The past few years have seen a revolution in our ability to map whole genome DNA from ancient humans. With the ancient DNA revolution, combined with rapid genome mapping of present human populations, has come remarkable insights into our past. This important new data has clarified and added to our knowledge from archaeology and anthropology, helped resolve long-existing controversies, challenged long-held views, and thrown up some remarkable surprises.
The emerging picture is one of many waves of ancient human migrations, so that all populations existing today are mixes of ancient ones, as well as in many cases carrying a genetic component from Neanderthals, and, in some populations, Denisovans. David Reich, whose team has been at the forefront of these discoveries, explains what the genetics is telling us about ourselves and our complex and often surprising ancestry. Gone are old ideas of any kind of racial 'purity', or even deep and ancient divides between peoples. Instead, we are finding a rich variety of mixtures. Reich describes the cutting-edge findings from the past few years, and also considers the sensitivities involved in tracing ancestry, with science sometimes jostling with politics and tradition. He brings an important wider message: that we should recognize that every one of us is the result of a long history of migration and intermixing of ancient peoples, which we carry as ghosts in our DNA.
"Reich gives us a window into what ancient DNA can tell us about human evolution, the peopling of the world, continent by continent, and the population mixing that makes us who we are today."
– Turi King, Nature
"Gives the first comprehensive account of this newly revealed prehistory [...] an astonishing book."
– Juliet Sam, Daily Telegraph
"Whole genome mapping hasn't just revolutionised our world, it has helped us rethink our past."
– Simon Ings & Liz Else, New Scientist
"The breakthrough that all archaeologists have been waiting for; a truly exciting account of the way in which ancient DNA is making us rethink prehistory. Essential reading for everyone interested in the past."
– Barry Cunliffe
"In just five years the study of ancient DNA has transformed our understanding of world prehistory. The geneticist David Reich, one of the pioneers in this field, here gives the brilliantly lucid first account of the resulting new view of human origins and of the later dispersals which went on to shape the modern world."
– Colin Renfrew, Emeritus Disney Professor of Archaeology at the University of Cambridge
"Reich's book reads like notes from the frontline of the 'Ancient DNA Revolution' with all the spellbinding drama and intrigue that comes with such a huge transformation in our understanding of human history."
– Anne Wojcicki, Chief Executive Officer and Co-Founder of 23andMe
"This riveting book will blow you away with its rich and astounding account of where we came from and why that matters. Reich tells the surprising story of how humans got to every corner of the planet, which was revealed only after he and other scientists unlocked the secrets of ancient DNA. The courageous, compassionate and highly personal climax will transform how you think about the meaning of ancestry and race."
– Daniel E. Lieberman, Professor of Human Evolutionary Biology at Harvard University and author of The Story of the Human Body: Evolution, Health and Disease
"Who We Are and How We Got Here dramatically revises our understanding of the deep history of our species in our African homeland and beyond. Reich's beautifully written book reads like a detective novel and demonstrates a hard truth that often makes many of us uncomfortable: not only are all human beings mixed, but our intuitive understanding of the evolution of the population structure of the world around us is not to be trusted."
– Henry Louis Gates, Jr., Professor of Literature at Harvard University and Executive Producer of Finding Your Roots
"This book will revolutionize our understanding of human prehistory. David Reich sheds new light on our past from the vantage of a sparkling new discipline – the analysis of ancient DNA. He places migration in the limelight, demonstrating that humans did not just evolve, they spread, often on dramatic scales."
– Peter Bellwood, Professor of Archaeology at Australian National University
"David Reich's magisterial book is a riveting account of human pre-history and history, through the new lens provided by ancient DNA data. The story of human populations, as he shows, is ever one of widespread, repeated mixing, debunking the fiction of a "pure" population."
– Molly Przeworski, Professor of Biological Sciences at Columbia University
"In this comprehensive and provocative book, David Reich exhumes and examines fundamental questions about our origin and future using powerful evidence from human genetics. What does "race" mean in 2018? How alike and how unlike are we? What does identity mean? Reich's book is sobering and clear-eyed, and, in equal part, thrilling and thought provoking. There were times that I had to stand up and clear my thoughts to continue reading this astonishing and important book."
– Siddhartha Mukherjee, author of The Emperor of All Maladies
"Powerful writing and extraordinary insights animate this endlessly fascinating account, by a world scientific leader, of who we modern humans are and how our ancestors arrived in the diverse corners of the world. I could not put the book down."
– Robert Weinberg, Professor of Cancer Research, Massachusetts Institute of Technology
Part I - The Deep History of Our Species
1: How the Genome Explains Who We Are
2: Interbreeding with Neanderthals
3: Ancient DNA Opens the Floodgates
Part II - How We Got to Where We Are Today
4: Humanity's Ghosts
5: The Making of Modern Europe
6: The Collision that Formed India
7: In Search of American Ancestors
8: The Genomic Origins of East Asians
9: Rejoining Africa to the Human Story
Part III -The Disruptive Genome
10: The Genomics of Inequality
11: The Genomics of Race and Identity
12: The Future of Ancient DNA
You may have missed it, but archaeology is undergoing a silent revolution. The story of our deep history used to be based on skeletal remains, linguistics, and the analysis of objects and tools our ancestors left behind, but since about three years archaeologists have a new tool in their arsenal. The analysis of DNA from old bones, or ancient DNA. David Reich has been at the forefront of developing this technique and argues that it is rewriting most of what we thought we knew about the last 350,000 years or so of human history.
