The Invisible History of the Human Race (21 page)

It strikes me that being cognizant of the grand historical arcs our families have lived through could also enable us to better see what qualities we have freely chosen for ourselves and what we have unthinkingly inherited from our great- and many-times-great-grandparents who lived in a different time and possibly wanted quite different things from their lives. If someone discovers that one or many of his ancestors were immigrants or exposed to the slave trade or a plague or famine, he may find that that knowledge illuminates some aspect of his life now, whether it’s an idiosyncratic word his father uses, his own reluctance to travel, the number of his own children, or his family’s penchant for not talking about family.

Historians, of course, have been telling us for hundreds of years that history matters and that we as a society cannot be free from the past if we don’t learn from it. Now the fascinating correlations found in this economic research suggest that distant historical events may influence the character of a modern family and that the choices of families can illuminate big history. Recall Ralph Waldo Emerson’s cry, “Why should not we also enjoy an original relation to the universe?” Maybe we can, but it will surely help if we can identify what was passed down to us and what we have freely chosen for ourselves.

Obviously, the circumstances of our lives shape us too. Education has a huge impact, as do job opportunities. Personal income can, of course, change everything. The influence of particular individuals, whether teachers, mentors, or spouses, also matters.

All these factors may interact with one another as well. It’s complicated and recursive. We are shaped by events, and then we shape people who initiate other events. We are shaped directly by people, and we shape others accordingly. Documents and ideas and feelings that are passed down may tell us about this; DNA is a record, and it is passed down too. What can it tell us?

You may not be able to leave your children a great inheritance, but day by day, you may be weaving coats for them which they will wear for all eternity.

—Theodore L. Cuyler

W
estray is an hour’s ferry ride from Mainland through the dark black water of the North Sea. The island of Mainland is itself an hour’s trip from the coast of Britain, which is, of course, itself a relatively small island off the western coast of Europe. Of the tens of millions of people who were either born on or swept into the British Isles over the last ten thousand years, there are six hundred people left in Westray, and only ten thousand in the Orkney island group, of which it is a part.

The road from the ferry terminal to Pierowall, Westray’s biggest town, rolls up and down the length of the island, traveling through pale green fields and sections of craggy rock, at points opening out to reveal vistas of the sea at either side. Along the eastern cliffs puffins are drawn with such precise lines they look prim against the wildness; on the beach fat selkies loll. Their velvet hides and anime eyes almost distract from the spectacle they create when they flop toward the sea—a reminder that evolution does not make überathletes for every niche but only does enough to get by. Even in May the Arctic wind has an icy hand.

Legend has it that a Spanish galleon sank off Westray’s coast in 1588. Sailors swam to the islands, and those who weren’t dashed on the rocky spires were welcomed. But on Westray’s neighbor, Papa Westray, it soon became clear there wasn’t enough food for the winter for everyone, so the locals pushed the poor sailors over the cliffs until there were none left.

On Westray, though, the ones who made it safely to shore proved helpful enough to keep. They married local girls, and the accidental immigrants and their descendants were thereafter known as the Dons. They were renowned as extroverted performers and great sailors, yet after the first generation the Dons kept to themselves. Romance with the locals was forbidden, and one young Don who broke the rule, so the story goes, was murdered by his cousins. The Dons would have made a striking contrast to the pale, light-eyed locals. For many years people on the island who had dark hair or olive skin were said to be descendants of these sailors.

It is a romantic origin story, and it’s not implausible, but in the absence of solid records it’s hard to determine if it is real. After all, this is the same island chain in which local lore had it that throwing a cat over your house in a particular direction would ensure a good wind for your sails. Who knows which of the old tales were true and which were concocted to explain an anomaly—like the birth of a dark-haired child to blond parents, who told their neighbors that young Angus’s Spanish ancestry was showing?

The day I caught the ferry from Mainland and drove to Pierowall’s tranquil half-circle bay, I saw a lot of lovely blue eyes but no dark-haired beauties. In the town archives, outside which lay the massive skeleton of a sperm whale, I read about the Dons and leafed through old photos. Here and there were pictures of olive-skinned youths, looking reasonably Spanish. But the records didn’t reveal much about who they actually were or even if they were native to the island.

