In developmental terms, there is one way in which nature seems to have a head start on nurture: an individual’s prenatal development, which is largely biologically driven, precedes his or her exposure to social environments. However, even in the case of prenatal development, environments (e.g., the uterine environment, the mother’s social setting) can have significant impacts on the developing fetus. Still, these environmental inputs are likely to have their immediate effects on the fetus through biological mediators such as hormone levels, immunological factors, blood chemistry, physical traumas, or infectious agents.In discussing possible factors that influence the relative impact of nature and nurture, we should not ignore the obvious-that one such factor may be gender itself. The causal cascades sketched out in Figure 1.1 may sometimes differ for males and females. The following findings are consistent with this hypothesis: Parents police gender more strongly in sons than in daughters. The process of childhood sex segregation is more extreme and intense in boys than it is in girls, and boys seem to police other boys’ gender-related behavior more strongly than girls police girls. Boys’ sextyped behaviors appear to be more impervious to adult influences than girls’ sex-typed behaviors are. After achieving gender labeling, young girls show behavioral effects (e.g., reduced levels of aggression) that boys do not.