SEX-TYPED PLAY IN OPPOSITE-SEX TWINS

To examine possible prenatal hormonal influences on sex-typed play, we compared girls with a boy co-twin to girls with a girl co-twin and gi rls with an older brother. In opposite-sex dizygotic twin pairs, the u terine environment may allow transfer of testosterone from the male to the female fetus. Singletons with an older brother provide a control for shared social environment. Girls aged 3 to 8 years (N = 91) were o bserved playing with sex-typed toys, and mothers completed questionnai res about the child's activities. Contrary to expectation, girls with a boy co-twin did not spend more time playing with boys' toys than gir ls with a girl co-twin or girls with an older brother. Although these results might suggest that normal variations in hormones do not contri bute to within-sex variations in childhood activities, they combine wi th other work to suggest factors to consider in evaluating hormonal in fluences on human behavior, including level and timing of exposure. (C ) 1997 John Wiley & Sons, Inc.