When Monica Buckley was growing up in a family of eight kids, she and her three-years-older sister, Laurie, competed for everything: boyfriends, clothes, and even their mother's love.
"She and I tried to attract the same boy once, and for decades afterward she held negative feelings about my 'winning,' " said Buckley, 45, an editor at ABA Publishing in Chicago.
"I was shocked about 10 years ago when she was in town and having dinner with my family. I made a joke about this long-ago rivalry, and she blew up at me as if it had been only yesterday."
Yet in the years since that dinner, the sisters' relationship has mellowed.
They supported each other through the deaths of their parents and through their divorces. E-mail and instant messaging have helped cool down what had been a volatile relationship.
"We always loved each other very much, and we see, now that we are middle-aged, that those resentments of earlier times hold little power in the face of extraordinary life changes," Buckley said.
A variety of situations and events connected with aging can serve as catalysts for change in sibling relationships. As the years pass, we may learn to rejoice in one of our closest human connections and discover a deep desire to reconnect with estranged siblings.
Watching his parents age, Robert Billingham, 52, has found increased pleasure in the time he spends with his three brothers, ages 54, 50 and 48.
"As our parents become more fragile, we start to see ourselves in them and start to re-evaluate if it is really worth being angry with our siblings," said Billingham, a professor of human development and family studies at Indiana University.
In families where members have been fairly distant emotionally, or in conflict, the death of the older generation also may shock siblings with the realization that life is too short to carry grudges.
"When you connect with siblings, you have the sense that life continues through and am-ong you as opposed to in a linear fashion: 'Mom's dead and I'm next,' " said Marcia Spira, associate professor of clinical social work at Loyola University Chicago.
The illness of a sibling also can change attitudes.
One of Spira's patients, "Julie," had a sister, "Karen," who was seven years older. Karen was a high achiever in academics, athletics and music. Julie felt lost in her sister's shadow.
As adults, they went their separate ways. Karen launched a career, married and had two children; Julie, an artist, struggled alone to make ends meet.
When Karen was diagnosed with cancer at age 44, Julie came back into the family fold, Spira said. She returned to Chicago from the West Coast, began to advocate for Karen's care and eventually went to nursing school.
The death of a spouse also can influence sibling togetherness, said Laurie Kramer, professor of applied family studies at the University of Illinois, Urbana-Champaign.
Biological ties are very meaningful to people in our society.
Widowed sisters commonly turn to each other for companionship and deeper bonds grow between brothers and sisters, especially when one needs the other's support.
Siblings may move in together, share finances or care for one another.
"As people age they're more mature and accepting," Kramer said. "They acknowledge that life is short, and they are more appreciative of the goal of being there and supporting one another."
Florence Leff, 90, and her brother, Lou Begoun, 95, are widowed. Each lives alone in an apartment at Gidwitz Place for Assisted Living in Deer-field, Ill.
They always have been close, but aging has changed the balance in their relationship.
"I was always the kid sister," Leff said. "He always took care of me, but I take care of him now. When I go for breakfast, if he's not there, I sit and wait for him until he comes down so I know he's OK."
This article was written for the Chicago Tribune.