siblings

Siblings are people who share at least one parent. The term encompasses full siblings (sharing both parents), half-siblings (sharing one parent), step-siblings (connected through remarriage), and adoptive or foster siblings. Sibling relationships begin in childhood but can persist across the life course, influencing family dynamics and individual development.

Genetic relatedness varies: full siblings about 50% of their genes; half-siblings about 25%; adoptive or step-siblings have no required genetic relation. Regardless of genetics, siblings often provide companionship and social learning opportunities, but can also experience rivalry, conflict, and competition for parental attention and resources.

Siblings influence development and behavior. Interactions with siblings can support language and social skills, empathy, and cooperation, though excessive rivalry can contribute to behavioral problems. Theories such as birth order have proposed patterns in personality and achievement, but evidence is mixed and context-dependent. Resource dilution theory suggests more siblings can dilute parental resources, while siblings can also serve as social tutors.

Cultural and family structures shape sibling roles. In many cultures, older siblings may take on caregiving responsibilities for younger children or for aging parents. Blended families, foster care, and adoption create diverse sibling networks with varying degrees of contact and legal recognition. Legal frameworks address guardianship, inheritance, and custody, which can affect sibling relationships in times of illness or death.

Across adulthood, many sibling relationships endure, providing support, shared memories, and mutual assistance, though closeness varies widely by individual history and life stage.