The Invisible History of the Human Race

by Christine Kenneally

  If we knew exactly how genes underlay these traits, and what particular genes they were, it would help piece together the history of the Melungeons. But the genetics of physical features is a nascent science. Simple traits that are shaped by one or a few genes are easier to identify. The moistness of one’s earwax, for example, can be linked to a single letter within a single gene.

  Many of our traits, however, are determined by several genes, with height being the classic polygenic trait. At least forty genes have been shown to contribute to it, and it’s likely that hundreds of genes affect it. If that seems like genetic overkill, consider how many different parts of the body contribute to height: Someone may have a long shinbone or a long femur, or his spine may be longer than average, or he might have all of these features—it’s likely that each of them is polygenic as well. Not even blue eyes and brown eyes are the straightforwardly Mendelian traits we used to believe they were. Despite what you probably learned in high school, it is possible for two blue-eyed parents to have a brown-eyed child.

  Long before we sequenced the human genome or identified genes that contribute to teeth, anthropologists knew from tracking traits in families that many dental traits were polygenic. In 2011 scientists identified EDAR as the first gene known to contribute to shoveling. But we are still a long way from the full picture.

  Of course, even when you are looking at genes, you are rarely looking only at genes. Some features are controlled by genes and also by whatever happens to be shaping them. We often think of genes as if they were master switches for the body—flick them one way, and you get blue eyes; flick them another, and you get brown. But genes can be influenced by a number of factors, including other genes, noncoding DNA, epigenetic markers (nongenetic attachments to cells), and chemical changes in the cell. The chemical changes are themselves often caused by larger systems in the body, which is, of course, shaped by the world in which it lives.

  The palatine torus, for example, is shaped by development. “It has a pretty strong relationship to latitude,” Scott explained, and is found predominately in Eskimo, Inuit, Siberian, and Native American populations. Scott also examined ancient Norse remains and found that it occurred frequently in medieval residents of Greenland. While it’s clear that there is a genetic component to the trait, it’s thought that mechanical stress, like chewing lots of cured reindeer meat, could cause a palatine torus to form.

  • • •

  Back in the nineteenth and twentieth centuries, Melungeons weren’t ostracized because they had shovel-shaped incisors, as no one could see the backs of their teeth. They were treated differently because they looked different. The face is an incredibly important part of human culture and biology, and indeed, without becoming too circular, it is the major interface between the two. What happens on our faces shapes our initial encounters with others and our most intimate relationships. It is a powerful guide to internal states, and not just psychologically: A significant number of abnormal facial traits are correlated with defects in certain organs. Human brains even have specialized face-recognition mechanisms. Still, we are only beginning to understand how the human face is put together.

  It’s widely accepted that facial features are strongly determined by our lineage. Children often look like parents, siblings like each other, twins may look exactly alike, and even grandparents can look like their grandchildren. For the first two years of my eldest son’s life, people in our neighborhood whom I didn’t know would stop me on the street and exclaim, “Your baby is a clone of his father.” It’s true of our second child too. Baby photos of my son and husband, taken some thirty-five years apart, could easily be of the same child.

  What makes family similarity so compelling and confusing is that it comes down to probability: Because you get 50 percent of your DNA from each of your parents, there’s a good chance you’ll resemble them both. There may be a reasonable amount of genealogical collapse in your family tree as well: If some of your great-great-great-grandparents who were married to each other were also first cousins, they brought more of the same DNA to the table when they had children. Their offspring are likely to have recycled more DNA from that lineage, and less variety was therefore passed down to you.

  Then again, you only get 50 percent of your DNA from each of your parents. Sometimes people don’t look like either of their parents or other members of their family. Some are tall where their parents are short or dark where their parents and siblings are fair. While appearance can be a persuasive pointer to ancestry, it is not always a reliable one.

  Of the studies that have specifically looked for genes implicated in facial structure, most have attempted to determine the cause of an abnormality. In 2012 a group of scientists in the International Visible Trait Genetics Consortium published one of the first genomewide association studies to identify genes that contribute to the face. Led by Manfred Kayser from Erasmus University Medical Center in the Netherlands, the researchers took three-dimensional photographs of more than five thousand people and examined more than two million markers in the genomes of more than ten thousand Europeans.

  The photographs were analyzed for forty-eight different facial characteristics, and the researchers tried to establish connections between the genomes and the different facial traits. They found five genes that contribute to the shape of the face. For example, the TP63 gene affects the distance between the eyes, while the PAX3 gene contributes to the distance between the eye and the nasion, the place where the nose meets the forehead. The findings suggest that, as with height, many genes contribute to the face’s particular contours and size, each with a relatively small effect. Kayser is optimistic that much of the genetic basis of human facial variation will be discovered.

