My theory is that social gender roles emerge from biological sex differences, and there is something innate that causes most humans to latch on to one binary gender identity in early childhood.

So how do you account for the fact that most people do not have a "gender identity" at all? If "gender identity" is innate and arises from biology, how come the term and concept only were invented and introduced in the 1960s & 1970s - and only began to come into widespread use amongst a significant chunk of the population in the 21st century? How did all the experts who over the course of many decades studied, charted & described the stages & processes of child development from infancy into adulthood - including how humans develop our sense of self (self-concept) & sense of worth - miss it? And how come even today when the idea that everyone has a "gender identity" and "gender" is so central to the human psyche is popular particularly amongst youth and those who consider themselves "progressive," do so many people find such views both untrue and objectionable?

I find it telling that the clinicians who came up with the term and concept of "gender identity" in the 1960s and helped to popularize it later through their influential books - Robert Stoller and John Money - not only were men, but they were sexologists whose clinical practices and research were heavily or mainly focused on a very small, select substrata of humanity: men with the "deviant" sexual interests that Money re-named "paraphilias" (previously, sexologists had called them "perversions," which was jettisoned coz it sounded too pejorative); persons with disorders of physical sex development (whom both erroneously and cruelly called "hermaphrodites, and for whom Money advocated genital surgeries to make them look more "normal"); and psychiatric patients who at the time were considered to have psycho-sexual "pathologies," including what was then called "transsexualism."

Indeed, Stoller and Money based their ideas on "masculinity," "femininity," "gender," "gender role" and "gender identity" not on in-depth study of the general population, but on their work with "transsexuals" and homosexual persons who represented only that small segment of the gay and lesbian population who fit the most stereotyped views of what homosexuals are like (in other words, those who fit either the "girly man"/"swish" or "stone butch"/"bull dyke" mold). [My apologies for using terms some might find offensive, but I'm trying to show the narrow frame of reference sexologists like Stoller & Money had.] In other words, Stoller and Money drew their ideas about "gender" and "gender identity" precisely from those persons in the population preoccupied with issues of "femininity" and "masculinity" and "hung up on" trying to "present" an image to the world based on sex stereotypes, albeit the sex stereotypes associated with the opposite sex rather than their own. Then they extrapolated from that select group ideas they claimed were "universal truths" that pertain to the entire human race. Similar to you saying that because you personally have a "gender identity," then "most humans" must have one too, and it's caused by "something innate" in our species arising from the fact that humans are anisogamous and sexually dimorphic.