Individual differences in young children's understanding of others' feelings and in their ability to explain human action in terms of beliefs, and the earlier correlates of these differences, were studied with 50 children observed at home with mother and sibling at 33 months, then tested at 40 months on affective-labeling, perspective-taking, and false-belief tasks. Individual differences in social understanding were marked; a third of the children offered explanations of actions in terms of false belief, though few predicted actions on the basis of beliefs. These differences were associated with participation in family discourse about feelings and causality 7 months earlier, verbal fluency of mother and child, and cooperative interaction with the sibling. Differences in understanding feelings were also associated with the discourse measures, the quality of mother-sibling interaction, SES, and gender, with girls more successful than boys. The results support the view that discourse about the social world may in part mediate the key conceptual advances reflected in the social cognition tasks; interaction between child and sibling and the relationships between other family members are also implicated in the growth of social understanding.

Although a number of studies have shown that brothers are highly correlated for delinquent behavior, much less research has been conducted on sisters. We propose that sisters, like brothers, show notable similarity for delinquent behavior, and also promote each other's delinquency through direct interaction. We examined these issues in 164 brother and sister pairs studied over a 4-year period (from early to middle adolescence) in a study of intact families in the rural Midwest. Sibling similarity for self-reports of delinquent behavior were highly correlated for both brothers and sisters. Conditional effects of high levels of hostile-coercive sibling relationships and older sibling delinquency predicted younger sibling delinquency in both brother and sister pairs. For brothers, conditional effects were also detected for high levels of warmth-support, in contrast to sisters. The conditional effects of older sibling delinquency and relationship quality were shown to predict change in younger sibling delinquency through adolescence. The results add to a growing literature on sibling effects as well as theoretical models that emphasize the role of social interaction between siblings as a risk factor for the development of delinquent activity in adolescence.

Aims Behavioral genetic research has suggested that sibling effects on smoking may reflect social rather than genetic processes. We utilize a genetically informative sample of adolescents to test this proposition, focusing on sibling relationship processes (social connectedness) shown to be influential in studies of deviancy. Design A combined twin-sibling design was employed to disentangle genetic and non-genetic effects. Participants We utilized a sample of 1421 adolescent sibling pairs participating in the US National Longitudinal Study of Adolescent Health (Add Health). These sibling pairs represent a spectrum of genetic relatedness and include monozygotic twins, dizygotic twins, biological siblings, half-siblings and unrelated siblings. Measurements Participants completed self-report questionnaires on smoking behavior, quality of relationship with their sibling (social connectedness) and peer and parental smoking. Findings Main effects of both shared environment and genetics were found on adolescent smoking frequency. Social connectedness between siblings moderated shared environmental influences on smoking frequency at each time period, as well as on change in smoking frequency. Shared environmental effects were more pronounced when siblings reported high levels of social connectedness. These environmental sibling effects on smoking were significant after controlling for parent and peer smoking. Conclusions This report extends prior research on sibling effects on smoking by identifying specific relationship dynamics that underlie transmission of risk within sibships and providing evidence that such relationship dynamics represent social rather than genetic processes.

Stability and correlates of individual differences in children's relationships with their siblings between early childhood and adolescence were studied in 39 sibling dyads, using home observations and maternal interviews in the early childhood period and interviews with mothers and children at the later time points. Stability of individual differences found over the 7 years increased with age. The behavior of the other sibling in the preschool period related to both older and younger siblings' behavior at the last time point. Life events were associated with increased warmth between the children. By preadolescence, gender and socioeconomic status (SES) were related to differences in the relationship. Multiple regression showed that preschool measures of sibling interaction contributed independently of gender and SES to the variance in individual differences in positive aspects of the relationship at early adolescence.