Gender Identity The factors that mediate and account for gender identity and sex differentiation include those attributed to nature, such as hormones and genes, and those attributed to nurture, such as environment. Research has demonstrated that hormones and genetics play an integral role in gender identity and associated behaviors (Wilson, 1999; Hines, 2006; Hines (2008). What are these hormones and how exactly have they been determined to influence gender identity? The following outlines scientific findings surrounding nature and its involvement in the development of gender identity.

Gender identity and human sexual behavior are involved in perceptions of oneself as male or female, gender role behaviors, and how sexuality is communicated to others (Wilson, 1999). How gender identity manifests and expresses itself is inherently different in men and women (Wilson, 1999). Research has demonstrated that testosterone exposure during early periods of development that are considered critical result in permanent behavior change in areas such as gender identity, sexual orientation, and childhood play behavior (Hines, 2006). These discoveries were made primarily through observation of individuals with hormonal abnormalities in prenatal development, leading to genital ambiguity, but research has also indicated that testosterone plays an important role in normal development with regard to making individuals more or less typical of their sex (Hines, 2006).

Research on prenatal testosterone and its impact on behavior began with studies with other mammals in which hormones were manipulated (Hines, 2006). The large body of research devoted to this topic indicated that testosterone and related hormones play a prominent role in behavioral and neural differentiation of the sexes, to the same extent as they influence the development of the genitalia (Hines, 2006). These hormone manipulation studies generally looked at hormone...

These periods differ in occurrence between species, even with some being prenatal and some being postnatal (Hines, 2006). It was noted by Hines (2006) that although the timing of developmental periods may differ between species, the observed changes in sex differentiation were similar and consistent. Furthermore, studies with both rats and non-human primates have found that developing females exposed to high testosterone levels exhibited higher levels of behaviors more typical seen in males (Hines, 2006). Similarly, taking testosterone away from developing male rats has been shown to reduce behavior that is typical of males and increase female-type behaviors (Hines, 2006). Based on this type of research, the mechanism by which testosterone is believed to change sex-related behavior is through neural development (Hines, 2006). There are several hormone-sensitive neural regions whose development is affected by the manipulation of testosterone. This manipulation has been observed to influence anatomical connections between regions of the brain and the usage and characterization of neurochemicals, as well as programmed cell death (Hines, 2006). It is the alterations in these neural structures that likely underlie behavioral changes that are observed due to the manipulation of testosterone during critical early developmental periods (Hines, 2006).
In regards to human development, research findings have suggested that critical prenatal developmental periods are when testosterone levels are most likely influential in behavioral and neural sex differentiation (Hines, 2006). Furthermore, The eighth to the twenty-fourth weeks of gestation have shown to be when significant differences in testosterone levels can be observed between male and female fetuses. Since prenatal hormone…