White Rhinoceros with a calf at Lake Nakuru national Park in Kenya. Credit:Martin Harvey/WWF The story shifts again, back to Vietnam where even the prime minister is rumoured to have survived a life-threatening illness after ingesting rhino horn. More than a cure for the country's rich and powerful, however, rhino horn has by now crossed into the mainstream. Young Vietnamese mothers have taken to keeping at hand a supply of rhino horn to treat high fevers and other childhood ailments. It is also the drug of choice for minor complaints associated more with the affluent lifestyle to which increasing numbers of Vietnamese have access; rhino horn has become a cure-all pick-me-up, a tonic, an elixir for hangovers. With this new popularity has come the essential paraphernalia common to lifestyle drugs the world over, including bowls with specially designed serrated edges for grinding rhino horn into powder. In a short space of time, rhino horn has become the latest must-have accessory for the nouveau riche. The sudden spike in Vietnamese demand, the miraculous fame of a saved official or his wife, and rhino horn's emergence as a symbol of status all came at a time when legal stockpiles of rhino horn were at an all-time low. Demand and supply. This is the irrefutable law of economics.

Or, as one expert in the illegal trade in rhino horn put it: ''It was a perfect storm of deadly consumption.'' The rhinoceros is one of the oldest creatures on earth, one of just two survivors - the other is the elephant - of the megaherbivores that once counted dinosaurs among their number. Scientists believe rhinos have changed little in 40 million years. The rhino's unmistakable echo of the prehistoric and the mystery that surrounds such ancient creatures - this is the animal that Marco Polo mistook for a unicorn, describing it as having the feet of an elephant, the head of a wild boar and hair like a buffalo - have always been its nemesis. As early as the first century AD, Greek traders travelled to the east, where the rhino horn powder they carried was prized as an aphrodisiac. But the rhino survived and, by the beginning of the 20th century, rhino numbers ran into the hundreds of thousands. They were certainly plentiful in 1915 when the Roosevelts travelled to Africa to hunt. Kermit, the son, observed a rhinoceros ''standing there in the middle of the African plain, deep in prehistoric thought'', to which Theodore the father is quoted as replying: ''Indeed, the rhinoceros does seem like a survival from the elder world that has vanished.''

The Roosevelts then proceeded to shoot them. Rhinos are epic creatures, gunmetal grey and the second-largest land animal on earth. Up to five metres long and weighing as much as 2700 kilograms, the white rhino, the largest of all rhino species, can live up to 50 years if left to grow old in the wild. In an example of advanced evolutionary adaptability, the black rhino will happily choose from about 220 plant species, eating more than 70 kilograms of plants a day. These impressive numbers, combined with some of the rhino's more limiting characteristics - it has very poor eyesight - have added to the myth that surrounds it. ''A slight movement may bring on a rhino charge,'' reported nature writer Peter Matthiessen in the 1960s. ''Its poor vision cannot make out what's moving and its nerves cannot tolerate suspense.'' Thus it was that the rhinoceros became a permanent member of the ''big five'', the roll-call of the most dangerous animals in Africa as defined by professional hunters.

But respect has always been tinged with derision. ''I do not see how the rhinoceros can be permanently preserved,'' Theodore Roosevelt is reported as wondering, ''save in very out-of-the-way places or in regular game reserves … the beast's stupidity, curiosity and truculence make up a combination of qualities which inevitably tend to ensure its destruction.'' In the 1960s, one eminent scientist described the rhinoceros as ''a very pathetic prehistoric creature, quite unable to adapt itself to modern times. It is our duty to save and preserve this short-tempered, prehistorically stupid but nevertheless so immensely loveable creature.'' Such disparaging remarks aside, they were, of course, right to be worried. We have been here before when it comes to saving the rhino. In 1960, an estimated 100,000 black rhinos roamed across Africa, absent only from tropical rainforests and the Sahara. By 1981, 15,000 remained. In 1995, there were just 2410 left on the continent. In 2006, the western black rhino was declared extinct. In Kenya, the numbers of black rhino fell from 20,000 at the beginning of the 1970s to 300 within a decade. This catastrophic fall in rhino numbers was the consequence of a poaching slaughter that consumed the country's wildlife as lucrative ivory and rhino horn was consumed to meet the growing demand in Asia; rhino horn also made its way to the Arabian Peninsula, where it was used to fashion the handles of traditional Yemeni daggers.

