The golfer Tiger Woods may be more indicative of the face of today’s United States than many realize. Woods, who claims African–American, European and south-east Asian ancestry, falls into that ever-increasing group of people who would find it difficult to describe their ethnicity in simple terms. Even those who give themselves a single classification, such as African–American, often have substantial admixture from other groups. This was actually one of the criticisms levelled at the first scientific publication on mitochondrial Eve in 1987. Because Cann, Stoneking and Wilson had sampled African–Americans living in the San Francisco Bay area as their representative ‘African’ population, critics noted that it was possible that the deepest lineages in their analysis – those indicating an African origin – may actually have been non-African. It was only in their second paper, in 1991, that Africans were included, indicating that the conclusions of the original publication were valid.
Tiger Woods is in many ways a person who could only have been born in the twentieth century. His complex web of ancestors, originating on opposite sides of the world, could have encountered each other in the United States only within the past 100 years. But Mr Woods is merely an obvious example of a phenomenon that has been ongoing for the past few centuries, resulting in the jostling together of people who, historically speaking, would never have met. Coupled with changing social attitudes towards race, people today are far more likely than their ancestors to have children of mixed ethnic backgrounds. While this is certainly a good thing socially, leading to the breakdown of racial stereotypes, it does mean that our genetic identities are becoming ever more closely entwined. Admixture is destroying the old, regional patterns of genetic diversity, replacing them with cosmopolitan melting pots of markers. It is likely that sampling 100 people in a nightclub in New York’s East Village would reveal every single one of the markers we have discussed in this book, all present in one small, potentially interbreeding population. The implications of this sort of mixing for our studies of genetic history will be the final stop on our journey.
A closing window
The third Big Bang of human history has led us into a new genetic landscape. The patchwork quilt of diversity that has distinguished us since human populations started to diverge around 50,000 years ago is now re-assorting itself, blending together in combinations that would never have been possible before. While the genetic markers themselves will not be lost, the context in which they arose may soon be gone. And although we can trace the genetic relationship among lineages as easily in a sample from our New York nightclub as from isolated groups all over the world, the result will have little meaning. This is because we cannot place the genetic analysis in a geographic location. Our coastal voyage to Australia, for instance, relies on the distribution of the oldest M130 chromosomes being limited to the southern part of Eurasia, and their absence from the Middle East. It is only by sampling indigenous people who have lived in these places for a long period of time – in this case, ideally, 50,000 years – that we can hope to infer the genetic makeup of their ancestors. Ancient, local populations are key, and the less admixture they have had the better. These are exactly the groups that are now being lost. Taking languages as a litmus test, isolated communities are being engulfed at an increasing rate. Moreover, because of the nature of modern industrial life, members of these communities are increasingly moving to cities, where their markers will enter the vast, swirling melting pot of cosmopolitan diversity. Unfortunately, when this happens the unique story they have to tell will be lost.
Some minority populations are rediscovering a sense of identity, fighting against the advancing wave of global culture. European activists such as the Basque ETA, French farmers who bomb McDonald’s restaurants and the ranks of anti-globalization protestors at economic summits – all are a sign of the growing realization that cultural identity is being lost on a massive scale. Ultimately, though, their methods are too extreme to achieve widespread support. And for most indigenous people, the rewards of becoming part of the global village are simply too enticing to be ignored. Decisions to leave ancient villages usually come down to personal choices – a perception that opportunity is better elsewhere, or that it has disappeared at home. In the end, because they cannot limit personal choices, it is a battle the activists are doomed to lose.
The story in this book could only have been told now. However, it is merely the outline of a much more detailed narrative, the whole of which will take many more years of research to decipher. We may have a view of the forest, but we still know very little about the trees. With the realization that their cultural identity is being eroded, though, many indigenous populations are now refusing to participate in scientific studies. A history of colonial exploitation, with incidents such as the horrendous medical experiments inflicted on the Australian Aborigines in the mid-twentieth century, has understandably led many indigenous people to be wary of scientists. Activists are also reasserting ancient taboos on ancestor disinterment, asking for archaeological material to be returned for proper burial. These cultural taboos can, and do, extend to giving samples for genetic studies. In a way, we are trying to excavate the past from the blood of people living in the present – an activity that can be interpreted as voyeuristic (or worse). A desire for cultural privacy, perhaps combined with the suspicion that the scientific results may not agree with their own beliefs, is leading more and more indigenous groups to choose not to participate. Scientists have a responsibility to explain the relevance of their work to the people they hope to study, in order for their participation to become what it really is – a collaborative research effort. Only then we can regain some of the trust we have lost.
