The Invisible History of the Human Race

by Christine Kenneally

  As time went on and different populations moved around and split into different groups, natural selection impacted different populations in different ways because it was also shaped by their different behaviors. According to Marcus Feldman, most of these changes were in response to the transition from a hunter-gatherer lifestyle to an agricultural one: “What we’re talking about here are the genes that allow you to use milk, genes that allow you to use wheat, which was not in the diet of the preagricultural people. Those kinds of things were stimulated by farming ten thousand years before now.”

  In the course of evolution humans have also lost huge numbers of working genes along with the abilities and traits they generated. In recent years scientists announced that human bitter-taste-receptor genes are losing their function. Identifying bitterness helps animals avoid toxic foods, precisely because so many of them taste bitter. For humans, however, an increase in meat consumption and a decrease in plant food, as well as the use of fire, which renders many toxins harmless, have meant that these bitter-taste-receptor genes are no longer maintained by natural selection. As a result they have effectively become useless.

  The degradation of our taste is only one element in a much more massive loss of functionality. In comparison to our ancient selves we now have a greatly diminished sensitivity to many diverse signals from the natural world. Lots of human genes related to smelling, seeing, and the ability to identify pheromones no longer work. Humans have four hundred functional olfactory receptor genes left from what was once a much larger set. Mice, by contrast, have more than one thousand functional olfactory receptor genes. The genome of modern mice is thus much more like that of the distant human and mouse ancestors of millions of years ago. In addition to smell and taste, it’s been suggested that even the range of human hearing is narrowing. In a few million years will we be deaf, taste-blind, and unable to smell anything? It’s not the direction we usually imagine that evolution will take us.

  • • •

  Four hundred and sixty years ago, at the beginning of the age of travel, a series of apocalyptic Mexican pandemics killed tens of millions of indigenous people, who died from a previously unknown (and never-again-seen) hemorrhagic fever. One pandemic killed 80 percent of the native Mexican population. The next one killed 50 percent of the remaining population. Coupled with devastating droughts, the introduction of smallpox, and terrible treatment at the hands of colonial invaders, the indigenous population of Mexico was devastated and its genomic diversity was forever reshaped.

  You might expect that the events of history that have most deeply shaped our psyches are the same events that have carved the genome. In some cases this is true. For the hundreds of years that the slave trade operated, it changed the lives of millions of people, and it may have left a legacy of individual distrust, as well as economic dysfunction, for generations after it ended. The slave trade also completely altered the topography of the human genome. The modern genome of many populations in countries into which slaves were transported reveals descent from them but also from the slaver population and other migrants.

  And yet here is the odd reality of the human genome: The history of the world may be writ in your cells, all of it personal to your lineage and some of it part of the broader context, but though you have been shaped by history, you have only been shaped by some of it.

  Fundamentally, disease and other catastrophes that give rise to bottlenecks affect the genome of future generations by bottlenecking the ancestral gene pool. Similarly, an event that wipes out a whole subpopulation is a genomic event because it removes a variety of the genome from the overall library. In that context landmark events like World War I or World War II or the 1918 flu pandemic may not be genomic events in the same way, even though, for example, the flu killed people from populations all over the world. While the virus profoundly affected some relatively small populations, such as the indigenous residents of Western Samoa, which had proportionately higher fatalities, they recovered. Western Samoa is now a self-sustaining population.

  The events of history that left a trace in the genome are not necessarily history’s most important events either. There could be many significant events that didn’t leave a mark, which is why ancient DNA is such an important tool. We can’t find ancient individuals whose Y chromosomes no longer exist today by examining the modern genome.

  • • •

  If lice had names, you could, theoretically, create a genealogy that connected all the lice that had ever lived to all the people whose heads had provided a home for them and then trace the joint genealogy of lice and men all the way back to Africa. In lieu of such records, the newly sequenced genome of the louse has confirmed the broad outline of the story. By identifying the four major subpopulations of lice, researchers have shown that their genomic tree can be overlaid on the human tree, and the story of both species’ migration can be traced together. A similar tale can be told in the Pacific by the divergence between two kinds of Helicobacter pylori, the bacteria that can cause stomach ulcers. H. pylori originated in Africa with humanity and it too has been shaped by subsequent bottlenecks and isolation. Researchers found that an ancient migration of people into New Guinea and Australia brought along an ancient version of the bacteria. By contrast, the relatively recent migration of a different group into Melanesia and then to Polynesia is validated by the way the DNA of their H. pylori has diverged from the ancestor of the New Guinea/Australia bacteria.

  As we learn to interpret the marks that the world has left on our own genome, we also acquire the ability to see how the world has shaped others species’ genomes. Curiously enough, when we play a significant role in an animal’s world, we can see our history in its genome too. The domestication of farm animals has completely changed their biology. At first the sculpting was somewhat accidental, but since Robert Bakewell formalized the enterprise in the mideighteenth century, we have been intentionally selecting and breeding cattle, horses, sheep, and other farm animals. The domestication of dogs and cats has been generally less utilitarian but no less significant for their genome.

