Sibling Relationships

Despite commonalties of shared factors such as social class; physical and mental health of family members; the parental relationship; the emotional climate of the family; and the child-rearing skills, values, and attitudes of parents, siblings are a good deal different from one another. Only about 50 percent of siblings' genetic background is shared. In terms of weight and height, they are about 50 percent similar, and the correlation between siblings and their IQ scores is only .47 as children and .31 as adults (Dunn and Plomin 1990). By comparing the shared and nonshared family experiences of siblings, it can be seen that differential treatment and expressions of affection and interest by parents and other kin, perceptions of this differential treatment by siblings, and the effects of peer groups and school experiences coalesce to create a separate "life" for each child growing up in the same family.