Stonework. Stone tools found between layers of volcanic rock on the island of Flores show humans were there about 800,000 years ago.
Ann Gibbons
Science 1998; 279: 1635-1637.
In 1968, a Dutch missionary living on the Indonesian island of Flores found stone tools alongside the bones of an extinct type of elephant called a Stegodon, known to have lived at least 750,000 years ago. If the tools were as old as the Stegodon, this was a spectacular discovery, for Flores lies beyond a deep-water strait that separates most Asian and Australian faunas. The tools meant that the only human species then living in Southeast Asia, Homo erectus, must have been able to cross this biological barrier, called Wallace's line.
But when the missionary, Theodor Verhoeven, reported his findings in the journal Anthropos, his claim was roundly dismissed. Although trained in classical archaeology, Verhoeven was an amateur, so researchers discounted his field work. And the accepted idea was that deep waters blocked human exploration until about 50,000 years ago. Although H. erectus was known from just 600 kilometers away on Java, most researchers were convinced that this early human lacked the social and linguistic skills needed to cross Wallace's line by piloting a raft over deep, fast-moving waters. Even after Dutch and Indonesian paleontologists backed Verhoeven's findings with new excavations and paleomagnetic dating in 1994, the claim was still considered dubious.
Stonework. Stone tools found between layers of volcanic rock on the
island of Flores show humans were there about 800,000 years ago.
M. J. MORWOOD
In this week's issue of Nature, however, an international team presents new dates for stone tools from Flores, based on a different and more reliable technique called fission-track dating, that confirm H. erectus's presence there 800,000 years ago. The authors propose that the early humans who left behind these simple flakes and cobbles were "capable of repeated water crossings using watercraft" and may even have had language, needed to cooperate to build rafts. The "cognitive capabilities of H. erectus may be due for reappraisal," says archaeologist Mike Morwood of the University of New England in Armidale, Australia, lead author of the paper.
Most researchers accept the new dates for the artifacts, but they are sharply divided over what the findings reveal about the toolmaker. A few questions linger about whether the artifacts are really tools--and no H. erectus bones have been found on Flores to dispel these questions. Some researchers add that H. erectus might have accidentally drifted over to Flores on a raft or even walked on some previously unknown land bridge, says Colin Groves of Australian National University (ANU) in Canberra: "The Flores data do not seem convincing that H. erectus made boats." Nonetheless, he agrees with others that the tools "are quite remarkable evidence of the distributional extent and environmental flexibility of our perhaps underestimated cousin, H. erectus."
H. erectus in Asia has long been eclipsed by its relatives in Africa, where the species is thought to have arisen more than 1.8 million years ago. In the first known exodus of human beings from Africa, H. erectus then spread around the globe, settling in China and Java perhaps as early as 1.8 million years ago (Science, 25 February 1994, p. 1087). But although these early humans spread thousands of kilometers over land and across shallow straits, they seemed to have been incapable of deep-water crossings. In technical, social, and organizational skills--not to mention language--H. erectus was thought to lag far behind later humans.
H. erectus's limitations seemed especially severe in Asia. Starting 1.5 million years ago, the Africans made better tools--two-sided stone hand axes--while the Asian members of the species either left almost no tools, as in Java, or only simple cobblestone choppers and flakes. "This group of Eastern hominids has always been regarded as impoverished in technological or cultural capabilities, as compared to their contemporaries in Africa," says Philip Rightmire, a paleoanthropologist at the State University of New York, Binghamton.
For the past 4 years, however, Dutch and Indonesian paleontologists have been coming up with support for Verhoeven's 1968 claim--and for a more flattering picture of Asian H. erectus. A Dutch and Indonesian group led by Paul Sondaar of the Natural History Museum in Rotterdam, the Netherlands, applied paleomagnetic dating, which is based on well-known reversals in Earth's magnetic field recorded in volcanic rock, to a rock layer just below 14 stone artifacts they had found in volcanic ash beds at a site called Mata Menge. The dates, about 750,000 years old, nicely matched Verhoeven's. But the results, published in 1994 and 1997 in French and Australian journals, were considered suspect. That was partly because of the lack of human bones and the uncertainties of this type of dating at the site, and also because the initial publication was in conference proceedings and was missed by many researchers, says Iain Davidson, an archaeologist at the University of New England in Armidale, Australia.
