Once upon a time in America

When the world was still in the grip of the last ice age some 15,000 years ago, an intrepid group of Stone-Age mammoth hunters tracked their prey over the bleak Arctic tundra. Crossing the stretch of land which then connected Siberia to Alaska, these early pioneers thereby became the first people to set foot in the New World.

When the world was still in the grip of the last ice age some 15,000 years ago, an intrepid group of Stone-Age mammoth hunters tracked their prey over the bleak Arctic tundra. Crossing the stretch of land which then connected Siberia to Alaska, these early pioneers thereby became the first people to set foot in the New World.

Or did they? This romantic image of the first Americans has captivated archaeologists for almost a century, but in the last few years it has started to give way to a very different picture. Thousands of years before the Statue of Liberty welcomed new immigrants, America may already have been a melting pot of ethnic groups from across the Pacific, north-east Asia, and even Europe.

The conventional theory about the first Americans became established following the unearthing in the 1930s of a set of beautifully crafted stone tools near Clovis, New Mexico. In the years that followed, trademark Clovis-fluted spear points surfaced in sites all over north America, relics of a culture that ended around 13,000 years ago. With this discovery, the story of the first Americans seemed to fall into place: when early big-game hunters arrived in Alaska, a huge ice sheet over Canada blocked their way through to the rest of the continent. But as the ice age drew to a close, a narrow ice-free corridor opened up allowing their descendants - the Clovis - free passage south into the Great Plains and beyond.

During the next 60 years, purportedly pre-Clovis artefacts kept turning up, only to be swiftly knocked down again. The Clovis story was elegant and stood the test of time. And yet some awkward sites remained; none more so than Monte Verde in south central Chile. In 1977, University of Kentucky archaeologist Thomas Dillehay began excavating this ancient settlement, which had been remarkably preserved under a blanket of peat. Radiocarbon dating fixed the site at 14,850 years old, centuries before the Clovis had even begun their trek southward.

For over a decade Dillehay battled to be heard over the so-called "Clovis Mafia", a group of powerful and intransigent defenders of the Clovis-first idea. When a group of die-hard sceptics finally visited Monte Verde in 1997, they had to admit that the date was right, thus precipitating a storm in the archaeology community. If the Clovis were not the first Americans, who were? And where did they come from, how did they get there, and when did they arrive?

Dozens of possibilities have since been put forward, and while no two scientists have the same answer, they agree that this is an exciting time to be in the field.

Ruth Gruhn of the University of Alberta, Canada, says that although Monte Verde was the turning point, dozens of lesser-known pre-Clovis sites in South America should have made it obvious long ago that Clovis were not the first.

At Quebrada Jaguay on the coast of southern Peru, for example, a small fishing village seems to have been in existence 13,025 years ago - a time when the Clovis were still throwing spears in north America.

Although some specialists still doubt the significance of Monte Verde, the many archaeologists now expressing strong doubts about the Clovis-first theory are not alone. Canadian geologists have been saying for years that the so-called "ice-free corridor" was more of a "huge impassable lake" right up until the end of the Clovis period. And anthropologists have noticed something strange about the handful of really ancient American skulls so far unearthed - they don't look anything like modern Native Americans. Instead, they resemble Polynesians or Ainu - an isolated ethnic group in northern Japan who look quite unlike modern Japanese.

"There was considerable diversity among the early people; they were much more diverse than Native Americans today. So somehow that diversity was reduced," says Richard Jantz, the University of Tennessee anthropologist who has been studying these ancient crania.

Jantz is one among a growing number of people who believe that the earliest Americans may have come from Japan.Thousands of years later Siberians colonised America, which explains why modern Native Americans and Siberians look alike. Jantz admits that right now this is just one of several different scenarios.

Recent DNA analysis also suggests that the Clovis were probably not the first people to have found their way to America. Theodore Schurr of the Southwest Foundation for Biomedical Research in San Antonio, Texas, has compared mitochondrial DNA from modern Native Americans with that from people from all over the globe. Schurr says that it looks from the DNA as though ancient Siberians crossed into the continental interior as far back as 40,000 years ago. Then, some time between 15,000 and 30,000 years ago, they were joined by groups from Japan and possibly even Europe.

Valuable though it is, DNA says nothing about how people might have got from Japan or Europe to America. Early navigators did travel by sea to Australia around 50,000 years ago, but no one is seriously suggesting that Stone-Age men and women sailed across the open oceans. A coastal route from Japan to north-west America, however, now looks reasonable. Anthropologist Dennis Stanford of the Smithsonian Institution in Washington DC says he can trace Clovis culture straight back to the Stone-Age Solutrean culture of Spain. While most of northern Europe and Canada were under ice sheets, argues Stanford, these ancient Solutreans could simply have followed the sea-ice round the north Atlantic and down to the north-east coast of America.

Solutrean culture ended thousands of years before Clovis began, but there are tantalising suggestions of intermediate sites that bridge the two cultures, in both time and technology. One is in Cactus Hill, Virginia: "The artefacts are such that if you found them with Solutrean you wouldn't pay any attention to them, but they're not quite Clovis. So I think that makes a nice, neat progression," says Stanford. "Our stereotype of the caveman is just bunk," says Stanford. "These Solutrean guys survived the ice age and were very ingenious. They were not guys with clubs wearing bearskin cloaks."

From his studies of hunter-gatherer communities - and his first-hand experience as a merchant marine in Alaska - Everett Bassett, an anthropologist at the University of Utah, concludes that people only turn to a maritime way of life when they are under extreme stress, because fishing is risky and ties you down. "Everything Dennis [Stanford] says is possible, but from what we know about the kinds of economic decisions people make, it's unlikely," he says.

Any archaeological evidence that would suggest otherwise is now, sadly, under water. If it were ever to resurface, it could answer one of the most intriguing mysteries of human migration.