When people think of long-term relationships, they usually think of parents and spouses. But the most lasting relationship is with siblings, says behavioral specialist Tom Lee.

Lee, a family and human development specialist in the Utah State University College of Family Life, said, "We knew our brothers and sisters before our spouses and will likely be associated with them longer than our parents."Several of the year's most popular movies deal with relationship conflicts between brothers and sisters. For most people sibling relationships are the longest and least well-defined relationship in their lives, he said.

"These relationships have the potential to be warm, supportive and to provide a sense of security and belonging. Although most adults see their siblings infrequently, they remain an important kinship throughout the years," Lee said.

Studies disclose that the majority of adult siblings feel close to each other emotionally, share a sense of responsibility towards each other and would like to live closer to each other.

Despite their indicated feelings, nearly half those surveyed only saw their siblings once or twice a year.

Lee said holidays are the usual times when people maintain ties with brothers and sisters. As families move, pursue careers and have their own children, ties with siblings become secondary.

Although research indicates that visits are infrequent, Lee said siblings still provide each other with an important sense of belonging and shared history.

"Even though most of the adults surveyed had never asked a sibling for help during a money or health crisis, many said they could, if needed. They also said they would, in turn, help a brother or sister if necessary."

Although this sense of security is hard to measure, it is nevertheless valuable in an insecure world, Lee said.