RETURN TO THE HOMINID JOURNEY....
By the 1950s, the long-suffering Java Man finally got some respect. Acknowledging that he is neither ape-man nor gibbon, scientists renamed him Homo erectus and welcomed him as a card-carrying member of the human genus. But today scientists have yet another bone to pick with the hapless Java Man.
The question is this: Is he a direct ancestor of us modern humans or an indirect one? Do we occupy the same branch of the human family tree? Or do we Homo sapiens represent a younger twig that split off from Homo erectus to follow a different evolutionary path? More than the good name of Homo erectus is at stake. At the heart of the conflict lies perhaps the most profound and bitterly contested debate in anthropology -- the mystery of how our species came to dominate Earth.
There are a few points on which anthropologists agree. Most believe that 1 million to 2 million years ago, groups of brawny, thick-skulled Homo erectus began to migrate from their African homeland, eventually colonizing the Middle East, Europe and Asia.
[Editor's note: As the April issue to press, scientists announced new findings suggesting that predecessors of Homo erectus had established themselves in mainland Asia before Homo erectus. A story on this will appear in the June issue of EARTH.]
Anthropologists also agree that by about 30,000 years ago, the only humans roaming the planet were people like us: lightly built, thin-skulled, fully modern humans called Homo sapiens. The dilemma is what happened during the murky millennia in between.
The debate has settled into two camps. One, the "multiregionalists," argues that after Homo erectus migrated out of Africa, his descendants formed separate populations. Isolated by geography, each population evolved independently, but occasional interbreeding insured a steady exchange of genes across regions. The result: separate populations of modern humans, each with distinct physical features. We see the same features as regional differences in people today. The multiregional view holds that neighboring populations of early humans must have bred with each other often enough to maintain the overall unity of humanity, but not enough to obliterate distinct regional features.
The opposing theory, known as "Out of Africa," contends that we modern humans emerged as a completely new species in Africa just 100,000 to 200,000 years ago. About 100,000 years ago, we began to migrate into the rest of the world. Instead of interbreeding with the locals, we replaced them, presumably driving all other human tenants on Earth to extinction.
To decide which theory is correct, anthropologists have duked it out with "bones and stones," the tangible evidence that early humans left behind in the form of fossils and tools. But increasingly many researchers are exploiting another source as well: the family history we carry in our genes. Since genetic studies began flooding the scene in the late 1980s, the debate has grown more heated -- and more complicated. Last year alone saw the publication of at least three new genetic studies that supported the Out of Africa view.
Yet even the staunchest supporters of Out of Africa concede that the issue is still unresolved. As Ian Tattersall, an evolutionary biologist and head of the anthropology department at the American Museum of Natural History in New York, explains, "The emergence of Homo sapiens is still the really big mystery in human evolution."