Adoption, Evolution, and Kin Selection

Key Research on Evolutionary Psychology and Inclusive Fitness Theory (Hamilton’s Rule) in Kin Selection, as they Relate to Adoption:

The concept of kin selection, also known as inclusive fitness theory, is more than 50 years old and is now widely accepted as a predictably strong evolutionary biological model that explains why people make sacrifices for others who have their genes. Called Hamilton’s formula, after its creator W.D. Hamilton, it explains that a person will take altruistic action like running into a burning building on behalf of close relatives, such as offspring. But that same person will take fewer risks for more distant relatives, such as cousins, and be willing to sacrifice more toward distant relatives than toward genetic strangers.

What is Kin Selection?

In general, kin selection theory predicts that parents will provide less beneficial behaviors to their unrelated children—which can include step and adopted children—relative to their biologically related children. This widely known scientific theory is ignored in most discussions of adoption policy, lawmaking, and advocacy. The research undermines the social engineering model promoting adoption of infants from unrelated families in the United States that led to nearly 3 million infant relinquishments between 1944 and 1975.

Kin selection and evolutionary biology and psychology also are strong predictors of how adoptive parents and their non-biological kin will relate and helps to explain why adoptees care about making connections with their kin, contrary to decades of messages from more contemporary social workers and mental health workers who have not acknowledged the role of biology in adoption. The role of evolutionary psychology in predicting harm to unrelated family members has been well documented in research on harm to stepchildren. See articles listed below.

  • Daly, Margo and Wilson, Martin. “The Cinderella Effect: Parental Discrimination Against Stepchildren.” Samfundsøkonomen 4 (2002): 39–46. The two sociologist shows that evolutionary psychology demonstrates parents will favor their biological children over children not related (stepchildren).
  • Daly, Margo and Wilson, Martin. Is the “Cinderella effect” controversial? A case study of evolution-minded research and critiques thereof,” in CB Crawford & D Krebs, eds., Foundations of Evolutionary Psychology. Mahwah NJ: Erlbaum (2008): 381-398.