There is the principle that there is a biological distinction between the male and female sex.
(I suspect the number of people who don't fit into the binary male or female is underreported.
Genetic - we are XX or XY, although there are a number of variations on that.
Anatomy - clearly on the anatomical level there are physical properties that we label male or female - penis, testicles, vagina, womb etc - but some individuals will be born with organs from both or neither category or other variations that are significant but not for this project. Surgery can alter the configuration.
Self-image - at this point the biological shades into the social - on some level we perceive ourself as male or female, irrespective of what our organs are. If this aspect becomes relevant I'd clearly need to read materials on transgender and transsexual theory and experiences.)
This distinction between "male" and "female" is probably more political than biology textbooks allow.
Specific societies construct gendered identities for its inhabitants to perform - which are legitimated as "natural" by the scientific categorization. These identities are policed through structures akin to the Repressive State Apparatus and Ideological State Apparatus, with positive images of the gender/sex match (blue for a boy, pink for a girl) and negative for the mismatch (the effeminate man, the butch woman).
Precisely because this is cultural/ideological rather than "natural", the values and characteristics which we tag as masculine or feminine will vary from period to period and place to place (men can now wear pink, women drink pints [and appear in BINGE NATION shock horror probe headlines]). We might note binaries such as active/passive, rational/irrational, logical/emotional, exterior/interior, concave/convex which map onto masculine/feminine. The binaries themselves are not always true binaries and may contradict each other. (Penetration is coded active, but engulfing is hardly passive.)
In reality all of us are at some point on a spectrum between (hegemonic) Masculinity and (hegemonic) Femininity.
(Ok - Masculinity and Femininity seem to be like genres. There is no text which belongs in one genre.)
The mechanisms which attempt to police the spectrum into a binary system "program" us to associate roles with genders. To take I Will Fear No Evil, a male imagining of a man in a woman's body, a man can be an entrepreneur, lawyer, businessman, doctor, judge, bodyguard or artist and a woman can be a secretary, nurse, muse, whore or mother. In the last forty years the division is less clear - but a man acting in the role of mother or a woman acting in the role of body guard becomes news in the man-bites-dog mode.
Narratives as interactions of characters will have different levels of verisimilitude/plausibility/realism/
ine is to write against the grain.
Narrative structure is one of the ways we group texts together. (medium, style, language being others, but even these get gendered - embroidery as feminine etc.) Because the available verisimilitudinous narratives are gendered, so genres are gendered. Romance, melodrama, paranormal romance, mis lit?, perhaps fantasy vs noir, western, sf, espionage, perhaps crime. Like the active/passive binaries this is neither "natural", nor "logical", nor consistent, and yes Tolkien wrote fantasy and Christie wrote crime. There are societal values attached to genres - with romance, melodrama, paranormal romance, fantasy being dismissed as escapist. (Is there an sfnal narrative? It tends to the Bildungsroman, or at least often depicts a passage from innocence to experience.)
Gendered behaviour is not the
natural property of a given sex - although the ownership of property has historically been policed. One wonders if the objection to gay/lesbian marriage is also an issue of property rights and the law of the father.
Now we come to the So What?
It is not necessarily a feminist act for a woman to write sf, as the writer could write within the codes. (No names, no pack drill.) But it can be regarded as one. It can challenge the narrative shape, the pool of available characters, the structures of the sentences. It inevitably becomes political as it challenges the hegemonic structures.