This report uses naturally occurring adoptions to tease apart the effects of heredity and rearing on the development of psychopathological disorder in the child. The quality of relationship between the child and his adoptive parents was assessed in four groups of subjects, and the degree of illness in the child was correlated with the quality of parent-child relationship. Quality of rearing and hereditary input both affect the development of psychopathological disorder, but the amount of variance explained by rearing tends to be low.
Rosenthal D, Wender PH, Kety SS, Schulsinger F, Welner J, Rieder RO. Parent-Child Relationships and Psychopathological Disorder in the Child. Arch Gen Psychiatry. 1975;32(4):466-476. doi:10.1001/archpsyc.1975.01760220078009