Because if a study finds that a person is more like their biological parents, then the genetic influence is likely stronger.
However, if a person is more like their adoptive parents instead, then the environment is more influential.
Adoption studies are a traditional behavioural genetics research tool that are useful for analysing how genetic and environmental factors interact to influence human traits like intellect and disorders like alcoholism.
Learn more about Adoption studies here:
https://brainly.com/question/12273843
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