People continue to misunderstand that there are very real biological differences between the average cisgender male and male-to-female transsexuals. Below is an important image to understand that I extracted from Transgender Chicago: The New Health Frontier.
The image above is the central nucleus of the bed nucleus of the stria terminalis (BSTc), in the thalamus. Note that heterosexual and homosexual males have nearly identical brain structures in that region. Note that biological females have very different structures in that region from those of the males. And finally note that MTF transsexuals have brain structures that are very close to the female’s and nothing at all like the male’s neurological structures.
There are numerous other studies that highlight the biological differences between MTFs and cisgender males. What this image and many other studies show is that, in the brain where our essential self lies, that MTFs truly are female, not male.
This also shows why both the AMA and the APA regard being transsexual as a medical condition – because it is. And transition, for those that need it, is one of the most successful treatments available.