Behavioral contrasts in twinships: stability and patterns of differences in childhood.

Semistructured interviews with 305 mothers of same-sex twins were conducted periodically over the course of the twins' first 6 years. During each of the interviews, the mothers were asked to contrast the twins on a variety of specific behaviors. From the body of reports, 5 ages and 16 behaviors were selected for analysis as most illustrative of the main developmental trends for intrapair differences and similarities. For each of the behaviors, intrapair contrasts were moderately stable across age spans as long as 18-36 months. A set of behaviors related to negative aspects of temperament and a set of behaviors related to sociability were obtained at 6 months and were replicated at later ages. Concordance rates for the identical twin pairs were uniformly higher than for the fraternal pairs, suggesting that genotypic similarity was associated with intrapair similarity for aspects of emotionality and sociability.

Cross-nursing: wet-nursing in a contemporary context.

Cross-nursing, or the breast-feeding of an infant not one's own, appears to be an increasingly popular, if not well reported, practice. The physical and psychologic effects are not well documented, but may be quite different from those of the institutionalized wet-nursing of the past. Three mothers who cross-nurse were interviewed; the practice appears to have had no ill effect on them or their infants. Cross-nursing is a logical and practical extension of the resurgence of breast-feeding and may, in turn, increase the incidence of breast-feeding by making it more attractive to employed mothers. Before the practice can be properly evaluated, however, more data are needed, particularly with regard to possible physical reactions in the infants. In the meantime, pediatricians should be aware that their breast-fed patients may be participating in a cross-nursing situation, and suggest prudent considerations.