Feminists

but it does sound plausible that hormones are a source of gender identity. Other than the obvious external gender differences, hormones are the other area of differentiation.

I was born female and grew up with two older brothers and a younger sister. There were very few girls in my neighborhood when I was in grade school, and none near my age. My sister was too young to leave the house or yard for playtime, so I spent a lot of time with my brothers.

I played softball with them and their friends because I was a good batter. Didn't know or care much about the game itself, just did what they told me to. I climbed trees, did little gymnastic tricks that one brother (a natural gymnast) taught me. Explored woods with them at my grandfather's farm, and learned about petrified wood, discarded snakeskins, and fossiles in the creek bed. On Sunday afternoons, we went either to a matinee at a neighborhood theater or caught a bus to the one skating rink in town. They always met up with friends, leaving me as the one girl in the group, especially at the theater. At the skating rink, I was on my own to make my own friends.

I never felt like "one of the boys." Never identified with them. On my own, when they were not around, I played with dolls and dressed up in my mother's cast off clothes and jewelry. At family gatherings, I joined the female cousins my age.

In my teens, I hung out with other girls, had crushes on boys, etc.

The point is that I think that gender identity is a personal, internal thing, based largely on hormones rather than on social or family conditioning. Conditioning can play a role, perhaps, especially on limits placed on gender related activities. But how someone identifies is, AFAIK, hormonal.