Ancient DNA has made it big time, with a write up in The New York Times by Carl Zimmer, From Ancient DNA, a Clearer Picture of Europeans Today. The primary sources of the piece are two papers published recently in Europe, Ancient human genomes suggest three ancestral populations for present-day Europeans (ungated version) and Genome flux and stasis in a five millennium transect of European prehistory. Like the earlier mtDNA work on ancient DNA what these results are suggesting is that European demographic history has been punctuated by periodic discontinuities. Here’s an important bit from the Zimmer article:

Archaeologists have found that early farming culture didn’t change drastically for the next 3,700 years. But about 4,000 years ago, the Bronze Age arrived. People started using bronze tools, trading over longer networks and moving into fortified towns. Dr. Pinhasi and his colleagues found that the era also brought a sudden shift in human DNA. A new population arrived on the Great Hungarian Plain, and Dr. Reich believes he knows who they were: the northern Eurasians.

It seems really unlikely that Europeans are special in this tendency, with broad world-wide trends as outlined in Towards a new history and geography of human genes informed by ancient DNA. For decades there have been books written about the coming for the Indo-Europeans. David Anthony’s The Horse, the Wheel, and Language is probably the best recent summation of the “they came out of the steppes” viewpoint. If there is a major update on this it now looks like the demographic impact of the Indo-Europeans was much greater than we had previous imagined. But are Indo-Europeans special? Probably not…earlier work suggested major discontinuities in Europe with the arrival of agriculture. Later in Africa you had the Bantu expansion, which replaced most of the local people. And as John Hawks points out the ancient Siberian who lived ~45,000 years ago probably comes from a group with no modern descendants. With the disappearance of the Ma’lta boy’s people ~20,000 years later from eastern Siberia it suggests that the heart of Eurasia has been roiled multiple times since the arrival of anatomically modern humans.

Addendum: I would take minor issue with the title of The New York Times piece. The picture isn’t really clearer, but cloudier. It’s just that the old clear picture was wrong, and the new cloudy picture is less wrong. Ultimately the clouds may clear, but we need more samples for that.