It was in Kenya's south, in the Tsavo National Park, that the war against rhinos reached its nadir - the park's rhino population fell from 9000 in 1969 to less than 100 in 1980. Since then, rhino numbers have rebounded thanks to a combination of legal protection - the trade in rhino horn was declared illegal under the Convention on the International Trade in Endangered Species (CITES) in 1975 - and beefed-up security. When I visited the Tsavo West Ngulia Rhino Sanctuary three decades after the massacre, I was met by guards in full military fatigues and armed with machineguns. ''These rhinos in here,'' one guard told me, ''they receive more protection than many African presidents.'' Kenya's population of black rhinos grew to about 600, with the continent-wide figure thought to be 10 times that number. Efforts to save the white rhino proved even more successful, with more than 20,000 in South Africa alone. A corner had been turned, it seemed, and the battle to save the rhino was counted among the great conservation success stories of our time. And then Vietnam acquired a taste for rhino horn.

In 2007, 13 rhinos were killed in South Africa. In the years that followed, the rate of killing grew steadily. From 2007 to 2009, one quarter of Zimbabwe's 800 rhinos were killed, and Botswana's rhino population has fallen to just 38. In South Africa, home to 90 per cent of the world's white rhinos, armed guards patrol the parks. Even so, 448 rhinos were killed in 2011. The following year, the number rose to 668. In the first 65 days of 2013, poachers killed 146 rhinos. At current rates the figure for this year will be close to 830. As a result, rhino populations could soon reach a tipping point that may prove difficult to reverse. The rhino death rate will exceed its birth rate within two years on current trends, according to Dr Mike Knight, chairman of the International Union for the Conservation of Nature's African Rhino Specialist Group. ''We would then be eating into rhino capital.'' Chief scientist of South Africa's National Parks Hector Magome agrees: ''If poaching continues, the rhino population will decline significantly by 2016.'' The importance of saving Africa's black and white rhinos is given added weight by the negligible numbers for the world's other three surviving rhino species - the almost 3000 Indian rhinos live in highly fragmented populations, while just 220 Sumatran and fewer than 45 Javan rhinos survive. Vietnam's last population of Javan rhinos was declared extinct in October 2011.

It is proving far easier to quantify the threats faced by Africa's rhinos than it is to arrest the decline for one simple reason: what worked in the past no longer holds. The recent upsurge in poaching has taken place in spite of the CITES regime of international legal protection. Security is also tighter than it has ever been. In South Africa's Kruger National Park, home to almost half the world's white rhinos, 650 rangers patrol an area the size of Israel or Wales. This falls well short of the one-ranger-per-10-square-kilometres ratio recommended by international experts, and more than 100 rhinos have already been killed in Kruger this year. Thus, those charged with saving the rhino are considering radical and hitherto unimaginable solutions. One such approach gaining traction is the controversial plan to legalise the trade in rhino horn, dehorn thousands of rhinos and flood the market with newly legal horns. Were this to happen, supporters of the proposal say, the price of rhino horn - which reached $65,000 a kilogram in 2012 - would fall, and the incentive for poaching would diminish.

Dehorning has long been opposed by conservationists - rhinos use their horns to defend themselves and while feeding. But the failure of all other methods has convinced some that the time has come to contemplate the unthinkable. ''The current situation is failing,'' Dr Duan Biggs, of the University of Queensland and one of the leading advocates for legalising the trade in horns, said recently. ''The longer we wait to put in place a legal trade, the more rhinos we lose.'' Dr Biggs and others point to the legalisation of the trade in crocodile products as an example of how such a plan could work. Critics counter that any legalisation of the trade in rhino horns is unenforceable. They also argue that lax or ineffective legal controls in Vietnam - where trading in rhino horn is already illegal - and elsewhere ensure that it will be impossible to separate legally obtained rhino horns from those supplied by poachers. ''We don't think it would stop the poaching crisis,'' says Dr Colman O'Criodain, of the World Wildlife Fund. ''We think the legal trade could make it worse.''

The debate about saving rhinos is riddled with apparent contradictions: that we must consider disfiguring rhinos if we are to save them; that rhino numbers have not been this high in half a century but the risk of their extinction has never been greater. And so it is that the story of the rhinoceros has reached a crossroads. It is a story that pits, on one side, a creature that has adapted to everything millions of years of evolution have thrown at it, against, on the other, the humans that will either drive the species to extinction or take the difficult decisions necessary to save it. Anthony Ham is a Melbourne journalist.