structural:expansion, quality:correction
Biological factors and views

Some gendered behavior is influenced by prenatal and early life androgen exposure. This includes, for example, gender normative play, self-identification with a gender, and tendency to engage in aggressive behavior. Males of most mammals, including humans, exhibit more rough and tumble play behavior, which is influenced by maternal testosterone levels. These levels may also influence sexuality, with non-heterosexual persons exhibiting sex atypical behavior in childhood.

The biology of gender became the subject of an expanding number of studies over the course of the late 20th century. One of the earliest areas of interest was what became known as "gender identity disorder" (GID) and which is now also described as gender dysphoria. Studies in this, and related areas, inform the following summary of the subject by John Money. He stated:

The term "gender role" appeared in print first in 1955. The term gender identity was used in a press release, 21 November 1966, to announce the new clinic for transsexuals at The Johns Hopkins Hospital. It was disseminated in the media worldwide, and soon entered the vernacular. The definitions of gender and gender identity vary on a doctrinal basis. In popularized and scientifically debased usage, sex is what you are biologically; gender is what you become socially; gender identity is your own sense or conviction of maleness or femaleness; and gender role is the cultural stereotype of what is masculine and feminine. Causality with respect to gender identity disorder is sub-divisible into genetic, prenatal hormonal, postnatal social, and post-pubertal hormonal determinants, but there is, as yet, no comprehensive and detailed theory of causality. Gender coding in the brain is bipolar. In gender identity disorder, there is discordance between the natal sex of one's external genitalia and the brain coding of one's gender as masculine or feminine.

Although causation from the biological— genetic and hormonal —to the behavioral has been broadly demonstrated and accepted, Money is careful to also note that understanding of the causal chains from biology to behavior in sex and gender issues is very far from complete. Money had previously stated that in the 1950s, American teenage girls who had been exposed to androgenic steroids by their mothers in utero exhibited more traditionally masculine behavior, such as being more concerned about their future career than marriage, wearing pants, and not being interested in jewelry.

There are studies concerning women who have a condition called congenital adrenal hyperplasia, which leads to the overproduction of the masculine sex hormone, androgen. These women usually have ordinary female appearances (though nearly all girls with congenital adrenal hyperplasia (CAH) have corrective surgery performed on their genitals). However, despite taking hormone-balancing medication given to them at birth, these females are statistically more likely to be interested in activities traditionally linked to males than female activities. Psychology professor and CAH researcher Dr. Sheri Berenbaum attributes these differences to an exposure of higher levels of male sex hormones in utero.