid comparison and rivalry. Research indicates that sibling deidentification is more frequent and intense among siblings who are more similar in gender, age, and birth order and may be especially salient during adolescence because of the developmental salience of identity development.
In addition, siblings may establish different relationships with their parents as away to improve the quality of their relationships with each other and, perhaps, reduce sibling conflict and rivalry. Increasing differentiation in siblings’ relationships with parents during adolescence has been associated longitudinally with increased warmth (between both siblings) and decreased conflict and competition among first-but not second-born adolescents. These effects also vary developmentally. Experts found that regardless of birth order, maternal warmth declined when children reached early and middle adolescence, and conflict increased for both siblings when the first-born transitioned into adolescence.
Most research has focused on the effects of parent-adolescent relationships on sibling relationships, but recent research has begun to focus on sibling influences on parent-adolescent relationships. This research has demonstrated that parents’ prior childrearing experience with their first-born siblings influences their expectations, behavior, and relationships with later-born offspring when they reach adolescence. For instance, parents’ experiences with their first-born children influences their expectations for their younger child’s adolescence, even with the effects of temperament controlled. Furthermore, parents have less conflict with and greater knowledge of daily activities for later-born than first-born adolescents. Longitudinal designs that examine changes in siblings’ relationships with each other and with parents at the same chronological age or developmental transition hold particular promise for unconfounding developmental and sibling effects.