Today we are in many ways the same Palaeolithic species that left Africa only 2,000 generations ago, with the same drives and foibles. It is ironic that the final Big Bang of human history, which has given us the tools to ‘read’ the greatest history book ever written – the one hidden in our DNA – has also created a cultural context where it is becoming increasingly difficult to carry out this work. The genetic data we have glimpsed shows unequivocally that our species has a single, shared history. Each of us is carrying a unique chapter, locked away inside our genome, and we owe it to ourselves and to our descendants to discover what it is. Since our ancestors came down from the trees, we have used our intellect to explore outward and extrapolate into the future. Over the past few thousand years we have changed our world – and our place in it – for ever. With the development of agriculture, and the cultural chain reaction it ignited, we gained the power to choose our own evolutionary trajectory. With this power, though, came increased responsibility. One responsibility that we neglect at our peril is that of self-discovery. Once the document of our journey has been lost it will, like the footprints of our ancestors as they left Africa to colonize the globe, be gone for ever.
To my wife, Trendell, and our daughters, Margot and Sasha (Y-chromosomes are overrated anyway …)
Acknowledgements
I have benefited enormously from the help and insight of many colleagues, who have provided data, interpretations and counter-arguments for the many theses I pursue in the book. Foremost among them is Peter Underhill, whose careful work on the population genetics of the Y-chromosome has allowed me to tell this story. It was Peter and his colleagues at Stanford who discovered most of the markers discussed in this book, and the field owes him a debt of gratitude. I have also learned a great deal from my work with Li Jin, a fountain of knowledge on the population history of east Asia, and from interactions with my Oxford colleagues Walter Bodmer, Tatiana Zerjal, and Chris Tyler-Smith, who have challenged me on various genetic details and always make for very stimulating company. Nadira Yuldasheva and Ruslan Ruzibakiev have been friends and co-workers during countless months of sample collecting in remote parts of Asia, and throughout the years of labwork that followed – bolshoi spasibe. Merritt Ruhlen and Richard Klein were happy to discuss their work on linguistics and paleoanthropology, respecti
vely, which was invaluable. Thanks also to Lluis Quintana-Murci, Matthias Krings and Mark Seielstad for in-depth explanations of their work over long, boozy meals in Paris, London and Boston – the hangovers were worth it. My colleagues at Tigress Productions in London, who believed in this project during the long television commissioning process, have created a wonderful film – thanks to Jeremy, Justine, Clive, David, Ceri, Jackie, Aidan, and Martin. We were lucky to have a great producer, Jennifer Beamish, whose sharp mind acted as a perfect sounding-board for many of the ideas in this book. A special thanks to my editor at Penguin, Stefan McGrath, whose enthusiasm for this project has never waned, and who was able to make deft use of both carrot and stick in order to get me to finish the book on time during our long filming schedule – I owe you a few beers. And finally, apologies to my wife, Trendell, and to my daughters, Margot and Sasha, for my long absences during this project. Even when I was home, I was often preoccupied – thanks for bearing with me.
Further Reading
The best overall summary of human genetic patterns, and their relationship to prehistory, is The History and Geography of Human Genes by Luca Cavalli-Sforza, Paolo Menozzi and Alberto Piazza (Princeton University Press, 1994). This extraordinary volume summarizes over thirty years of work on classical genetic polymorphisms in human populations, and is the best single-volume reference available on the more technical aspects of much of the material in this book. Cavalli-Sforza’s more approachable Genes, Peoples and Languages (Penguin, London, 2000) presents some of his ground-breaking work for a general audience.
