I'm not sure. Frankly, the idea of looking into the history of rape in porn feels me with the creeps, so I'll pass; but porn has exploded in popularity since the 1990s or so with the rise of the internet; this is around when things started getting really ugly with rape culture, cries about rape culture, and the rise of celibacy among women; although I'm well aware all of these predate the rise of the internet, and all have other factors as well, it seems interesting timing to me.