  In 2008 geneticists at the University of York discovered that mice have left genetic trails in much the same way as humans. Rodents that traveled into Orkney on Viking ships ended up leaving much of their DNA in the mouse populations on the island. Indeed, the Scandinavian mice left a pattern so clear that scientists have found they can draw an accurate map of human movements based on mouse movements alone. A more recent study tracked marauding mice of the early tenth century into Greenland from Iceland and before that from either Norway or the northern part of Britain. The researchers looked for, but did not find, Viking mouse DNA in the mice of Newfoundland. Like the short-lived New World Viking settlement, the Viking mice did not leave a lasting imprint.

  Similarly, certain ancient maritime trade routes and the spread of pastoralism from Africa throughout the Near East and the Mediterranean coastline are revealed by an analysis of the Y chromosome and mtDNA of modern-day goats.

  • • •

  In the same way that looking back into our immediate family’s past may change how we think about time and history and our place in it, so too does taking on the idea of our more distant ancestry. Once upon a time, history was living memory plus all the increasingly fuzzy spans of time that came before it. Now we may use written records and the artifacts and fossils that came before records. Using all of these sources of information with DNA teaches us simultaneously about human history, the forces of evolution, and ourselves. Ancestry brings together history and science without any artificial seams between them. It explains our immediate family in the context of the human family and vice versa.

  Ancestry takes account of the evolutionary mechanisms that have shaped the human species and the one-off events—the drifting of genetic markers and traits that have also shaped different parts of the genome. It includes all of human history, from our great-to-the-200th-degree-grandfathers to our two m
ost recent grandfathers and the social and genetic legacies that they passed on. It implicitly includes each of us, because the end result of any lineage is—at least at the present moment—after all, us.

  Ancestry teaches us that when people spend long periods of time together, they form populations. It opens the door to the idea that those populations are shaped by both drift and selection. It shows us that members of a population may share physical traits, but they also share genetic markers of their history that don’t have anything to do with their traits. Ancestry teaches us that we can learn more about our children by knowing their grandparents.

  The study of ancestry, of course, has its complications. Examining the threads of heredity and influence through time can threaten what we tell ourselves about self-determination, both on the social scale and on the personal scale. This happened when people in the United States turned to caring more about their American heritage than their British, and this is surely true for other postcolonial countries. But it applies to our personal lives too.

  Genealogy doesn’t always lead to an enlightened sense of self either. When describing the heritage of the English upper classes, one English artist spoke of the objects in their homes as having been chosen only because they signaled “historic affiliations.” He saw their family trees projecting from their foreheads “like antlers,” weighing them down with responsibility.

  Still, if you find your ancestry explains something about your experience of yourself or your family members or your body, then it’s a worthwhile pursuit. If your ancestry provides you with a framework for a cluster of ideas or thoughts or feelings that you have never connected before but that suddenly seem related in light of what you’ve learned, then it’s not only interesting but also productive.

  As for the ever-controversial subject of race, if you find it’s too hard to let go of the word, it may help to redefine it as ancestry. In this sense, race is a record: The traces of “race” in our genome are what is left of our ancestors’ lives. In the same way that the medical community is beginning to explore the idea of personalized medicine, you may find that thinking about personalized race helps you better utilize information about individual and group differences when you consider your history or your health.

  • • •

  In medieval times monks wrote on animal skins, and when they needed more vellum they scraped the original writing from old texts and wrote over it. With the help of modern technology it is often possible to make out not just the monks’ final words but also the earlier ones because of the traces they left in the vellum. In addition to the story told directly by the words, the way they were layered over one another also tells a story. These documents are called palimpsests, and now scientists have learned how to read another layer in them by analyzing the DNA of the vellum so as to learn when the animal whose skin it once was lived.

  Our DNA is a palimpsest too, and thousands of stories have left their traces in our personal genome. As humanity evolved and traveled, and as families do the same, new stories are layered over old ones, and we can learn more by understanding when and how they were written over one another. (Cultures are palimpsests too. The way we make decisions, such as whom to trust or whether to get divorced, may lead us back to personal events or much larger social events from a long time ago.)

  But DNA is not only a record of history; it is also the stuff of which we are all made—an evolving set of instructions for the construction and operation of our bodies. DNA can shape how we feel, how we behave, and what we look like, and, of course, all of these qualities can shape how people treat us.

  DNA and our life experiences make our bodies palimpsests. As we learn how to interpret the body in the context of its genetic code, we begin to understand how the hand of fate, the choices of families, and the enormous journey of DNA through deep time affect our lives right now.

  Part III

  How What Is Passed Down Shapes Bodies and Minds

  Chapter 13

  The Past Is Written on Your Face: DNA, Traits, and What We Make of Them

  It is hard to hide our genes completely. However devoted someone may be to the privacy of his genotype, others with enough curiosity and knowledge can draw conclusions from the phenotype he presents and from the traits of his relatives.