Three other books stand out as indispensable introductions to human prehistory, more from the perspective of stones and bones than DNA: Richard Klein’s The Human Career (2nd edition, University of Chicago Press, 1999), Brian Fagan’s People of the Earth (8th edition, HarperCollins, New York, 1995) and Chris Stringer and Robin McKie’s African Exodus (Pimlico, London, 1996). All three take a very broad view of human prehistory, and Klein’s book in particular is tied together with a persuasive argument (which I also pursue in the present volume) that the intellectual leap that took place in Africa around 50,000 years ago allowed our species to colonize the rest of the earth.
1 The Diverse Ape
The best English translation of Herodotus’ History I have found is that by David Grene (University of Chicago Press, 1987). It is written in a vernacular style that manages to communicate the excitement of the Greek historian’s world in a fresh way – nearly 2,500 years after it was written.
Darwin’s Beagle journal has been published and reprinted many times – the version I have used is The Voyage of the Beagle (Modern Library, New York, 2001), with an interesting introduction by Steve Jones. Many of the biographical details of Darwin’s life came from Janet Browne’s wonderfully readable Charles Darwin: Voyaging (Alfred A. Knopf, New York, 1995) – the first in a planned two-volume definitive biography. Darwin’s On the Origin of Species (Harvard University Press, Cambridge, MA, 1964) and The Descent of Man (Princeton University Press, 1981) are so well known that they need no introduction.
Carelton Coon’s work was summarized in his two influential books The Origin of Races (Alfred A. Knopf, New York, 1962) and The Living Races of Man (Alfred A. Knopf, New York, 1965). Daniel Kevles’s excellent summary of the perversion of a naïve ideal can be found in his In the Name of Eugenics (Alfred A. Knopf, New York, 1985), and additional material is covered in Stephen Jay Gould’s The Mismeasure of Man (W. W. Norton, New York, 1981) and Jonathan Marks’s Human Biodiversity (Aldine de Gruyter, New York, 1995).
2 E pluribus unum
The title of this chapter – Latin for ‘out of many, one’ – is the motto on the Great Seal of the United States of America, found on all US coins.
The history of blood group studies and their application to human population genetics has been summarized in Arthur Mourant’s seminal book The Distribution of the Human Blood Groups (Blackwell, Oxford, 1954). Much of my examination of Lewontin’s work comes from many hours spent discussing genetics and human diversity with him, but many of his ideas are explained in The Genetic Basis of Evolutionary Change (Columbia University Press, New York, 1974) and Human Diversity (Scientific American Press, New York, 1982). His original paper analysing human genetic variation was published in the Journal of Evolutionary Biology (6: 381–98, 1972) – one of the most important twentieth-century publications in the field of human genetics.
Theodosius Dobzhansky’s Genetics and the Origin of Species (Columbia University Press, New York, 1982) and Motoo Kimura’s The Neutral Theory of Molecular Evolution (Cambridge University Press, 1983) are good summaries of these scientists’ contributions to population genetics.
Cavalli-Sforza’s work is summarized in The History and Geography of Human Genes and Genes, Peoples and Languages (see above). The original papers describing human population trees were published by Edwards and Cavalli-Sforza in V. E. Heywood and J. McNeill (eds.), Phenetic and Phylogenetic Classification (The Systematics Association, London, 1964, pp. 67–76), Cavalli-Sforza and Edwards in Proceedings of the 11th International Congress of Genetics (2: 923–33, 1964), and Cavalli-Sforza, Barrai and Edwards in Cold Spring Harbor Symposium on Quantitative Biology (29: 9–20, 1964). Cavalli-Sforza and Bodmer’s The Genetics of Human Populations (W. H. Freeman, San Francisco, 1971) is a classic textbook – luckily, it has recently been reprinted by Dover after being unavailable for many years.
Parsimony is discussed in much greater detail in Elliot Sober (ed.), Conceptual Issues in Evolutionary Biology (MIT Press, Cambridge, MA, 1984), and in Arnold Kluge’s contribution to T. Duncan and T. F. Stuessy (eds.), Cladistics: Perspectives on the Reconstruction of Evolutionary History (Columbia University Press, New York, 1984, pp. 24–38).
