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Love to hear about mAmMaLiAn BiOlOgY.
No one tell them about cows.
Like, this person was literally replying to Nonbinarybot by citing "mammalian biology" and it's trivially easy to give an example of a mammal besides humans that doesn't exhibit binary gender.
They reach for essentialism and end up disproving their own thesis.
Because the further down the evolutionary family tree you go, the murkier gender as we understand it gets, and the less human traits look like absolutes.
We talked about this ages ago, but most animal species display considerably greater sexual dimorphism than humans, to the extent that you have to conclude that human gender expression is, by comparison, *weirdly malleable*.
In fact, it's arguably one of the defining traits of our species. Certainly it must have been selected for at some point in the past. So all your prove by going into "mammalian biology" is that human gender is barely a thing.
Because the third gender present in, for example, cows ("freemartins") is a 100% predictable genetic trait based on certain circumstances of fraternal twins. But no one knows what makes a human trans, or even gay.
Binary genders is just one strategy that species on Earth use to recombine their DNA in their offspring. It's not universal - not even for mammals - and even when it does exist, hardly any two species manifest it in the same way as each other.
If you come at us with "biology" as an argument, be prepared to have the full weight of four billion years of evolutionary history brought down on your transphobic head.
