What made you study siblings?
Bank: We simply couldn't answer some of the questions our patients were asking. We could not account for why siblings fight at certain times. We didn't understand the ambivalence of the love-hate relationship.
Kahn: We saw repeated examples of siblings who are loyal, caring and nurturing. It didn't square with the idea that they could only be rivalrous.
What do you mean by sibling "bond"?
Bank: It's a relationship which flourishes when there is a vacuum of parental care. The kids turn toward each other and become stand-in parents. Brothers and sisters who have shared the same bedroom, the same dog or the same friends develop a special closeness and sometimes a special misery. The most intense bonds won't occur if Mom and Dad give the kids what they need.
Do you mean bonding will occur only with indifferent or abusive parents?
Bank: No, but when the world caves in, your parents are beating you both up, and there's no one else to turn to, people need contact; and just as Hansel and Gretel did, brothers and sisters can usefully turn to each other.
So sibling bonding can be good or bad?
Kahn: It can be positive if you're living in a hostile world such as siblings in a concentration camp or in a neighborhood where the other kids are brutal.
Bank: It can be negative if the kids are too close. If kids are pushed together by parents and not allowed to develop into separate people, they drag each other down. This might occur if, for example, a 7-year-old and an 11-year-old have the same bedtime, or if parents insist a handicapped child keep up with a normal child.
How common is sibling incest, which is a type of bond?
Kahn: It is estimated that it occurs with 25 people out of 1,000—five times more frequently than parent-child incest. There are two kinds. One is rapacious, where an older, more powerful sibling takes advantage of the younger. If incest becomes nurturing—the other type—it could last for years.
Bank: An older boy using his younger sister is dangerous. But in the erotic, nurturing kind of incest, these kids are reaching out. Sibling incest is not a sign of perversion or sinfulness. It's a sign the whole family needs help in finding good ways to show love.
Should parents stop kids from fighting?
Bank: Parents have been blamed too much for the struggle between children. Youngsters have a way of making each others' lives difficult, even though the parents wish they would get along. Aggression can teach kids to be good winners and losers.
When should parents intervene?
Bank: When it becomes physically damaging or humiliating to one child, when one degrades the other in front of friends. It's a delicate balance. A parent has to let the kids work it out even when the shouting gets loud.
What problems does a healthy child face with a troubled sibling?
Kahn: Well-adjusted siblings often fear that what troubles the other is contagious. They're often torn between the wish to get away and guilt about abandoning brother or sister.
Does the sibling bond weaken once kids leave the nest?
Kahn: Parents die but the sibling, for better or worse, is somehow there. People derive comfort from having siblings, even if they never speak to them. They may hate each other, but they get together for holidays.
If siblings hate each other as children, can they ever become friends?
Bank: Yes, but it takes a commitment on one sibling's part to decide it's important enough to shake up a longstanding relationship. Accept small changes and meet on neutral turf, not in the parents' home, so you won't play out the same old movie. Open yourself to how the other person feels. Don't feel guilty about what you did as a child.
How can parents encourage healthy sibling relationships ?
Kahn: Encourage kids to be separate and unique but not at the expense of another person. They should be close, so they can learn from each other, but not so close they fuse.
After doing all your research on siblings, did either of you wish that you had come from a larger family?
Kahn: People who want to know about being siblings should write a book together. Working with Steve was like having a brother. We struggled, we sometimes competed, but we cared.
"Parents are shapers of personality," says Michael Kahn, but "siblings are powerful forces, too." That's why Kahn and fellow psychologist Stephen Bank spent eight years interviewing some 1,000 brothers and sisters for a major new study, The Sibling Bond (Basic Books, $16.95). They found that feelings and attitudes established between siblings in childhood—whether expressed through rivalry, loyalty or incest—often continue throughout life. What fascinated the researchers especially was the deep bond that can develop among youngsters when a parent disappears through death or divorce, becomes abusive, or is emotionally out of contact. Kahn, 46, who teaches psychology at the University of Hartford, and Bank, 41, who teaches at Wesleyan University, met at the University of North Carolina, where each received his doctorate. Bank has one younger sister ("We're becoming closer as adults as we have more in common"), and Kahn was an only child. Both have children: Bank and wife Elaine, a real estate manager, have two; Kahn and wife Ruth, a special education consultant, have three. The psychologists talked about their findings with PEOPLE'S Lynne Baranski.