DNA USA

by Bryan Sykes

  The large-scale commercial transatlantic traffic in slaves had its beginnings in the middle of the fifteenth century when the Portuguese began to trade extensively on the coast of West Africa. These early contacts culminated in the construction of a permanent trading post, Elmina Castle, in present-day Ghana, in 1497. Ghana’s colonial-era name, the Gold Coast, prior to independence from Britain in 1957, describes the early ambitions of the Portuguese to find the precious metal in the African interior. Slavery was not the original purpose nor, contrary to some modern assumptions, did it start with the arrival of the Europeans. Since the twelfth century there had been a lucrative export trade in West African women wanted as domestic servants in North Africa and Arabia. What the Europeans did do was to create a demand for African slaves in the New World that, at least in the early days, complemented the trade with the Muslim world by favoring men. Neither was the picture painted by Alex Haley’s influential book Roots of white traders rounding up Africans deep in the interior an entirely accurate one for it was often ruthless African rulers who caused their own people, or captives in war, to be led in chains to the trading posts on the Atlantic coast.

  A great deal has been written about the inhumane conditions of the Middle Passage, when Africans were taken first to Brazil or the Caribbean and then, after “seasoning,” as the process of acclimatization was euphemistically called, sold on to tobacco and cotton plantations in the United States. So much so that I need to provide here only the briefest summary of the economics. For more than a hundred years before they began to arrive in North America, African slaves had been taken across the Atlantic to the Portuguese and Spanish colonies in South America, particularly Brazil, where they were forced to work the sugar plantations. The early British colonies in North America, beginning with Jamestown, Virginia, in 1607, very nearly failed and were saved only by the cultivation of tobacco. The original plantation workers were not African slaves but indentured servants, mainly poor immigrants from England, though including a few Africans, along with some enslaved Native Americans. After their contracted term, by which time they had worked off the debts incurred by the cost of their passage, they were free to settle and even helped to do so with “freedom dues,” which included land, seed, tools, and guns. Not only did these workers have to be replaced but they began to compete with their former employers and the price of tobacco started to slide. Matters deteriorated even further for the landowning elite in the 1640s when increasing numbers of immigrants survived their years of indenture. They responded by increasing the term, so that more would die before completion, and halted the grant of land as part of the dues. Their other solution was to look to Africa as a source of labor. By the late 1660s slavery had been legalized, and the terrible process of transformation to the centuries of despair had begun.

  As the European powers, principally the British, French, Dutch, Spanish, and Portuguese vied with one another to control Atlantic trade to the New World during the mid-1600s, several African kingdoms expanded their territories, displacing hundreds of thousands of people and, in so doing, helping to create more slaves for export. This trade became highly regulated, with the relations between European slavers and the African merchants being on an equal footing. Licenses were granted and rent paid for port facilities. Slave raiding by maverick Europeans was rare and brought swift retribution in the form of confiscations and the withdrawal of licenses and other privileges.

  Although the African slave trade has had an enormous influence on the demographic and genetic composition of America, the United States was by no means its principal destination. In recent years a great deal of careful work has been done to uncover the numerical details of the trade. The most comprehensive of these is the initiative by the W.E.B. Du Bois Institute of African and African American Studies at Harvard, which has collated the details of about 70 percent of voyages. Combined with other sources, we now know such details as gender ratio, survival rates, and ethnic origin. The figures are mind numbing. There were a total of around 54,000 voyages between Africa and the New World involving the shipment of more than 11 million slaves. By far the greatest number, 4 million, were taken to Brazil, mainly by the Portuguese. Mexico, Cuba, and other Spanish colonies imported 2.5 million, the British took 2 million to their Caribbean “possessions,” and the French 1.5 million to theirs. All told, the plantations on mainland America took somewhere between four and five hundred thousand African slaves.

  Although the slave trade began in the Portuguese colonies around the Gulf of Guinea, and West Africa remained the focus of the export trade throughout, it spread out in both directions to Senegal to the northwest and south to Cameroon, Congo, and Angola, and then all the way around the Cape of Good Hope to Mozambique and Madagascar.

  We also know about the resistance: African slaves did not go quietly. There are records of some four hundred mutinies on the Middle Passage. Thousands of slaves committed suicide by jumping overboard. Nor was the trade completely without vocal critics. Two African kingdoms—Djola, in modern Chad, and Balanta in Guinea-Bissau—banned the trade within their borders and tried to suppress it in neighboring states. Some religious organizations, both Christian and Muslim, objected to the Atlantic slave trade on moral grounds. Indeed it was an Islamic scholar who, as early as 1614, formulated the very first legal argument to undermine its legitimacy. But these were mere whispers of disapproval compared to the deafening roar of commerce.

