In case you have not followed the adventures of the Yamnaya (proto Indo-Europeans from the Steppe), I recommend this recent Harvard lecture by David Reich. It summarizes advances in our understanding of deep human history in Europe and South Asia resulting from analysis of ancient DNA.
The new technology of ancient DNA has highlighted a remarkable parallel in the prehistory of Europe and South Asia. In both cases, the arrival of agriculture from southwest Asia after 9,000 years ago catalyzed profound population mixtures of groups related to Southwest Asian farmers and local hunter-gatherers. In both cases, the spread of ancestry ultimately deriving from Steppe pastoralists had a further major impact after 5,000 years ago and almost certainly brought Indo-European languages. Mixtures of these three source populations form the primary gradients of ancestry in both regions today.
In this lecture, Prof. Reich will discuss his new book, Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past.
There seems to be a strange glitch at 16:19 and again at 27:55 -- what did he say?
See also Reich's 2018 NYTimes editorial.