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Tuesday, November 28, 2017

The ancient genomics revolution (Skoglund & Mathieson 2017 preprint)

Two former Harvard scientists Pontus Skoglund and Iain Mathieson are working on a new review paper on the wide range of scientific breakthroughs provided by ancient genomics over the past decade. The preprint is available at Dropbox here. There's also a thread about the preprint at Mathieson's Twitter account here.

I've read through it a couple of times, especially the parts about Europe, and haven't been able to spot any major problems; the authors obviously chose their words very carefully, and their geography is beyond reproach. [Edit: first problem spotted, see here]

Now, you might think that geography is easy, but apparently not when it comes to the location of the Pontic-Caspian steppe. Recent media articles have claimed that it's located in West Asia, and, I kid you not, even that it's hilly (for instance, see here), while scientists from Max Planck and other supposedly high brow places seem to think that it's in Central Eurasia (see here). Nope, as Skoglund and Mathieson correctly point out, it's actually located in (far) Eastern Europe, while Central Eurasia is generally posited to be further to the east. From the preprint (emphasis is mine):

Anatomically modern humans were widely distributed in Europe by at least 42,000-45,000 BP (3; 41). The oldest genomic data from a modern human in Europe is the Oase 1 individual from present-day Romania dated to 37,600-41,600 BP. This individual, which had a direct Neanderthal ancestor in the past four to six generations, did not contribute detectable ancestry to later Upper Paleolithic populations (24). During the Upper Palaeolithic, a major transformation ~30,000-35,000 years ago was likely associated with the replacement of the Aurignacian with the Gravettian culture in western Europe(28). As the Last Glacial Maximum (LGM) came to an end and the ice sheets receded, Europe was repopulated, possibly from southern European and central Eurasian refugia (28). Another transformation may have taken place during an interstadial warm period ~14.5 kya, replacing the original recolonizers with a population that would come to form the Mesolithic populations of Europe (28; 93). These Mesolithic populations were outside the genetic diversity of present-day Europe (114; 131) and themselves display a clinal structure, with an east-to-west cline (32; 37; 38; 47; 57; 62; 72; 78; 112; 130). The origin of this cline is not clear, although it plausibly reflects two or more major sources of ancestry in the post-LGM or post-14.5kya expansions.

Starting from the southwest around 8,500 BP, the Mesolithic ancestry of Europe was largely replaced (29; 38; 42; 130; 131) as a new type of ancestry related to that found in Neolithic northwest Anatolia (73; 87) and, ultimately, to early farming populations of the Levant and Northern Iran (11; 56) expanded throughout Europe. This ancestry rapidly reached the extreme edges of Europe, with direct evidence of its presence in Iberia at 7300 BP (86), in Ireland at 5100 BP (14) and in Scandinavia at 4900 BP (131). This “Anatolian Neolithic” ancestry was highly diverged relative to the “hunter-gatherer” ancestry of the populations that previously inhabited Europe (F ST ~ 0.1, similar to the divergence between present-day European and East Asian populations) (73; 132). Across Europe, its appearance was closely linked in time and space to the adoption of an agricultural lifestyle, and it now seems established that this change in lifestyle was driven, at least in part, by the migration. However, the Anatolian Neolithic migrants did not replace the hunter-gatherer populations. Over the next 4000 years, the two populations merged, and by 4500 BP, almost all European populations were admixed between these two ancestries, typically with 10-25% hunter-gatherer ancestry (29; 38; 42; 50; 62; 71; 73; 130; 131). Across Europe, this “resurgence” of hunter-gatherer ancestry (10) was independent–driven by local hunter-gatherer populations who lived in close proximity to farming groups (7; 62; 72; 130).

The next substantial change is closely related to ancestry that by around 5000 BP extended over a region of more than 2000 miles of the Eurasian steppe, including in individuals associated with the Yamnaya Cultural Complex in far-eastern Europe (1; 38) and with the Afanasievo culture in the central Asian Altai mountains (1). This “steppe” ancestry is itself a mixture between ancestry that is related to Mesolithic hunter-gatherers of eastern Europe and ancestry that is related to both present-day populations (38) and Mesolithic hunter-gatherers (46) from the Caucasus mountains, and also to the populations of Neolithic (11), and Copper Age (56) Iran. Steppe ancestry appeared in southeastern Europe by 6000 BP (72), northeastern Europe around 5000 BP (47) and central Europe at the time of the Corded Ware Complex around 4600 BP (1; 38). These dates are reasonably tight constraints, because in each case there is no evidence of steppe ancestry in individuals immediately preceding these dates (47; 72). Gene flow on the steppe was extensive and bidirectional, as shown by the eastward flow of Anatolian Neolithic ancestry–reaching well into central Eurasia by the time of the Andronovo culture ~3500 BP (1)–and the westward flow of East Asian ancestry–found in individuals associated with the Iron Age Scythian culture close to the Black Sea ~2500 BP (143).