Now new dating of ash layers from Mata Menge confirms these findings. The ash contains minerals such as zircon that are ideal for fission-track dating. Over time, atoms of uranium-238 in a zircon grain in volcanic rock undergo spontaneous fission, producing fragments that streak across the crystal lattice like a meteor in the sky and leave tracks about 10 micrometers long. By chemically etching the crystals, geochronologists can see and count the tracks; the more tracks they see, the more time has passed since the rock crystallized.
Using this method on 50 individual grains of zircon from ash layers just above and below the tool-bearing sandstone layer, Paul O'Sullivan and Asaf Raza at La Trobe University in Bundoora, Australia, where the technique was pioneered, came up with ages of 800,000 to 880,000 years for almost all of the grains. Although it's easy to undercount the tracks, fission-track dating is considered reliable in the right hands, such as those of O'Sullivan's team. "The research group is tops, as good as they come," says Andrew Carter, a geochronologist at the London Fission Track Research Group. "I can't find any faults with it at all. They've gone out of their way to undertake more grain analysis than is conventional."
But some researchers still wonder exactly what's being dated on Flores--human artifacts or just shattered rock. Smithsonian Institution paleoanthropologist Rick Potts notes that the ratio of 14 artifacts to 45 stone pieces recovered at the site in 1994 is only 31%, and he thinks at least 50% of stones at a site should be tools. "If this were a site in Africa, the fact that most of the rocks are not artifacts would make us doubt it as a lithics site," he says.
However, Morwood, an archaeologist invited to work with the Dutch and the Indonesians to check the authenticity of the tools and the stratigraphy at the site, insists that there is "absolutely no doubt about them being artifacts." Other experts who have seen these artifacts agree that they're the real thing. "I think yes, having seen a few," says Peter Bellwood, an archaeologist at ANU. Furthermore, some of the flakes are made of chert, a rock not found at the site, suggesting that the tools were made elsewhere.
Other hints of H. erectus's presence on Flores come from the creatures that lived there, say Morwood and Sondaar. Sometime after 900,000 years ago, Flores's pygmy stegodons, giant tortoises, and giant Komodo dragons all suddenly went extinct. They were replaced by large stegodons, which apparently swam there in herds. Human hunters may have arrived and driven the pygmy stegodon and other animals to extinction, says Sondaar--making this the earliest extinction to be blamed on humans. All this has convinced those who have worked at Mata Menge that H. erectus was there--and that they arrived by raft or other watercraft. Even when the sea level was at its lowest, these humans would have had to cross 19 kilometers of water to get to Flores from the closest island of Sumbawa--after a 25-kilometer crossing over treacherous waters between Bali and Sumbawa. And an even longer crossing would be needed if they came from Sulawesi to the north, says Morwood. "You've got to be talking about watercraft," he says. That has broad implications for H. erectus in Asia and beyond: "They were intelligent, thinking animals. Once you take into account the use of watercraft and their rapid radiation out of Africa, you have to rethink H. erectus. They must have had language for the collective effort needed to achieve this sea travel." He speculates that the species reached the southern Indonesian island of Timor, where undated tools have also been found--and from there, perhaps even Australia.
Few others are willing to go so far. "Australia would have been out of sight, whereas the island-hopping route to Flores was marked by huge volcanoes visible from afar," says Bellwood. And Groves points out that the tectonics of these volcanic islands is so unstable that there may even have been a land bridge briefly connecting them. "Let's be cautious about what conclusions we draw about the navigational skills of H. erectus," says Groves.
Even if H. erectus did float to Flores, it could have been by accident, on a primitive raft, adds Davidson. Monkeys have been seen floating on makeshift rafts of mangrove tree limbs and vegetation in Indonesia, he says. Still, says Rightmire, this "does help to dispel the notion that H. erectus in general, and Eastern H. erectus in particular, were relatively slow to react to challenges posed by the environment," because they not only navigated deep-water straits but adapted to life on an island, where the environment is thought to have been far different from the forest habitat of the mainland.
The new findings also fit well with other work showing that Asian H. erectus has been underrated. Controversial new dates from sites in Java suggest that H. erectus persisted there from as early as 1.8 million years ago until as recently as 30,000 years ago, implying that they were able to adapt to varied terrain and climate. Other new studies suggest that H. erectus left behind sophisticated hand axes in southern China (see sidebar on p. 1636). For those who have worked on Flores and long believed in H. erectus's presence there, the new results are vindication. Says Sondaar: "I am happy that the finds of Verhoeven are finally recognized."