Emily's Cat
Rarely prone to hissy-fits
Is it your contention that a female with big boobs is more female than a female with small boobs? Will you confidently agree that a male with a weak jawline is less male than one with a strong jawline - eg. that Silas Weir Mitchell is less male than Henry Cavill?If secondary sex characteristics vary, then sex varies.
SEX IS NOT DETERMINED BY A HOST OF GENES, HORMONES, AND OTHER VARIABLES.Anything determined by a host of genes, hormones, and other variables can not be binary.
Let's get some terminology locked down. In this context, you're conflating three different words: defined, determined, and discerned. These aren't the same terms when we're speaking of biology.
Definition has to do with categorical inclusion/exclusion. Sex is defined based on the type of evolved reproductive system an individual has. Those reproductive systems evolved very clearly and explicitly within the context of two (and only two) distinct gamete types. Note that I refer to the evolved reproductive system - this is intentional and important. We can observe that there are two differently sized gametes among all mammals, birds, and most fish and reptiles. And we can observe that within each species that has two differently sized gametes that are used for reproduction, there are two systems that have evolved to support those gametes and to allow reproduction to occur. Those systems vary by species - the reproductive system of a finch isn't identical to the reproductive system of a wallaby. But it has been repeatedly and consistently observed that within each sexually reproductive species, there are two distinct systems that are each associated with the production of one gamete or the other. There is NO reproductive system that has EVOLVED to support the production of a) BOTH GAMETES or b) A THIRD GAMETE.
Determination has to do with the process by which a fetus develops into one or the other sex. The mechanism of determination varies by species in some profound ways. For example, in alligators, sex determination happens via the temperature of the nest: above a certain temperature the zygote will develop as a male, below that it develops as a female. There is no temperature that will cause an alligator egg to produce offspring that are something in-between male and female - and there is no reproductive system in between those two categories. In humans, the mechanism of determination is via the SRY gene that is normally located on the Y chromosome. Things can go wrong in development. In alligators, if the temperature fluctuates a lot in the nest, you can end up with a mix of some male and some female babies. I suspect it can even result in some with mixed up systems. In humans, the SRY gene can be faulty, it can be translocated on the X chromosome due to mutation, or the receptor for the SRY can be damaged - all of these can result in disorders of sexual development. That means that sex doesn't DEVELOP as expected for the species... but it does NOT produce a new and different sex, nor does it produce an in-between sex.
Discernment has to do with how we infer an individual's sex based on observable features. 99.998% of the time, we can discern the sex of an infant in-utero way before birth via ultrasound, because genitals form relatively early in the development process. When we're looking at adults, we frequently use secondary sexual characteristics to discern a person's sex, and we're very, very, very good at it - we can accurately discern the sex of a post-pubertal individual by facial conformation alone over 90% of the time. The characteristics that we use to discern sex have a fair bit of variation within the same sex, and some of them even overlap with members of the opposite sex.
What you keep doing is mixing up those three things. You keep making the mistake of saying that because the secondary characteristics of sex show variability along a spectrum, that sex itself shows variability along a spectrum. This isn't true. It's as false as saying that because it's cloudy outside and you can't see the sun, the sun must not exist. You're mistaking a correlated observation with the thing itself.