  After the announcement of Kayser’s groundbreaking findings, another team found evidence for the influence of many noncoding segments of DNA on the structure of the face. Soon after that, another team announced that their study using 3-D photographs of almost six hundred subjects had identified twenty genes that strongly influenced facial structure. Variations in one of these genes’ codes were such useful predictors of facial shape that the team was able to build reasonable approximations of a subject’s face based on his DNA alone. Overall, this kind of work may aid in the reconstruction of faces from ancient remains and ultimately even be used in forensic police profiling.

  • • •

  On the ancient meeting ground of Gulkula in Arnhem Land—the northeastern corner of Australia’s Northern Territory—an elder called Gulumbulu demonstrated one way to span the worlds of whitefellas and blackfellas (Australian for white and black people): She was teaching her daughters and granddaughters the old ways while simultaneously sharing them with a large group of tourists—white Australians and visitors from other countries. Gulumbulu was a teacher at Garma, the country’s largest alcohol-free, Aboriginal-driven festival of dance, film, and storytelling. Every day of the festival men and women streaked with white paint and wearing bright red wraps or yellow headbands danced on an open field on the edge of a large forest, which stretched many miles to Kakadu National Park. Huge mounds created by magnetic termites formed gray tombstones among the gum trees, and the woods were full of stinging green ants whose formic acid smelled like citrus. Beyond them an ocher escarpment dropped down to the inviting green Gulf of Carpentaria.

  One morning I trudged up an unlit dirt road in the predawn hours with fifty paying tourists. We followed a group of elders to the edge of a cliff and sat quietly until the sun began to rise. This was a “cry for country” for women only, and the elders’ gatekeepers warned, “No photos!” Just before dawn broke, birds began to sing, and the creaky-voiced Aboriginal ladies lifted their voices up as well, lamenting all the land that had been lost. It was sad and eerie and beautiful, until a spat broke out when one tourist furtively tried to take a photo and another crankily told her to stop. Yet another woman raised her voice and cried out with the elders. She was not one
of them, and her skin was white. The women around her looked upset: Who was she to join in on the singing?

  As we walked back from the morning ceremony, the woman who had sung told me about herself. She grew up in a poor family in New South Wales and was raised mostly by her single mother. When she left school, she sometimes traveled into small towns in the outback. More than once local Aboriginals singled her out from the group she was traveling with and said to her, “You are one of us.” They welcomed her to spend time with them. As far as she knew, she was white, so she always took this to be not much more than a simple act of kindness. Much later she discovered that her mother was indeed half Aboriginal, a fact that had been concealed from her all her life. Years later, when she found herself on the cliff in the dawn light, she felt as if she belonged. The elders were the aunties she had never known, and she cried for her mother and her mother’s father and everything that her family had lost as well.

  We tend to associate some features with different kinds of ancestry. In the TV series African American Lives, host Henry Louis Gates Jr. discussed the DNA analyses of various guests, like the comedian Chris Rock and actor Don Cheadle. The show’s guests described their family lore about Native American ancestry; relatives had made remarks like “That’s Indian hair” and “You do have high cheekbones.” Similarly, it’s often said that there are only six faces in Ireland. The Y-chromosome data suggests that there is in fact a great deal of genetic overlap in Ireland, but we don’t yet know how much all Irish genomes overlap, and if that might produce similar features. How much of the past is inscribed on our faces?

  The Oxford geneticist Sir Walter Bodmer has long been interested in the face: “The fact that identical twins are so similar in their facial features, and they of course share essentially all their genetic make up, shows us that facial features must be largely genetically determined. The evolution of facial differences together with facial recognition must have been a very important part of the social and cultural evolution of the human species, and it’s most probably connected with belonging and being recognized as a member of a group. The face also, almost certainly, plays an important role in choice of mate.”

  Bodmer and his colleagues are currently investigating faces in their study of British regional genetics. He explained, “It is a common observation that there seem to be facial characteristics that are associated with particular regions or countries even when they are basically closely related, such as within Europe. There are, of course, very obvious differences between major ethnic groups, such as Europeans and East Asians.”

  But this raises a question: If the genomes of the small British groups weren’t distinctive enough to look different in a medical study, how could they produce different types of faces, even subtly different ones? “Even within Europe there has to have been sexual selection with respect to facial features, and that means, on the whole, picking people who are somewhat similar. I think that’s been a very powerful force during evolution,” Bodmer said. His team is in the process of taking three-dimensional photographs, each with 3,500 points of reference (“a full canvas”), of subjects who participated in the first stage of the study.

  In retrospect the woman at the “cry for country” ceremony believes she should have realized she was not actually white, especially because of the way other Aboriginals treated her. Yet no one else in her life had guessed her ancestry. She looks like her mother, who looked like her own father, who was recognizably Aboriginal. Could other Aboriginals tell that she was part Aboriginal because they were Aboriginal themselves?

