There is this common way of talking about gender these days (at least I see it from popular twitter accounts), which asserts that gender is some complex phenomenon that science does not yet fully understand—but that nevertheless it is some natural phenomenon in humans.
But of course we—at least feminists—do understand what gender is. Gender is a system of social subordination anchored in sexual exploitation and social reproduction, whereby women's subordination to men is institutionalized. Far from natural, it's socially constructed.
There is no natural, pre-social notion of gender, because gender had to be created—not by God, but by people—in order to regiment sex/gender roles, to create and institutionalize men's dominance and women's subordination.
That gender is something "science doesn't understand yet" is a facade for oppression: socially-imposed differences—gender—are placed within the purview of scientific objectivity, natural—as if given to us by God—for us to "discover"—not engineered by human beings for social aims.
Obviously the program of understanding gender "scientifically" is the legitimizing of research programs into "brain sex", how gendered characteristics are "produced by DNA", etc. Social characteristics are made biological and thus made invisible as social. But it doesn't end here
In keeping with this program of "understanding" gender "scientifically", gender is conceptually reduced into smaller categories. Gender as such—a social phenomenon—is elided, instead broken down into aspects of psychology, behaviour, interests, expression, sexual wants, etc.
Gender as a concept is then built bottom-up, as though masculinity and femininity sit alongside mass and charge as natural properties, inhering in species of matter and arranged so as to produce gender socially. Gender essentialism is the bedrock of this view.
We see this explicitly in the natural sciences: gender identity is a "masculine" or "feminine" role during sexual intercourse (dominance/submission respectively). What makes one sex role "masculine" and the other "feminine" is somehow never questioned https://twitter.com/iHateCogsci/status/1241740525604147200
But gender is not built up from the natural world; it is imposed top-down by patriarchy, with all its intersections. The prescriptions of the male and female sexes—sex/gender roles—become masculinity and femininity—natural properties, proper to the sexes.
Gender is imposed on the social world and then ideologically read back to us from the natural world, "discovered" as though gender, masculinity and femininity, sexed social prescriptions, were out there in DNA and brains, behaviour and sexuality—given by God.
We should refuse to talk abt gender in this way. There is nothing pre-social that could make anything the case about masculinity or femininity. Dominance/subordination produce sex/gender roles made natural/biological as masculine & feminine—as sexed traits. That's the whole story