...[scientists from] the University of Barcelona—used MRI to examine the brains of 24 female-to-males and 18 male-to-females—both before and after treatment with cross-sex hormones. Their results, published in 2013, showed that even before treatment the brain structures of the trans people were more similar in some respects to the brains of their experienced gender than those of their natal gender.   It is definitely a need, not a want. Saying it's a want is like saying people choose to be gay or choose to have schizophrenia or choose to have an IQ of 170. Source: https://www.scientificamerican.com/article/is-there-something-unique-about-the-transgender-brain/