It is clear to many of us that there are two genders. Particularly to those of us that have studied biology.
Biology addresses sex, not gender (whether ascribed gender or gender identity), and there are vastly more than two ways in which the various biological attributes grouped under “sex” line up; which is why when (as is, to be sure, quite common) binary sex distinctions in biology and medicine are used they are drawn differently in different contexts.
I mean, there's documented cases of non-chimeric fertile females (in the sense of “people who produce ova and can reproduce with people who produce sperm”, which isn't the only biological definition of sex but is the one most relevant to fertility and reproduction) with 46,XY karyotype and normal male coding sequences in SRY and other genes associated with sex determination. Simplistic generalizations about sex and biology, aside from having dubious relevance to gender discussions, are pretty invariably factually wrong.
When you say "studied biology" do you mean took a few general biology classes in college or did a PhD program in the relevant sub-field of biology?
There are animals for example that have 2 sexes but more "genders" (to the extent that it is correct to apply this terminology) - e.g. Ruffs (a european bird) have several male forms that differ in size, plumage and sexual behavior ( https://en.wikipedia.org/wiki/Ruff#Biology_of_variation_amon...).
Even if no similar mechanism exists in humans, there are social constructs that may serve similar roles - there are communities of "3rd gender" people in India for example, for thousands of years now.
Toward your comment, can't we establish harm is caused by targeted misgendering/deadnaming by asking the transgender people who have been harassed by it how they feel about it? Doesn't that seem not even necessary? What line on harm needs to be drawn exactly before we can make a rule "don't deliberately harass transgender people on our platform via their dead identities."
Just the same as it would be extremely annoying to work with someone that refused to use your name (and not at all forced speech to demand that they get it right; for many trans folx the old name is literally not their legal name anymore). Pronouns are a form of self expression, gender identity is real, and you only need to look at the stats for violence against trans people to the see the active harm in pretending otherwise.
Rules enforcing some level of decency have a place on public forums (even if it's not as cut and dry as pedophilia or violent activity); that's why you're here being transphobic rather than /b/.
Could you reference some of these stats? This argument comes up very often in discussions about trans peoples issues. But, not once have I seen or read someone citing a particular statistic or even pull up a number out of thin air. It is always claimed, there are stats showing increased violence against trans people. Where are the statistics?
As for sources, hard stats can be difficult for any hate crime (compounded by the fact homicide against trans individuals isn't often recorded as violence against their actual gender) and especially considering that the total trans population is small (and thus vulnerable to effects of small numbers) but the FBI hate crime database [0] and the NCAVP reports [1] are good places to start. Transequality center also collects good resources.
Somehow, I don't believe you've really wondered about this too much...
[0] https://ucr.fbi.gov/hate-crime/2017/tables/table-1.xls
It's disingenuous to lump these together as equivalent to misgendering. Child exploitation and violence are against the law of pretty much all nations in the world, and there is a clear consensus. As well as harm caused.
That line hasn't been drawn yet for gender. For one it's not clear how many genders exist. Are they fluid day by day, can people change in and out of them at will. Do I misgender someone if I fail to keep up. Is this a biologically supported concept, should we really open the Pandoras box of forced speech, etc.. etc..