Who were the first people in North America? From where did they come? How did they arrive? The prehistory of the Americas has been widely studied. Over 70 years a consensus became so established that dissenters felt uneasy challenging it. Yet in 2001, genetics, anthropology and a few shards of flint combined to overturn the accepted facts and to push back one of the greatest technological changes that the Americas have ever seen by over five millennia.
The accepted version of the first Americans starts with a flint spearhead unearthed at Clovis, New Mexico, in 1933. Dated by the mammoth skeleton it lay beside to 11,500 years ago (11.5kya), it was distinctive because it had two faces, where flakes had been knapped away from a core flint. The find sparked a wave of similar reports, all dating from around the same period. There seemed to be nothing human before Clovis. Whoever those incomers were around 9,500BC, they appeared to have had a clean start. And the Clovis point was their icon - across 48 states.
An icon that was supremely effective: the introduction of the innovative spearpoint coincided with a mass extinction of the continent's megafauna. Not only the mammoth, but the giant armadillo, giant sloth and great black bear all disappeared soon after the Clovis point - and the hunters who used it - arrived on the scene.
But from where? With temperatures much colder than today and substantial polar ice sheets, sea levels were much lower. Asia and America were connected by a land bridge where now there's the open water of the Bering Strait. The traditional view of American prehistory was that Clovis people travelled by land from Asia.
This version was so accepted that few archaeologists even bothered to look for artefacts from periods before 10,000BC. But when Jim Adavasio continued to dig below the Clovis layer at his dig near Pittsburgh, Pennsylvania, he found blades and blade cores dating back to 16,000BC. His findings were dismissed as erroneous; too astonishing to be credible. The Clovis consensus had too many reputations behind it to evaporate easily. Some archaeologists who backed Adavasio's conclusions with other similar data were accused of making radiocarbon dating errors or even of planting finds.
Decisive evidence would have to come from an independent arena. Douglas Wallace studies mitochondrial DNA, part of the human chromosomes that is passed unchanged from mother to daughter. It only varies when mistakes occur in the replication of the genetic code. Conveniently for Wallace's work (piecing together a global history of migration of native peoples) these mistakes crop up at a quite regular rate. The technique has allowed Wallace to map the geographical ancestry of all the Native American peoples back to Siberia and northeast Asia.
The route of the Clovis hypothesis was right. The date, however, was wrong - out by up to 20,000 years. Wallace's migration history showed waves of incomers. The Clovis people were clearly not the first humans to set foot across North America.
Dennis Stanford went back to first principles to investigate Clovis afresh, looking at tools from the period along the route Clovis was assumed to have taken from Siberia via the Bering Strait to Alaska. The large bifaced Clovis point was not in the archaeological record. Instead the tools used microblades, numerous small flint flakes lined up along the spear shaft to make its head.
Wallace's DNA work suggested migration from Asia to America but the Clovis trail contradicted it. Bruce Bradley stepped in to help solve this dichotomy, bringing with him one particular skill: flintknapping and the ability to read flint tools for their most intimate secrets.
He spotted the similarity in production method between the Clovis point and tools made by the Solutrean neolithic (Stone Age) culture in southwest France. At this stage his idea was pure hypothesis, but could the first Americans have been European?
The Solutreans were a remarkably society, the most innovative and adaptive of the time. They were among the first to discover the value of heat treating flints to increase strength. Bradley was keen to discover if Solutrean flintknapping styles matched Clovis techniques. A trawl through the unattractive flint offcuts in the storerooms of a French museum convinced him of the similarities, even though five thousand kilometres lay between their territories.
The divide was more than just distance; it crossed five thousand years as well. No matter the similarities between the two cultures, the possibility of a parallel technology developing by chance would have to be considered. More evidence emerged from an archaeological dig in Cactus Hill, Virginia. A bifaced flint point found there was dated to 16kya, far older than Clovis. Even more startling was its style. To flintknapper Bruce Bradley's eye, the Cactus Hill flint was a technological midpoint between the French Solutrean style and the Clovis points dating five millennia later. It seemed there is no great divide in time. The Solutrean flint methods evolved into Clovis.
If time could be discounted, Bradley's critics pointed to an obstacle that was hardly going to go away: crossing the Atlantic Ocean in small open boats. How could Stone Age people have made such an epic journey, especially when the Ice Age maximum would have filled the Atlantic with icebergs.
Dennis Stanford returned to his earlier hunch, looking for clues among the Arctic Eskimo peoples. Despite the influx of modern technologies, he was heartened to discover that traditional techniques endured. Clothing makers in Barrow, Alaska, recognised some Solutrean bone needles he showed them as typical of their own. The caribou skin clothing the Inuit still choose to wear could equally have been made by people in 16,000BC. And for Eskimo peoples the Arctic is not a desert - but a source of plentiful sea food. If the Solutreans had the Clovis point it would have made a formidable harpoon weapon to ensure a food supply. Would modern Eskimo ever consider a five thousand kilometre journey across the Atlantic?
The answer it seems is yes - they have undertaken similar journeys many times.. Most encouraging was the realisation that Inuit people today rely on traditional boat building techniques. 'Unbreakable' plastic breaks in the unceasing cold temperatures whereas boats of wood, sealskin and whale oil are resilient and easily maintained. The same materials would have been available to Solutrean boat builders. Even if the Stone Age Europeans could make those boats, would it survive an Atlantic crossing?
Stanford believes the boats' flimsiness is deceptive. With the Atlantic full of ice floes it would be quite possible for paddlers in open boats to travel along the edges, always having a safe place to haul out upon if the weather turned in.
All this evidence was still essentially circumstantial, making the Solutrean adventure possible not proven. Douglas Wallace's DNA history bore fruit once more. In the DNA profile of the Ichigua Native American tribe he identified a lineage that was clearly European in origin, too old to be due to genetic mixing since Columbus' discovery of the New World. Instead it dated to Solutrean times. Wallace's genetic timelines show the Ice Age prompted a number of migrations from Europe to America. It looks highly likely that the Solutreans were one.