Brothers and sisters can have both positive and negative effects on each other's development.
- Older siblings are "agents of socialization," passing along behaviors to younger siblings.
- Parents playing favorites often taints sibling relationships.
- Only children go through different socialization processes.
Whether the overachieving oldest, the lonely middle or the rebellious youngest, siblings' traits rub off on one another in the long run, according to a new body of research published in the journal New Directions for Child and Adolescent Development.
Only children, meanwhile, often go through a different process of socialization.
"I can't say only children won't develop these competencies, but they're going to learn them through different relationships," said Laurie Kramer, a professor of applied family studies at the University of Illinois and co-editor of the journal volume on siblings.
Until recently, the impact of sibling socialization remained largely ignored compared to parent-child relationships.
"Parents are very, very important, but [focusing solely on parents] overlooks the fact that 70 to 80 percent of kids in the U.S. are growing up with other children in the family," Kramer said "Those opportunities for interaction or experiencing the same life events are very powerful."
Older siblings particularly serve as "agents of socialization" who teach younger siblings by example about informal social behaviors, such as how to act around friends. Younger siblings are highly susceptible to acquiring older siblings' negative habits, including underage drinking and smoking.
However, younger siblings with diverse interests or more dominant personalities can affect older siblings similarly.
Age difference and gender, which might normally preclude friendships, don't hold as much sway in forming sibling relationships.
"I tell parents to not worry so much about whether you have two girls, or two boys and a girl and what the age differences are," Kramer said. "Don't worry so much about what you're working with."
Parents certainly aren't absent from sibling dynamics, either, and children are acutely aware of preferential treatment.
"Siblings report that what bothers them is when parents play favorites, especially in an ongoing fashion," said Katherine J. Conger, an associate professor of family research at the University of California, Davis, who co-edited and published research in the recent journal volume on siblings.
"Social comparison can also be hurtful if parents are always holding up Suzy as the smart one, and why can't you be more like your sister?" Conger said.
But teaching parents and children how to foster positive social interactions at home can promote healthy sibling relationships for life.
Working with children as young as four years old on conflict management, emotionality and perspective, Kramer has witnessed promising changes in sibling relationships.
Conger agrees with Kramer's findings.
"Siblings can learn to play cooperatively and even unlearn conflicting patterns of behavior from a very young age," Conger said. "But part of it is re-training parents so that they also promote positive social interactions and don't just respond to squabbles with the age-old 'just leave your sister alone!'"