by Tim Flannery
Importantly, the advances of the last decade have removed one hypothesis from the competition; that a great aridity at the peak of the ice age 25,000–15,000 years ago destroyed the megafauna. This must be incorrect, because all evidence indicates that the megafauna had vanished continent-wide some 20,000 years earlier, at a time when Australia’s climate was a just a little drier and colder than at present. We have no evidence of any major climatic anomalies occurring at this time, although the record is not finely dated enough to have registered a short, severe event, such as a drought lasting a century or less.
It is increasingly evident to me that the magic millennium—the one in which modern Australia was forged—is the forty-sixth before our own. This, it seems, is when the megafauna become extinct, people arrive in Australia and the fire genie is let out of the bottle.
All of this bodes well for the Future Eaters hypothesis, but I must emphasise that scientific hypotheses can never be proved, only disproved; and it was with this in mind that Bert Roberts, Chris Turney and I cast around for a simple, elegant and independent experiment that might do just that.
Throughout its history Tasmania has been intermittently joined to the mainland, allowing plants, animals and humans to enter from the north before being cut off by a rising sea. The earliest evidence of humans in Tasmania dates to around 35,000 years ago. Was it possible, we wondered, that an ancestral Bass Strait had kept people out of Tasmania until that time? If so, we had a perfect test for the hypothesis: if we could demonstrate that the Tasmanian megafauna became extinct 46,000 years ago, while people arrived 10,000 years later, then humans could have had nothing to do with the extinction. If, however, Tasmania’s megafauna survived until the arrival of people 35,000 years ago, then climate could be ruled out as the causative factor; this is because it is difficult to imagine a scenario where Victoria’s megafauna, a few hundred kilometres to the north, was exterminated by climate change 46,000 years ago while leaving Tasmania’s giant marsupials abundant and widespread.
Only a new dating program could provide the answers, and it was in search of preliminary information—sufficient to support a grant application—that in August 2003 Chris Turney and I stood in an old Hobart storehouse watching a forklift shift pallets full of rocks, bones and artifacts. We were looking for a set of cardboard boxes that held thousands of bones of Tasmania’s megafauna, excavated from a swag of sites right across the Apple Isle. As we opened box after box, we discovered to our joy that few of the bones had been cleaned. Though barely studied, they indicated that Tasmania was home to a curious, insular megafauna that included a small marsupial lion and several distinctive short-faced kangaroos. As I write, our Tasmanian samples are being subjected to a series of tests.
Despite the progress of the last decade, the last word is yet to be had in the great megafaunal extinction debate. And, as always, we may just be a single bone away from a revolution in our understanding.
19
World Conquest
After the extinction of the megafauna, the kangaroo’s grip on Australia strengthened. Now more than nine out of every ten species of surviving ground-dwelling marsupial herbivores belonged to the kangaroo family—fifty-one species in Australia and twenty more in New Guinea. It was a triumph that had yet to reach its apogee, for around 8500 years ago wallabies began turning up well beyond their natal shores, indicating that the family had begun to go global.
Fifteen thousand years ago the sea was over 100 metres lower than it is today, allowing Australia, New Guinea, Tasmania and the islands of their continental shelves to coalesce into a single landmass of over 10 million square kilometres. Known as Meganesia it was—with a single exception—the only place on Earth to see a kangaroo. That exception is the spire-like Goodenough Island off southeastern New Guinea. Surrounded by deep ocean, it is a continental fragment that has been isolated for millions of years, and the forests ringing its summit are home to a distinctive forest wallaby known as the black dorcopsis (Dorcopsis atrata). If you ruffle its black pelt an underfur of startling white is revealed, and often one or both paws of this collie-sized creature is also white. In the dense and mossy tangles it inhabits, where sunlight is seldom seen, these may serve as signals. The black dorcopsis is a relic from an earlier time, and may have reached its island home overland millions of years ago. Little changed in its island home, the dorcopsis gives us some idea of what the forest wallabies of an earlier age were like.
Around 8500 years ago, other dorcopsises began appearing on islands that had never been part of Meganesia. This story was revealed as archaeologists probed caves throughout the southwest Pacific as part of a research initiative known as the Lapita Project, which was aimed at exploring the expansion of the Austronesian people. They are the ancestors of the Polynesians and several other peoples, who today are spread from Madagascar to Easter Island. The project took its name from an Austronesian style of pottery known as Lapita ware, and it resulted in a detailed chronology of the Austronesians, who were, before the European imperial age, the most widely distributed group of humans on Earth. It also revealed an extraordinary story of ecological change in a region that spans two-thirds of the globe.