  Numerically speaking the transatlantic slave trade peaked in the eighteenth century then diminished and finally ceased in the nineteenth. The Thirteenth Amendment to the Constitution technically abolished slavery in the United States in 1865, after the Civil War, but as we shall see, it continued in one form or another for many years beyond that. Brazil was the last country to abolish slavery, in 1888. By its end the slave trade had forcibly transported 11,313,000 Africans, the vast majority to the Americas. The first U.S. census, in 1800, put the total population at almost 5.5 million, of which 1 million, mostly American born, were classified as “black,” a proportion of just over 18 percent. By 1860 the huge influx of overwhelmingly white Europeans had swelled the total population of the United States to 31 million, but the black population of almost 4.5 million still made up 14 percent of the total. Pretty clearly from these figures, African DNA was prospering in antebellum America despite the horrors of the slavery system.

  Passenger lists from the ships bringing European immigrants to America are a vital resource for their descendants. Even though the work of the Du Bois Institute and others has cataloged the voyages of the slave ships, there is one crucial difference between the two. While the manifests certainly recorded the numbers, they were completely anonymous. African Americans almost never know the names of their ancestors aboard the ships that brought them to America. Their identity was unimportant to the traders in human cargo, and for generation after generation their descendants were left wondering if they could ever know who their ancestors were and where they had come from. This is a privilege that most European Americans take for granted. At least there are records available, even if they do not always yield all the answers. But for African Americans they are just not there, and this is where DNA has been able to help. As we have seen, European Americans have embraced genetics as a new tool with which to elaborate their own family histories, often finding they can pinpoint the name and the home of their own ancestors in Europe. I think this is wonderful, but it is a luxury that African Americans just do not share.

  However, DNA can be, and has been, extremely valuable in overcoming the centuries of silence, and can reconnect African Americans to their ancestral origins. I first saw how and why when I was filming a short documentary for British television about a woman who was searching for her roots. An Afro-Caribbean, her name was Jendayi Serwah, and her parents had arrived in Britain from Jamaica in the 1950s. Since she was a small girl growing up in Bristol, in southwest England, Jendayi had always had a very strong attachment to her African roots. She had traveled to
Ghana and gone through a ceremony to change her name to Jendayi, and she always wore African clothes. As part of the film I had been asked to analyze her mitochondrial DNA.

  Unsurprisingly, to me anyway, she was in the clan of Lubaya, one of the thirteen African maternal clans to have been identified at the time. It was a very clear result. Searching my database, which was comparatively small back in 2001 when we were filming, I found a close match with a Kenyan Kikuyu whose results had been published in an academic paper in 1996. Documentary makers, reveling in the element of surprise that has become the staple diet of reality shows, love what they call “the reveal.” In this case the plan was that I should not tell Jendayi what I had found until the cameras were rolling. I have since learned to be wary of this technique and refuse to go along with it if I suspect the genetics news may be unwelcome. But I was completely unprepared for what came next. I was not at all surprised that Jendayi’s DNA had come from Africa. That is what I expected, given that it had traveled down the maternal line. So I gave her the results in a rather matter-of-fact manner, expecting a “Thank you, that’s interesting” sort of response. Far from it. Jendayi was absolutely overjoyed. Tears of happiness ran down her cheeks as she gave me a big hug. I was dumbstruck—after all, what else had she expected?

  The cameras were packed away and Jendayi left with the crew. The film went out a few weeks later, but still I couldn’t forget Jendayi’s response. I called her at home in Bristol and arranged to go and see her. What was it that had given rise to such an emotional response? It was this: She explained that her knowledge of her African roots had been secondhand, something that was taken from history books. Not that she didn’t believe these histories, even though they were almost always written by whites, but they were always generalized and impersonal. What the DNA result had given her was proof of a quite different kind. Instead of having to rely on vague histories written by others, she carried a message from her ancestors in every cell of her body, in her own DNA. It was a secret document, a talisman of her African roots carried across the Atlantic in a slave ship by a black woman, her ancestor. Passed on through generation after generation of mothers and daughters to her own mother and then to her, it had slid unseen past slave owners who had strived to erase any sense of individual identity from her ancestors. And now her secret document could be read for the very first time. Its meaning was released, and she could see—almost taste—the savannah and the forest of her ancient homeland.

  Africa, as we know, is the cradle of humanity and the ancestors of every man, woman, and child on the planet began their journey under an African sun. Humans have lived in Africa far longer than anywhere else, and so their genes have had longer to evolve and change. As a direct result of this antiquity, there is more variety among African DNA sequences than in the rest of the world put together. Since genetics is fundamentally about variety, African DNA is an especially rich confection, a real treat for geneticists like myself. Once again, it is mitochondrial DNA that comes out on top as the clearest window into the deep past, as it does in all indigenous populations, because it is the history told by women alone, untroubled by the frequently erratic behavior of men.

