The statement that the female body plan is the “default” in mammals can be misleading, as it simplifies the complexities of sex determination and development. While it is true that in the absence of specific signals, certain aspects of fetal development might proceed in a way that aligns with female anatomy, this doesn’t mean that a mammal is inherently female or male until those developmental cues kick in.
From conception, an individual’s genetic sex is determined by the combination of sex chromosomes inherited from their parents, either XX (female) or XY (male). This genetic difference dictates the development of sex characteristics throughout gestation and into adulthood. In mammals, it is the presence of the Y chromosome and the SRY gene (Sex-determining Region Y) that triggers the development of male characteristics. Without this Y chromosome, the embryo will develop female characteristics, as the default pathway without the influence of male hormones is female.
However, this does not mean that the “female body” is the default in a genetic sense—it means that, in the absence of male influences (testosterone and the action of the SRY gene), the body will develop female traits. The idea that we are genetically female or male from conception is backed by the fact that the presence of the Y chromosome dictates male development, and the absence of it results in female development. The gender or sexual characteristics that manifest later in life are a direct result of this genetic blueprint, not simply a default body plan that is “switched” from male to female or vice versa.
Regarding intersex individuals with conditions like Complete Androgen Insensitivity Syndrome (CAIS), although they may appear female because their bodies cannot respond to male hormones, their genetic sex is still male (XY). The body’s inability to respond to androgens leads to a female phenotype, but genetically, they remain male. This highlights that although external sex characteristics can vary, the underlying genetic sex determined at conception remains the primary factor in sexual development.
Therefore, the argument that the female body is the “default” oversimplifies the complex biological processes involved in sexual differentiation and ignores the crucial role of genetics in determining whether an individual is male or female from conception.