At the moment, though, there is no evidence of humans in the rest of North America, or in South America, prior to the LGM, so although an early entry into the Americas, before the ice sheets spread across from coast to coast, is a possibility, it remains a hypothesis with no firm archaeological evidence to support it.
But what about genetic evidence? Can we be sure that Siberia was the ancestral home of the first Americans, and can genetic analyses offer any further insight into dating the colonisation of the Americas?
Mapping Native American Genes: Calgary, Canada
I travelled to Canada to meet up with American geneticist Tracey Pierre. We were to meet, not at a university or a research lab, but at a First Nation Powwow, near Calgary, Alberta.
Having flown over the Rockies, from Camloops to Calgary, I arrived at the powwow early in the morning, before the events of the day had begun. There was a circle of tepees around a central, circular, roofed arena and I had a moment of déjà vu when I saw them: they were so similar to the Evenki chums in Siberia. Some even had stoves inside them, although there was really no need for heating in Alberta in July.
People were wandering around the camp in various states of preparedness and some of the dancers were already fully decked out in beaded costumes and feather headdresses. There were, too, lots of very excited small girls, many in costumes which were largely pink. But, despite the range of colours, including bright neon pinks and greens, and the very untraditional fabrics that some costumes employed, there was a definite style that everyone had adhered to. This was a Tsuu T’ina (formerly Sarsi) get-together, and the identity of this First Nation group was stamped on their costumes and would be reiterated throughout the day, as the master of ceremonies listed again and again the families and chiefs who were present.
Walking around the powwow ground, listening to the drumming and watching the dancing, I felt a mixture of emotions. It was clear that the Tsuu T’ina people had a strong sense of identity. Their culture was under threat, and they needed to keep it alive, somehow to sustain it in the wider Canadian culture they were now part of. The powwow was like a metaphor for this struggle: inside the covered arena, Native Americans drummed and danced and honoured their leaders and ancestors. Outside, there was the ring of tepees which men entered in T-shirts and jeans and came out of dressed in their costumes, as warriors. And outside the tepees was a village of burger vans and hot-dog stalls, white Canadians selling Native American kitsch, and a fairground.
But when I met Chief Big Plume in his tepee the struggle for culture didn’t seem so futile. He was a strong leader, and exuded an amazing sense of pride in his heritage and his people. He sat on a bison skin, dressed in a regal red robe with weasel skins sewn, hanging, on to the sleeves. He wore a magnificent eagle-feather headdress. Invited in, I sat down beside the Chief and asked him about stories of the origin of his people.
‘As it was told down through the generations, there was an argument within the camp. A dog had knocked down a tripod with a warrior’s hunting tools – his arrows, his quiver. So there was an argument and a separation of people.’
He described a small splinter group heading south. They made off, across the frozen water of the Great Slave Lake.
‘There was a young child on her grandmother’s back, and there was a horn sticking out of the ice. The child was asking for the horn, so they had to stop the migration. They started to chip away at that ice, to bring out the horn, and it split the ice. The clans already on the south side continued migrating south. The ones in the north stayed in the north.’
So the wanderers were cut off from their original home – and became the ancestors of the Tsuu T’ina. It was a wonderful story, and I was intrigued by the mention of ice. I had read about another Native American tale, told by the Paiute, involving ice, where a raven pecked at a great wall of ice until it cracked and allowed people to pass through. It is tempting to see these stories as memories of a time when much of North America was covered by massive ice sheets, though it’s impossible to know if the oral traditions actually stretch back that far.1
I asked the Chief what he thought about connections with Siberia. He knew the theories and thought it very likely that his people had originally come from north-east Asia. I showed him some photographs, and he was very interested in the Evenki chums, and their similarity to tepees. He also thought the Evenki resembled some of the more northern Native Americans. Then it was time for the Chief to get back to the powwow, as the afternoon’s events required his presence. I left the tepee and went off to find Tracey.
