The Westermarck theory maintains that incest avoidance arises from the physical proximity of siblings during a critical period of early childhood. This proximity gives rise to an inhibiting effect on post childhood sexual interest. Two recent studies of sibling relationships have verified and refined the Westermarck theory, indicating that the critical period extends through the first four years of childhood.
The theory and the studies have implications for child welfare laws, policies and practices surrounding the placement of siblings in foster care. Namely, the findings provide powerful reasons for placing siblings together during the critical period in order to minimize the risk of post childhood sibling incest. Although public child welfare systems currently recognize the value and benefits of placing siblings together, these systems fail miserably in this area because of a lack of resources. By focusing on children in the critical period of development, resource-poor public systems can marshal their will and target their resources to actually place this discrete group of siblings together, avoid increasing the risk of post childhood sibling incest, and realize all the benefits of maintaining sibling relationships.
David J. Herring,
Foster Care Placement: Reducing the Risk of Sibling Incest,
University of Michigan Journal of Law Reform
Available at: https://scholarship.law.pitt.edu/fac_articles/296