  As we have seen already, the first detailed research on mitochondrial DNA of any indigenous people concentrated on Native Americans, mainly because the labs concerned were based in the United States. As we have also seen, within a region mitochondrial DNA falls naturally into a relatively small number of clusters, each with its own founder, the clan mother, and her matrilineal descendants. The early start of research into Native Americans meant that their mDNA clusters claimed the first four letters of the alphabet, A–D. By the time the first comparable studies emerged from African volunteers, the cluster notations had progressed through the alphabet to L.2 This has meant that, despite African mitochondrial DNAs being by far the most varied anywhere in the world, they all belong to just one supercluster, L. Within L are three clear subdivisions that elsewhere would have had their own separate alphabetical notation and that thoroughly deserve their description as superclans. According to the internationally agreed classification, these three superclans are given the uninspiring monikers L1, L2, and L3. Such is the range of different mDNAs in Africa that each of these three superclans has its own substantial clusters. L1 is divided into five clusters, L1A–E; L2 into four, L2A–D; and finally L3 into seven clusters, L3A–G. If you can stand it, even these are broken down into L1A1, L1A2, and even L1A1A. Now we are entering the world of the phylogenetic aficionados, and we must tread warily because each step takes us in further away from real people and into the shrouded domain of the theoretician.

  I have in the past attempted to humanize this excruciating yet necessary process by giving names to the clan mothers of each group, much as I did with the seven major European clusters and others around the world. After all, they were real individuals, and they lived long enough to have at least two daughters who lived long enough to have at least one daughter of their own. One of the qualifying conditions for clan mothers is that they must have at least two daughters. Being the most recent common ancestor of the whole matrilineal cluster, a woman with only one daughter would have a child who lived more recently than she did. Since my rule of thumb is to choose a name beginning with the cluster’s alphabetical notation, all the African clan mothers begin with L. They are listed in the appendix. I would use them here rather than their alphanumeric equivalents, but having tried it, I found that the narrative gets even more confusing than it already is.

  Figure 3. Maternal family tree of Africa. Circles are clusters of individual African mDNA sequences with connecting lines representing mutations. Cluster letters follow the international nomenclature—for example, the arrowed cluster is L1C1a1. The star marks the position of “Mitochondrial Eve,” the root of the maternal tree. Gray circles are nodes with no extant sequences. M and N are the founder clusters of all mDNA found outside Africa. Redrawn from A. Salas et al., American Journal of Human Genetics 71 (2002), 1082.

  By 2002 the collection of samples from many different parts of Africa had reached the point where the maternal family tree could be drawn with little anxiety that it would need any major revisions, and I have drawn a simplified version in Figure 3. It certainly doesn’t look simple, but it is the best I can do without losing all pretensions to scientific accuracy. On the tree, circles are particular mDNA sequences, and the interconnecting lines represent the mutations that have occurred between one sequence and the next. For those of you who are strong enough to follow these mutations through the family tree, I have put them in the appendix.

  The first feature of the African maternal family tree that strikes home is its delicious complexity and that is because there has been more time for it to grow in Africa than anywhere else. The geographical location of the many different clusters and subclusters is also very revealing, not just about ancient events in the continent’s history but about more recent known migrations, and about the effects of slavery. At the very root of the tree is a woman from whom we are all maternally descended. She lived about 170,000 years ago, most probably in East Africa. How do we know this? You are by now familiar with the principle that mutations accumulate in DNA over time, which is how we estimated the ages of the major Native American clusters. If we do the same kind of calculation for African mitochondrial DNA, the time it has taken for all the complexity seen in the tree to have accumulated is around 170,000 years, which is how we arrived at the date for our common maternal ancestor. There may be room for adjusting this figure if, for example, the mutation rate were slightly different, but it will not be far off. Fortunately, unlike with the equivalent estimates for Native American and European mDNA cluster ages, we are saved the complication of trying to identify the various founder sequences that have arrived from elsewhere. Since our ancestors started out in Africa, they did not come from anywhere else.

  We also know that it all began with one woman whose existence was first realized in 1987 in a classic Nature paper by A
llan Wilson and his colleagues from the University of California in Berkeley.3 Using the much cruder methods of DNA analysis of the time, they showed that all reconstructions of the human maternal family tree led back, by an inevitable logic, to just one woman. Almost as inevitable was her instant nickname, “Mitochondrial Eve.” Even though she has been dead for many millennia, we are able to reconstruct her mitochondrial DNA sequence by working backward from the branches of the maternal tree to its root. No one alive today has her sequence, since after such a long time, all her lines of descent have experienced several mutations. We know she is at the root of the family tree because her sequence, even though it is a reconstruction, is the closest of all human mitochondrial DNA sequences to our nearest living primate relative, the chimpanzee. It is also the sequence that is closest to mDNA recovered from the remains of our nearest extinct human relatives, the Neanderthals.

  However, though we are certainly all descended from Mitochondrial Eve, she was not the only woman alive at the time, and the best theoretical estimate is that she shared the planet with five thousand others. But she is the only woman to have matrilineal descendants living in the present day. The others, or their maternal descendants, either had no children or had only sons whose mitochondrial DNA was not passed on. In succeeding generations these maternal lineages became extinct one by one, leaving Eve’s descendants as the sole survivors. Starting with her nearest neighbors on the family tree in superclan L1, their present-day geographical settings reveal a good deal about how humans spread throughout Africa and out into the wider world.