David Reich and his teams specialise in paleogenetics, the science of genetics in ancient humans, which created a true revolution in our understanding of our past, overturning many standard theories about migrations and mixing of peoples around the globe.
Some of these findings include: the fact that most Europeans and Asians have a few percent of Neanderthal genes in their genome, demonstrating that interspecies sex occurred some 50,000 years ago or earlier. He also demonstrates how the early humans migrated out of Africa in different waves, with different outcomes in Asia and Europe, or how native Americans moved into the continent in three waves, some of which can be timed, others not. The insight generated by human population genetics also sheds some light on the interaction between peoples within the same continent. In Europe, it is clear that some peoples completely disappeared as the result of viral contamination by tribes that migrated into their geographic area (as in current Germany), or were exterminated, rather than the merging of cultures which was always assumed. In Iberia, for instance, it is clear that in some incumbent human tribes all men were killed, because the existing genetic traits could only be traced back through mitochondrial DNA - through the feminine lineage - meaning that women were kept alive. It also shows the importance of dominant men in history, including Genghis Kan, who through and power and wealth managed to have a substantially more than average offspring.
Reich's discoveries also led to quite some reaction from anthropology and archeology academia, which is not surprising considering the fact that many acquired ideas were undermined, but questions were also raised about the ethical aspect of conducting genetic research on ancient burial sites, with or without the consent of the tribes still living there. The issue became especially sensitive in the context of Native American tribes: genetic insights could confirm or disprove a genetic lineage between current tribes and the bones found in burial grounds.
The genetic findings also allow to measure the effect of the caste system in India, demonstrating that despite the thousands of years of cohabitation, genetic distinctiveness of brahmins and untouchables has remained.
On the positive side, this new technology allows for a much more precise understanding of how we as humans are all the same species, with lots of common ancestors, who often intermingled and migrated in ways that were never even considered a decade ago.
It is fascinating, illuminating and highly promising for even more research findings in the coming decades.