That day Gene Roddenberry and Bob Guccione met in a bar on Alpha Centauri

...People sometimes dismiss the “why slash” [women writing male/male romance novels] question, comparing it to men’s taste for lesbian porn. But why do men like lesbian porn? The most common answers are: because I like women and two are better than one; and I don’t like some other man blocking my view. Some men probably see the male protagonist as a rival. A woman may have similar reasons for liking slash: that two men are better than one, or because she likes to visualise male objects of desire without a woman intruding, or because she regards the heroine as a rival rather than a placeholder. Penley adds another possibility, stemming from the observation that in slash the authorial point of view typically shifts, with the writer identifying with each protagonist in turn. Perhaps its fans like to imagine what the objects of their desire feel during sex, and to identify with them as both the giver and recipient of sexual pleasure? And perhaps the possibility of a similar shifting point of view is also why some men like to watch or think about two women together?

In 1994 Catherine Salmon, a student at McMaster University in Hamilton, Ontario, and long-time slash fan, approached Donald Symons, an expert on sexual psychology, to supervise a research project on slash. He had never heard of slash, and so dumbstruck was he by her initial email that, as he says in the introduction to the book they ended up co-writing, “Warrior Lovers: Erotica, Evolution and Female Sexuality”, he “had to re-read it very slowly to make sure that it actually said what it had seemed to say”. Once he got over his astonishment, the pair set out to use the theories of evolutionary psychology to explore why slash might appeal to straight women. They started with the biologically driven differences between the two sexes’ mating strategies. Evidence from many cultures suggests that men and women value the same characteristics when they seek a long-term mate: intelligence, honesty and kindness are at the top of the list for both. But what appeals for a quick fling – and what strikes the two sexes as erotic – greatly differs.

For men, brief affairs with strangers are (in evolutionary terms) cheap side-bets on extra offspring. For women, they mean running the risk of bearing children, half of whose genes come from men they have not vetted and who would tie up their reproductive potential for years. As a consequence, men are far less picky than women when it comes to their erotica. They focus on appearance, youth and specific body parts, and like anonymity and variety. Women, by contrast, pay attention to a broad range of signals of quality in a potential mate: not just looks, but strength, competence, resources and status. Their objects of lust are not interchangeable.

The women in pornography act out a male version of sexuality: they are keen on impersonal, no-strings sex, need no foreplay and are focused much more on how things look than how they feel. There is no back-story or character or plot development. Erotica aimed at women, conversely, reimagines men as women would like them to be, at least in their wooing and screwing. They are tough, talented, widely admired and complex. They talk about their feelings and notice what women wear. Most importantly, they prove their worth by going through some sort of ordeal for the beloved’s sake. For women, what is erotic about the hero is the effort he puts into winning his true love, says Salmon, now at the University of Redlands, California – and here, the heroes of slash excel. “How much more could you do to prove your love than change your sexual orientation to be with someone?”

“To encounter erotica designed to appeal to the other sex is to gaze into the psychological abyss that separates the sexes,” Symons wrote. And slash, the pair concluded, was firmly on the “romance” side of that abyss. Though it was sometimes called “gay fiction”, that was a misnomer. When Salmon showed some sexually explicit slash to gay friends, they found it merely entertaining. Female romance fans, by contrast, commented favourably on a male/male romance. “Slash is romance, even though it’s two guys,” says Salmon. “They’re men who behave the same way as the men in romances.”