From what researchers have found so far, it looks like gender identity has a biological side as well as a social one

Brain imaging studies show that in many transgender people, certain features of their brains don’t line up neatly with the sex they were assigned at birth. In fact, some brain structures look more like those of people who share their gender identity, or fall somewhere in between. Scientists think this likely comes from how the brain develops under the influence of things like prenatal hormones and genetics.

Those early influences can’t just be undone later in life, which is why people often describe the experience as being “born in the wrong body.” But physical traits can be changed through things like hormone therapy or surgery, and that’s why transition can make such a huge difference. For a lot of people, bringing their body into line with their identity dramatically improves mental health and quality of life.

That said, gender isn’t only about biology. Social expectations and cultural ideas about what it means to be “male” or “female” play a huge role too. So while there’s good evidence that biology is part of the picture, gender is really shaped by both our brains and the world we grow up in. And since there’s still a lot we don’t know about the human brain, scientists are careful not to reduce gender down to a single explanation.