The Journey of Man: A Genetic Odyssey Read online

  Praise for

  The Journey of Man

  “[Wells] navigates gracefully from his home waters of genetics into paleontology and climatology and back again.” —The New York Times Book Review

  “The Journey of Man is the best account available of the story of human origins and dispersals, based on the newly emerging discipline of archaeo-genetics. Wells has himself contributed to some of the work discussed, and so writes with authority about the molecular genetics, and he succeeds well in establishing the broader intellectual context in which the work is situated, so that the book carries more conviction than the good overviews by science writers and journalists that are becoming available.” —The Times Higher Education Supplement (London)

  “In this companion to a PBS special, Wells, a geneticist formerly associated with Oxford University, offers a worthy addition to the field of DNA analysis.… In addition to relating the always interesting story of humankind’s spread from Africa into the far corners of the world, the author attempts to answer some of the big questions that have concerned paleoanthropology.… Fortunately for the lay reader, Wells has a knack for clear descriptions and clever analogies to help explain the intricacies of the science involved. Both entertaining and enlightening, this book is a good addition to popular science collections.” —Library Journal

  “The Journey of Man is packed with important insights into our history and our relationship with each other.… [It] is fascinating and oozes charm.… Who needs literature when science is this much fun?” —The Guardian

  “[An] engaging primer of the field of population genetics.… In Mr. Wells’ detailed but clear prose, the story of us all is slowly, logically revealed.… Mr. Wells often succeeds in transforming complicated scientific conclusions into vivid and insightful analogies.… The Journey of Man encourages the reader to ponder the state of humanity today.” —The Dallas Morning News

  2003 Random House Trade Paperback Edition

  Copyright © 2002 by Spencer Wells

  All rights reserved under International and Pan-American Copyright Conventions.

  Published in the United States by Random House Trade Paperbacks, an imprint of The Random House Publishing Group, a division of Random House, Inc., New York, and simultaneously in Canada by Random House of Canada Limited, Toronto.

  RANDOM HOUSE TRADE PAPERBACKS and colophon are trademarks of Random House, Inc.

  This work was originally published in hardcover in 2002 by Princeton University Press in the United States and Canada and by Penguin Group in the United Kingdom and European Union.

  The author and publisher are grateful to the following for permission to reproduce extracts:

  The Songlines by Bruce Chatwin, published by Jonathan Cape, used by permission of The Random House Group Limited;

  “Buffalo Soldier” by Bob Marley, reproduced by permission of Music Sales Limited and EMI Music Publishing;

  “Little Gidding,” Four Quartets, by T. S. Eliot, reproduced by permission of Faber & Faber Ltd.

  Library of Congress Cataloging-in-Publication Data

  Wells, Spencer

  The journey of man: a genetic odyssey / Spencer Wells.

  p. cm.

  Originally published: Princeton, N.J.: Princeton University Press, © 2002.

  Includes bibliographical references.

  eISBN: 978-0-307-83045-6

  1. Human evolution. 2. Human genetics. 3. Human population genetics. I. Title.

  GN281.W44 2004 599.93′8—dc22 2003066679

  Random House website address: www.atrandom.com

  v3.1

  The aim of science is not to open the door to infinite wisdom,

  but to set a limit to infinite error.

  Bertolt Brecht, Life of Galileo

  Contents

  Cover

  Title Page

  Copyright

  List of Maps

  List of Figures

  Preface

  1 The Diverse Ape

  2 E pluribus unum

  3 Eve’s Mate

  4 Coasting Away

  5 Leaps and Bounds

  6 The Main Line

  7 Blood from a Stone

  8 The Importance of Culture

  9 The Final Big Bang

  Dedication

  Acknowledgements

  Further Reading

  About the Author

  Maps

  Southern Asia

  North-east Africa and the Middle East, showing the locations of desert and steppe

  Eurasia, showing the mountain ranges of central Asia and the Eurasian steppe belt

  Figures

  1 The evolutionary ‘genealogy’ of two related molecules

  2 Proof that modern humans originated in Africa

  3 MtDNA genealogy, showing the split into M and non-M lineages outside Africa

  4 Y-chromosome genealogy, showing the split into M130 and non-M130 lineages from an M168 ancestor

  5 Mitochondrial DNA (mtDNA) mismatch distributions of two expanding populations

  6 M89 defines the main Y-chromosome lineage in non-Africans

  7 Descendant lineages of M89 characterizing the main geographic regions in Eurasia

  8 M45 is the ancestor of most western Europeans and Native Americans

  9 Genealogical tree showing the relationship among the Y-chromosome markers

  10 The spread of Y-chromosome lineages around the world

  Preface

  Most of us can name our grandparents, many our great-grandparents, and some our great-great-grandparents. Beyond that, we enter a dark and mysterious realm known as history, through which we can only navigate with hesitant steps, feeling our way with whispered guidance. Who were the people that came before? Where did they live? What were their lives like?