One of the most astonishing discoveries pertinent to our story was made in January 1991 by Dr Peter Bellwood, an archaeologist with the Australian National University. He was working on the starfish-shaped island of Halmahera in eastern Indonesia in ‘Gua Siti Nafisa’—the cave of Miss Nafisah’s dreaming. Whatever Miss Nafisah dreamed there, she could not in her wildest imaginings have guessed what lay buried beneath her nodding head. Bellwood sounded the sediments of the cave floor, unearthing bones, stones and shards of pottery that spoke of forgotten millennia of human existence. In the lowest levels he found
Wallace’s Line, where the faunas of Australia and Asia meet.
several jawbones of a dog-sized creature he could not identify. These he brought back to Canberra, and it was with some astonishment that I found myself in Peter’s lab later that year, pronouncing them to be the jaws of the chocolate-coloured forest wallaby of southwestern New Guinea, known as Dorcopsis muelleri. Such creatures are utterly unknown in the entire Moluccan region (including Halmahera) today. Indeed the cave that harboured the bones lies in the northern hemisphere, near Wallace’s Line (where the faunas of Asia and Australasia abut), separated by hundreds of kilometres of open sea from the wallaby’s ancestral Meganesian homeland.
A full study of the bones revealed that forest wallabies thrived on Halmahera for millennia, but between 3000 and 1900 years ago they vanished. Peter later found abundant remains of the same creature, this time dating to 8500 years ago, in caves on the island of Gebe, which lies between Halmahera and New Guinea. In both cases the wallabies vanished when the ancestors of the Polynesians settled the islands, bringing with them pottery, new plant crops and dogs. These people also began to replace the original Halmaherans, a process that continues to the present.
How did the wallabies reach the islands? They were, it seems, among the very first animals to be deliberately introduced to a new home by humans. And it was not the mobile Austronesians that did this, but the Aboriginal people of Gebe and Halmahera. These people almost certainly had only rudimentary watercraft—perhaps dugouts or rafts—for the movements occurred long before the great double-hulled Austronesian sailing canoes appeared. For the introduction to be successful several animals would have had to be carried on a long journey. Such long-distance voyaging so early in the Australasian region is itself astonishing, but anyone who has struggled with a wild forest wallaby will realise that the creatures on those cramped watercraft were almost certainly tame—perhaps the joeys of females which had been hunted. Studies of the fossil wallaby’s teeth even indicated a potential source area—Missool Island—off the southwestern coast of New Guinea.
But why would people carry tame wallabies from one island to another only to let them loose in the jungle? I suspect that their motive was similar to that of the nineteenth-century acc
limatisation societies which brought rabbits, foxes and deer to Australia—to enrich the game available on their island homes. Both Gebe and Halmahera have arisen out of the ocean too recently for an extensive fauna either to have reached them or to have evolved there; their indigenous mammals consist only of bats, rats and possums. As far as we know, Halmahera’s Aborigines did not fully domesticate the wallabies, yet their taming and transport represent the earliest human manipulation of a kind that would lead to animal domestication and agriculture. Their achievement is thus a signal landmark on the road towards human domination of the globe.
Other studies done under the auspices of the Lapita Project reveal that such transportation was not unique to the Moluccan Islands. Ample evidence has been found that the New Guinea pademelon (Thylogale browni) was introduced by Aboriginal people into a swath of islands lying to New Guinea’s north and east. The best documentation comes from the large island of New Ireland in the Bismarck Archipelago, where several excavations record its abrupt arrival around 7000 years ago. New Ireland is a recently formed landmass whose only indigenous land mammals were two species of rats. People have also introduced two possum species, a rat and the pig to the island, so the pademelon was hardly alone in being carried across the sea. From New Ireland the wallaby spread as far north as the islands of Tabar and Lihir, and eastwards to Buka Island in the northern Solomons. (On Buka, however, just a single foot-bone has been found, which may have arrived in a traded skin or other artifact rather than as a living animal.) Still, the spread of kangaroos through an intricate archipelago lying north of Australia, and extending eastwards for over 3500 kilometres, is an astonishing expansion. This, however, was only the first stage in the kangaroo’s world conquest.
Since 1791 Europeans have carried kangaroos across the globe, the first living one arriving in London that year. A century and a half later, wild populations had become established in Hawaii, New Zealand and even Europe itself. The Hawaiian population originated around 1916 from a single pair of brush-tailed rock-wallabies (Petrogale penicillata) that escaped from a menagerie on the island of Oahu. Today their descendants inhabit rocky slopes in the outer suburbs of Honolulu, and are diverging so rapidly in genetic structure and appearance (having become redder and smaller) that scientists have predicted the Oahu population will eventually be proclaimed a separate species.
New Zealand is home to six different kinds of kangaroos, five of which were released on Kawau Island in 1845 by Governor George Grey, who was governor of South Australia before being posted to New Zealand. He brought with him parma wallabies (Notamacropus parma), tammar wallabies (Notamacropus eugenii), brush-tailed rock-wallabies, black-striped wallabies (Notamacropus dorsalis) and swamp wallabies (Wallabia bicolor). Grey performed a valuable service to conservation in bringing the tammars to Kawau, for within eighty years of their trip across the Tasman the population that they had been drawn from (mainland South Australia) was extinct. Now, under the auspices of a New Zealand-born premier of South Australia, New Zealand tammars have been returned to restock national parks where they have been absent for nearly a century.
