Shown above is an editorial spread (click to see at full size) from 'The Science Fiction Book: An Illustrated History' by Franz Rottensteiner, published in 1975. The book went into great detail on almost every major theme that could be found in science fiction, including sex (or a lack there of). I love caption they have in the lower right hand corner:
"SF authors may generally avoid sex in their plots, but the details on these pages make it clear that science fiction illustrators do not feel the same reticence."