Gideon Lewis-Kraus, New York Times, January 17, 2019

{snip}

David Reich’s lab is folded into a corner of a glassy, long-corridored labyrinth at Harvard Medical School.

{snip}

In his recent book, Reich ranks the “ancient-DNA revolution” with the invention of the microscope. Ancient DNA, his research suggests, can explain with more certainty and detail than any previous technique the course of human evolution, history and identity — as he puts it in the book’s title, “Who We Are and How We Got Here.” Though Reich works with samples that are thousands or tens of thousands of years old, the phrase “ancient DNA” encompasses any old genetic material that has been heavily degraded, and Reich’s work has been made possible only by a series of technological and procedural advances. Researchers in the field ship or hand-carry the bones to Harvard, where clean-suited technicians expose them to ultraviolet light to prevent contamination, then bore holes in them with dental drills. These skeletal remains are often rare — one pinkie-finger fragment that researchers in a lab in Leipzig used to demonstrate the existence of a long-extinct form of archaic humans was one of only four such bones ever found. Minuscule portions of genetic code are isolated and enriched, then read by expensive sequencers; statistical techniques then plot the relationship between this particular sample and thousands more in enormous data sets.

{snip}

He got his first opportunity to study ancient DNA when Svante Paabo — a Swedish geneticist who had worked with Wilson — enlisted Reich in his efforts, based out of a lab in Leipzig, to sequence the entirety of the Neanderthal genome. Reich’s analysis helped demonstrate that most living humans, with the general exception of sub-Saharan Africans, have some Neanderthal ancestry. “

{snip}

So in 2013, Reich, along with a veteran of Paabo’s lab and a longtime mathematician collaborator, retooled his shop at Harvard Medical School as one of the country’s first dedicated ancient-DNA labs. The idea, he writes in his book, “was to make ancient DNA industrial — to build an American-style genomics factory” that would liberate such fields as archaeology, history and anthropology from hitherto insoluble debates.

He was more successful than even he anticipated. By the end of 2010, only five ancient genomes had been sequenced in total, but in 2014, 38 were done in one year. Soon the number will be close to 2,000. Reich’s lab alone is responsible for at least half of the published output, which doesn’t include some 5,500 more bones in the process of being analyzed and 3,000 more in storage. “Ancient DNA and the genome revolution,” he declares in his book’s introductory overture, “can now answer a previously unresolvable question about the deep past: the question of what happened.”

{snip}

One longtime premise is that as these early humans spread out in all directions over the land, groups of them encountered places that struck their fancy, pitched their tents and more or less stayed “home” for the duration of prehistory. This is not just a pet theory of academic prehistorians but the natural way that human beings have tended, over the millenniums, to connect their identities to where they live.

{snip}

Reich believes he has proved, to the contrary, that human history is marked not by stasis and purity but by movement and cross-pollination. People who live in a place today often bear no genetic resemblance to people who lived there thousands of years ago, so the idea that something in your blood makes you meaningfully Spanish is absurd. Paabo had shown that early humans mated with Neanderthals, but that was only one small part of the swirling “admixture” that characterized human interbreeding. Even after the Neanderthals became extinct, roughly 40,000 years ago, the archaic human populations of the earth — Reich gives them names like Ancient North Eurasians — were utterly unlike the populations we see today.

{snip}

Ancient DNA’s “big bang,” as more than one geneticist described it to me, came with the 2015 publication, in Nature, of a Reich paper called “Massive Migration From the Steppe Was a Source for Indo-European Languages in Europe.” On the basis of genetic information culled from 69 ancient individuals dug up by collaborating archaeologists in Scandinavia, Western Europe and Russia, the paper argued that Europeans aren’t quite who they thought they were. About 5,000 years ago, a “relatively sudden” mass migration of nomadic herders from the east — the steppes of eastern Ukraine and southern Russia — swept in and almost entirely replaced the continent’s existing communities of hunter-gatherers and early farmers. These newcomers were known to exploit many of the cutting-edge technologies of the time: the domestication of horses, the wheel and, perhaps most salient, axes and spearheads of copper.

{snip}

After Europe and India, there were similar mass migrations identified in Africa, the Middle East and Southeast Asia.

{snip}

With the relatively recent rise of everything we associate with “culture” — technologies like agriculture, metallurgy and eventually writing — much of this continuous “admixture” began to give way, it seemed, to discontinuous episodes better characterized as “replacement” or “turnover.” That is, about 5,000 to 9,000 years ago, human history was, at least in a few crucial places, less about various groups coming together and more about some groups blotting out their neighbors.

{snip}

Now it seemed as though culture was less about the invention and spread of new ideas and more about the mass movements of particular peoples — and the resulting integration, outcompetition or extermination of the communities they overran.

{snip}

In October 2016, the paper — with such well-regarded Pacific archaeologists as Stuart Bedford and his mentor, Matthew Spriggs of the Australian National University, among the 31 authors — was published in Nature as “Genomic Insights Into the Peopling of the Southwest Pacific.”

{snip}

The First Remote Oceanians, as the paper calls them, were not, after all, a heterogenous group; they were of unmixed Asian descent.

