Mating. Reproduction. The survival of the species. How much more crucial does it get?

      You’d think homo sapiens would have sorted out that one pretty sharpish. But no. Since the start of civilization, human sex has been absurdly complicated by a steady dripfeed of self-appointed experts: moralists, pundits, visionaries, ju-ju men, zealots and learned academics – all claiming to know the magical secrets of lovemaking. And they were all prepared to sell their wisdom to you at a very reasonable price. Just as every generation likes to think it invented sexual intercourse, we also like to think we invented sex advice, or at least built it on a very limited number of predecessors: the Kama Sutra, maybe Marie Stopes’ 1918 Married Love and the 1970s The Joy of Sex. But in fact today’s maelstrom of lovemaking manuals, videos and DVDs has a far richer and more twisted heritage than that. The genre is way older than the novel, and takes us right back to an ancient Chinese tomb-hoard of books first written in 300 BC.

      Every era has had its Dr Ruths dictating to us the correct way, the right place, the essential time, the appropriate shape, the perfect partner and, of course, the ultimate naughtiness. And what a proud parade: they feature, to mention but a few, Roman poets, medieval woman-haters, Victorian adventurers, astral travellers, gay sandal-makers, dope peddlers, racial-purity