In chapter 4 of the book Sex/Gender: Biology in a Social World, author Anne Fausto-Sterling explores the potential role of prenatal hormone exposure in behavioral differences between men and women. What conclusions does she come to, and what are the implications of those conclusions?
To see what scientist Anne Fausto-Sterling concludes about the effects of hormone exposures on the differences in gender behavior, we must first look at her arguments concerning brain development.
Of the many studies Fausto-Sterling cites in chapter 4, titled "Of Hormones and Brains," in her book Sex/Gender: Biology in a Social World, one was conducted to see the difference in brain development among rats of different genders. She specifically cites a study performed by psychologist Janice Juraska who compared brain tissue in both sexes of rats raised in an Isolated Condition (IC) vs. raised in an Environmentally Complex condition with lots of rats of the same sex. Using measurements of the hippocampus, the part of the brain associated with long-term memory, Juraska found that in rats raised in IC "there was a clear sex difference" (p. 36). More specifically, "neurons from males were more highly branched than ones from females" (p. 36). She further found differences in the hippocampus of rats raised in EC conditions "but with a surprising twist" (p. 36). The results were reversed: the females had more highly branched neurons than the males.
Fausto-Sterling concludes the study shows that environment plays a role in the sex differences of brain development.
In addressing the role prenatal hormones may play in sex differences, Fausto-Sterling looks at studies of girls born with Cortical Adrenal Hyperplasia (CAH). CAH girls receive an abnormally high amount of androgen halfway through their fetal development stage, resulting in a very masculine appearance. Though scientists don't yet fully understand the process, they can postulate that in CAH girls high levels of adrenal testosterone moved through the circulatory system, resulting in their brains receiving abnormally high levels of testosterone. Scientists wonder if the high levels of androgen also change children's behavior observed through play.
Fausto-Sterling asserts that studies in difference in play behavior between CAH girls and normal girls have inconsistent findings. But the one consistency is that CAH girls "prefer more masculine toys," like blocks and trucks, than control girls who are more likely to play with dolls and Easy-Bake Ovens (p. 40).
Fausto-Sterling lays out three different tentative conclusions scientists have drawn based on behavioral studies of CAH girls. They conclude toy preferences are a result of "social responses to the developmental disorder"; in other words, their behavior is socially induced just like in the study of rats raised in EC environments (p. 41). But in the case of CAH girls, the assumption is that their behavior is induced by their parents' responses to their disorder.
Hence, while nothing is conclusive, Fausto-Sterling leans more toward the conclusion that, based on the brain studies of rats, it's more likely that behavior differences are a result of the environment rather than a direct result of hormones, although hormones cannot entirely be excluded as a factor. This would imply that gender distinctions are a product of social environment rather than a direct product of brain development or hormonal influences.