Out of Eden: The Peopling of the World (2 page)

A
CKNOWLEDGEMENTS

S
INCE PUBLICATION
of the landmark Cann, Stoneking and Wilson out-of-Africa paper sixteen years ago, many in countries from all round the world have contributed to the understanding of our past through the growing gene trees of modern humans. These include the participants in the studies, lab staff, PhD students and post-docs right up to the heads of particular laboratories. As far as possible I have tried to give appropriate credit by citing relevant papers; but while refereed publications are scientists’ main visible research product, they depend not just on thorough, careful, hard work, but to some extent on that more fluid and transferable currency, original ideas. Ideas, like good tunes move from lip to lip sometimes hiding their origins. They are rarely explicitly credited and, in multi-author papers, the originator is sometimes difficult to deduce.

Work on mitochondrial DNA was pioneered in the US, during the late 1970s, by Wesley Brown and Douglas Wallace. The late Allan Wilson, the senior author on the 1987 Cann paper, is acknowledged by all to have been an inspiration to those who followed him. In this book I cite mainly papers from after that time. With the increasing pace of research during the 1990s and after the turn of the twenty-first Century, new people entered the scene. Without underplaying the work of many other groups and associates, I would like to
identify what I regard as an inner circle of scientists who have pioneered the ‘phylogeographic approach’ to tracing prehistoric human movements. Based in scattered parts of Europe, in some ways they are self-identified, since several other geneticists disagree with their methods. Among this inner circle are geneticists Martin Richards, Antonio Torroni, Silvana Santachiara-Benerecetti, Peter Forster and Toomas Kivisild working with Richard Villems. Their work was revolutionized by the mathematics required for the new tree-building. Again I would like to identify Hans-Jürgen Bandelt poly-math and mathematician and Vincent Macaulay physicist, statistician and mathematician, who did much to pioneer such methods and have both helped many teams including several, recently, from Russia and China. In a tensely competitive research field members of this group are surprising in the degree to which they all share their insights with each other.

The Y chromosome picture was pioneered initially by English geneticists from Leicester (Mark Jobling and Matt Hurles) and Oxford (Chris Tyler-Smith), but has subsequently been dominated by well-financed American laboratories with Peter Underhill’s (under Luca Cavalli Sforza) and Mike Hammer’s teams being the best examples. With large panels of gene markers, they have made extraordinary strides in bringing the Y-chromosome tree up to the same fine detail as that of mtDNA. Since mtDNA is relatively short there is a limit to what she can reveal and the Y chromosome will inevitably overtake her although dating will continue to be a problem. Lluis Quintana-Murci (now in Paris) made significant contributions to both the mitochondrial and Y chromosome stories.

When not expressing my own ideas and opinions, I have cited relevant papers that signaled a particular advance. Giving credit, where due, can be as important a function of the bibliography as that of showing the text-argument really is evidence-based. Popular genetics books without bibliographies run the risk of giving the reader the impression that the author worked it all out on his own. But citing publications is only one aspect of acknowledging my debts
in compiling this book. While writing
Out of Eden
I have received an enormous amount of help directly from various people in terms of their time spent patiently explaining things to me, constructively criticizing my ideas, and offering their own insights. First and foremost is Martin Richards who, by good luck, I contacted when his own boss was unavailable a few years ago. Martin has given of his time unstintingly, including a critical reading of the book. He is, in my view, one of the main illuminati in this field. Next, in terms of hours on the phone and otherwise, is Vincent Macaulay followed by Hans Bandelt, Peter Forster, Toomas Kivisild and Chris Tyler-Smith. For the Malaysian Orang Asli genetic study, in addition to UK coauthors Catherine Hill, Martin Richards, William Meehan, James Blackburn, Mike Ward and Douglas Clarke, I would also like to thank our overseas collaborators, in particular Adi Taha without whose extraordinary efforts the study would have failed, Patima Ismail my Malaysian genetics collaborator, David Bulbeck who encouraged me to follow the route of his study, Muhamad Mahfuz Bin Nordin, and Norrulhuda Mohamad Halim, Norazila Kassim Shaari, Joseph Maripa Raja, Antonio Torroni, Chiara Rengo, Orang Asli participants, the JHEOA and, of course, Discovery Channel for financial support.

There are other geneticists who have given me their time and insights. Over several years and while writing this book, I attended a magnificent series of guest seminars organized by the late Ryk Ward covering many aspects of bioanthropology. Tim Crow explained his view of human speciation on the Y-chromosome to me. Chris Tyler-Smith, Peter Underhill, Mark Jobling, Matt Hurles, Mark Stoneking and Lluis Quintana-Murci have all given good counsel. Roger Dawkins and Joe Williamson kindly read my proofs in record time and offered very useful advice.

I have also had much educational help from archaeologists, including particularly Derek Roe, who taught me hands-on about blades, Andrew Sherratt, who corrected some of my misconceptions on the importance of size reduction and hafting in the Palaeolithic,
again hands-on, read the whole book and gave constructive criticism on the Prologue and
Chapters 2
–
3
, David Bulbeck, who read
Chapters 4
–
7
wearing both his archaeological and anthropological caps. Zuraina Majid took me through the cultural sequence of Lenggong Valley pebble tools. Susan Keates gave much assistance in references and read
Chapters 5
and
6
for me. Seife Berhe organized the Eritrean field visit and kindly took me over the ancient reefs he had found. Ipoi Datan facilitated my visit to Niah caves. Graeme Barker, Ian Lilley, Chris Stringer, Mike Morwood, Tim Reynolds, Beatrice Clayre, Sandra Bowdler, Rob Foley, Marta Lahr, William Davies, Paul Pettitt all gave me their time and insights.