Why did we have to wait so long for the ancient DNA revolution? This is perhaps the only part where I feel the book misses a beat. Reich does not really go into this, but DNA is notoriously unstable and quickly degrades after an organism dies. What little DNA you can retrieve is typically fragmented and mixed with DNA of microbes that feasted on the corpse when it died. With effort, care, the right techniques, and extreme measures to prevent contamination with human DNA from for example the researchers themselves, it is possible to isolate, amplify and puzzle together the genome of humans that died many millennia ago. Reich details how this technique works and what you can do with the data. I struggled a bit to get a clear understanding of the finer details. Even so, you will come away from this with at least the broad picture. We *can* isolate DNA from archaeological samples and we *can* use this to reconstruct how human populations are related.
Ancient DNA pioneer Svante Pääbo showed that Neanderthals, one of our evolutionary cousins, and humans mated with each other before Neanderthals went extinct (see his book Neanderthal Man: In Search of Lost Genomes). Today, non-Africans have some 2% Neanderthal in their DNA. The pace of discovery has accelerated tremendously since. Reich is at pains to stress that this book is not a definitive overview. New discoveries are constantly being made, refining or negating previous theories. Even Reich has had to backtrack on some of his published findings as more data have accumulated. Nevertheless, he wants to give an overview of what we know at the moment, acknowledging that this field is rapidly progressing. And this is where things get interesting.
The story of human evolution has long run along these lines: we evolved in Africa and then we left and spread around the world (the out-of-Africa hypothesis might sound familiar), our evolution resembling a tree that keeps dividing into smaller branches. So, all groups alive today can be neatly traced back to common ancestors. Ancient DNA reveals a picture that is much more complicated. Populations have mixed, split up, various split-off groups breeding with others again etc. The whole resembles a complex network more than anything else. Reich and others have even inferred so-called ghost populations, groups of people whose remains have not yet been found, but who have left distinctive traces in ancient DNA. Excitingly, for some of these we have recently found remains, confirming these predictions. Reich takes us on a world tour, showing how ancient DNA is challenging virtually all our previous ideas.
The history of Europe is one of continuous mixture and splitting of groups. South Asia has seen the incursion of migrants from the north, the Indo-Aryans (yes, the very same Aryans the Nazis got all obsessed with – ironic, as ancient DNA is now showing that this group wasn't the pure-bred human lineage they imagined). The idea that the Clovis people were the first humans to move into the Americas at the end of the last ice age? Sorry, nope, there were already people there who since disappeared. East Asia? Polynesia? Far from the simple stories of a single migration following one path, here too we can now reconstruct ghost populations and multiple waves of migrations and displacements. And what about Africa? Yes, we went out of Africa. But other groups went back in afterwards, and complex waves of migration are the rule here too.
Basically, if Reich's work is to be believed, whatever archaeology book you read next, you'll need to take it with a grain of salt and wonder how ancient DNA would change the story. Reich makes no secret of the fact he thinks this method yields superior data and insights – things we just couldn't deduce from the archaeological record so far. I think he has the data on his side so far, though there will no doubt be dissenters.
Human race has become a taboo topic. Anthropology has been so horrifically abused in the past to justify eugenics that no sane career scientist is willing to go there anymore. As a result, anthropologists and biologists have reached a politically correct consensus that whatever differences we can discern are so small as to be negligible, and, anyway, variation within groups is far great than variation between groups. By collectively avoiding this topic, Reich says, we are leaving the stage to crooks and ideologues with potty, pseudo-scientific ideas. Just because the orthodoxy of no meaningful differences can no longer be maintained, doesn't mean the heretics are right. Reich bravely aims for a new middle ground. Ancient DNA is showing that the old stereotypes of human race are just plain wrong. I have to applaud his bravery for being willing to table this topic.
All we can say for now is that the present-day structure of the human population is not the same that existed only a few thousand years ago. If anything, we are complex mosaics; mixtures of groups that themselves differed from each other and were results of previous mixtures etc. Many of these details are still being worked out, and the prospect of establishing an ancient DNA atlas of humanity, detailing all the mixtures and migrations over the millennia is an exciting one. In places it will corroborate archaeological finds, written records and legends and myths, in many other places it will present a far richer story than what we have been telling ourselves so far.
One last thing worth mentioning: the illustrations. Here, finally, is a book that makes good use of timelines and maps. From the endpapers giving a grand overview of the book, the timelines at the start of chapters putting the details in context, to the custom-drawn maps and figures: they are legible, use clear fonts, use contrasting symbols that work in greyscale, and avoid clutter. Editors at publishing houses should pay close attention.
Who We Are and How We Got Here is a fairly technical read, but stick with it. Once the story gets going, it is an incredibly exciting overview of a revolution in the making.
David Reich is a Professor of Genetics at Harvard University and a Howard Hughes Medical Institute Investigator. In 2015 he was highlighted by Nature magazine as one of "10 people who matter" in all of science for his role in transforming the field of ancient DNA "from niche pursuit to industrial process". In 2017 he was awarded the Dan David Prize in the Archaeological and Natural Sciences for the computational discovery of intermixing between Neanderthals and modern humans.