According to the book "Sibling Identity and Relationships: Sisters and Brothers," siblings relationships -- even those that are strained or tumultuous -- are just as integral to identity formation as connections to parents. People develop concepts of themselves in relation to others. For instance, if your brother is excessively talkative and social, you may perceive yourself as quiet or introverted because, compared to him, you are not particularly outgoing. This perception then influences your personality -- you may develop into a quiet or pensive person far into the future.

Since they tend to consistently interact beginning at young age, siblings learn to socialize from one another. They learn which behaviors elicit attention, anger, concern and affection in others. They begin to understand the dynamics of manipulation and, ideally, manage to assert themselves to get their needs met. In an article for Psych Central about sibling influences on adult behavior, Dr. Rick Nauert states that, through one another, brothers and sisters come to understand how to behave at school and among friends. They can also begin to unravel the mysteries of opposite genders. Eventually, they may learn to resolve conflict through compromise and negotiation. These are skills that will assist them throughout life.

Brothers and sisters can assist each other with the development of healthy attachments. Everyone seeks human connection, which is often attained through relationships with parents. In situations where parents or caretakers are inadequate, neglectful or even abusive, siblings can turn to one another for affection. Even when parents and caretakers are nurturing and supportive, children might become overly attached. Siblings can interrupt this dynamic by providing companionship or distraction during times of separation from parents.

The developmental significance of siblings during childhood is undeniable. These relationships tend to be meaningful during adulthood as well. Although you may be separated by the demands of higher education, your careers, spouses and children, siblings' presence can still be a constant during times of success, celebration, crisis and grief. As losses increase with age, siblings rely on each other more and more for social support. Men and women both report that the support of sisters in particular greatly impacts their well-being, according to "Adult Sibling Relationships" through The Ohio State University Extension.