(Wikimedia Commons)
(Wikimedia Commons)

A brief history of migration

Harvard geneticist David Reich uses the genome as a prism for understanding our history as a species and detecting remnants inherited by modern humans.
Hindustan Times | By Sanchita Sharma
UPDATED ON MAY 06, 2018 09:23 AM IST


By David Reich; Oxford University Press

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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 human ancestors 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” and detecting remnants inherited by modern humans.

In Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past, he traces human history from the Neanderthals and other “ghost populations” whose lives have been reconstructed from shards of genetic evidence and are now being used to understand race and 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. A 40,000-year-old Romanian skeleton was found to contain just 6% to 9% Neanderthal genes. Meanwhile, half the genes of Northern European and British skeletons from about 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 one of the pioneers in analysing ancient human DNA.

The chapter on India is an example of the genetic potpourri that is modern man. “The collision that formed India” happened 2,000 to 4,000 years ago, when new migrations from central Asia, what is modern-day Kazakhstan, led to the Into-European culture replacing the Indus Valley way of life.

Over the centuries that followed, India became a medley of the first wave of settlers who moved from Africa, people from the Steppes in Asia, and the influx that followed from modern-day Iran around 7,000 BCE. Almost every ethnic group in India today can trace their ancestry to settlers from these first three waves of migration, writes Reich.

His book suggests that the biological differences among human populations often do not conform to cultural and racial stereotypes. So when I say, “I’m Indian”, what does that really mean? The book has enough clues to make for some very interesting answers.

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