Gender is biological, the level of testosterone in an individual determines this

The argument

Proponents of this view argue that testosterone is a significant biological chemical contributing to mammalian development, and that early levels of exposure to it determine permanent behaviour. The claim is about timing as much as chemistry: exposure during development is said to shape the organism durably rather than to produce a passing effect, which is why the argument treats it as a cause of disposition rather than of mood. Higher levels of testosterone are predominantly present in males, generating some of the characteristics associated with gender stereotypes, such as choice of toys as children and sexual orientation. The evidential weight of the argument rests on variation within a sex rather than on the difference between sexes, because a purely social account can explain the latter by upbringing. Females with high levels of prenatal exposure to testosterone can develop congenital adrenal hyperplasia ("CAH"), and women with that high prenatal exposure have shown more typically male behaviours — a preference for stereotypically male toys, and more interest in rough play — than females born without the condition. What makes this decisive, on the argument's reading, is the gradient. The behaviour is more present than in females born without CAH, but not as present as it is in individuals born male, so the effect tracks the quantity of hormone rather than falling into two categories. A social explanation would predict behaviour to follow the category a child is raised in; instead it follows a continuous biological variable, and lands these women between the two social groups rather than in either of them. Because the level of exposure to testosterone prenatally is said to determine male or female behaviours in this graded way, proponents conclude that gender is biological rather than social — a product of developmental chemistry that socialisation may modify but does not create.

Premises

Counter-arguments

Testosterone cannot be used to argue whether someone is more male or female. It is known to exist in high quantities in males, and significant research has been done to associate high levels with male characteristics that associate with gender roles. This finding has been used to explain and even defend stereotypically male behaviour. There is little, if any, research, however, in the dynamics of testosterone levels and female aggression. We therefore do not know enough about testosterone to conclude that it causes and drives male aggression. Aggression is simply classified as male behaviour and testosterone a male hormone. Testosterone therefore cannot be used to categorise individuals as male or female. Women who are athletic are associated with having higher levels of testosterone and therefore being more genetically male. Testosterone levels can influence muscles, but this varies from person to person. Some people make better athletes with lower levels.

Rejecting the premises

[Rejecting P1] The premise overstates the evidence at both ends: prenatal androgen exposure is associated with some sex-typed behaviours, but the effects are averages with wide overlap between groups, and the claim that testosterone determines sexual orientation is not supported by the research literature at all. [Rejecting P2] The CAH case cannot carry the conclusion, because the condition brings confounds the premise ignores — visible virilisation at birth, surgery, lifelong medical management and parents who know the diagnosis — and because toy preference and rough play are not gender: most women with CAH have a female gender identity, which is the claim the argument needs and the evidence it cites tells against.