The paper suggested that the old archaeological consensus — that the Lapita advances reflected the joint contributions of Austronesian and Papuan peoples — could be replaced by a much starker story. The genetic record can be more “parsimoniously explained,” the authors remark, by at least two separate migrations to Vanuatu: first, the Austronesians, with their East Asian ancestry, and then, hundreds of years later, the Papuans. This wasn’t a story of “admixture” but one of successive waves of migratory “turnover.”

{snip}

“I think the important finding for archaeologists and for historians and sociologists and anthropologists is that this group moved thousands of kilometers over many hundreds of years, through a region occupied by long-established, sophisticated people, and hardly mixed with them.” He observed that “essentially everybody was surprised.” They were surprised, in part, because archaeologists since the 1960s had been trained never to assume the purity or coherence of a people, a slippery slope to the conclusion that certain peoples came by their advantages “naturally.”

{snip}

But in practice, the paleogenomicists have totally altered the environment in which prehistory is being studied by everyone. The landscape is dominated by four well-funded, well-connected labs, three of which — Paabo’s in Leipzig, along with those of two of his protégés, Reich at Harvard and Johannes Krause, who runs a newer outfit in the small German city Jena — collaborate closely with one another, to the point that some critics accuse them of collusion. The power of these top labs extends to samples, data and even technology: Proprietary chemical reagents let them isolate and enrich ancient samples much more accurately and cost-effectively than other labs can. One geneticist compared competing with the big labs to battling an entire navy “with a little dinghy, armed with a small knife.” Another told me: “A small lab focusing on a particular site would not be able to place their work in the context of the bigger picture. The only way I can get access to that data is if I give my bone to David or Johannes and wait until they process it — and bury me in the list of contributors to their paper.”

{snip}

There thus reigns, in the world of ancient DNA, an atmosphere of intense suspicion, anxiety and paranoia, among archaeologists and geneticists alike. In dozens of interviews with practitioners of both disciplines, almost everyone requested anonymity for fear of professional reprisal. Many archaeologists described a “smash and grab” culture in which hopeful co-authors source their bones by any means necessary. Among teams at work on any given excavation, it takes only a single colleague to deliver a bone to one of the industrial giants for the entire group to lose control of their findings. Museums, too, are being swept up by the perverse incentives: One of the geneticists told me stories about having brokered an agreement to sample a particular collection, only to arrive and discover that someone else showed up the previous day to claim the same bones under a false pretense. The weaker the institutions of the country, the harder it is for local researchers to have a fighting chance. Scientists in Turkey and Mexico told me that museum curators routinely had to explain that they had promised their native bone collections elsewhere. As one ancient-DNA researcher in Turkey put it to me, “Certain geneticists see the rest of world as the 19th-century colonialists saw Africa — as raw-material opportunities and nothing else.”

{snip}

Some archaeologists who had collaborated on the 2015 paper about Indo-European invasions withdrew their names to protest conclusions they saw as echoes of Kossinna — the mass migrations of advanced Indo-Europeans into Central Europe. (Reich got the critics back on board by adding a note, on Page 138 of their paper’s 141-page supplementary materials, that said their work in fact contradicted Kossinna, not because he was wrong about mass migration but on a technicality: The European ancestral homeland had, in fact, been far to the east, near the Caucasus and nowhere near present-day Germany.) The analogue was hard to counter. Geneticists had indeed swept down from their laboratory enclaves to extend their sovereignty over what had always been the terrain of archaeology.

{snip}

After the publication of Reich’s paper, the indigenous Kanaks of “neighboring” New Caledonia declared a three-year moratorium on any genetic research, for fear that their limited sovereignty might be undermined.

{snip}

While so much of Reich’s work has conjured the notion of sweeping, wholesale replacements by one population of another, the Jena paper proposed instead a much more gradual process. Their samples demonstrated not a single decisive turnover event but at least 500 years of ongoing traffic between Papuans and Austronesians — plenty of time to explain how the former had managed to pick up the latter’s languages, for one thing. Whatever happened in that period was clearly complex, but it seemed to them inaccurate to describe it as the one-off snuffing out of one group by another. “

{snip}

While the Jena samples showed at least 500 years of Austronesian-Papuan mixture, Reich’s follow-up argued — on the basis of a single sample from a single island — that the First Remote Oceanians had been replaced by at least one wave of belated Papuans. Otherwise, the paper had little to add. Reich had, however, updated his analysis of the original skulls with improved, “higher-resolution” statistical techniques. One new data point, which Reich saw as a refinement, struck some critics as a significant revision: While Reich emphasized to me in his office that the first paper conclusively demonstrated no mixture between the Austronesians and the people they encountered, the updated analysis showed that Teouma’s “Lapita individuals had a nonzero proportion of Papuan-related ancestry.” It “remains striking,” the new paper remarked, that these first migrants were only “minimally admixed” — but admixed they were.

{snip}

[A]rchaeologists had told the ni-Vanuatu for decades that they were the descendants of the Lapita voyagers; now they had to go back and advise them to alter the commemorative postage stamps to feature not black people but Taiwanese aboriginals. A national self-image was not something to take lightly. “One can only feel,” one forum contributor wrote, “a collective sense of betrayal in all of this.”