Science, bitch.

>A sex difference in the human brain and its relation to transsexuality
https://pubmed.ncbi.nlm.nih.gov/7477289/
>White matter microstructure in female to male transsexuals before cross-sex hormonal treatment.
https://pubmed.ncbi.nlm.nih.gov/20562024/
>Regional gray matter variation in male-to-female transsexualism
https://pubmed.ncbi.nlm.nih.gov/19341803/
>Structural connections in the brain in relation to gender identity and sexual orientation
https://www.nature.com/articles/s41598-017-17352-8
>Transgender brains are more like their desired gender from an early age
https://www.ese-hormones.org/media/1506/transgender-brains-are-more-like-their-desired-gender-from-an-early-age.pdf
>Neurobiology of gender identity and sexual orientation
https://pubmed.ncbi.nlm.nih.gov/29211317/
>Neuroscience and Sex/Gender
https://www.jneurosci.org/content/40/1/37