Tracey herself was a Native American, of Navajo origin. She had studied archaeology as an undergraduate, and, realising how few Native Americans there were working in the field of genetics and phylogeography, she had made it her job to plug that gap. It was not an easy task. Even for Tracey, there was much suspicion and wariness to overcome among Native American communities. And understandably so. Genetics has been much misused in the past, and, when it came to Native Americans, there had been some gross misconduct perpetrated against them.
‘A lot of times in the past, there’s been research conducted without the knowledge, consent or participation of the tribes who are under study. In one particular study, involving the Navajo and Apache tribes, the FBI used DNA samples that were acquired through hospitals and prisons. It’s a classic example of why tribes are wary and suspicious of genetic research,’ explained Tracey.
This malfeasance had been picked up by Tracey’s Ph.D. supervisor, Peter Forster, who had been asked to review the paper and who had spotted the ethical blunder. I was amazed by the story. It seemed as if I was hearing about some dreadful anthropological story from the nineteenth century. But this was a twenty-first-century tale.
To many Native Americans, genetic science is too closely tied up with US government attempts to classify racial groups and confer rights accordingly. In 1887, when the Allotment Act was brought in, Native Americans were assessed on the basis of ‘blood quantum’. This meant that anyone who was less than half-blood was denied land rights: their land would be appropriated and given to ‘white’ settlers. The US government also requires Native Americans to carry official ‘Certificates with Degree of Indian Blood’. Artists cannot sell their work as ‘Indian’ if they do not have federal certification. It seems a highly divisive approach in a multicultural society.2
Tracey was at the powwow to enjoy the dancing, but also to take some more mtDNA samples. That day, she had little success in persuading people to swab their cheeks. Gaining the trust of people who had seen their heritage trampled upon and their DNA stolen would be a long process, but Tracey believed it was worth it, and that the history she was finding in the genes belonged to the people – her people – who had given her their genetic material.
Tracey’s own doctoral research focused on later migrations within established Native American populations, but I asked her what mtDNA analyses had to say in general about the colonisation of the Americas. Firstly, she was very clear that the genetics confirmed a Siberian homeland of the palaeoindian ancestors of the Native Americans.
‘So far, mtDNA analyses have identified five major lineages, A, B, C, D and X, that are indicative of Native American populations today, and these can be traced back to southern Siberia.’
‘So does that mean that all Native Americans originally came from Siberia?’
‘That’s what the genetic evidence is implying at this point, and the archaeological record supports it, too. For decades, scientists have been suggesting there’s a link with Siberia, based on physical attributes – and I think the genetics now proves that.’
As well as those mtDNA haplogroups, there were also Y chromosome variants (Q and C) in Native Americans that could be traced back to the Russian Altai.3, 4 Tracing the route up through northern Siberia was complicated by the fact that people had cleared out of there during the LGM, and moved back in afterwards. But the Siberian genetic origin of the Native Americans certainly supports the hypot
hesis of a migration westwards across Beringia.
