Adoption Studies

Studies that investigate babies that are adopted very early in life to determine the influence of socialization and genetics on psychological variables. The first studies aimed at separating “nature” and “nurture” were conducted in 1924. The rationale for conducting adoption studies is that if adopted children's characteristics are more like those of their biological parents, it is more likely that genetics play a determining role for the development of these characteristics than nonshared environmental influences. For example, psychological traits of adopted children tend to be more similar to their biological parents than their adoptive parents: IQ scores of adopted children were more similar [Page 13]to their biological than their adoptive parents, and adopted children are ten times more likely to develop schizophrenia if their biological mother suffered from schizophrenia. If twins are investigated in adoption studies, the role of heredity can be identified relatively clearly. Advances in the Human Genome Project have allowed scientists to begin identifying DNA differences responsible for certain attributes and behaviors to better understand the interaction of heredity and environment. For more information, see Plomin, DeFries, McClearn, and McGuffin (2001).