  —Philip Kitcher, The Lives to Come:

  The Genetic Revolution and Human Possibilities

  Wayne Winkler’s parents moved to Detroit in the 1950s, but each summer when Winkler was a child they would return to Hancock County, Tennessee, to visit his father’s family. On one trip when he was twelve years old, Winkler read an article in the Hancock County Post about Melungeons. “One of the most fascinating mysteries in Tennessee lore concerns the unknown origins of the Melungeons,” it began. The article went on to describe the Melungeons as “a dark-skinned people whom some romantics compare in appearance to Othello immortalized by Shakespeare.”

  Winkler wanted to see some of these elusive Melungeons. He went to ask his father about them, but the elder Winkler had little to say on the subject. Later Winkler’s mother told him that, in fact, his paternal grandmother was a Melungeon—which meant that not only was Winkler’s father a Melungeon but Winkler was too. He later discovered that his paternal grandfather was a Melungeon as well.

  Although Winkler had always known that his family had Native American and white ancestry, this new affiliation was a complete surprise. “I had always assumed that my dad’s family was mostly Indian, because that’s what they looked like and that’s what they always said,” Winkler recalled. When he eventually asked his father why he had always described himself as being an Indian, his father replied, “Everybody knows what an Indian is. It takes all day to explain what a Melungeon is.”

  Despite—or perhaps because of—the fact that part of his family history had been obscured, Winkler was enthralled, and he felt proud to be part of a new group. The timing was right too: Winkler learned about his Melungeon ancestors the same year that James Brown’s “Say It Loud, I’m Black and I’m Proud” was a hit. As Winkler described it, being born at the beginning of the civil-rights movement meant that even though he grew up in an era in which the South was still segregated, there was a growing consciousness and pride among many American groups who didn’t pass as white. In 1968 a local Tennessee group even began to put together a play about Melungeon history.

  Winkler felt encouraged by the liberal tendencies of the times, and the fact that his father and aunt were open to his questions. “My aunt Hazel gave me a collection of articles she’d copied from old newspapers and magazines,” he explained. “That was my first research material. But it didn’t answer questions; it raised questions.” But other members of Winkler’s family were not open, and it did not become any easier to find out more about himself or his ancestry. When he asked some relatives about being Melungeon, Winkler recalled, “They would say, ‘Yeah, I don’t remember that stuff.’ It was just kind of putting me off.”

  Winkler had one uncle who offered little but still managed to communicate a great deal. “He was kind of a character,” Winkler recalled, “kind of a volatile character, particularly when drinking. He was drinking quite often, so he was somebody you kind of watched yourself around.” Still, the old man was indulgent toward Winkler to an extent other family members found surprising. Years after the uncle’s death, Winkler’s mother said to him, “Your uncle would never have talked about being Melungeon.” But Winkler replied, “Mom, let me show you something,” and handed her a book. It was Jean Patterson Bible’s Melungeons Yesterday and Today, published in 1975. Winkler’s uncle had given him an inscribed copy as a gift. “I think that was his way of saying, “Yeah, okay, this is who we are,” said Winkler.

  When Winkler was a boy, the same uncle had taken him for a walk near the family farm. “He showed me this little unmarked graveyard, and he said—I hate to use this word, but he said—‘What this is, is a nigger graveyard.�
�� There were just a few headstones in it, and I said, ‘That’s our names on there. My grandmother Stanley’s name is on there.’ And he said, ‘Yeah.’ That’s all he said.”

  • • •

  Who were the original Melungeons? Where did they come from? Finding the answer became a lifelong interest of Winkler’s, and he spent years researching the topic. At the most basic level the Melungeons, so called by the people around them and then increasingly by themselves, were a group of interconnected families who lived in certain counties in Tennessee, Virginia, and Kentucky. Many of the same surnames occur again and again in Melungeon groups: Bunch, Goins, Collins, Kennedy, Miner, Mullins, Osborn, Bowman, Moore, and Wright. The name on Winkler’s grandmother’s headstone was Givens, her maiden name. Another headstone in the plot was engraved Bunch.

  Mystery surrounded these people for hundreds of years. Old photos of Melungeons from the last two centuries are a study in the unusual. According to various historical documents and oral histories, their features were Caucasian but they had dark skin, dark eyes, and thick, dark hair. The Melungeons were considered nonwhite by the white people around them, but no one knew what or who they were. Some believed they were a mix of white and Native American. Others thought they were the progeny of white people and escaped slaves. Others believed they descended from all three. In Winkler’s childhood “Melungeon” was a term of abuse. Adults who grew up in neighboring white hamlets remember being told to behave, or the Melungeons would come get them.

  Melungeons, along with other nonwhite groups in the United States, experienced many episodes of legally sanctioned discrimination. Ever since Europeans arrived on the North American continent, people of different races had been subject to different laws. According to Winkler, in colonial times the British outlawed marriage between two different races: In 1662 they banned marriage between blacks and whites; in 1691, between whites and Indians. In 1846 eight Melungeon men were prosecuted for voting, which was deemed illegal for them “by reason of color.” In 1924, Virginia’s Racial Integrity Act increased the penalties for interracial marriage (which was already illegal). It also redefined who was and who was not “white,” so that marriages which might have been legal before, for example, between Indians and whites, were now prohibited. Virginia banned marriage between whites and nonwhites.