DiLalla, L.F. (1996). Differential mother-sibling interactions in late infancy: Evidence of increased differential treatment. Paper presented to the Behavior Genetic Association, June, Pittsburgh, PA. Abstracted in Behavior Genetics, 26, 583-584.

The study of twin siblings can aid our understanding of differential mother-child relationships without the confounds of studying siblings at different ages or at different time points. An earlier report ( DiLalla, L.F., 1995, Behav. Genet. 25, 261) examined infant twins’ behaviors and found that at 7 months of age there was little differential maternal treatment, whereas at 9 months MZ twins behaved more similarly and were treated more similarly, suggesting some reactive gene-environment correlation. In a follow-up of these twins at 14 months maternal warmth and control variables and child task and attention variables were coded for 69 MZ and 83 DZ pairs. Both MZ and DZ twins were significantly correlated in their task orientation (average r = .36) and neither were correlated in their attention to mother (average r = .16). However, mothers tended to treat MZ pairs more similarly than DZ pairs when talking to the children (r difference = .24) and acknowledging their behaviors (r difference = .20). This suggests that although environmental effects almost completely account for the infants’ behaviors, mothers nonetheless are responding to some characteristics in the infants shared more by identical than fraternal twins. Sibling interactions are discussed.