  In this book I will argue that the answers to these questions can be found in our genetic code, which makes us uniquely human – but also makes us unique individuals. Our DNA carries, hidden in its string of four simple letters, a historical document stretching back to the origin of life and the first self-replicating molecules, through our amoebic ancestors, and down to the present day. We are the end result of over a billion years of evolutionary tinkering, and our genes carry the seams and spot-welds that reveal the story.

  It is not the code itself that delivers the message, but rather the differences we see when we compare DNA from two or more individuals. These differences are the historical language of the genes. In the same way that you wouldn’t include ‘water-dwelling’ in a classification of fish, because all fish live in water, the identical bits of our genetic code tell us nothing about our history. The story is in the differences, and this is what we study.

  This is not a book on human origins. Rather, it is about the journey we have taken as a species, from our birthplace in Africa to the far corners of the earth, and from the earliest evidence of fully modern humans to the present day – and beyond. The argument pursued throughout is that genetics provides us with a map of our wanderings and gives us a rough idea of the dates – and it is up to us to reconcile this data with the archaeological and climatological record in order to fill in the picture. Of course, every journey must have a beginning, and this one is no exception. It begins with the scientific effort to make sense of human diversity, which leads us to the birthplace of our species. The methods we use to infer our African origins are the same ones we then use to trace humanity’s global journey. It is the journey itself that is the main focus, and for this reason most of the details of our hominid ancestors have been left out.

  This book was originally conceived as part of a documentary film project of the same name. It has since taken on a li
fe of its own, and it stands alone as a unique entity, providing greater detail on the scientific background than is possible on television. The film, on the other hand, presents an (almost) first-hand experience, conveying the excitement and adventure of the journey in a way that only moving images can, so I hope that readers of this book will enjoy it equally.

  Although it was often difficult to juggle the film and the book at the same time, this did provide some significant advantages. For me, the chance to retrace my own personal ‘journey of man’ and to meet people from around the world – to see how they live and to discuss the scientific results with them – were profound and wonderful experiences. I hope that a sense of this has come through in print.

  The title was chosen for a reason – and it wasn’t sexism. The journey we trace is primarily one made by men, because it is the Y-chromosome, inherited from Adam down the male line, which gives us our keenest tool for deciphering the journey. The Y helps to place the stones, bones and languages in context better than any other part of our genetic code, and ultimately gives us the genetic answers we are looking for. Of course, in order to leave descendants, these early human groups must have included women; while the journey we follow may leave out some female-specific details, the resolution we can achieve only by following the male lineage is worth the omission.

  What follows is a scientific detective story guided by the temporal order of events. We begin with a deceptively simple question: how do we decide if the concept of human ‘race’ has any validity? Are we indeed all one species, or are there discrete divisions among human groups? After all, we appear to be so different from one another. The answer to this question, first provided by my PhD adviser at Harvard, Richard Lewontin, gives us a clue about the journey—but it doesn’t reveal the crucial details.

  The second main question concerns our geographic distribution. How did we come to occupy every corner of the globe? The DNA markers are able to provide us with the details. The methods for doing this, developed over the course of half a century, have been greatly influenced by Luca Cavalli-Sforza, with whom I was lucky enough to work as a postdoctoral fellow at Stanford in the 1990s. It was Luca’s insight, as a geneticist with a passion for history and a talent for mathematics, which provided us with a time machine capable of resurrecting the stories of the past from people living in the present. This book could not have been written without his intellectual presence, and it is impossible not to feel humbled while taking in the view from his shoulders.

  One of the most compelling things about being on an archaeological dig is the sense that you are actually seeing and handling implements that were last touched by human hands hundreds or thousands of years ago. Often the sense is so great that a feeling of déjà vu comes over you, and it seems as though you have somehow been transported back in time. When, as a child, I saw the Tutankhamun exhibition that toured the United States, I was struck by the combination of modern skill and ancient subject matter. It seemed as though the pieces, although fabulously exotic, could have been made the week before by a skilled craftsman. The fact that they were nearly 4,000 years old was extraordinary, and sparked in me a curiosity for the past that has never diminished.

  Genetics, at least the branch of it that informs the subject of human origins and migrations, is necessarily less visually compelling than archaeology, despite the fascinating stories it tells. Mark Read’s wonderful photographic portraits included in the hardcover edition of the book go a long way towards correcting this imbalance. Because of the expense of including high-quality color photographs in the paperback edition, which we wanted to keep reasonably priced, we have chosen to make Mark’s images available online, along with the maps, at the following Web address: www.atrandom.com/journeyofman. As this book was going to press, this website was in preparation. I have been lucky enough to work with Mark on several occasions, both in the course of sample-collecting expeditions in Asia and during the making of the film. He is a talented and dedicated artist, and his work adds enormously to the book. Mark’s photographs reflect the way people actually live today, because our knowledge of genetic history is inferred from the blood of people living in the present—it is their living genomes that give us our clues. Every one of us is carrying his or her personal history book around inside us—we simply need to learn how to read it.

