Sex is fundamental to our existence, but expressing it always involves some pussyfooting around — otherwise we’d have to come to grips with gonads and gestation, when fulfilling our biological purpose is the last thing on our mind. Even the word “sex” is often too straightforward, so we rely on euphemism and innuendo to obfuscate the obvious for the sake of modesty. There has always been one haven, however, for letting it all hang out: art, from antiquity on, has made disrobed humans look more like demigods than animals.