Updated: Sep 18, 2019
A key insight that Genomics yields is how early humans migrated and formed current day populations. The process starts by reading the genomes of several individuals at, say, a million genomic locations (a small fraction of the 3 billion total). These locations are chosen because they vary substantially between individuals. This yields a sequence of a million characters for each individual. The sequences for the various individuals are then compared to each other to identify the extent of similarity. In general, individuals with a recent common ancestor (e.g., siblings at an extreme, or those who are part of an tight-knit community with little intermarriage outside) will have more similar sequences than those whose most recent common ancestor goes further back (e.g., people from different parts of the earth who have had little contact for long). The extent of similarity can help estimate how long back their common ancestor lived.
This has led to some surprising insights. The most prominent of these is that all current human populations outside of Africa have a common ancestor who lived perhaps 60,000-100,000 years ago. In contrast, the most recent common ancestor of ALL humans, including Africans, dates further back to 200,000-300,000 years ago. The natural inference here is that modern humans seem to have evolved first in Africa and that all modern populations outside of Africa stem from a single more recent wave of migration out from Africa.
Then what happened? In particular, how and when did India get populated? Soon after the very first wave out of Africa? Or much later? Was it a single wave into India or were there multiple waves? If there were multiple waves, did each successive wave wipe out the previous ones or did it seamlessly mix in with the previous waves?
This and related questions are explored in Early Indians by Tony Joseph. I will write a separate account of the salient elements of this story, given that some of the key data analytical steps are those we also explore in a course I teach at IISc. As reviews on Amazon show, reactions to this topic tend to get highly polarised; therefore, the inferences need careful scientific treatment. Regardless, I certainly recommend anyone interested in the area to read this book.