Gender is not a binary. Even looking purely at the biological expressions found in humans, there are more than two. Equivalents to the variations that humans refer to as intersex occur in other mammals to.
When you add in gender identity and/or gender expression, there are even more variations and layers.
Now, you may be thinking, well, but I’m only writing about heterosexual cisgender characters, so none of this is going to come up.
And I would say to you, my friend, that actually, it does. For example if fictional author A, writes in their book a sentence like one of the following, then fictional author A has made a statement about gender on the whole, and not just their character:
“Susie decorated her bedroom in pleasing girly pink.”
“As a dude, Josh hated discussing feelings.”
“Susie muttered, ‘Men, it’s probably the penises that keep them from understanding high heels.’”
In each of those sentences an assumption is made not just about the character, but about the gender as a whole.
Now, fictional author A might say to me, well, yes, but I’m in close point of view here, can I help it if my character doesn’t always think the most evolved thing?
And I would say to fictional author A, that first, yes, you can. But second, sure. Characters will not always think the most correct thing. But any choices you make where your character thinks a thing that is wrong should be intentional and not accidental. And should be done with the awareness that this might hurt a reader if it is not immediately countered within the story.
Let’s go back to our Susie character. If she says, ‘Men, it’s probably the penises that keep them from understanding high heels.’
And the character she is talking to responds, ‘I don’t know. My brother’s the one who taught me how to walk in heels.’
The story has now countered Susie’s thought. And yes, I can hear fictional author A, now. Fictional author A is like okay, but now my story will be a gazillion words long if every time someone says something, I have to counter it.
And I say, perhaps. Or perhaps you don’t need that sentence at all. Again, I’m not telling you how to write your story. My goal here to help you make intentional choices. These may be things you keep an eye out for when revising, instead of trying to be perfect in the first draft. Whatever process works best for you.
Intersex Society of North America - https://isna.org/faq/what_is_intersex/
Note: Much of ISNA’s info refers to intersex folks as falling outside the gender binary, rather than being a totally normal part of the gender spectrum.https://www.apa.org/pi/aids/youth/sexual-orientation
Note: APA’s definition of pansexual vs. bisexual is technically correct, but the parameters of both are changing within the queer community, so consultation with current members of the community is best there.
Gender Essentialism is Flawed – Here’s Why: https://www.healthline.com/health/gender-essentialism
Also, I’m going to collect all the resources here, for reference. That post will get expanded as we go on.