Not surprisingly, much of the confirming evidence for erectus is fire. There is a hearth in east Africa dated at 1.7–1.5 million years before the present. Cave fires sustained by H. erectus have been dated at over a million years old in France (Escale Cave), Spain (Torralba-Ambrona), and perhaps Hungary (Vértesszöllös); at Choukoutien, China, charcoal remains date from approximately 450,000 years ago; in Sangiran, Java, from perhaps 1 million years ago. The site at Torralba is particularly interesting because the distribution of charcoal and mastodon bones suggests that fire may have been used actively in the hunt, not merely for cooking afterward. While bones and charcoal give somewhat different dates, some older and some younger, they appear together, hand with brand.4
The pace accelerated with the appearance of Homo sapiens. Fossil records suggest an emergence between 200,000 and 100,000 years ago. Genetic records, encoded in DNA, recommend a more recent appearance, perhaps less than 100,000 years ago. Again, the source is Africa, and again another ring of fire radiated outward, a rhythm of anthropogenic burning that added to the other disturbances of the Pleistocene. The timing of its appearance, however, involves sparse evidence and complicated calculations. Migrations occurred not once but several times; new arrivals likely interbred with old residents; fire had to interact with other environmental parameters, particularly with a climate that often dramatically reversed itself within a span of centuries, a transformer that charged biotas into a kind of alternating current. That human procession, however, marched by torchlight.
By 40,000 years ago, H. sapiens had spread anthropogenic fire across Eurasia and the great land bridges—the Sunda and the Sahul—that joined Indonesia and Greater Australia to Southeast Asia. The colonization of the New World followed, synchronized with the ebb and flow of northern ice sheets that elevated Beringia from the seas and kept open a steppe corridor through central Alaska and along the eastern flank of the Rockies. Although some artifacts suggest an entry around 30,000–25,000 years ago, the substantive, confirmatory caches document another wave, or waves, that arrived in the New World with the waning of the Wisconsin glaciation around 11,000 years ago. Within 1,500 years, these new pioneers—big-game hunters—reached the southern tip of the Americas, Tierra del Fuego; the land of fire. The colonization of more remote islands occurred later, in historic times and by boat rather than by land: Greenland, by Inuit and Norse; the Atlantic islands, by Europeans from the tenth to sixteenth century; the Pacific Islands by Melanesians and Polynesians, from 1300 B.C. to around A.D. 900. Anthropogenic fire reached Antarctica only on the eve of the twentieth century. By then Homo’s ring of fire had encircled the Earth many times over.
CARRYING THE FIRE
Just when anthropogenic fire appeared in Australia is unclear. There is evidence for an abrupt, dramatic surge in burning around 40,000 years ago, coincident with the first documented fossils of Homo. But there are tantalizing suggestions that humans and their fires may have arrived much earlier. Homo erectus reached Java more than a million years ago; Homo sapiens swarmed over Asia about 100,000–70,000 years ago. Whether the venerable Wallace Line was as effective a barrier to humans as to other Asian mammals is unknown. For 50 million years Wallacea—a cluster of volcanic islands and deep-water channels—had segregated Southeast Asia from Greater Australia. Only mice, rats, and humans made the passage. One other migrant, the dingo, almost certainly traveled with humans, along a route that avoided Wallacea proper.5
The strength of the Wallace barrier flickered inconstantly. Over geologic time, it depended on systems of volcanic arcs, which varied according to plate mechanics. Over the span of the Pleistocene, its geography rose and fell with glacial tides. During glacial maxima, as ice sheets abstracted more and more of the world ocean, sea level fell, and what had been broad seas became channels. Even at its minima, however, a journey across Wallacea demanded at least eight voyages, and never fewer than fifty kilometers of sea had to be spanned. Two major routes seem probable, a southern route through Java and Timor and a northern route through Borneo.