Whereas early mtDNA studies had indicated anything up to five separate migrations into the continent, the newest data – looking at complete mitochondrial genomes – suggested that there was just one.5 In the 1980s, genetic, dental and linguistic studies suggested that there were probably three waves of colonisation from Siberia into the New World, corresponding to three language groups among Native Americans: Amerind, Na-Dene and Aleut-Eskimo. (Although, it has to be said, this is a very conservative number; some linguists would claim there are more than 160 language families.) The first Y chromosome studies, also in the 1980s, seemed to suggest either one or two waves of colonisation. In 2004, the results of a large Y chromosome study showed that the Native American population had two major founding Y chromosome haplogroups: Q (76 per cent) and C (6 per cent). But rather than these two lineages representing separate migrations, the mixture of Y chromosome types among living Native American men was best explained by a single, polymorphic (i.e. containing more than one Y chromosome type) founding population.4 A recent study of Native American genes from DNA inside the nucleus has also supported the idea of a single wave of migration.6
This also makes sense if Beringia is viewed less as a ‘land-bridge’, with migrating Asians beetling across it, and more as a ‘staging post’, receiving incomers from various parts of Asia – some of whose descendants, bearing that mix of lineages, then went on to colonise the Americas. It also means that it would be naive to look for a geographically discrete ‘homeland’ in Asia – people could have been coming in from lots of different regions. Instead, it is really Beringia that was the homeland of the first Americans.7
The genetic data also suggest a timescale for the colonisation, with modern humans spreading into Central Asia by 40,000 years ago.8 Fossils of modern humans from Tianyuan Cave and Yamashitacho also date to around 35,000 to 40,000 years ago, hard evidence that people were in East Asia by that time.9 Analysis of Asian and New World nuclear and mtDNA suggests a three-stage model of colonisation. First, there was a gradual population growth, and a movement of Amerind ancestors into northeast Asia, between 43,000 and 36,000 years ago. The effective founding population was small, perhaps only a couple of thousand, and this is why Native Americans have much lower rates of genetic variation than Asians: the people who went on to colonise the New World were only a small ‘sample’ of the gene pool in Asia. The proto-Amerind population grew and spread throughout Beringia between 36,000 and 16,000 years ago, then there was a ‘population bottleneck’ around 20,000 years ago – at the height of the LGM. As the world warmed up again, between 18,000 and 15,000 years ago, there was a major population expansion throughout the Americas. Based on genetic variation, the founding population could have been as small as just 5000 people.10 The range of dates suggested by Y chromosome analysis is later, at 10,000 to 17,000 years, but the upper end of this range overlaps with the mitochondrial dates. It may seem strange that there is such discrepancy between dates worked out from different genetic trees, but there are a number of reasons for this. Variation in mutation rates could throw a spanner in the works, when scientists are basing their calculations on an assumption of a steady rate of mutation. Genetic drift within a population could also muddy the waters.8 But that’s not to say the genetic dates are of no value. And if there is some overlap, it suggests that, despite all the potential pitfalls, we can place some trust in the reconstruction of our past from our genes.
So this genetic contribution to the debate, with dates of a population expansion later than 20,000 years, makes a pre-LGM migration between the ice sheets seem very unlikely. It doesn’t rule it out, though, and Stephen Oppenheimer believes that the founder mtDNA lines may have arrived in Beringia well before the LGM, becoming cut off from the founder Asian populations for at least a thousand years, and spreading throughout the Americas – before the way was sealed off by the ice sheets. He argues that the greater genetic and linguistic diversity in South America fits well with a model of early – pre-LGM – colonisation of the entire continent, with North America becoming largely depopulated during the LGM. The spreading ice sheets meant that the North American population dwindled, and was driven into a refugium in the far north – in modern-day Canada and Alaska. After the LGM, people could once again expand across North America.7
But whether the first wave of colonisation into most of North America happened after the LGM, or represents a repopulation after the initial colonisers were pushed back, it is clear that it happened long before Clovis appears in the archaeological record.
How did the first colonisers get down into North America when the way was blocked by ice? The ice-free corridor between the Laurentide and Cordilleran ice sheets didn’t appear until between 14,000 and 13,500 years ago.8 Again, the genetics seemed to indicate an answer: the ivy trail of mtDNA lay along the coast.
Exploring the Coastal Corridor: Vancouver, Canada
I therefore made my way to the coast, to the city of Vancouver, at the mouth of the Fraser River where the Coast Mountains come down to the sea. In 1808, a fur trader named Simon Fraser set out with a band of twenty-three men, in four birch-bark canoes, to explore the great river that would eventually bear his name. They paddled 800km downriver, all the way to its mouth on the west coast of Canada: they were the first non-indigenous people to see the mouth of the Fraser River. Along the way, they encountered various groups of indigenous people. Sometimes the blue-eyed, pale-skinned Fraser was taken for a supernatural being, one of the ‘transformers’ from the beginning of time. But when he reached the Pacific, Fraser was met by fierce Musqueam warriors armed with bows, spears and war clubs. They were right to be defensive, for these men would indeed transform their land. The trade routes Fraser mapped out facilitated the Gold Rush of 1858 and western Canada experienced its own industrial revolution as mining, fishing and forestry took off. Today, the economy has changed yet again, with information and knowledge becoming powerful commodities.1 And up in the foothills, on Burnaby Mountain to the east of Vancouver, is the campus of Simon Fraser University, rising up the slopes like a concrete Aztec temple.
