7 Ways Your Siblings May Have Shaped You

Oh, how the world changed when his parents went out, leaving him in the hands of his big brother. "That was always a great opportunity for him to have fun, typically at my expense," he recalls. While he could stay up late and watch shows like Gunsmoke, those privileges came at a price. His brother spoon-fed him putrid concoctions from the fridge, once shocked him with a live wire, and another time wrapped him head to toe like a mummy, so that only his nostrils peeked out. "I didn't ever suffer permanent injury," he says, laughing. "Except maybe to my mind."

Ah, siblings: both a blessing and a curse. Approximately 80 percent of Americans have at least one brother or sister; in fact, kids today are more likely to grow up with a sibling than a father, experts say. What's more, the sibling relationship is the longest relationship that most people will have in their lives. Yet brothers and sisters have gotten short shrift in the research about what affects who we are and how we behave, experts say. They've been "amazingly neglected," says Judith Dunn, a professor of developmental psychology at King's College London.

Not least among those now paying attention are psychoanalysts, whose principal preoccupation has traditionally—and with good reason—been the powerful influence of parents. Many psychoanalysts now concede that people can be shaped as much or more by their siblings, says Jonah Schein, an associate clinical professor of psychiatry at the Weill Cornell Medical College who held a conference called "Missing: Siblings in Psychoanalysis" last fall.

"My brother certainly did have a big impact on my life," says Lew Bank, 61. Some 50 years after being mummy-wrapped in his parent's basement, Bank is a psychologist and a senior scientist at the Oregon Social Learning Center who studies siblings—an interest that was piqued in part by his strong relationship with his brother. Though the extent of the sibling influence varies greatly from family to family and person to person, "there's growing evidence to suggest that siblings shape each other in important ways," says Laurie Kramer, a professor of applied family studies at the University of Illinois at Urbana, Champaign. Here are a few:

• They may buffer stress. Warm sibling relationships can be protective, says Dunn, and seem to buffer kids against stressful events, like parents' separation.

• They provide good practice. Research has clocked the rate of sibling squabbles at anywhere between six to 10 disputes per hour for certain childhood age groups, says Kramer. While these conflicts can be a headache for parents, they can help kids make developmental strides in a "safe relationship" and provide good training for interacting with peers, says Kramer. "You know there's nothing really that you can do to make this [other] child terminate the relationship." No matter what, he'll be there tomorrow at the breakfast table. That safety enables siblings to practice behaving in ways they aren't able to with other people. Sibling spats help kids learn what they think is right; to negotiate and compromise; and to tolerate the negative emotions that crop up in life. "This is the bright side," Kramer says. "Obviously, there's an unpleasant side as well."

She adds, "Some evidence suggests that when kids have good relationships with siblings, they're more likely to develop good relationships with their peers." But we're still learning about that, she says.

• They may help raise our vulnerability to mental-health issues. Sibling strife during mid-childhood is a predictor of increased anxiety, depression, and delinquent behavior in adolescence, the University of Denver's Clare Stocker has reported. What's more, a 2007 study in the American Journal of Psychiatry found that men who had poor relationships with even one sibling before age 20 were significantly more likely to become depressed by age 50 than men who got along with their siblings, independent of their relationship with their parents. This effect may not hold true for women, who weren't included in the study, notes Robert Waldinger, an associate professor of psychiatry at Harvard Medical School and leader of the research.

• They can grease a slide into bad behavior. Drinking. Smoking. Delinquency. Some research suggests that siblings' bad habits rub off. "If you have a sibling who is participating in those types of activities, then you're at higher risk for participating yourself," says Katherine Jewsbury Conger, an associate professor of human development and family studies at the University of California-Davis who has studied those effects. Patricia East, a research scientist at the University of California's San Diego School of Medicine, has found that girls were more than four times more likely to become pregnant as a teen if a sister had a baby as a teen, compared with girls whose sisters weren't teenage moms.