The Journey of Man: A Genetic Odyssey (30 page)

Furthermore, human ‘races’ seem to have very recent origins. For the most part, physical traits that distinguish modern human geographic groups only appear in the fossil record within the past 30,000 years. Most older fossil Africans, Asians and Europeans are very similar to each other. While we know nothing about our ancestors’ skin colour, hair type or other surface features, the evidence from bones suggests that our concept of race is actually a very recent phenomenon. It was probably the fragmentation of human groups as a result of the last ice age that produced the distinct ‘racial’ morphologies we see in modern humans – not hundreds of thousands of years of separate evolution, as Carleton Coon and others had argued. For example, sinodonty – the distinctive tooth pattern common to north-east Asia and the Americas – first appeared in the fossil record less than 30,000 years
ago. Before then Asian teeth were very similar to those seen elsewhere in the world.

The other reason for genetic uniformity among human populations is that humans are mobile, and groups have intermixed throughout their history. When this happens, their patterns of genetic variation become dispersed throughout the mixed population. So, even in cases where the genetic markers arose after modern humans migrated out of Africa – like most of the markers we have followed on the Y-chromosome – they will still be widely distributed as a result of subsequent mixing.

The dynamics of language extinction indicate that human mixing is now accelerating. Languages seem to die out primarily through the incorporation of small, previously isolated populations into a larger, dominant population – in the same way that Manx was subsumed into English-speaking Britain. It is rarely the case that a minority population actually dies – rather, it is simply incorporated into the majority. But is there any real data on the rate at which this is happening?

The answer is yes. Most developed countries have a national census, where the people living in the country are counted and subdivided into demographic units. The reasons for this may be pragmatic – apportioning political representation or government funds, for instance – but the data also reveals deeper truths about society. Perhaps the best-known census is that held every ten years in the United States, the most recent of which was in 2000. Aside from showing that the population of the USA was 281.4 million, an increase of 13 per cent over that in 1990, it also detailed a changing ethnic landscape. For the first time in 2000, people were able to subdivide their ethnicity accurately. The number of racial categories expanded from five to sixty-three, and for the first time combinations of minority groups could be reported.

In total, 6.8 million people described themselves as a mixture of ‘white’ and a ‘minority’ group. Of course, this ignores the mixing that has created the category of white, which could mean anything from Irish to Lebanese to Moroccan. As we have seen in previous chapters, this mix alone encompasses a wide range of populations and markers. In terms of the official ‘mixed’ category, many people who have mixed ancestry actually consider themselves to be one race to the exclusion
of the other, suggesting that the true number of mixed Americans is actually much higher than what was actually reported. For instance, surveys carried out by the US Census Bureau show that, while only. 25 per cent of black/white mixed respondents considered themselves white, around half of white/Asian and white/Hispanic respondents, and 81 per cent of those with mixed white/Native American ancestry thought of themselves as white. One of the results of the 2000 census is that it became clear that America is far more of a melting pot than it may have imagined.

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.

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.

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, respectively, 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.

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.