Grundworth, Untitled, c.1930. Danny Moynihan, London

The Barbican Gallery is showing one of its most ambitious and frankly titillating exhibitions ever this autumn, having borrowed from far and wide to present Seduced: Art and Sex from Antiquity to Now (running until January 27 2008).

The introduction sets a mature tone – we’re all here in the world because of this fundamental human act, so no sniggering.

However natural a fact of life it might be, it hasn’t prevented an over-18s only tag being necessary. Most will agree it’s spot on. The images on show range from the tame to those that only the most extremely liberal of parents would be happy for their young ones to lay eyes on – for example the Robert Mapplethorpe photo of a rather deep anal fisting.

Censorship, particularly as it arose from the Enlightenment onwards, is as unavoidable a theme of the show as the erotic is an irresistible one to artists. However, the curators assert that what makes this a display of art, rather than pornography, is that the latter is one-dimensional, with one purpose, while they have chosen works that have something else, not least an emotional element.

Unknown artist, Satyr embracing a Nymph, Pompeii. Roman, c.45-79AD. National Museum of Archaeology, Naples. Photo © Soprintendenza per i beni Archaeologici delle Province di Napoli e Caserta

Some of this stuff may be aesthetic, but some saucy art was created with the same intention as porn – take the Victorian stereoscopic photography. The fact is, art can be pornographic, porn can be arty.

Opening the exhibition is a fig leaf created to preserve the modesty of a cast of Michelangelo’s David for when Queen Victoria passed it by, which suggests that it is only in modernity that we have become prudish, but it’s difficult to imagine that the urge to squirm when you are later voyeur to most explicit images is a socialised norm.

Seduced ends with Nan Goldin’s slideshow of intimate portraits of couples, Heartbeat. They’re uninhibited in front of the camera, and quite comfortable to be naked with their children. What can be uncomfortable is that erotic art puts you in a private situation of which you shouldn’t be part.

Unknown Artist, Woman and man with oysters, Victoria and Albert Museum, London, Far East Dept © V&A Images/Victoria and Albert Museum, London

However, remove yourself a few thousand years, and from the realistic medium of photography, and no matter how many naked bodies are portrayed, it doesn’t feel like pornography. Now we’re in the land of art, which really got off the ground in Ancient Greece and Rome, with plenty of nudity as a lynchpin.

There’s a rather beautiful Greek marble of a hermaphrodite, c.500BC ceramics decorated with cavorting heterosexuals and homosexuals, Roman paintings of satyrs and nymphs, an unusual wind chime with bells strung off a penis… Some of these ‘obscene’ objects were put away in 1795 in the Gabinetto Secreto (Secret Room) of the Naples museum housing objects found at Pompeii and Herculaneum.

In 1857, Britain’s Obscene Publications Act was passed. The year before, a Dr George Witt gave his collection of ancient erotica to the British Museum, forming the restricted access Secretum. Now dispersed, this is a chance to see pieces from the collection back together, from tiny cameos of rude things to an amber phallus.

k r buxey, Requiem, 2002. Heather and Tony Podesta Collection, Washington DC © the artist

Sexy art from other cultures is showcased, too (Persian, Turkish and Asian). A collection of quite beautiful late 18th/early 19th century Japanese woodblock prints show partners (usually a man and a woman, in one image a woman and an octopus) part-kimonoed, handkerchiefs nearby for mopping up the fluids. In one, a lucky male recipient has a geisha engaged both atop his member and playing her shamisen. Multi-tasking, eh?

Chinese paintings by Wang Sheng (late 17th/early 18th century) take the intimacy outside, with great attention given to mosses, flowers, rocks and trees. Poetry accompanies Sheng’s rather sweet scenes – ‘Her body is made of snow / Her limbs of jade…’.

Contrast this with Nobuyoshi Araki’s visceral black and white photographs of snails in body parts, dissected fruits, a close-up of touching tongues with a hair intruding – these large prints by the gallery staircase bring the senses to the fore – your eyes can feel the wet surfaces, the skin, the isolated fleshy shapes. (There’s more than a hint of Man Ray here. And Araki, known for tying up women, has taken a few leaves out of the Surrealist book; the early movement resurrected and re-illustrated the Marquis de Sade’s writings, and used them in their films.)

Upstairs takes us well into the 20th century and contemporary art and sex. Artist and Muse demonstrates the move away from historical subjects at the turn of the century, with sketches of reclining nudes by Auguste Rodin, Gustav Klimt, Egon Schiele and Picasso. JMW Turner proves he could draw figures, too – and doing remarkable things, curator Martin Kemp points out.

Jeff Koons, Ilona on Top (Rosa background), 1990. Private collection, courtesy Galerie Max Hetzler, Berlin © Jeff Koons

Two stuffed, headless, copulating couples by Louise Bourgeois evoke lovers being absorbed in each other; Francis Bacon likewise huddles two naked figures with faces tucked away. Andy Warhol’s film Kiss breaks Hollywood’s Hayes Code whereby couples weren’t allowed to snog on screen for more than three minutes.

Another Warhol film is shown across the way. The half-hour Blowjob (1963) shows just the man’s face, and is juxtaposed with k r buxey’s response, Requiem (2002), showing her face while she receives oral sex. The idea is to question why the female orgasm has less emphasis placed on it in pornography.

Other contemporary works here play with porn – Jeff Koons sends it up with over-the-top candy colours, Thomas Ruff shows how blurring it gives it artistic qualities and Marlene Dumas turns it into paintings. It all goes to show how fine the art-porn line is, but is also a sad indication of the flood of mass produced, in-your-face, unsentimental and boring representations of sex we now swim among.

There’s something to be said for mystery and concealment, the magical stories behind the historical paintings, the mythical gods taking on the forms of animals to cavort with their chosen, the tiny pocket books with their kinky illustrations. Censoring things to keep them personal is not the same as inhibition, as Tracey Emin’s neon signs suggest at the end: ‘Is Anal Sex Legal? Is Legal Sex Anal?’