family environment and the larger social context with their rearing parents. In the absence of systematic biases in the selection of adoptive families by birth parents or vice versa, similarities between an adopted child and his or her adoptive parents are best explained by shared environmental (or common environmental) influences. A full adoption design also includes birth parents in order to enable the estimation of inherited influences on development. Similarities between birth parents and the adopted child suggest genetic influences (due to shared genes and a lack of shared rearing environments). Similarities between adoptive parents and adopted children indicate environmental processes (due to shared rearing environments and the lack of shared genes), although evocative rGE effects may also cause parent–child similarities.
