The Invisible History of the Human Race

by Christine Kenneally

  The big red group in Leslie’s analysis showed a massive, genetically homogeneous area in the southeast of England. History tells us that this DNA would not have been significantly influenced by the DNA of the Roman (genetically Gallic) army. Indeed, the biggest influx of people in the period were Saxons, so it’s most likely that the group originated with the Saxon onslaught. This would rule out the theory that the Saxons had no genetic impact on the locals at all.

  But how much of the region’s modern genetic profile is actually ancient-Briton DNA, and how much is Saxon-marauder DNA? There are many possibilities. If a huge number of Saxons raced in and killed almost all the locals, the proportion might be only 10 percent Briton. If instead only small groups of adventurous Saxons came to Britain, the population could be as much as 90 percent Briton. The only way to know for certain would be to match the DNA against that of the marauders themselves or against a modern group descended from them. In the absence of a handy source of ancient DNA, the team looked to continental Europe for genomes.

  “What we decided to do,” Leslie explained, “was find a group of European samples and compare the DNA of the British groups to Europeans from different parts of Europe.” The team had access to over six thousand samples from a European medical study, on which they ran the same kind of analysis and found fifty-one distinct groups, most of whom had contributed nothing to Britain. (Ancient Italy, for example, was not represented in the modern British gene pool, confirming what historians have already said about the absence of actual Romans in Roman-occupied Britain.) By contrast, the analysis confirmed that Orcadians have a considerable amount of Norwegian DNA, which is predictable from the historical record of the Viking invasions, which began in the ninth century, as well as from other early genetic studies.

  As far as the big red group in England’s southeast was concerned, the team found that what slowly emerged from the cataclysm of AD 410 was a genome that was 75 percent ancient British and up to 25 percent Saxon, meaning that while the genome of the natives of England’s southeast was not completely replaced, it became strongly Saxon flavored during the Dark Ages.

  According to Robinson, the likeliest explanation for this genetic state of affairs is that, in the absence of the Romans, the state—and the local population—fell apart, literally. Other historians have suggested that as many as 1.5 million of the 2.5 million Britons died, but Robinson believes that only one quarter million may have survived and that for a long period there was complete chaos. Local warlords fought one another in addition to having to deal with ongoing Saxon raids. People lost crops, suffered from starvation and disease, and had to abandon their settlements. Families could not raise even two children. All the towns were abandoned too, to the point that the Saxons believed they were haunted.

  By contrast, the conditions of fifth-century England were just the sort to which Saxon settlers were accustomed. “Saxons were coming in who, although they looked more primitive on the face of it, had societies that worked at the small scale. Every man would have had to bear arms since he was young,” Robinson said. But their already being well adapted to a violent, nonmonetary culture does not mean that hundreds of thousands of Saxons flooded in, all in the period around AD 411.

  “My view is it only takes about four hundred Saxons arriving each year for a period of seventy-five years and good reproductive success to have them contributing 25 percent of the DNA,” Robinson said. “Effectively the Britons still enjoyed a high reproductive success, as their genes were in people who culturally were Saxon.” Still, it took a long time for English culture to resume where it had left off. It wasn’t until centuries later, when the Normans invaded, that the British once again saw pots that were as good as the ones that had been produced in Roman times.

  What of Rheged, Elmet, and Dumnonia? The surviving genetic markers suggest that the ancient fringe kingdoms not only survived Roman rule but also still, to some extent, kept to themselves. We often think of the Celtic population of Britain as a wild, poetic, and singular group of ancient people, though in fact the study confirmed there was not one large group of Celts but many. How did the different groups of ancient fringe DNA survive both Roman rule and the Saxon onslaught? According to Robinson, it was because the Celts in the west had never been fully controlled by the Romans in the first place.

  “There was a Roman military presence,” Robinson said, “but the ordinary Iron Age peasants were left to get on with things. If they misbehaved, they would be slaughtered. It was like native states in British colonial India. Provided the local maharaja wasn’t anti-British, he was allowed to get on administering his society by his own laws.” The different Celtic groups were able to repel the onslaught because they still had their own leaders and weapons and were able to organize themselves. They also sustained themselves economically because they still knew how to barter and exchange goods and services. Enough of them survived to have children, who in turn had children, whose descendants today walk the streets of Cumbria and Cornwall.

  Robinson already knew from the written record that these kingdoms hadn’t disappeared into the post-Roman vacuum, but no one had ever imagined that they might once more be visible—twenty-first-century ghosts shaped by great socioeconomics and good enough DNA.

  • • •

  How did Leslie and his colleagues effectively resurrect people who hadn’t been seen for a millennium? The key to their approach was that they didn’t go looking for a specific Celtic gene or a Saxon allele. Rather, they looked at patterns across the genome, which most analyses ignore. That enabled them to identify very small but significant differences between people who are otherwise overwhelmingly the same. “It’s a collection of very slight differences but across lots and lots of bits of the genome,” Donnelly said. “You need to integrate all of this information in order to see the whole pattern of subtle difference.”

