Sex and gender are more complicated than people want to believe. And in a world where many, many brave folks are coming forward to say that they don’t want to be categorized with the sex they were born with, or that they don’t identify with a particular gender at all, or a hundred other combinations of some or all of these things, others (who have never questioned what’s on their birth certificate) are confused.

How can this be true, they ask? Gender is the same as sex, isn’t it? And we just are what we are?

Well, here’s the thing – it turns out that chromosomally, cellularly, and biologically, sex and gender are not black and white, not easily defined, and are often fluid. And that’s not even layering a social or psychological aspect on top of it all.

Don’t believe me? Good, you shouldn’t – I’m a writer, not a biologist!

But Rebecca R. Helm is a biologist, and she recently tweeted an insanely insightful thread about how complicated it can be to classifying biological gender.

The best way to combat confusion is with knowledge, so buckle up and let’s go for a little learning ride, shall we?

First, she acknowledges that, on the outside, determining one’s biological sex might seem simple.

But right away, when you learn just a tiny bit more about those X and Y chromosomes, things begin to get more complicated.

And she keeps going, giving us a rundown of things possible and known, and everything out there that’s still a mystery, until – even though I’m educated and consider myself fairly quick on the uptake – I had to admit I was out of my depth.

And what should we do when we’re out of our depth? Defer to the experts, of course, who are comfortable in the deeper water and willing to hold your head above water, too.

So, let’s all take Rebecca R. Helm’s advice and just try to be kind to people.

Biological sex might not be simple to parse or grasp, but you know what is? Listening to what another human being is telling you about the body they inhabit and referring to them how they ask you to.

That’s something we can all start doing right now.