But it is the red-necked wallaby (Notamacropus rufogriseus) that has proved to be the most remarkable traveller. The Tasmanian red-necked wallaby is a hardy creature used to foraging in alpine snows—a capacity that has assisted it in becoming established as far afield as New Zealand’s North Island, Britain’s Peak District and Ashdown Forest, and Germany’s Black Forest (where it thrives on the estate of Prince Reuss). World War II boosted the European populations of this robust Tasmanian, destroying fences around zoos and menageries and allowing it to hop to freedom through bomb-holes. The South Island of New Zealand alone was home to 750,000 before control programs in the 1960s reduced their population to around 3500.
A colony of grey kangaroos, which now numbers around fifty individuals was established more recently in the Rambouillet forest west of Paris. It originated thirty years ago in a bungled theft of animals from the Emance nature reserve. The locals now seem quite proud of their kangaroos—the Emance school magazine is called the ‘Joking Kangaroo’, and the town’s mayor says that the roos are just part of the local scene.
With colonies of kangaroos now firmly established in Europe and the Pacific Islands, it will be interesting to see where kangaroos next appear in the twenty-first century.
20
A Dingo-driven Revolution
A profound revolution occurred throughout Australasia over the past 5000 years, the key elements of which were encapsulated by Rhys Jones and linguist Nicholas Evans in 1997:
… dramatic changes took place in the human population of Australia some five millennia ago. In the archaeological record this shows up as the emergence of the ‘small tool tradition’ using flaked points, hafted adzes or microliths, but also as evidence of large-scale gatherings, advances in plant food technologies (especially cycads and seed grinding), the arrival of the dingo, and exploitation of more marginal environments.
Archaeologists refer to this phase of cultural development in Australia as one of ‘intensification’—more archaeological deposits, more cultural diversity and more people. It is a change as profound in its own way as the arrival of agriculture in Europe. But what could have precipitated such a revolution? It was, I believe, launched by the arrival of man’s best friend, the dog. Let us begin by asking why Halmahera’s wallabies vanished. The island is a quarter the size of Tasmania, yet so rugged that even now parts of it remain uninhabited making extinctions by human hands alone unlikely. At around the same time Gebe lost its wallabies, and two species of pademelon (Thylogale) vanished from the rugged alpine grasslands of West Papua (previously Irian Jaya). These extinctions were, I believe, caused by the dog, which had been carried to Australia around 4000 years ago by Austronesians. (It may have arrived later in New Guinea and Halmahera.) But why would dogs, which spread throughout Australasia, cause wallaby extinctions only on Halmahera, Gebe, and in the highlands of West Papua? Despite a moderately good fossil record, fossils of thylacines have never been recorded from any of these regions. In places such as Papua New Guinea and Australia, thylacine remains occur where similar wallabies survived. Perhaps being hunted by thylacines taught wallabies how to avoid being eaten by dogs.
The dingo has been implicated in the extinction from the mainland of the thylacine, Tasmanian devil and Tasmanian native hen, but evidence for a far more surprising impact comes from studies of Aboriginal languages. One of the most perplexing mysteries of Australia’s past is how Aborigines inhabiting over seven-eighths of the continent came to speak dialects derived from a single, recent language family. Known as Pama-Nyungan (Pama and Nyunga mean ‘person’ in two geographically distant Australian languages), its dialects are as differentiated as the Indo-European languages. Only in parts of Arnhem Land and the Kimberley do more ancient languages survive.
In 1997 Rhys Jones and Nicholas Evans pinpointed the time and place of origin of this successful language family. It arose, they demonstrated, around 5000 years ago (around the time the dingo arrived) in eastern—quite possibly northeastern—Arnhem Land. This is striking information because today the putative ancestral home of Pama-Nyungan is surrounded by people who speak utterly different, more ancient languages. So how was Pama-Nyungan so successful at displacing all other languages to the south of it, but not its immediate neighbours? In this it is resembles English, which has replaced the native languages of North America, but has been unable to drive Gaelic from the British Isles.
Often where languages have spread rapidly, technological innovation has been cited as a cause. In the case of Britain it was (in part at least) maritime innovations and the industrial revolution. The Indo-European language group, which some 7000 years ago began to spread from a source in western Asia into Europe and India, provides another well-studied example. The domestication of the horse has often been cited as the primary cause, though agriculture is becoming a more favoured explanation. For Pama-Nyungan, both the coincidence
in timing, and the pattern of its spread, indicates that the acquisition of dogs was a likely cause. Pama-Nyungan speakers would have had little advantage over their neighbours whom, one assumes, had also acquired dogs from the Austronesians on the northern coast. But the dog-less people to the south may well have found themselves at a disadvantage.
At first it is difficult to see what advantages dogs could have brought to Aborigines, for in historic times they were primarily used for warmth and companionship and, except in dense forests, they were not valued as an aid in hunting. Indeed, noisy dogs can be a disadvantage for hunters on the open plains, and Aborigines often go to considerable lengths to leave their dogs in camp when they hunt. It is important, however, to remember that this situation is the outcome of 4000 years of accommodation and learning about each other by dogs, people and marsupials. A quite different situation may have existed when Pama-Nyungan first began its spread. Then dogs were a new element in the Australian fauna, and the marsupials had yet to learn how best to evade them.