  The Australian Aborigines maintain their sense of connection to their ancestors and their homeland through a musical story—something Bruce Chatwin and others have called a ‘songline’. These songlines reflect the actual journey taken by their ancestors during the Dreamtime, a period in the distant past, before collective memory. In a sense, this is precisely what we are trying to do with our studies of DNA—resurrect a global songline for everyone alive today, describing how they reached their current location and what the journey was like. As secular Westerners we have lost our traditional songlines to a greater extent than other peoples around the world, so it is perhaps appropriate that Western science has developed the methods for rediscovering them. However, our research does not take place in a vacuum, and science can sometimes run roughshod over cultural beliefs. I would hope that this book might be a small step towards changing the field into what it really is—a collaborative effort between people around the world who are interested in their shared history.

  So, with that as an overview, let’s start our genetic excavation. The past awaits …

  1

  The Diverse Ape

  So God created man in his own image, in the image of God created he him; male and female created he them. And God blessed them, and God said unto them, Be fruitful, and multiply …

  Genesis 1: 27–8

  Creation myths can be found at the core of all religions. Most seek to answer the child’s question ‘where do we come from?’ – to explain our existence and our place in the world in a succinct way. But while they may attempt to explain how we originated, creation myths fail to account for the spectrum of cultures, shapes, sizes and colours we see when we look at people around the world. Why do we look so different from each other, and how did we come to inhabit such far-flung places?

  Herodotus, the fifth-century BC Greek historian, provided posterity with far more than a description of the Greco-Persian wars. He also gave us our first clear descriptions of human diversity, viewed through an idiosyncratic classical lens. We learn of the dark and mysterious Libyans, the barbaric man-eating Androphagi of the Russian north, and hear descriptions of people who seem to resemble the Turks and Mongolians. Herodotus relates fanciful tales of griffins guarding precious hoards in the mountains of Asia, and we are treated to exotic descriptions of tribes in northern India who collect gold from the burrows of ants. Overall, it is a tour de force – the first ethnographic treatise in Western literature and, despite its obvious flaws, a valuable snapshot of the known world at that time.

  If we were to assume the role of a naïve modern-day Herodotus and fly an equatorial route around the world, the diversity of people and places would be astounding. Imagine for a moment being on a plane above the Atlantic Ocean at the very centre of the Cartesian globe, 0° longitude, 0° latitude – about 1,000 km west of Libreville, Gabon, in west-central Africa. If we imagine the plane flying east, and allow ourselves the science-fiction trick of being able to scan the ground from our vantage point in the sky, we will get a small sample of humanity’s diversity.

  The first people we encounter are Africans – specifically, central Africans, speaking Bantu languages. They have very dark skin, and live primarily in small villages hacked from the forest. As we move further east, we still see dark-skinned people, but these look somewhat different. They are the tall, thin Nilotic peoples of east Africa – some of the tallest on earth. They live on grassy savannahs, and are almost completely dependent on their cattle for survival. Scattered in amongst these groups are people who speak yet another language – one which is as different from Nilotic and Bantu as they are from each other, even though they live close by – the Had
za.

  As we continue east we encounter a huge body of water – so vast that it is impossible to see across it, and it seems an eternity before we reach an archipelago known as the Maldives. The people here seem quite different from those we saw in Africa, and speak yet another language. Their skin is dark, like that of the Africans, but their faces are different – nose shape, hair type and other minor details. They are clearly related to the Africans, but differ in obvious ways.

  As we continue on our journey – above the same enormous body of water – we see a large island rising up ahead of us. We have reached Sumatra, and here we encounter yet another type of human, somewhat smaller than the Africans and peoples of the Maldives, with yet another facial appearance – very straight hair, lighter skin and a thicker layer of skin above the eyes. Further east, passing countless other islands, we again encounter people with very dark skin, known as Melanesians. They are unlike the Africans in many other ways, so is their dark skin a characteristic that evolved in this region? Or is it indicative of a close connection with Africa?

  Next we encounter the Polynesians, living on small coral atolls separated by thousands of miles of open ocean. They appear to be somewhat similar to the Sumatrans encountered before but, as always seems to be the case, they are different. The biggest question is why they are living in such remote locations – how did they get there?

  Continuing on our route, we encounter the coast of Ecuador, in western South America. In the capital, Quito, we find an odd mix of people. There seem to be two main types: those who in some respects resemble the peoples of the Maldives, but with lighter skin, and those who in many ways resemble the Sumatrans and Polynesians. It seems odd to find such divergent types of humanity living in the same place, since the other locations we have visited tended to be more homogeneous. Why is Ecuador different? A disparate mix of people is found further east on the continent, where on the north-eastern coast of Brazil we encounter Africans again – but living far from Africa! During the long journey back to our starting point we ponder the tapestry we have just seen, and try to formulate an explanation for the pattern of diversity.