Zuckerkandl and Pauling’s work on the use of molecules to infer evolutionary history was published in several journal articles during the early 1960s; perhaps the best summaries are in M. Kasha and B. Pullman (eds.), Horizons in Biochemistry (Academic Press, New York, 1962, pp. 189–225) and Journal of Theoretical Biology (8: 357–66, 1965). Rebecca Cann, Mark Stoneking and Allan Wilson’s work on mitochondrial Eve was published in Nature (325: 31–6, 1987), and followed up by Vigilant et al. in Science (253: 1503–7, 1991). The analysis of complete mtDNA sequences (showing an unequivocally African origin for world mtDNA lineages) was published in Nature by Ingman et al. (408: 708–13, 2000).
An excellent historical summary of early palaeoanthropological work is Eric Trinkaus and Pat Shipman’s The Neanderthals (Vintage, New York, 1992). Additional material can be found in the books by Brian Fagan and Richard Klein cited above, as well as in Java Man (Little, Brown, London, 2000) by Garniss Curtis, Carl Swisher and Roger Lewin, and in Robin McKie’s Ape Man (BBC, London, 2000).
3 Eve’s Mate
Other DNA studies supporting an African origin for modern humans were published by Wainscoat et al. (Nature 319: 491–3, 1986), Tishkoff et al. (Science 271: 1380–7, 1996) and Jin et al. (Proceedings of the National Academy of Sciences USA 96: 3796–800, 1999). There are others, analysing different regions of the genome, but all show essentially the same pattern – greater genetic diversity within Africa.
Two good technical reviews on the structure and evolution of the Y-chromosome are Jobling and Tyler-Smith’s in Trends in Genetics (11: 449–56, 1995) and Lahn et al.’s in Nature Reviews Genetics (2: 207–16, 2001). Early papers on Y-chromosome variation were those by Casanova et al. (Science 230: 1403–6, 1985), Lucotte and Ngo (Nucleic Acids Research 13: 82–5, 1985), Dorit et al. (Science 268: 1183–5, 1995) and Hammer (Science 378: 376–8, 1995). DHPLC and its application to Y-chromosome population genetics is discussed in Underhill et al. (Genome Research 7: 996–1005, 1997). The paper by Underhill et al. dating Adam to 59,000 years ago was published in Nature Genetics (26: 358–61, 2000).
4 Coasting Away
Bruce Chatwin’s The Songlines (Vintage, London, 1987) gives a general introduction to aboriginal culture. Other good sources on Au
stralian prehistory are A. W. Reed’s Aboriginal Myths, Legends & Fables (Reed New Holland, Sydney, 1993), Kleinert and Neale’s Oxford Companion to Aboriginal Art and Culture (Oxford University Press, 2000) and Tim Flannery’s The Future Eaters (Reed New Holland, Sydney, 1994). The archaeology and geology of Lake Mungo is described in Allan Fox’s Mungo National Park (Beaten Track Press, Yarralumla, 1997). The dates for the Lake Mungo human remains are currently being revised, and I benefited greatly from my discussions with archaeologist Doug Williams, Executive Officer of the Willandra Lakes World Heritage Area, based in Buronga, New South Wales.
A good introduction to African geography and climate is Lewis and Berry’s African Environments and Resources (Unwin Hyman, Boston, 1988). Robert Walter and colleagues’ research on African coastal dwellers was reported in Nature (405: 65–9, 2000). The mtDNA evidence for a coastal exodus from Africa was published by Lluis Quintana-Murci in Nature Genetics (23: 437–41, 1999). The Y-chromosome data on the distribution of M130 (also known as RPS4YT) is taken from three publications: Kayser et al. (American Journal of Human Genetics 68: 173–90, 2001), Underhill et al. (Annals of Human Genetics 65: 43–62, 2001) and Wells et al. (Proceedings of the National Academy of Sciences USA 98: 1044–9, 2001). The archaeological evidence (or lack thereof) for an Upper Palaeolithic coastal migration is presented in Peter Bellwood’s Prehistory of the Indo-Malaysian Archipelago (University of Hawaii Press, Honolulu, 1997) and Gregory Possehl’s and Charles Higham’s articles on south and south-east Asian prehistory, respectively, in The Oxford Companion to Archaeology (Oxford University Press, 1996, pp. 52–7).
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