- I'm a cis-man and I like fun shirts. - You do.

Our gender plays a big role in how we define ourselves and others.

But it's not something science fully understands.

And, funnily enough, we don't really know why I like fun shirts, either, but no one questions that so let's just move on.

A lot of us may never really think twice about defining ourselves as a man or a woman, but there are many who do think about it, a lot.

In reality a lot of biological, sociological, and psychological factors go into the definitions of “man” or “woman,” or neither.

For example, when babies are born at a hospital, they're assigned a sex based on primary sex characteristics, like genitalia.

Yeah. Someone literally looks at the baby and makes a decision.

They're mainly going by visual inspection.

And though hormones like testosterone play a big role in developing the primary sex organs that you have at birth,

sexual differentiation continues beyond birth,

with a lot of outwardly visible changes, and awkwardness, peaking at puberty.

And these processes rely on a whole host of hormones, and receptors, and other factors that come from at least 70 different genes on different chromosomes.

So really, biological sex is not black or white because there are so many variables going into it that are not necessarily correlated with one another.

Which is why there's good evidence to say there are more than two biological sexes.

For example, testosterone is important for developing the internal genitalia, but it needs to be converted by an enzyme for the external genitalia to be made.

So someone could have testosterone, plus all the effects that leads to during development through puberty, and be “male” in a lot of ways internally.

But because they're missing one enzyme, things might look a little different on the outside.

The thing is, most people don't know their genetics or what's going on inside of their abdomen.

So how come anyone confidently proclaim, well anything, when it comes to gender?

When I say I'm a woman, I'm actually referring to my gender identity.

This might be related to or influenced by primary or secondary sex characteristics, but knowing our gender identity comes from the brain.

The fascinating thing is we don't really know a ton about what influences this identity.

Like how I might say, "I'm a confident or anxious person."

But I don't really know what exactly in my brain makes me like that.

There are a few regions in the brain that are different between sexes, including the interstitial nucleus of the anterior hypothalamus and the bed nucleus of stria terminalis, which is part of the limbic system.

In men, these areas are both larger and have more neurons in them.

And studies to date, albeit small ones, do show the sizes of these areas correlate with the gender identities of transgender men and women.

Other studies have found differences in white matter microstructures between men and women.

Transgender men who have not yet received hormone treatments had patterns more similar to those sharing their gender identity, not what they were assigned at birth.

In other words, the sex they were assigned at birth didn't accurately predict their white matter patterns.

While there are so many different areas of the brain that seem different between men and women, some researchers argue that there are more similarities than differences and there isn't really a typical “male” or “female” brain.

But given that, all of us have incomplete information on our true biological sex, and that we don't fully understand the neuroscience behind gender.

Or any complex trait, like why you like this fun shirt.

True. It doesn't make sense to burden some individuals with proving how they feel.

Because scientifically, none of us can explain why we feel like a man or a woman.

And as none of us can say that, by making a minority of people try to prove that with a burden of proof, we're causing a lot of health problems.

For example, the suicide attempt rate among transgender people ranges from 32–50% in a number of different countries,

whereas the overall population average in the US is estimated around 0.04 to 1.1%.

Both of these numbers are too high, but the stats for transgender people are particularly so, especially when recent studies show these numbers decrease when transgender people are socially accepted.

While there are, of course, a lot more scientific questions to ask, we could save hundreds of thousands of lives by removing social stigma.

We know that science will catch up eventually, but in the meantime we should all recognize that this is more complicated than man, woman, trans or non-binary.

And as is the norm in science, the more we learn, the more nuanced it gets.

And that diversity in people and ideas is what makes this world so cool.

If you wanna learn more about what your DNA says about your sexuality, different than identity, click here.

Thank you for watching. I'm sure you'll have a comment on this video,

so make sure you leave it below, and share the video too.