A BRIEF HISTORY OF HUMAN MIGRATION

WHO WE ARE AND HOW WE GOT HERE By David Reich; Oxford University Press ₹1,584

Philosophers and theologists have racked their brains for centuries over the existential questions of where we come from, and why we are who we are. While they struggle, geneticists have found clues in fragments of DNA gleaned from the bones of humans who lived tens of thousands of years ago, and have reconstructed human migrations in their efforts to trace our origins and evolution over the past 100,000 years.

Harvard geneticist David Reich says he used the “genome as a prism for understanding the history of our species”.

In Who We Are and How We Got Here, he traces human history from the Neanderthals and other “ghost populations” whose lives have been reconstructed from genetic evidence and are being used to understand race, identity.

The Neanderthals were replaced by our closest ancestors, the Homo Sapiens, about 44,000 years ago, but their genes survive. All humans outside Africa, but no modern Africans, carry about 2% Neanderthal genes, Reich writes. Meanwhile, half the genes of Northern European and British skeletons from 5,000 years ago are from herders from the Asian steppes!

“The problem is not just that people have mixed with their neighbours, blurring the genetic signatures of past events. It is actually far more difficult, in that we now know from ancient DNA, that people who live in a particular place today almost never exclusively descend from the people who lived in the same place far in the past,” writes Reich, who is a professor of genetics at Harvard Medical School, and a pioneer in analysing ancient human DNA.

The chapter on India is a prime example. “The collision that formed India” happened 2,000 to 4,000 years ago, when new migrations from central Asia led to the Indo-European culture replacing the Indus Valley way of life.

Over the centuries that followed, India became a medley of early settlers from Africa, people from the Steppes in Asia, and from modern-day Iran around 7,000 BCE. Almost every ethnic group in India today can trace its ancestry to settlers from these first three waves of migration, writes Reich. So when I say, “I’m Indian”, what does that really mean? The book has enough clues to make for some very interesting answers.