Evidence for early human presence, however, is indirect. During the glacial epoch of 150,000–100,000 years ago, there is a geologic record of deposition, debris flooding, and vegetation change—from rainforest to scleroforest—and charcoal that has been interpreted as a possible consequence of human activity. There is, it appears, a pulse of change that subsequently settles into a more routine, but altered landscape. During this initial outburst, burning increased fourfold. It is suggested that early humans might have followed the Sahul savannas, then gradually encroached by fire into more heavily forested lands as seasonal and secular drought permitted. Once established, they could have used fire to keep open major corridors and hunting sites against reclamation by rainforest.6
Another line of evidence concerns the Pleistocene remains of hominid skulls. While the skulls all differ from those typical of contemporary Aborigines, they fall into two distinct groups, “robust” and “gracile.” The robust shape is the more ancient, as close to H. erectus as to H. sapiens. One speculation is that it represents a hybrid or intermediate type such as Homo soloensis, which flourished in Java between 300,000 and 100,000 years ago. Or it may represent an earlier subspecies of H. sapiens, analogous to the Neanderthal of Europe. Either way the hominid possessed fire, and if the geologic record prior to the last glacial epoch expresses a pulse of anthropogenic activity, then the robust Australian was the likely agent. There are, however, no sites that directly date Homo to these early times.7
The gracile Australian arrived later, probably crossing into the Sahul during the last glacial maximum, around 55,000 years ago. By 40,000 years ago this hominid had spread to both southwestern and southeastern Australia. From then onward the archaeological record is firm. Both robust and gracile skulls coexist, and probably there was interbreeding. Eventually the gracile form predominated. The modern Aborigine—remarkably varied in physical traits—is the evident outcome. By 20,000 years ago the Aborigine had colonized the perimeter of Australia, including Tasmania (then joined to the mainland), and had penetrated up rivers to the freshwater lakes of the interior. The climate overall was wetter, colder, and probably less intensely seasonal than today. Only the most arid core, small offshore islands, and the higher mountains of the southeast were not fully settled. As the last of the Pleistocene glaciations (c. 30,000–12,000 years ago) waned, sea level rose. At its minimum (roughly 16,000 years ago) sea level had plummeted 150 meters below current values. As the world glaciers receded, however, the seas returned. By 14,000 years ago the resurgent ocean submerged most of the Arafura plains that bonded Australia to New Guinea. By 12,000 years ago, the relentlessly rising seas permanently separated Tasmania from the mainland. By 8,000 years ago, Australia and New Guinea became separate islands. Two millennia later, the sea level stabilized and the littorals claimed approximately their present positions.8
The rising seas did not end all human migration to Australia. The earliest migrants had depended on watercraft; but these were primitive affairs, little more than log rafts, probably of Asian bamboo. With time the seas to the north, west, and east of Australia became the scene of maritime cultures, and Australia was visited many times, intentionally or accidentally. Around 4,000 years ago, a new stone toolkit of delicate flakes arrived; so did the dingo, macrozamia cultivation, and new styles of hearths. The likely origins are the Indian subcontinent, whose inhabitants exploited the new technology of seacraft and monsoonal winds to bypass the Wallace barrier. The introductions quickly spread across Australia. The eastern mountains, in particular, experienced an order-of-magnitude increase in human activity. Polynesians must have visited the Australian coast during their voyages. In the seventeenth century Malaccan traders and trepang gatherers began routine visits to the northern coastline of Australia, a practice that continued, intermittently, until the twentieth century. The impact of Malaccans and Polynesians, however, was minor: the patterns of Aboriginal life had been laid down over the preceding millennia, an existence that more or less bypassed the Neolithic revolution which was, on other continents, transforming foragers and hunters into herders, farmers, and urbanites. The phenomenal isolation of Australia continued until European colonization in the eighteenth century, and when it again broke down, the rate and magnitude of change proved almost catastrophic.9
If it is not clear just when Homo first arrived in Australia, neither