Science Questions with Surprising Answers
Answers provided by
Dr. Christopher S. Baird

Are gender traits completely a result of societal expectations?

Category: Biology      Published: June 18, 2013

drawing of kids
Public Domain Image, source: NOAA.

No. Gender traits in humans are largely determined by biophysical processes. There seems to be a vocal political faction that is trying to convince people in the name of liberty and equality that gender traits are completely learned, and therefore arbitrary. But this claim disagrees with scientific evidence. In general, boys play more with cars and girls play more with dolls not because their parents are perpetuating outdated gender stereotypes, but because their brain is telling them to. This fact does not mean that boys have to play with boy toys, or that boys who play with dolls aren't really boys. It is just a scientific observation about average behavior and its link to fetal development.

As most of us learned in school, human males possess XY chromosomes in their DNA code, while females possess XX chromosomes. When a baby is first forming in the womb, its sex chromosomes dictate sexual differentiation between a male and female body. The process is complex and multifaceted, but the main player is a hormone called testosterone. Without testosterone, a baby grows into a girl. With testosterone, a baby grows into a boy. Testosterone dictates the development of male reproductive organs and secondary sex characteristics. Testosterone also has an effect on the baby's developing brain. As a result, boys' brains end up larger than girls' brains (this does not mean they are smarter). The testosterone also signals to the brain as it develops in the womb to think like a male. Without the testosterone present, female brains develop more neural interconnections (the white brain matter). That is why females are able to multitask more effectively than men.

The key factors in gender differentiation are testosterone in the brain and the ability of the cells in the brain to react to the testosterone. What happens when testosterone is present in the fetal brain, but the cells are not able to respond to it? This situation is known medically as androgen insensitivity. Interestingly, without testosterone's action being carried out in the brain, the brain grows into a female brain. People with androgen insensitivity have the male genes (XY), but look, feel and think like females. They play more with dolls than cars as infants. The fact that people with androgen insensitivity have male genes but have female gender traits is strong evidence that gender traits are determined by the proper response of fetal brain cells to the presence or absence of testosterone. Most people with androgen insensitivity don't even know they have male genes until medical tests are done because their female brains make them feel so fully female. From a philosophical perspective, the brain dictates a person's identity and traits. Therefore, people with androgen insensitivity can be legitimately called females despite the fact that they have male genes. They are not freaks or mutants, but are full-fledged females, as the "maleness" in their DNA never gets activated.

Dr. J. Imperato-McGinley of Cornell University, who is at the forefront of endocrinology research, has published:

"Gender identity change from female to male has been demonstrated in subjects with 5α-reductase-2 deficiency from different areas of the world (see recent review Imperato-McGinley and Zhu, 2002). These subjects demonstrate that exposure of the brain to androgen (testosterone) in utero, during the early postnatal period, and at puberty, appears to have a greater impact in determining male gender identity than does sex of rearing and sociocultural influences. Normally the sex of rearing and androgen exposure of the brain act in concert to determine the male gender. Subjects with 5α-reductase-2 deficiency demonstrate that in a laissez-faire environment, when the rearing (female) is discordant with the biological sex; the biologic sex will prevail if normal activation of male puberty is permitted to occur (Imperato-McGinley et al., 1979b and Zhu et al., 1998). Studies of gender in subjects with 5α-reductase-2 deficiency underscore the importance of androgens, which act as inducers and activators in evolution of male gender identity in man."

Topics: boy, brain differentiation, female, gender, gender roles, gender stereotypes, gender traits, girl, male, skin, testosterone