GENETICS AND HI STORY
An excerpt from David Reich’s new book, Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past, recently touched off a media and cultural firestorm in the United States. Appearing as an op-ed in The New York Times, “How Genetics is Changing Our Understanding of ‘Race’”, it had Reich stating that he is “worried that well-meaning people who deny the possibility of substantial biological differences among human populations are digging themselves into an indefensible position, one that will not survive the onslaught of science”. This was not unlike tossing a grenade into the public square. But perched at Harvard, as one of his generation’s most eminent human population geneticists, Reich will move forward unscathed. The reason is simple: Who We Are... is mostly not a controversial book, but a wondrous one. It sheds light on the nascent field of ancient DNA, paleogenetics, which is exposing the human past by tracing population histories. Give a paleogeneticist a single genome, and they will unfurl the history of whole peoples.
A theoretician by background, Reich explains how he entered the field through a collaboration with Svante Pääbo, director of the Max Planck Institute for Evolutionary Anthropology in Germany. Pääbo’s group had just sequenced a Neanderthal, and the early results indicated that they had mixed with modern humans after they left Africa. Because this contradicted long-held orthodoxy, Reich and his colleagues were brought in to do a deep analysis. To his surprise, the evidence of mixing with Neanderthals held up.
From this exposure, Reich swiftly caught the bug. Soon he was central to the discovery of the genome of a new human population, the Denisovans, cousins of the Neanderthals who lived in eastern Eurasia. They seem to have mixed with ancestors of the modern people of New Guinea, and left their genetic mark all across the eastern and southern reaches of Asia.
Along with startling new fossil finds in Africa, Reich and his colleagues have also pushed back the date of the origin of our own modern human species. Ten years ago, many would claim modern humans emerged 50,000 years ago, but the latest work convincingly puts it beyond 200,000 years.
But the major thrust of Reich’s research over the past five years has been exploring more recent prehistory. It would appear that nearly every region of the world has undergone massive population upheaval within the past 10,000 years. Europe, where samples are most numerous, was transformed 5,000 years ago with a migration of peoples from the Eurasian steppe. Reich notes that Europe and India seem to exhibit a parallelism. Both Eurasian peninsulas’ genetic character emerges from the collisions between herders from the Eurasian steppe, farmers from West Asia, and indigenous hunter-gatherers.
When it comes to India, Who We Are... pulls back the veil on disagreements between American and Indian scientists over interpreting results. While Reich is ever politic, he clearly believes the science will converge on results which may discomfit Indians who hold an ‘indigenist’ viewpoint on the origin of South Asian peoples. In fact, during the writing of this review, Reich’s lab released new results utilising ancient remains from the Swat valley of Pakistan, Afghanistan and Central Asia to say that Indo-European languages arrived after 2000 BC from the Eurasian steppe!
Who We Are... is a dispatch from the front lines of one of the exciting areas of modern science. The message is simple: the science is coming, prepare yourself.