Reared-apart/reared-together Chinese twins and virtual twins: Evolving research program and general intelligence findings.

China's One-Child Policy (1979-2015) limited rural families to two children and urban families to one child. This practice, which led to the abandonment of hundreds of thousands of female infants, is indirectly responsible for the separate placement of infant twins. The availability of this sample launched the first prospective study of these pairs.