A couple of items.
Reich: In Europe where we have the best data currently—although that will change over the coming years—we know a lot about how people have migrated. We know of multiple layers of population replacement over the last 50,000 years. Between 41,000 and 39,000 years ago in western Europe, the Neanderthals were replaced by modern human populations. The first modern human samples we have in Europe are about 40,000 years old and are genetically not at all related to present-day Europeans. They seem to be from extinct, dead-end groups.All our current postmodernist obsession with post-colonialism and group identity look strangely irrelevant when you step back and watch the broader sweep of history. First we were stardust, then animals, then a wandering people barging hither and thither as circumstances permitted.
After that, you see for the first time people related to later European hunter-gatherers who have contributed a little bit to present-day Europeans. That happens beginning 35,000 to 37,000 years ago. Then the ice sheets descend across northern Europe and a lot of these populations are chased into these refuges in the southern peninsulas of Europe. After the Ice Age, there’s a repeopling of northern Europe from the southwest, probably from Spain, and then also from the southeast, probably from Greece and maybe even from Anatolia, Turkey.
Again, after 9,000 years ago, there’s a mass movement of farmers into the region which almost completely replaces the hunter-gatherers with a small amount of mixture.
And then again, after 5,000 years ago, there’s this mass movement at the beginning of the Bronze Age of people from the steppe, who also probably bring these languages that are spoken by the great majority of Europeans today.
Both Reich and Zhang make obvious points which do not fit well with postmodernist historical thought.
Reich: We should think we really don’t know what we’re talking about. When you see these replacements of Neanderthals by modern humans or Europeans and Africans substantially replacing Native Americans in the last 500 years or the people who built Stonehenge, who were obviously extraordinarily sophisticated, being replaced from these people from the continent, it doesn’t say something about the innate potential of these people. But it rather says something about the different immune systems or cultural mismatch.It is little remarked upon but the first transportation revolution of 1500 (enabling for the first time sustained long range shipping) made the whole world a single integrated biosphere. No longer were diseases, flora, and fauna constrained to their originating ecosystems. With global transportation came global diffusion.
Zhang: On the point of immune systems, one of the hypotheses for why people from the steppe were so successful in spreading through Europe is that they brought the bubonic plague with them. Since the plague is endemic to Central Asia, they may have built up immunity but the European farmers they encountered had not.
The obvious parallel is Columbus bringing smallpox and other diseases to the New World, which we think of as this huge, world-changing event. It reminded me that huge migrations replacing previous populations have happened many times before in human history.
Reich: Absolutely. The contact between people from Europe and Africa and the New World was a profound Earth-shattering event for our species, of course, in the last 500 years. But there have been profound and Earth-shattering events, again and again, every few thousand years in our history and that’s what ancient DNA is telling us.
Some of it was beneficial (potatoes to Europe for example) and some tragically destructive (Black Death to Europe for example and the whole portfolio of Old World diseases to the New World.)
The first transportation revolution of 1500 dictated a world wide increase in disease and loss of life, the greatest impact of which fell in the New World because of their long isolation. Despite the way it is presented in postmodernist texts, this was neither planned nor intended. It was an ineluctable consequence of the transportation revolution of 1500, without malice or awareness.