Contributer Ann Leckie is the author of Ancillary Justice.
Science fiction is often assumed to be a genre that mostly appeals to men, both as writers and as readers. Ask for a list of the most influential early science fiction writers, and likely you'll get back names like HG Wells or Jules Verne, or Asimov or Clarke. And in the narrative of the history of science fiction, it's common to point to the seventies as an era when women finally began to be interested in reading and writing it. Before that? Mostly dudes.
Except this isn't actually true. For one thing, there's an argument to be made that the first science fiction novel was Mary Shelley's Frankenstein. Shelley drew on the real science of the day to make her monster, and questions about the consequences of technological advances, and responsibility for those consequences, are still ones that concern science fiction today, even if we don't imagine anymore that a corpse could be brought to life with electricity.
So, you could plausibly say that science fiction was invented by an eighteen year old woman in 1816. And over the next hundred (or more!) years there were actually quite a few women who wrote novels and stories about the future, or about all-women utopias (or both). It was actually a pretty popular kind of thing. If you're curious, you can pick up the e-book anthology Feminist Sci Fi: An Anthology for a whole buck fifty. Or go down that table of contents and google the names--you can find many of these writers' works on the web, since they're public domain by now, stories by Charlotte Perkins Gilman, Rokheya Shekhawat Hossein, Alice W. Fuller, and Francis Stevens, among others.
Now, maybe you'd argue that Shelley, and these others, their works aren't really science fiction the way we think of it. After all, at the time a lot of stories of the future were more or less explicitly political, or social commentaries, and not the working out of scientific or technological ideas in fiction that we tell ourselves is the real, pure thing.
You wouldn't be alone. There are those who disagree with the idea of Frankenstein as the first science fiction novel and instead say sci-fi really began with the pulps. In particular, with Amazing Stories, edited by Hugo Gernsback. In that case, let me introduce you to Claire Winger Harris. In 1927 she took third place in an Amazing Stories contest with The Fate of the Poseidonia. Gernsback expressed surprise at one of the winners being a woman, "...for, as a rule, women do not make good scientifiction writers, because their education and general tendencies on scientific matters are usually limited. But the exception, as usual, proves the rule, the exception in this case being extraordinarily impressive." Harris went on to sell Gernsback several more stories.
It's been claimed that Harris was the first American woman to write science fiction under her own name. (Francis Stevens also wrote for the pulps--she appeared in Weird Tales ten years before Harris sold her first story, but she did so under a masculine pen name.) Whether this is true or not, it does bring up an interesting point about the women pioneers of science fiction.
There may well be many more women who wrote for the pulps in the twenties, thirties, and forties than we know about. Several women SFF writers of the time (and later) wrote either under their initials (like C.L. Moore), under a male pseudonym (Francis Stevens, Andre Norton), or else had an ambiguous first name (Leigh Brackett). We'll never know how many of the writers in the pulps who are now just names to us were women writing under an assumed name. Maybe none of them. Then again, as recently as the seventies, James Tiptree Jr famously concealed her real-world identity for quite some time, while also being quite well-known and carrying on correspondence with other writers in the persona of Tiptree--until curious and determined fans dug the information out. What if they never had? We would never know that James Tiptree Jr was actually Alice Sheldon.
The truth is, there are many more women who wrote science fiction and fantasy than the writers I've named here. Women have been writing SFF since the beginning--pretty much whatever beginning point you want to pick.