Still, behind their eyes, beneath their skin, below the membranes of their cells there is something in the DNA of Westrayans that marks them and no one else. The origin of that distinction is not yet clear, but whatever it was, the scientific team that detected it in 2012 discovered that even the Orkney Mainlanders don’t have it. Is it a legacy of the Dons or something much older and weirder?

It’s not just the Westrayans who are different from everyone else. If you examine all the longtime residents of all the Orkney Islands together, they too have something inside their cells that distinguishes them from everyone else in Britain. Throughout the British Isles, in fact, clusters of people carry distinctive traces of ancient events within them. Celtic kingdoms, barbarian invasions, Norse raids from more than a thousand years ago—traces of these distant, almost mythical moments in time are written in the bodies of the good and ordinary people of Devon, Anglesey, Westray, and many other places.

These traces were discovered by an Oxford team that has found a way to read the book of history in human DNA to a level of detail that is completely unprecedented. Indeed, it is the closest thing we have to a time machine. Which is not only to say that it’s merely our best shot at traveling through time; in fact,
it’s quite close to it.

 • • • 

In 1980 Peter Donnelly, an ex-Queenslander who attended Oxford as a Rhodes scholar, was deemed so bright that at twenty-nine he was appointed the youngest full professor in England (and, it’s reputed, the youngest full professor in that country in more than a century). Donnelly is now director of the Wellcome Trust Centre for Human Genetics and a professor of statistical science at St. Anne’s College, Oxford. Refuting all the stereotypes of outsize genius, he is towering and deep voiced, and if life had led him that way, he could have made an unusually tall but dignified magistrate. Although he trained as a statistician, his work increasingly took him into genetics, and over a period of about ten years he changed from a mathematician who dabbled in genetics to one of the world’s leading geneticists.

I met with Donnelly and his colleague Stephen Leslie at one of the genetic world’s most pleasantly located meetings, by the beach in Lorne, Australia, some nine thousand miles from Westray. As the afternoon tide hit its low point and turned around again, Donnelly and Leslie walked me though a brief history of genetic research in the twenty-first century, which has so far featured one particularly huge upheaval.

While genes were discovered around the beginning of the twentieth century, it wasn’t until 1953 that the double-helix structure of DNA—the stuff that genes are made of—was discovered by James Watson, Francis Crick, and Rosalind Franklin. Almost five decades later a human genome was sequenced for the first time. Despite this enormous and expensive step, the project of linking specific genes to traits or diseases has until recently proceeded painstakingly, one gene at a time. Researchers would pick “
their favorite gene,” Donnelly said, and investigate only that. “It wasn’t based on the idea that there was only one gene involved in the condition,” Donnelly explained; rather, it was simply too expensive to look at anything else.

The problem with candidate gene studies, however, was that a promising result—say, the discovery that a majority of patients with a particular disease appear to share a marker that a group of healthy people do not—might not actually have anything to do with the actual disease. “
Now we know that people in Scotland will have genetic variants that differ from people in, say, Tuscany,” Leslie explained. “It could be just by chance or it could be by natural selection, but there will be differences between Scots and Tuscans.” The danger with candidate gene studies, he said, “was that you thought you were seeing something that was associated with having a particular trait, but actually what you were seeing was something associated with being Scottish or Tuscan.” (The other problem with candidate gene studies is that “almost all of those results turned out to be wrong,” Donnelly said. “One of the lessons of that era is how bad experts were at picking candidates.”)

Around 2007 not only did it become possible to investigate many places in the genome simultaneously, but also the cost of doing so quickly dropped. In a matter of years candidate gene studies were replaced by genomewide association studies. Researchers now had an eagle’s-eye view of an individual’s entire genome, and they were able to compare tens of thousands of sites in the genomes of tens of thousands of people to identify meaningful correlations with a trait or disease or with the history of a population.

Scientists have known since before they had the technology to measure them that regular genetic differences—what geneticists call “population structure”—probably existed. “For as long as we have measured traits in human populations, we’ve known that the distribution of those traits vary in different parts of the world, depending on which population is measured,” said Donnelly. “For a long time we only knew about a few markers, like blood groups, which we have measured since the 1930s.”

Indeed, blood is the classic example: The A blood group is found mostly in Europe, while there’s considerably less type A in Asia. The B blood group is more common in Africa than in Europe. The Rh factor, named for the rhesus macaques used to investigate the trait, refers to the presence or absence of a set of red-blood-cell antigens, and it differs too among populations: Rh-negative blood occurs far more often in Europe than in Asia. Even within particular European populations there are differences in blood groups. The Irish Blood Transfusion Service, for example, gets more O-negative when it collects blood in the western part of Ireland than in the east.