  Essentially the genetic groups in the project looked like different blends of very similar material, somewhat like arabica and robusta coffees or like close hues on a color wheel. The Cornish were genetically royal blue while the Devonians were light blue—fundamentally the same, but still categorically different.

  What this means is that one of the big stories of ancient British genetics is a tale of people staying put. None of the history would be detectable in the biology if many people hadn’t lived in the same place and married someone from their own neighborhood for generation after generation. In the case of Saxon Britain, that means local boys partnering up with local girls from the 400s until at least the 1860s—about fifty-eight generations who married their high-school sweetheart or her peasant equivalent. By contrast, the backstory of the big red genetic group is not so much one of a large homogeneous community as one of an area that lacked significant geographic or historical barriers, a place where DNA has washed freely back and forth since Roman times.

  Curiously, although the differences between the different British groups are definitive, they pose no challenge for genomic medicine. “Broadly speaking, Caucasians in the UK are very, very similar genetically,” Peter Donnelly said. “We looked for population structure quite hard early on in disease studies because we didn’t know whether we had to worry about it, and it turned out that you don’t really need to worry about it. If you are looking at how common genetic variants affect disease susceptibility, geographic differentiation in the UK is not a big problem.”

  It may be that when scientists begin to consider very rare disorders, the genetic groups will become medically relevant, but in the meantime the story of ancient British genetics is a story about overwhelming sameness and minuscule but definitive difference—all crammed into the same small forensic package.

  • • •

  There were a few anomalies in the analysis that puzzled Leslie. Here and there a single person who belonged to one genetic group seemed to be living in the wrong location with a different group. For example, a genetically Devonian person in the Newc
astle region had four grandparents who were all born in the area around Newcastle. If the DNA analysis was correct, it meant that in the mid-1800s, eight Devonians moved to the region and paired up, with each of the four unions bearing children. Of that new generation one child from each of the four couples must have paired up with another, and then these two couples must have had at least one child, who then paired up with the child from the other couple. If the people involved had been Jewish or Catholic, this might have made sense, but there were no obvious religious differences keeping the grandchildren of Devonians from marrying the locals.

  Leslie reran the analysis over and over, but no matter how many times he did, the anomaly wouldn’t go away. “It was driving me absolutely insane,” he recalled, “because I believe the genetics more than I believe anything else. I wanted to understand what’s going on, so I started to track the odd individual that really looked out of place.”

  Leslie went back into the history books and discovered that there was a significant relationship between the two locations in the midnineteenth century. “It turns out that about 150 years ago Devon was a strong mining area (as was its neighbor Cornwall), and this area up in the northeast was a strong mining area as well. There was a miners’ strike up north, and the mine owners brought scab labor up from Devon and Cornwall, and these people—there is a huge amount of evidence for this—these people came up and they were ostracized. Because they were strikebreakers, the local people would not talk to them, would not socialize with them, would not marry them. If you go online and look at genealogy Web sites, you can see these family trees of people that have all eight great-grandparents born in Devon, but they are living up there in Newcastle, working in the mines.”

  Here is where it becomes clear that this kind of fine-grained genetic history is the flip side of the family-history coin. Although genealogy is not widely valued in academia, it meshes perfectly with, and helps explain, social history. These small stories about individual lives reveal the way that individual choices shape the biology and the history of whole populations.

  • • •

  For all the extraordinary answers that the project provides, its greatest contribution may be the number of questions it raises. For instance, despite the power of their terrifying invasions beginning in the late eighth century, the Danish Vikings rapidly disappeared in England, leaving some tantalizing material remains but not a lot in the way of genetics. Culturally they bequeathed only a few place names, typically ones ending in “-thorpe” and “-by,” like Coningsby and Cumthorpe, said Robinson. Why did they enter with such thunder but vanish so quickly? How, on the other hand, did the Norwegian Vikings reshape the population of the Orkneys, changing the language, the artifacts, and the genetics?

  What about Westray? How did the locals get to be so different even from the other Orkney islanders? As far as the genetic analysis goes, says Leslie, it’s unlikely to have been the result of a single shipwreck. And how, after hundreds of years, do the Orcadians remain so different? Even though it’s been a long time since the Vikings roared in, there hasn’t been enough intermarriage across Orkney to subsume the ancient legacy. What are the social forces that laid down these archaic patterns still reflected in the modern genome? Why haven’t the modern Westrayans married the other Orcadians more often? It’s not as if they don’t have boats.

  When I visited Mainland, an Orcadian told me he liked the Westrayans well enough—it was the people from Wick on the Scottish mainland, “the dirty Wickers,” whom you never married. He laughed at the silliness of the idea, the relic of school teasing, and yet . . . We know that human conflicts, beliefs, and borders can structure the genome, but do these minor, trivial prejudices that we don’t take seriously date back from further in time and influence our biology more than we know?

  What about the Orkneys’ DNA? If it’s 25 percent Norwegian, where does the balance come from? People have debated the degree to which the Norwegians slaughtered the Picts, Robinson said. But the genetics suggest the Picts live on in Orkney still.

