The Incredible Human Journey (50 page)

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 hypothesis
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 particular 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.’