Anybody who can’t deal with “cis” as the opposite of “trans” never took high school chemistry. Or biology. :dubious:
Statements similar to this have cropped up a couple of times in this thread, and I want to make sure that people actually understand what this means. Men’s greater (average) athletic capability is due to different patterns of hormone secretion, not to differences in genes for muscle development or anything like that.
The differences between the female-format and male-format body plans is instructed by hormones produced by the gonads, first during specific phases of embryonic development (when they instruct the formation of the urogenital system and some other areas), and again after puberty. The body’s cells respond to these hormones by changing their gene expression (which genes are active and when), which leads to the various downstream developmental differences.
Interestingly, both XX and XY cells are capable of responding appropriately to either set of signals, which can lead to some very interesting abnormalities. If the gonad, for some reason, ends up with a different sex-chromosome complement than the rest of the body, or if the hormone signals that the embryo is exposed to, or its ability to respond to those signals, are altered, this can override the XX or XY status of the body’s cells and result in the development of the opposite-sex body plan (as in androgen insensitivity syndrome, mentioned upthread).
The genetic difference necessary to spark off these different hormonal programs, on the other hand, is miniscule: one gene. The Y chromosome is, to put it bluntly, a piddly little bit of nothing that has around 50 genes on it, about half of which are shared with the X (which, by contrast, is one of the larger chromosomes in humans and carries ~850 genes); men have maybe 20 genes that women don’t (out of around 20,000), and most of them are mainly involved in sperm formation.
The only Y-chromosome gene that is necessary to form an anatomically normal male is the SRY gene (although without the other Y-specific genes the resulting man will be sterile). If you take two genetically identical single-cell XX embryos and artificially add the SRY gene to one, at the end of development you will end up with one female and one (sterile) male, who despite having identical genetic material (except for that one added gene) will show typical sex-specific differences in hip width, muscle mass, etc.
So there is no “genetic” component to greater male athletic performance aside from the SRY gene itself. Men and women have a ~99.9% identical gene complement (although men have to deal with being haploid for about 5% of them), and there are no significant differences in overall allelic variation. Furthermore, both sexes will at some point use pretty much every gene; the differences are in how and when each gene is active, not in which genes or alleles each sex possesses.
Since most of the size / strength / shape differences that are relevant to this discussion are a result of pubertal hormone exposure, a person who transitions in childhood and receives hormone replacement treatment such that they are never exposed to the pubertal hormonal program of their biological sex could end up well within the normal range of the sex corresponding to their gender identity* on pretty much every metric. Even if you believe that trans women who transition in adulthood or do not undergo hormone replacement have an unfair athletic advantage, there’s no comparable reason to ban trans girls who have undergone hormone replacement throughout puberty. Currently very few trans children have the opportunity to receive such treatment, but that will probably change over time.
- Is there any compact term for “the biological sex corresponding to a person’s gender identity”? Because that’s a really clunky phrase…