After driving around the campus a couple of times, I eventually managed to find the Department of Biological Sciences and track down Professor Rolf Mathewes in his book-lined office.
Rolf studied pollen in both ancient (palaeoecological) and modern (forensic) contexts. As well as using pollen to track down criminals, he had been investigating the possibility of ice-free refugia along the northern Pacific coast. His studies had been concentrated around the Haida Gwaii (formerly Queen Charlotte Islands) off the west coast of British Columbia. In the early 1980s, radiocarbon dating of plant fossils had suggested that the islands were ice-free perhaps as early as 18,000 years ago – when the mainland was still covered with ice. Genetic studies of fish, birds and mammals have also suggested that the islands acted as refugia for a variety of species, soon after the LGM. With sea levels lower than today, the exposed areas of the continental shelf may have provided a ‘coastal corridor’ along which humans could have migrated soon after the LGM, as the edge of the continental ice sheet began to melt back. Rolf and his colleagues had taken samples from beneath the sandy seabed of Dogfish Bank, part of the now-submerged continental shelf between the Haida Gwaii Islands and the mainland, as well as a sample from the south-western coast of the islands. They had then carried out detailed pollen analysis – and radiocarbon dating – on these cores.2
Rolf was very excited about the acquisition of a new microscope with built-in digital screen and camera, and he used it to show me some pollen from the Dogfish Bank core.
‘This is one pollen grain of a sedge,’ explained Rolf, zooming in on a tiny grain. ‘It’s only about one-thirty-thousandth of a millimetre in size, 30 microns. More than half the pollen on this slide is sedge pollen.’ microns.
‘And have you been able to date this sample?’ I asked.
‘Yes, and it’s very exciting,’ said Rolf. ‘This partic
ular sample dates to somewhere between 17,000 and 18,000 years ago.’
‘So if there were sedges growing there, that meant the ice had retreated?’
‘Absolutely,’ replied Rolf. ‘The mainland of British Columbia to the east had a huge ice sheet on it which was still kilometres thick. But these islands off the mainland were already deglaciating, much earlier than most people thought when I started this work back in the 1980s. In fact, we published the discovery of these early ice-free sites in the Queen Charlotte Islands in Science – it’s the earliest known area for deglaciation and this early vegetation.’
‘So, 17,000 years ago, the ice sheets were pulling back from the west coast of Canada?’
‘That’s right, but the Queen Charlotte Islands had their own little ice cap, which was much thinner than the big one. This is one of the reasons why this area deglaciated earlier. It’s not like a single wall of ice that’s pulling back.’
The pollen in the Dogfish Bank sample showed that this coastal plain was exposed between around 17,000 and 14,500 years ago – after the glacial ice retreated and before the sea-level rise from all that melting ice flooded it. Careful analysis of the pollen in the sediments from beneath the seabed showed that Dogfish Bank had been a wetland environment, with lots of sedges, along with various grasses, horsetails, willow and the dwarf evergreen shrub, crowberry. Pollen from wetland species like bayberry, as well as fossil green algae, indicated that the land was marshy.2
‘Do you think people could have lived here?’ I asked.
‘Well, based on this – absolutely,’ said Rolf. ‘This was dry land, with vegetation growing on it.’
‘And do you think the coast could have formed a route for the first colonisation of the Americas?’ I asked.
‘There were a number of sites from the Gulf of Alaska right down the side of British Columbia that were free of ice, from 16,000 years ago. And, each summer, the green patches would have expanded. There were even forests starting to form on the Queen Charlotte Islands when the inland corridor was still locked up in ice,’ explained Rolf.
The Incredible Human Journey Page 36