An overview of the areas of sibling research that laid the foundation for the modern understanding of sibling issues is presented. Attention is focused on the importance of sibling relationships for personal development, socialization and adaptation, and on the existing shortage of relevant work at the same time. The main stages of the development of sibling theory in their continuity are considered, starting from the first studies devoted to the search for a connection between the order of birth and achievements and dated to the end of the 19th century, to the term “individual environment” developed by the genetics of behavior in the second half of the 20th century. It emphasizes the role of A. Adler, who has made sibling a central feature of family life and personal development and has long determined the future direction of empirical family research. It shows a gradual shift in the interest of researchers from studying the influence of birth order, gender, and age intervals between siblings on personal characteristics. In this connection, an analysis of the nature of sibling relations on the basis of reciprocity and complementarity, undertaken by Dunn, is given. Early works on the jealousy and rivalry of children in the family, the study of the impact of parental differential treatment on them, as well as the influence of child characteristics on siblings in families with sick children are considered.
