Scientists in Britain have identified the oldest skeleton ever found on the American continent in a discovery that raises fresh questions about the accepted theory of how the first people arrived in the New World.
The skeleton's perfectly preserved skull belonged to a 26-year-old woman who died during the last ice age on the edge of a giant prehistoric lake which once formed around an area now occupied by the sprawling suburbs of Mexico City.
Scientists from Liverpool's John Moores University and Oxford's Research Laboratory of Archaeology have dated the skull to about 13,000 years old, making it 2,000 years older than the previous record for the continent's oldest human remains.
However, the most intriguing aspect of the skull is that it is long and narrow and typically Caucasian in appearance, like the heads of white, western Europeans today.
Modern-day native Americans, however, have short, wide skulls that are typical of their Mongoloid ancestors who are known to have crossed into America from Asia on an ice-age land bridge that had formed across the Bering Strait.
The extreme age of Peñon woman suggests two scenarios. Either there was a much earlier migration of Caucasian-like people with long, narrow skulls across the Bering Strait and that these people were later replaced by a subsequent migration of Mongoloid people.
Alternatively, and more controversially, a group of Stone Age people from Europe made the perilous sea journey across the Atlantic Ocean many thousands of years before Columbus or the Vikings.
Silvia Gonzalez, a Mexican-born archaeologist working at John Moores University and the leader of the research team, accepted yesterday that her discovery lends weight to the highly contentious idea that the first Americans may have actually been Europeans.
"At the moment it points to that as being likely. They were definitely not Mongoloid in appearance. They were from somewhere else. As to whether they were European, at this point in time we cannot say 'no'," Dr Gonzalez said.
The skull and the almost-complete skeleton of Peñon woman was actually unearthed in 1959 and was thought to be no older than about 5,000 years. It formed part of a collection of 27 early humans in the National Museum of Anthropology in Mexico City that had not been accurately dated using the most modern techniques.
"The museum knew that the remains were of significant historical value but they hadn't been scientifically dated," Dr Gonzalez said.
"I decided to analyse small bone samples from five skeletons using the latest carbon dating techniques. I think everyone was amazed at how old they were," she said.
Robert Hedges, the director of Oxford's Radiocarbon Accelerator Unit, who also dated the age of the Turin shroud, carried out the radiocarbon analysis, which is accurate to within 50 years.
"We are absolutely, 100 per cent sure that this is the date," Dr Gonzalez said. The study has been peer-reviewed and accepted for publication next year in the journal Human Evolution.
At 13,000 years old, Peñon woman would have lived at a time when there was a vast, shallow lake in the Basin of Mexico, a naturally enclosed high plain around today's Mexico City, which would have been cooler and much wetter than it is today.
Huge mammals would have roamed the region's grasslands, such as the world's largest mammoths with 12-foot tusks, bear-sized giant sloths, armadillos as big as a car and fearsome carnivores such as the sabre-toothed tiger and great black bear.
The bones of Peñon woman, named after the "little heel" of land that would have jutted into the ancient lake, were well developed and healthy, showing no signs of malnutrition.
Dr Gonzalez found that the two oldest skulls analysed were both dolichocephalic, meaning that they were long and narrow-headed. The younger ones were short and broad – brachycephalic – which are typical of today's native Americans and their Mongoloid ancestors from Asia.
The findings have a resonance with the skull and skeleton of Kennewick man, who was unearthed in 1996 in the Columbia River at the town of Kennewick in Washington state. The skull, estimated to be 8,400 years old, is also long and narrow and typically Caucasian.
James Chatters, one of the first anthropologists to study Kennewick man before it had been properly dated, even thought that the man may have been a European trapper who had met a sudden death sometime in the early 19th century.
Kennewick man became the most controversial figure in American anthropology when native tribes living in the region claimed that, as an ancestor, his remains should be returned to them under a 1990 law that gave special protection to the graves and remains of indigenous Americans.
The debate intensified after some anthropologists suggested that Kennewick man was Caucasian in origin and could not therefore be a direct ancestor of the native Americans living in the Kennewick area today.
Dr Gonzalez said that the identification of Peñon woman as the oldest known inhabitant of the American continent throws fresh light on the controversy over who actually owns the ancient remains of long-dead Americans.
"My research could have implications for the ancient burial rights of North American Indians because it's quite possible that dolichocephalic man existed in North America well before the native Indians," she said.
But even more controversial is the suggestion that Peñon woman could be a descendant of Stone Age Europeans who had crossed the ice-fringed Atlantic some 15,000 or 20,000 years ago.
This theory first surfaced when archaeologists found flint blades and spear points in America that bore a remarkable similarity to those fashioned by the Solutrean people of south-western France who lived about 20,000 years ago, when the ice age was at its most extreme. The Solutreans were the technologists of their day, inventing such things as the eyed needle and the heat treatment of flint to make it easier to flake into tools. They also built boats and fished.
Bruce Bradley, an American archaeologist and an expert in flint technology, believes that the Solutrean method of fashioning flints into two-sided blades matches perfectly the Stone Age flint blades found at some sites in American. One of these is the 11,500-year-old flint spear point found in 1933 at Clovis, New Mexico.
Dr Bradley said that the flint blades that came into America with the early Asian migrants were totally different in concept and mode of manufacture. Both the Clovis point and the Solutrean flints shared features that could only mean a shared origin, according to Dr Bradley.
Studies of the DNA of native Americans clearly indicated a link with modern-day Asians, supporting the idea of a mass migration across the Bering land bridge. But one DNA study also pointed to at least some shared features with Europeans that could only have derived from a relatively recent common ancestor who lived perhaps 15,000 ago – the time of the Solutreans.
Not every specialist, however, is convinced of the apparently mounting evidence of an early European migration. "I personally haven't found it very convincing," Professor Chris Stringer, the head of human origins at the Natural History Museum in London, said.
"For a start, there are lots of examples in archaeology where various artefacts from different parts of the world can end up looking similar even though they have different origins," he said.
"Most humans in the world at that time were long headed and it doesn't surprise me that Peñon woman at 13,000 years old is also long headed."
Nevertheless, the remarkable age of the young Palaeolithic woman who died by an ancient lake in Mexico some 13,000 years ago has once again stirred the controversy over the most extraordinary migration in human history.
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