Because the map is not the territory?
That's an argument for bringing our map closer to the territory, i.e., applying the word "gender" in humans to the same concept we use for animals. Not for completely messing up our map.
applying the word "gender" in humans to the same concept we use for animals
I'm not aware of the word "gender" being commonly applied to non-human animals for any concept, other than grammatical gender. You might be thinking of the concept usually referred to as "sex".
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.