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'Who We Are and How We Got Here' review: The reshaping of human history

Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past David Reich Oxford University Press ₹495  

History is no longer what it used to be. Thanks to ancient DNA. Large stretches of our understanding of our own past have been rewritten in the last five years, based on the analysis of DNA extracted from individuals who lived thousands, or hundreds of thousands, of years ago. Many “facts” we took for granted have been proven to be false, and many questions left dangling in the air as historians, archaeologists and anthropologists fought it out among themselves have been given convincing new answers.

So if you haven’t been paying attention to what has been happening to our history in the last half-decade, this is a good time to catch up, and Who We Are and How We Got Here is an excellent place to start. The author of the book, Professor David Reich of Harvard Medical School, is not a disinterested observer of a fast-developing field; he is a participant and, in fact, a driver, of the ancient DNA revolution and it is his and his team’s research that has accomplished much of the reshaping of human history.

So this book has the feel of a first-hand account from the trenches that also carries with it a high-level perspective of what is going on where and why.

Here’s a short list of things that have changed about our past in recent years because of ancient DNA. We now know that in both Europe and South Asia, “a mass migration of farmers from the Near East after nine thousand years ago mixed with previously established hunter-gatherers, and then a second mass migration from the Eurasian Steppe after five thousand years ago brought a different kind of ancestry and probably Indo-European languages as well.” We also know that native American populations, before the arrival of Europeans in America, derive ancestry from not one, but four migrations from Asia. We know that much of East Asian ancestry derives from major expansions of populations from Chinese agricultural heartland. In 2010, we learned that modern humans had interbred with Neanderthals and in 2014, we learned that our ancestors had interbred with Denisovans as well. Each of these discoveries was made possible by the co-analysis of ancient DNA with the DNA of present-day individuals.

The India connection

The book devotes an entire chapter to ‘The Collision that formed India’. The “collision” it refers to is what happened between 4000 and 2000 years ago, when the Indus Valley Civilisation collapsed and a new influx of migrants from south-eastern Steppes, where Kazakhstan today is, brought Indo-European languages and the accompanying culture.

What followed the collapse and the new influx was a millennium or two of mixing that formed the Indian population of today — a mixture of at least three ancestral groups: descendants of the original Out of Africa migrants, Iranian agriculturists who spread to South Asia sometime after 7000 BCE, and pastoralists from the south-eastern Steppes who arrived after 2000 BCE. There are other ancestral groups that contributed to our ancestry too — the Austro-Asiatic speakers and Sino-Tibetan speakers, for example — but almost every group in India today has ancestry from the first three ancestral groups mentioned.

As the book was written before a new paper authored by 92 scientists and co-directed by Reich was released in early April this year, titled ‘The Genomic Formation of South and Central Asia,’ some of the finer details in that paper are missing in the book. But it more than makes up for it through sharp insights drawn from the data, as well as the inside stories on how some of the terms that are now in common use such as “Ancestral North Indian (ANI)” and “Ancestral South Indian (ASI)” came to be formed, in 2008, as the scientists involved in the study “groped toward a formulation that would be scientifically accurate as well as sensitive to” political considerations.

The 2008 study had found that West Eurasian (West Asian, Central Asian and European)-related mixture in India ranges from as low as 20% to as high as 80% in different Indian population groups. These proportions provide clues about past events, says the book, such as language spread, social stratification under the caste system, and unequal social power between men and women. Today, ANI ancestry in India derives much more from males than females and this pattern, says the book, “is exactly what one would expect from an Indo-European speaking people taking the reins of political and social power after four thousand years ago and mixing with local peoples in a stratified society, with males from groups in power having more success in finding mates than those from the disenfranchised groups.”

Genetic differences

One of the striking finds is that the degree of genetic differences between groups in India today is at least three times greater than that among European groups. This is mostly because of the practice of endogamy — or rules prohibiting marriage outside a well-defined community — which increases the genetic differences between groups over time.

“People tend to think of India, with its 1.3 billion people, as having a tremendously large population… But the truth is that India is composed of a large number of small populations.” Reich also shows how the argument that caste is largely a recent innovation of the British doesn’t hold up to genetic scrutiny.

But this book ought to be read not mainly for its Indian chapter, but for the new light it throws on prehistory and the way it explains the reasoning behind the new findings and the science of population genetics itself. Professor Reich catches a field of knowledge in that rare moment when there is an explosion in its explanatory power, in its reach and in its impact. Not to be missed.

Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past; David Reich, Oxford University Press, ₹495.


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