Some biological differences between groups may have little to do with how individuals actually live their lives, yet they may still be potent with meaning. They may reveal how long the groups have been separate, how long they have lived in one area, whom they mixed with in the past, and whether their bodies have adapted to local conditions. Combined with historical records, artifacts, or information about the biology of other groups, they may tell us when population differences arose and why they happened. Essentially, one can use the living tissue of human beings to work out what the lives of their ancestors were like up to hundreds and thousands of years ago. It’s like William Blake’s poem about seeing the world in a grain of sand, except that instead of a metaphor it’s real: What you will see is the history of the world in a handful of human cells.

One of the earliest attempts to read deep history in the living body was a project that compared blood types and populations. Historical genetics began by looking at very small parts of the genome, the Y chromosome, which is passed from father to son, and mitochondrial DNA (mtDNA), which is passed down by mothers. (For more about the Y chromosome and mtDNA, see chapter 9.) Methods developed over the last ten years investigate more of the genome and are powerful enough to detect differences between inhabitants of different continents. “I set a project for first-year PhD students,” Leslie said, “where I give them a few hundred markers and teach them a statistical method for modeling genetic data and population structure. I give them markers for 120 Africans and 120 northern Europeans. They can write a program in half a day and run it in seconds and work out who’s from Africa and who’s from Europe just from genetic markers alone.”

Yet there is little these procedures can reveal about a group like the pre-twentieth-century population of Britain. “If you use the standard method to try and split Britain, you’ll see nothing much. What you’ll see is Orkney split, and Wales split, and that’s it. You’ll see no fine-scale structure at all,” Leslie said.

Now, with the advent of genomewide studies, researchers can survey the genomes of thousands of people for population structure. Often this happens in case-control studies, where the idea is to account for ancestral traces in DNA that might otherwise confound medical studies. Donnelly led the 2005 Wellcome Trust Case Control Consortium, a sampling of seventeen thousand genomes that is now regarded as the gold standard for all case-control studies in modern genetics. A year earlier, he and Sir Walter Bodmer, one of Britain’s best-known geneticists, had begun another study. Many years before that Bodmer and his wife, scientist Julia Bodmer (who passed away in 2001), had proposed a genetic study to uncover the origins of the British people. Bodmer pursued the idea for years, and when he took it to Donnelly, they conceived of a study that would be important for the investigation of disease in the British population, but the two scientists hoped it would also give them a completely new view on history.

 • • • 

If we consider the entirety of human history, it becomes quite obvious that if people live near one another long enough, their DNA will eventually become blended. In fact, so inclined are people to mix it up with everyone around them that there is always a clear reason for cases when they don’t, which is to say that barriers to reproduction must be high. They might be physical factors like mountains, oceans, or extraordinary distances. They might be strongly enforced beliefs. Like the Dons, the Orthodox Jewish community in Brooklyn, New York, as in many other cities around the world, lives in close proximity to other ethnic groups but marry only one another; genetically it’s as if they lived on an island.

Still, even when people marry only within their own group or live on an actual island, their DNA is never static. As time passes and DNA is passed from one generation to the next, changes naturally arise in the genome. While some are not passed on, others diffuse through the gene pool. If the group does not mix with others, such changes may become characteristic of that particular group.

In order to have the best shot at finding the characteristic genetic traces of British ancestry, the Oxford team focused on areas with rich archaeology and were selective about the genomes they chose: They looked only at people whose four grandparents were born in rural areas within eighty kilometers of one another. Sampling anyone’s genome is essentially the same as taking a smaller sample of their parents’ genomes and an even smaller sample of their grandparents’ genomes. It was this aspect of the genome in which the team was especially interested.

“Effectively we’re looking back in time to what the genetics of that area looked like when those grandparents were born.” Leslie explained. “The hope is that if the four grandparents were born in Cornwall, then their parents were born in Cornwall, and so on. We were hoping to get right back to when people didn’t move a lot and lived in their own little communities for generation after generation.” Many of those who responded to the team’s call for subjects were of retirement age, which meant the average birth year of their grandparents was around 1885.