It’s not an evolutionary phenomena, it’s a societal phenomena. Little children assume gender identity unconsciously, because everyone around them has a gender identity, so they get a lot of messages and sooner or later feel like they have to decide whether they will play a role of a “boy” or a “girl”. If their decision doesn’t match their physiology, an inner conflict arises, a great inner conflict. A conflict of such strength and intensity that to resolve the conflict one goes to such an extreme measure as basically mutilating their body.

The resolution of this conflict isn’t forcing them into the “appropriate” gender identity, it’s getting rid of gender identity altogether, but since everyone around them has one, it’s unthinkable and it’s not even considered an option.

It’s a sick society. People are obsessed with their identities and teach little children to be the same.