ABSTRACT
Measures of personality and psychopathology reveal differences between siblings growing up in the same family that are almost as great as those between unrelated children growing up in separate families. This notable finding suggests, as pointed out by Maccoby and Martin, that many of the family environment and parental child-rearing variables that people presumed to be important in influencing children's development in fact account for little of the variance among children. The factors contribute to the differences between siblings are presented. One possibility is that parents be have differently toward different children and that growing up in the "same" family environment involves different experiences with the parents for each child. There has been relatively little direct systematic evidence from which to judge the contribution that differential parental treatment may make to the development of individual differences within pairs of siblings. A theory predicting that children increasingly evoke some differences in their parents has been proposed by Scarr and McCartney.
