adoption studies

Meaning: Adoption studies are a behavioral genetics method. An adopted child shares genes with the biological parents but, after early separation, not the home. The child shares the home with the adoptive parents but not genes. Comparing how closely the child's trait (IQ, temperament, alcoholism, schizophrenia) matches each set of parents helps estimate how much variation comes from genes and how much from environment. They are often paired with twin studies.

On the MCAT: A passage gives adoptee correlations with biological and adoptive parents. A higher correlation with biological parents suggests a genetic contribution. A higher correlation with adoptive parents suggests an environmental contribution. Limitations are also tested. Adoption agencies often place children in homes similar to the biological family. The prenatal environment is shared with the biological mother. Adoptive homes cover a narrower range of environments than the general population.

Common confusion: Resemblance to adoptive parents is usually read as environmental, since they share no genes with the child, but selective placement can add genetic overlap. Finding a genetic influence does not mean the trait is fixed or caused by genes alone. Heritability describes variation within a population, not one person, and genes and environment often interact.