Temporary exhibition: Martian Museum of Terrestrial Art

Barbican Art Gallery, London

The Barbican's reputation for putting on unusual and slightly risky (or do I mean risqué after Seduced: Art and Sex from Antiquity to Now?) shows continues with the Martian Museum of Terrestrial Art, an exhibition of post-1950s works displayed as if unearthed by a group of extra-terrestrial anthropologists anxious to understand what humans mean by "art".

This is of course the six million dollar question - us confused humans continually struggle to define what "art" is, let alone make convincing arguments for our value judgements of it.

The curators, inspired by an essay in Kant After Duchamp by Belgian art historian Thierry de Duve in which an alien anthropologist descends to earth, have taken works by 100 artists ranging from Joseph Beuys to Maurizio Cattelan, with a host of relatively "difficult", largely conceptual artists in between.

It is the continuation of a trend now noticeable across museums and galleries in Europe and beyond: displays of 1970s-inspired works, often rather ugly, uncertain and uncomfortable, frequently involving accumulations of junk, of which the Unmonumental exhibition on show in New York's New Museum has been a leading example.

But unlike these rather po-faced shows (in times of war, economic crisis and religious turmoil, difficult art is clearly good for us), the Barbican show has its tongue firmly stuck in its cheek.

With themes such as Kinship and Descent; Magic and Belief; Ritual; and Communication (with a raft of sub-sets underneath) it talks as much about the misconceptions of 19th- and early 20th-century ethnography and their associated museum displays as it does about contemporary art.

It works because the show's curators have chosen artists who, at least in the works displayed here, are acutely conscious, some might say self-conscious, of the history of art and the way it is interpreted.

It is an essay in the discomfit, uncertainty, and sometimes playfulness that many exhibit about the meaning of art, of being an artist, the source of creativity, the purpose of it all. You won't find the likes of Rothko, Kiefer or Hirst's more romantic dead animal vitrines: an Art and Language spoof on a Jackson Pollock is as close to the transcendental or sublime as you are going to get here.

The opening section (Kinship and Descent: subsection Ancestor Worship) is one of the more successful. The first work you see is a gilded copy of Duchamp's Fountain by US artist Sherrie Levine (Fountain - Buddha, After Duchamp 6) in which the plain readymade has turned into a vulgar gold piece of repro tat.

In fact Duchamp is everywhere: in Robert Filliou's Optimistic Box no 3, 1968 (an empty, miniature chess box with the hopeful words "You won't imitate Marcel Duchamp" in it) to Thomas Hirschhorn's giant cigarette lighter (in the Totems subsection) emblazoned with the names and portraits of artists including Duchamp, Beuys, Warhol and Malevich.

The audio guide is, appropriately, a central part of the joke: in this case a confident, BBC-style announcer of the Martian variety comments authoritatively: "Totems refer back to founding figures and embody groups' guardian spirits… these can be accumulations of several figures, and can be 'elective' rather than 'biological' ancestors."

There are other, equally thought-provoking sections. In Magic and Belief (subsection Transformation) a rather boring-looking case by Cornelia Parker - a tie, a piece of bread, gloves, a pack of playing cards, all sliced in half - is indeed transformed by the label, which lists the objects and then adds that they were cut by the same guillotine that beheaded Marie Antoinette.

Why is that so affecting? Who cares about the history of the blade that did the cutting? Parker has built part of her career challenging us to question why certain associations - a feather from Freud's couch; Charlotte Brontë's pin-cushion - have such power to excite and stimulate the imagination.

In another work by Filliou, a box and swabs containing dust wiped from Cimabue's La Vierge aux Anges, 1270, is displayed. The audio guide speculates that, for humans, masterpieces have such special qualities that even the dust that comes into contact with them has magical properties.

Of course it is quite the opposite, a commentary on how the obsession about the artist-as-genius invites admiration for even the most third-rate scrawl, as long as the hand of the master created it. Until now, I've never found an audio guide that makes you laugh out loud.

There are other amusing touches. A cupboard-sized room viewed through a plate glass window has been turned into a Department of Unidentified Objects for all those bits of art so silly or weird that they defy explanation. Dr Lakra's Untitled (Cupido Lupita), 2006, a hideously tattooed pink plastic doll, falls happily into this category.

Of course for several critics all this jiggery pokery - the bright green labels, the phoney Martian language (based, funnily enough, on a 26-letter alphabet), the brass lines on the floor that links artworks, the audio guide - is all a bit much; "heavy-handed" said the Guardian's Adrian Searle.

And it is true that after a while you feel that you have had enough, somewhere around the middle of the gallery's difficult mezzanine floor. Nevertheless, the Barbican has boldly gone where few have gone before.

Jane Morris is a freelance arts writer and editor