  It turns out that some people are better than others at making judgments about ancestry based on looks. For decades psychologists and anthropologists have investigated a phenomenon called own-race bias. At least forty different experiments have demonstrated that people are better at remembering faces when the face appears to be the same race as their own. This is true no matter what the race of the observer or the observed is. It’s also been shown that people are better at predicting how well they will perform a face-recognition task when the race of the photographed face is thought to be the same as their own, which is to say we overestimate our ability to judge how well we recognize faces from races other than our own. It’s not entirely clear what the mechanism responsible for own-race bias is. One of the most important implications of own-race bias is that in eyewitness situations the testimony of a witness may be considered less reliable if the accused is of a different race.

  Most studies of own-race bias have relied on self-reported race. In 2012 Mark Shriver, an anthropologist at Penn State University who studies the interplay of faces and genes, ran an experiment that investigated the connection between genetic markers of ancestry and the ancestral cues we detect on people’s faces. He asked more than two hundred subjects who lived in New Mexico to assess the component ancestries of fourteen Hispanic faces based on front- and side-view photographs. The genomes of the people in the photographs had been analyzed with respect to their mixture of Native American, European, African, and East Asian ancestry.

  Shriver found that most observers made a better guess at the admixture of the photographed individuals than someone who simply guessed randomly. Still, the guesses were far from perfect, suggesting that, while we have some general ability to detect ancestry, it’s not uniformly reliable. Shriver’s results were consistent with other studies that show the more similar the observer’s ancestry is to the ancestry of the person in the photograph, the better the observer is at guessing the correct family history. The most plausible explanation for this is that the observers had learned to interpret the features of faces with which they were most familiar.

  • • •

  Human skin color is another important case study in the way that genes shape traits. An inherited trait, the many varieties of skin color have emerged in a surprising way from the intersection between environment and behavior in the last hundred thousand years. When humans left Africa and began to live in the Northern Hemisphere, the color of their skin became lighter. This has long been attributed to natural selection and the need for skin to make vitamin D. As the details of human genetic history are being uncovered, some changes look more like a case of relaxed selection rather than natural selection. Many genes are involved in skin pigmentation; the MC1R gene (melanocortin 1 receptor) is critical in the production of melanin, which darkens the skin. In Africa today at least eleven different mutations to MC1R have been identified, but eight of these are so-called synonymous mutations, which do not actually affect the related amino acid in the protein structure or the protein’s function. The fact that most of the African MC1R mutations are synonymous means that what the gene does is critical in that particular context. Outside of Africa MC1R has undergone many more mutations, and many of them do have an effect on melanin production. So what has been hard won by positive selection in the bright light of Africa—strict genetic control of dark skin that protects against damage from strong ultraviolet radiation—disappears when it no longer affects survival. Outside Africa it appears there are many ways to turn white. The nonsynonymous mutations to MC1R are diverse and vary from region to region, but most lead to the same result: reduced melanin production. Some mutations merely alter the function of MC1R, while others completely shut it down. The red hair and freckles of many people in the British Isles results from just such a mutation.

  Skin pigmentation is affected by more than genes. It may even be that lighter skin was inherited from Neanderthals, as regions of the genome that contribute to skin color show influence from the Neanderthal genome. Yet change did not happen only in the distant past. There is evidence from ancient DNA that lighter skin, hair, and eye pigmentation was strongly selected for in Europe in just the last five thousand years. The change could have resulted from the greater success of people who were able to process more vitamin D, or it could have resulted from sexual selection, where people with lighter pigmentation were more successful in reproduction.<
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  There is much to be learned about how DNA shapes traits and how traits then shape our experience of the world, either because of our abilities or because of the way people treat us. One of the most crucial aspects of this nexus is the way that genes affect our well-being, either by predisposing us to disease or by protecting us from it. As with everything else to do with DNA, the forces of fate and randomness play a huge role in people’s health, and as always the family is often the crucible of this drama.

  Chapter 14

  The Past May Not Make You Feel Better:

  DNA, History, and Health

  The laws of genetics apply even if you refuse to learn them.

  —Alison Plowden

  When Jeff Carroll was sixteen he dropped out of high school. At twenty he joined the army and was posted to Europe. He served in Germany for a year, and on his first trip home for Christmas, his father told him that his mother was showing signs of Huntington’s disease, a condition that Jeff had never heard of. Huntington’s is the cruelest diagnosis. Patients slowly lose control of their bodies, as well as their memories and their ability to think. They may undergo personality changes too, often becoming aggressive toward their loved ones. The degeneration is slow and relentless, unfolding over the course of years. Although Cindy Carroll was in her midforties when her body started to jerk without warning and she forgot one of her best friends’ names, she lived for many years afterward.