Ever since researchers discovered what appeared to be a new, tiny species of human on the Indonesian island of Flores in 2004, they have debated the ancestry and origins of Homo floresiensis ("the hobbit"). Dating of stone tools found on Flores now suggests that the hominid's ancestors arrived on the island at least 1 million years ago, about 200,000 years earlier than previously thought. The find raises the possibility that the hobbit’s forebearers on the island will eventually be found, but it leaves unresolved debates over just who those ancestors were.
The hobbit fossils were found in Flores's Liang Bua Cave and dated to between 95,000 and 17,000 years ago. At the time, many researchers assumed that they were descended from hominids who left behind stone tools at the Flores site of Mata Menge, about 100 kilometers southeast of Liang Bua. Six years earlier, a team led by Michael Morwood, now at the University of Wollongong in Australia, had dated the Mata Menge tools to about 800,000 years ago and concluded that they were probably made by the early human H. erectus. When the hobbit was first discovered, Morwood and his colleagues suggested that H. erectus might be its ancestor, although some researchers countered that it was simply a diseased modern human—now a minority viewpoint.
Now a team including Morwood, and led by Adam Brumm of Wollongong, reports tools from a new site: a cattle yard called Wolo Sege just 500 meters east of Mata Menge. The researchers have found a total of 48 stone artifacts, including flakes struck from cobbles and a stone core similar to those found at Mata Menge. Argon-argon radiometric dating on a volcanic deposit immediately overlying the tools yielded dates ranging from 1.02 million to 1.08 million years, with error margins of no more than plus or minus 60,000 years, the team reports online today in Nature.
The dating "is very solid," says geochronologist Paul Renne of the Berkeley Geochronology Center in California. And because the colonization of Flores by early hominids, which required a difficult sea crossing, was probably a very rare or even one-time event, "it is very probable that the Wolo Sege tools were made by the direct ancestors of H. floresiensis," says William Jungers, an anthropologist at the University of Stony Brook in New York state.
The researchers emphasize that these dates provide only a minimum age for the first hominids on Flores, because the dating was done on the volcanic rock overlying the tools. Below the tools lies a geological formation dated all the way back to 1.8 million years ago or more.
But who made these 1-million-year-old tools? Morwood and his colleagues originally suggested that the small-brained hobbit was the descendant of a group of H. erectus that colonized Flores and then shrunk in an evolutionary process called "island dwarfism." That hypothesis is still favored by many researchers, because H. erectus is known to have occupied Indonesia as early as 1.8 million years ago. But more recently, Morwood's team has argued, based on the hobbit's very primitive anatomy, that instead of H. erectus, a smaller, pre-erectus hominid such as H. habilis or even an australopithecine, somehow made it to Flores.
If so, researchers say, it would mean that H. erectus was not the first hominid to leave Africa and travel widely across the world, a conclusion already suggested by habilis-like fossils found at Dmanisi, Georgia. It's therefore critical, Jungers says, "that we recover skeletal remains of these tool-makers to help us choose between these competing hypotheses for the origins of the hobbits."