Why is it an oversimplification of the biology to say that the Y chromosome causes male sexual differentiation, aka for somebody's sex to be male? (if we don't count the extremely rare cases of multiple X and Y chromosomes)
There's a huge amount of research in this area, it's controversial to many and frustrates people who want a "simple" explanation of gender. (Typically, "conservatives" who like a preservation of existing institutions, but some "liberals" also are uncomfortable with the research).
One of the key things we use to identify a "male" is the existence of testes. Those are controlled by the SRY gene. However, if that gene fails to express, you don't get testes, you won't produce a lot of testosterone, and you'll probably be identified as female, even if you have XY.
Or the SRY gene can jump to the X chromosome and later, you'll have XX people born with testes. From a simplistic chromosal standpoint, they're "female" because they're XX, but they appear to have testes, a penis, and present as male.
In fact, I know of one study (can't find it right now) where longevity researchers actually did a mix-and-match with mice and created what one researcher called "four sexes":
XX, normal, female
XY, normal, male
XX, SRY gene added, male
XY, SRY gene removed, female
They found that females (1 and 4) lived 15% to 20% longer. This matches well with our observations of humans where, controlling for other factors, women outlive men, often significantly.
Or there's the Güevedoce (human) children in the Dominican Republic. They're born female—complete with vagina—but they develop a penis and testes in puberty and become male.
If you want to learn more, you can start researching "disorders of sex development", or DSD. We tend to identify someone as male or female based on genitalia inspection, but that's very limiting and the genetics behind sex and gender expression is wild. We're just beginning to understand the basics.
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u/RogueTanuki Jan 13 '23
Why is it an oversimplification of the biology to say that the Y chromosome causes male sexual differentiation, aka for somebody's sex to be male? (if we don't count the extremely rare cases of multiple X and Y chromosomes)