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% If the evidence from Java holds up, it means that protohumans left their African homeland hundreds of thousands of years earlier than anyone had believed, long before the invention of the advanced stone tools that, according to current textbooks, made the exodus possible. It would also mean that Homo erectus had plenty of time to evolve into two different species, one African and one Asian. Most researchers are convinced that the African branch of the family evolved into modern humans. But what about the Asian branch? Did it die out? Or did it also give rise to Homo sapiens, as the new Chinese evidence suggests?
Answering such questions requires convincing evidence -- which is hard to come by in the contentious world of paleoanthropology. It is difficult to determine directly the age of fossils older than about 200,000 years. Fortunately, many specimens are found in sedimentary rock, laid down in layers through the ages. By developing ways of dating the rock layers, scientists have been able to approximate the age of fossils contained in them. But these methods are far from foolproof. The 200,000-year-old Chinese skull, in particular, is getting only a cautious reception from most scientists, in part because the dating technique used is still experimental.
Confidence is much stronger in the ages put on the Indonesian Homo erectus fossils. The leaders of the team that did the analysis, Carl Swisher and Garniss Curtis of the Institute of Human Origins in Berkeley, are acknowledged masters of the art of geochronology, the dating of things from the past. Says Alan Walker of Johns Hopkins University, an expert on early humans: "The IHO is doing world-class stuff." There is always the chance that the bones Swisher and Curtis studied were shifted out of their original position by geologic forces or erosion, ending up in sediments much older than the fossils themselves. But that's probably not the case, since the specimens came from two different sites. "It is highly unlikely," Swisher points out, "that you'd get the same kind of errors in both places." The inescapable conclusion, Swisher maintains, is that Homo erectus left Africa nearly a million years earlier than previously thought.
Experts are now scrambling to decide how this discovery changes the already complicated saga of humanity's origins. The longer scientists study the fossil record, the more convinced they become that evolution did not make a simple transition from ape to human. There were probably many false starts and dead ends. At certain times in some parts of the world, two different hominid species may have competed for survival. And the struggle could have taken a different turn at almost any point along the way. Modern Homo sapiens was clearly not the inevitable design for an intelligent being. The species seems to have been just one of several rival product lines -- the only one successful today in the evolutionary marketplace.
The story of that survivor, who came to dominate the earth, begins in Africa. While many unanswered questions remain about when and where modern humans first appeared, their ancestors almost surely emerged from Africa's lush forests nearly 4 million years ago. The warm climate was right, animal life was abundant, and that's where the oldest hominid fossils have been uncovered.