Four summers ago, when I had just returned from researching my novel The Voices in the Kimberley, western Australia, I went to hear two Aboriginal writers speak at the South Bank in London. From their discussion, it was clear that they did not approve of white fiction writers having anything to do with Aboriginal issues. When question time arrived, I put up my hand and asked whether this meant that a novel by a white writer set in the Kimberley (where 50 per cent of the population is Aboriginal) should not have any Aboriginal characters. It was a deliberately provocative question, but the barrage that came back was unexpectedly fierce. "You stole our land," one of the writers shouted. "You raped our women. Now you want to steal our stories!"

On the face of it, Germaine Greer's manifesto for a new Australian identity, Whitefella Jump Up, invites a similar response. She advocates a return to Aboriginality for white as well as black Australians: reversing colonisation, if you like. Ultimately, she envisages an Aboriginal republic run on hunter-gatherer principles, distancing itself from the consumerism - and the wars - of the British and the Americans. Greer suggests that, to kick-start the transition, white Australians look in the mirror and say out loud, "I was born in an Aboriginal country, therefore I must be considered an Aboriginal."

At best, this sounds like a mantra from a dodgy self-help book for guilt-ridden whites with an identity crisis. At worst, it seems like the final, fatal blow in a 200-year history of taking: the appropriation of identity itself. But this, remember, is Germaine Greer writing, and though she may at times allow her emotions to direct her reasoning, she is not stupid. Her book is not, she says, another essay on how to solve "the Aboriginal problem"; she is at pains to point out that she is writing for her "own mob" - the whitefellas - and that it is their problem she is addressing.

We have all heard about how the Aborigines' loss of connection with the land has caused them to lose touch with their spirituality. Now it is time to look at the less widely acknowledged problem of "whitefella spiritual desolation". Settler guilt, Greer says, has created a culture of denial in which whitefellas drink to dull the pain. Furthermore, white Australians are destroying the environment because they know, deep down, that the land is not theirs. "If we truly felt that this country was our home," she writes, "we could not despoil it in this manner."

Apart from finding it hard to feel sorry for white Aussies hitting the Foster's, when Aborigines are dying from alcohol-related problems such as diabetes and domestic violence at a far higher rate than white folk suffer, I have difficulties with Greer's reasoning. Her emotional premise is fair enough - many white Australians share Greer's unease about their relationship to the land. But Aussies are hardly the only people in the world seemingly hell-bent on destroying their country, cutting down its trees, overfishing its oceans, pumping toxins into its air and rivers.

As for whitefella spiritual desolation, that is not an Aussie prerogative, either. The west is full of people suffering from the loss of the spiritual beliefs which sustained their grandparents, and attempting to patch over that loss by "borrowing" from whatever ancient tradition happens to be in vogue. The problem is that what is borrowed necessarily becomes simplified and adapted to fit, with the result that the tradition so revered in the first place is gradually eroded. We are all guilty of this: I know that I am every time I roll out my mat and practise yoga.

In Australia, where whitefellas live alongside the remnants of an incredibly rich spiritual tradition, in which every rock, every gum tree, every goanna was invested with spiritual significance, the desire to "borrow" must be particularly strong. In my novel The Voices, a white teenager named Billy looks to the land and the spirits of the land for the meaning he lacks in his whitefella world, and ends up becoming involved in a botched circumcision attempt by a young Aboriginal girl who herself has only a half-baked understanding of her ancestral traditions. The book is, in many ways, an allegory of what happens when one culture attempts to cure itself with the medicines of another. It might benefit the former, but it speeds up the demise of the latter.

Aboriginality is much more in vogue than it was even ten years ago. Between the censuses of 1991 and 2001, an extra 144,632 Australians ticked the Aboriginal box - a figure that cannot be explained by population growth alone, nor (one hopes) by attempts to profit from claims over land rights. Being associated with the British is about as unfashionable these days as a pair of plus fours. As Germaine Greer herself admits, if the Australians voted for an Aboriginal republic rather than just a republic, "it would be a lot sexier".

But isn't Greer advocating precisely the sort of cultural "borrowing" that we're all up to? Let us adopt those aspects of Aboriginal culture that would benefit us, she seems to be saying, while retaining those aspects of our culture which work all right already, such as the legal system. We'll have your spirituality, thanks, and we'll have your respect for the land, too, but we'll say a polite no thanks to your law. (Spearing through the thighs? I think not!) Greer is urging white Australians to embrace a hunter-gatherer culture and eat kangaroo instead of beef, but she is not suggesting that they abandon their houses, head into the desert and start digging up witchetty grubs. Surely, this is pick'n'mix cultural shopping, a modern-day panacea, not a post-colonial U-turn. And anyway, what's in it for the blackfella?

One problem with "Aboriginality" is that it is hard to define. There is not, and never has been, any such thing as an Aboriginal culture, only many distinct and separate groups. At the time of settlement, there were roughly 250 Aboriginal languages spoken; now there are roughly 50, and most of those are on the way out. As Greer says, when a language becomes extinct, a whole way of seeing the world dies with it. So where are we supposed to find this Aboriginality? Among the families of Redfern, scene of the Aboriginal riots last February, none of whom has ever lived out bush, whose children are on hard drugs and whose men spend half their lives in jail? Or should we go and root out the Aborigines of Arnhem Land, who have so far been relatively successful in keeping the whitefellas at bay?

There is no touchier political issue in Australia than how to organise a society that allows Aborigines to thrive. Since the introduction of "reconciliation" in 1991, a heavy blanket of political correctness has smothered debate. Most white fiction writers, I was told by someone in Sydney, "know better" than to tread on Aboriginal territory. Yet out in the Kimberley, where whitefellas and blackfellas have been mustering cattle together for more than a hundred years, no one tried to scare me off. In this part of Australia, where black and white cultures overlap as well as collide, it would have been more shameful to have turned my back. Too much wearing of kid gloves can end up suiting embarrassed governments more than it suits the minorities requiring protection.

For this reason, I welcome Greer's manifesto - as I welcome any book that reminds us what a pitiful waste it is that the accumulated wisdom of a people who lived in harmony with the land for more than 50,000 years has been virtually lost in fewer than 200. No doubt white Australia has a lot to learn from black Australia, and suggestions for a way forward are certainly more useful than endless hand-wringing.

Whether Greer provides enough to satisfy a questioning, reasoning reader more concerned for blackfella spiritual desolation than white, however, and whether she is entirely sincere about opening up the debate, are less certain. She invites her readers to "disagree with me by all means", but acts like a hurt child when they do. At the end of the book, there is a series of commentaries by black and white critics alike, some complimentary, some not. All very thought-provoking, and generous of Greer, one at first assumes. But then the old battleaxe comes back for the "last word" (and this is surely why so many overly polite Poms love her). She cuddles up to those who agree with her (significantly, an Aboriginal fellow of Melbourne University who praises her for "dreaming big") and launches acerbic personal attacks on those who do not. Of Marcia Langton, a respected professor of Australian indigenous studies, Greer wails that they used to be friends "and I thought we always would be".

Drop the ego, Germaine! This is too important an issue. Let us hope that the Marcia Langtons of this world go on picking up Greer's baton, undeterred.

Susan Elderkin was listed by Granta magazine as one of the 20 best young British novelists of the past decade. The Voices, which was shortlisted for the Ondaatje Prize, is out in paperback from Perennial