with the recognition that gender and sex aren’t binary. Is there a biological basis for this? I do not want "Gender Studies" references. I want real BIOLOGICAL, you know code mother nature put in you.
Sex is basically binary in mammals (do you have the gene that triggers producing sperm versus the gene that triggers you producing eggs), the only exception being incredibly rare intersex disorders. Read more here: http://nautil.us/issue/43/heroes/why-sex-is-binary-but-gende...
Based on sex, people have different traits, physical and mental. Some of these traits are close to binary between the sexes (having a uterus, etc.). Some traits are a matter of distributions (such as differences in physical strength, or willingness to take risks).
Society then considers certain behaviors and traits more masculine or feminine, and creates norms and roles around these. Some of these norms and roles exist on a spectrum, some are more binary.
Gender for a long time was used either as a synonym for sex, or only this case of describing language (gendered pronouns). In the mid-1900s academics in the social science used it to mean "the social norms and roles society creates based on biological sex." Then more recently some academics have re-defined gender again to mean "ones own innate conception of one's male/female identity." There isn't any scientific proof that such a thing exists or doesn't exist, nor can there be, because we don't have mind reading machines.
Sexual identity has also been redefined recently. So now if you were born with the egg producing equipment, but are taking male sex hormones some people will now define you as of the male sex. Frankly, I find this redefining of words to be pretty Orwellian.