The Structure of Child Adoption Based on the Relationship Between Adoptive Parents and Adoptive Children in Finland

Abstract Humans, like many other primates, possess the ability to adopt, and the practice of child adoption exists across human societies. It is well-known that there are three distinct categories of child adoption—kin adoption (i.e., when a relative adopts a child), intrafamilial adoption (i.e., when a stepparent adopts a child) and stranger adoption (i.e. when a child is unrelated to the adoptive parents). However, there is a lack of studies providing exact information on the relationship between adoptive parents and children. We calculated the relative frequencies of the adoption types using high-quality register data covering all child adoptions in Finland between 1999 and 2021 ( n = 7422). Stranger adoption was the most common category of child adoption, followed by intrafamilial adoption, with kin adoption being the least frequent. Among stranger adoptions, it was found that single females were more likely to become adoptive parents than single males. In intrafamilial adoptions, stepfathers were more frequently adoptive parents than stepmothers, and female same-sex couples were more likely to be adoptive parents than male same-sex couples. In the case of kin adoptions, grandparents were the most common adoptive parents, followed by aunts and uncles. Maternal kin were more likely to become adoptive parents than paternal kin. The findings are discussed regarding evolutionary theories on parental investment and substitute parenting.