  There’s also the question of what genetic patterns the invaders brought with them. Not all Vikings came from the same village, nor did all Saxons. If they came from different villages where the locals had married only the locals, their groups may have reflected the different populations that were ancestral to them. There are mysteries upon mysteries here, and with this new method we may now begin to be able to untangle them.

  Naturally, this method may be applied in other countries as well. Adding the multidimensional genetic record to the historical and material record may confirm our existing knowledge, as well as contribute completely new insights and resolve old debates. Picking apart the most ancient migrations from the more recent ones will be part of the challenge of the future. In the meantime a general rule of thumb is that the stuff that is everywhere is likely to be the oldest, having had lots of time to spread out.

  Robinson is excited about the possibility of taking fine-grain genetic history out of rural areas: “I think if you went into the cities, you would get a great mixture and all sorts of extraordinary things would turn up.”

  These methods can also be used to learn about any individual’s ancestry. “The bits that are documented in my family are Lowland Scots, Welsh, southern Irish, and English,” said Robinson. “It’s very, very mixed, but I am fascinated to know what it is in my genetic component that resulted in my maternal grandfather having racist abuse shouted at him in the 1920s.

  “They shouted, ‘Where’s your monkey?’ because he was a dark person with curly hair. His hair was white by the time I knew him in the 1960s, but whether he was very dark and Neapolitan in ancestry, or whether he was descended from a Lascar on the coal boats to Cardiff or something, I don’t know. His name was Jones. I just have no idea.”

  There are many ways to read the book of DNA. Leslie and his colleagues’ new method complements rather than replaces older ones. Even as the analysis of the whole genome grows ever more sophisticated, scientists and citizen scientists have found increasingly clever ways to wring knowledge from the Y chromosome.

  Chapter 9

  DNA + Culture

  History doesn’t repeat itself, but it does rhyme.

  —Mark Twain

  In 2002 Thomas Robinson, an associate professor of accounting at the University of Miami in Florida, had his DNA tested by an English company called Oxford Ancestors. Robinson knew very little about the origins of his family. A few years earlier an uncle on his mother’s side had done some research and traced the family back to Virginia. But Robinson’s father had been estranged from his own father, so Robinson knew almost nothing about his background on that side. All he had was a family Bible with some names from his father’s family in it.

  Robinson began searching records, and after plugging away for a few years he finally got a clue that his father’s ancestors had come from the Lake District in England. Wondering if DNA would take the search further, he submitted a sample to Oxford Ancestors, which identified twelve markers on his Y chromosome, offering some suggestions about where his Y might have come from in Europe. Robinson also tested with Family Tree DNA and received similar results.

  Sometime after that Robinson got a call from an Oxford Ancestors representative. The caller told him that the company’s head scientist, Bryan Sykes, wished to speak to him. “He has some very exciting news he’d like to talk to you about,” the representative said.

  What the heck is this guy calling about? Robinson wondered. He started to run through worst-case scenarios. The most frightening possibility, he thought, was that he might find out that he was descended from Hitler (Robinson has blond hair and blue eyes). Fortunately this did not turn out to be the case. In fact, the geneticists at Oxford Ancestors had recently compared their DNA analyses with a study that had just been carried out by another lab at Oxford and found that Robinson’s Y chromosome, which is passed only from father to son, was Mo
ngolian. This was a surprise to Robinson, but not as big a surprise as the fact that he was related to the Mongolian: He was told that he was a direct descendant of the most famous Mongolian in the history of the world, Genghis Khan.

  • • •

  Genghis Khan lived from 1162 to 1227, and although scientists now argue that he was effectively a one-man genomic event, for centuries he was known as “the Destroyer.” Khan and his hordes killed about forty million people—the same number as the entire population of present-day Argentina.

  In fact the Mongol Empire removed such a large number of people from Asia that it had an unprecedented impact on the planet. Because so many millions of people disappeared, there was an enormous amount of reforestation. The fact that there were more trees meant that the forests absorbed more carbon dioxide, and overall the world’s carbon dioxide levels dropped a fraction (0.1 part per million). The Mongol invasion is the only known human event to have had such an effect. (The Black Death killed up to seventy-five million people in the fourteenth century, but because the plague was relatively short-lived compared to the Mongol Empire, which lasted nearly two hundred years, it didn’t have the same impact.)

  Although Genghis Khan did not remain in the areas he defeated, significant amounts of his DNA did. As he pillaged his way through Asia, he distributed his DNA by raping countless women and fathering many children. When he fathered sons, he passed down his Y chromosome to them. But Genghis Khan didn’t just spread his Y by propagating copies of it; he also killed the carriers of other Y chromosomes in those areas (that is to say, he slaughtered all the men), and in so doing he increased the relative presence of his own Y. Because the Mongol Empire lasted through a few generations of Khans, not all the glory goes to Genghis, though. After his death many of his sons ruled sections of Asia, so the Khan Y kept spreading long after Genghis himself was gone.