I cannot praise and recommend my agents Julian Friedmann and Carole Blake highly enough to anyone who is lucky enough to get on their list. They went over and above the call of duty.

Constable & Robinson, my publishers, have put much patient and good-natured effort into transforming something written with half an eye to academics into something with more sparkle and accessibility. I think they did a good job. At the top of the list are the editorial team: Pete Duncan (my editor), John Woodruff, Anna Williamson, Sara Peacock and Jane Anson. Bill Smuts, the illustrator, translated my numerous sketches into great maps. But there are others, including Gary Chapman, Sallie Robins and Jennifer Duthie.

There are a number of others not in the above groups who have helped me. Georgina Harvey who researched on the Toba literature and put me in touch with Eelco Rohling oceanographer, who illuminated the pre-history of Red Sea salinity for me. An old friend, George Wells, brought me up to scratch on the 200-year history of the two language origin paradigms. Roger and Geeta Kingdon introduced me to Jonathan Kingdon’s work, John Robinson was a great source of references and support. Finally of course, Freda my wife, who has always taken better photos than me, has supported me throughout.

Acknowledgement of the above does not necessarily indicate their agreement with the views expressed in this book.

P
REFACE

I
MAGINE AN AIRLINE CHECK-IN QUEUE
in Chicago or London. Seven people stand there, looking in different directions. One is a solicitor of Afro-Caribbean origin, another a blonde-haired girl whose family come from northern Europe, another a computer expert who was born in India. The fourth is a Chinese teenager listening to music on a Walkman. The fifth, sixth, and seventh are all attending a conference on rock art and come respectively from Australia, New Guinea, and South America. All seven are quiet, and avoid eye contact because they neither know one another nor feel related in any way. Yet it can be proved they are all related and ultimately all have an African female and male ancestor in common.

In all our cells we have genes. Genes are made up of DNA, the string-like code of life that determines what we are, from our fingernails to our innate potential for playing the piano. If we analyse the genes of any one of these seven people, we can trace the geographic route taken by their ancestors back to an ultimate birthplace in Africa, at the dawn of our species. Further, if we take any pair of them and compare their genes, we will find that they share a more recent ancestor – living, in all probability, outside Africa (see
Figure 0.3
). What is more, I believe that we can now prove where those
ancestors lived and when they left their homelands. This remarkable proof has become fully possible only within the last decade, as a result of pioneering work by a number of people.

Many of us have wondered what we would find if we could perhaps board a time machine and travel back through the generations of our ancestors. Where would it take us? Would we find ourselves to be distantly related to some famous or notorious person? How many generations would we pass through before we arrived at the first humans? Does our line continue back to monkeys, and beyond to worms and single-celled creatures, as Darwin maintained? We know from dry biology lessons at school that this ought to be so, but as with the uncertainty of what happens to us after we die, it is hard to grasp.

We are now so used to the pace of technical advances that the sense of wonder fades with each new one. Yet, until very recently, geneticists could only dream of using our genes to trace the detailed history of how we conquered the world. The reason for their pessimism was that the majority of the genes they examined shuffled themselves around at each generation and were common to most populations anyway. Their task was like trying to reconstruct a previously played card game from the pack of cards
after
it has been shuffled. So it was nearly impossible to draw an accurate genetic family tree going back even a few hundred years, let alone back to the beginning of our species. Most human populations look very similar beneath the skin, so where could one start?

The use of gender-specific gene lines, the so-called Adam-and-Eve genes, has in the last ten years changed all that. In contrast to all other genes, mitochondrial DNA (a collection of genes outside the cell nucleus) is inherited only through our mothers, and the Y chromosome is inherited only by men. These two sets of gender-linked genes are passed on unchanged from generation to generation, with no shuffling, and can therefore be traced right back to our ancestors, to the first mammals, and even beyond to worms and worse. We can thus construct two family gene trees, one for our
fathers and one for our mothers. As a result, in any population, of whatever size, we can trace any two individuals through one of these two gene trees back to a most recent shared ancestor on the tree. Such an ancestor may have lived 200, 5,000, or 150,000 years ago, but all ancestors can be assigned a place on the newly constructed Adam-and-Eve genetic trees. These are real family trees of modern human gene lines, with real branches. Each branch on each tree can be dated, although the accuracy of such dating still leaves much to be desired.

Many regional human gene trees have now been fitted together, like a large jigsaw that is started by assembling the edges using certain clear landmarks. In this way, a picture of the Adam-and-Eve gene lines spreading from Africa to every corner of the world has been pieced together over the last decade. It has got to that satisfying point, as with jigsaws, when the whole structure suddenly links up and takes shape; the remaining pieces, though many, are now being placed on the tree and on the map with increasing ease and speed. The pace is now so rapid that people working at the cutting edge on one geographic region may still be unaware of breakthroughs in another region. The whole branching tree can now be laid flat on a world map to show where our ancestors and their gene lines travelled in their conquest of the world.

The new knowledge has resolved some of the apparent paradoxes thrown up by the contrast between the cultural and biological stories of the last 150,000 years. We can now even start to hang the regional human fossil relics of that period in their correct places on the genetic tree of life.

Many questions have been answered. It turns out that, far from the world being a common genetic melting pot with massive to-and-fro prehistoric movements and mixings, the majority of the members of the modern human diaspora have conservatively stayed put in the colonies their ancestors first established. They have dwelt in those localities since well before the last ice age. We can also trace the dates of specific migrations over the last 80,000 years. Thus,
from a picture of great diversity and lack of definition, we have the opportunity to move to a highly specific and regional focus on the branching networks of human exploration.