Copper and Bronze Age population movements (14; 78 Martiniano, 2017 #8761; 85; 112), as well as later movements in the Iron Age and Historical period (70; 119) further distributed steppe ancestry around Europe. Present-day western European populations can be modeled as mixtures of these three ancestry components (Mesolithic hunter-gatherer, Anatolian Neolithic and Steppe) (38; 57). In eastern Europe, further shifts in ancestry are the result of additional or distinct gene flow from Anatolia throughout the Neolithic and Bronze Age in the Aegean (42; 51; 55; 72; 87), and gene flow from Siberian-related populations in Finland and the Baltic region (38).

And I really like this part; sounds ominous for the Out-of-India (OIT) crowd, doesn't it? Hopefully we won't have to wait too long for the relevant paper from Harvard, which, I can assure you, is coming sooner or later.

There are no published ancient DNA studies from South- or Southeast Asia. However, data from neighboring regions provides clues to the population history of this region. In particular, present-day South Asian populations share ancestry with Neolithic Iranian (11) and Steppe (56) populations. This strongly suggests Neolithic or Bronze Age contact between South Asia and west/central Eurasia, although only direct ancient DNA evidence from the region will resolve the timing and structure of this contact.


Pontus Skoglund and Iain Mathieson, Ancient genomics: a new view into human prehistory and evolution, preprint 2017

See also...

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...

Who's your (proto) daddy Western Europeans?

Ancient herders from the Pontic-Caspian steppe crashed into India: no ifs or buts

Monday, November 13, 2017

Who's your (proto) daddy Western Europeans?

Considering the increasingly large numbers of paleogenomic samples being released online nowadays, it's no longer practical for me to try to highlight most archaeological cultures and even genetic clusters in my Principal Component Analyses (PCA) of the ancient world. Thus, from now on, I'll be focusing attention in such PCA on the main population shifts that have led to the formation of the modern-day West Eurasian gene pool and genetic substructures, like on the PCA plot below, which includes the new Lipson et al. 2017 data (available at the Reich Lab here).

The relevant PCA datasheet can be gotten here. By grouping several hundred ancient samples into just nine clusters, I'm attempting to highlight four key processes and resulting genetic shifts in Europe, the Near East and Central Asia:

- European forger populations mixing with genetically much more southern early farmers of Near Eastern origin, mostly during the Neolithic, bringing about the total disintegration of the Europe to Siberia Hunter-Gatherer cline

- "Old Europeans" being overrun and largely absorbed by Y-haplogroup R1-rich Kurgan pastoralists from the Pontic-Caspian steppe during the Eneolithic and Bronze Age, leading to the formation of at least one major new cline from the Bronze Age steppe into post-Kurgan expansion Europe

- the ancient Near East "imploding" or becoming significantly more compact in terms of genetic structure, likely due to a variety of major population expansions from the chalcolithic onwards from the eastern and western parts of the Fertile Crescent, as well as probably the Caucasus and Europe (note how the post-Neolithic western Asian cluster stretches out towards Europe)

- fully nomadic and very wide ranging pastoral and warrior cultures dominating the entire Eurasian steppe during the Iron Age, leading to the emergence of progressively more East Asian-admixed populations from west to east across the Eurasian steppe

An interesting outcome of the denser sampling from space and time in West Eurasia is that Y-haplogroup R1b, once so elusive in the ancient DNA record, is now popping up all over the place. The new Lipson et al. dataset, for instance, includes two R1b "Old Europeans" from Blatterhole in Germany dated to the Middle Neolithic. Below is the same PCA as above except with all of the ancients belonging to R1b marked with an X. The two Blatterhole samples are sitting in the largely empty space between the European/Siberian Hunter-Gatherer cline and most of the "Old Europe" cluster. The relevant PCA datasheet is available here.

So it may seem that we're back to square one in the long running effort to pinpoint the origin of Y-haplogroup R1b-L51, which encompasses almost 100% of modern-day Western European R1b lineages, and thus probably ranks as Europe's most common Y-haplogroup. But at this stage I'd say no, because R1b-L51 is a subclade of R1b-M269, of which the oldest sample comes from the Bronze Age steppe. In fact, as can be seen in the above PCA, this sample is sitting in exactly the right spot to be one of those pastoralists who overran "Old Europe", or at least a very close relative thereof.

Or am I wrong? Feel free to let me know in the comments.

I didn't bother creating a similar plot of ancient samples belonging to Y-haplogroup R1a, because, unlike R1b, this marker is still non-existent in samples from outside of Eastern Europe and Siberia dating to before the late Neolithic. And I doubt that this is simply due to a lack of the right ancient material. Moreover, the recent discovery of Y-haplogroup R1a-M417, which encompasses almost 100% of all modern-day R1a lineages on the planet, in a North Pontic steppe sample belonging to the Eneolithic Sredny Stog culture means that it's game over for the naysayers as far as the steppe origin of most modern-day R1a lineages is concerned (see here and here).

In other words, if you're still hoping to see R1a, and especially R1a-M417, pop up in non-steppe derived ancient individuals in, say, such far away places as South Asia, then you'll probably be waiting forever.

For the linguistic implications of all of this, see...

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...

Update 15/11/2017: After a couple of days of messing around with the Lipson et al. dataset, I'm certain that Late Copper Age sample Protoboleraz_LCA I2788 shows significant steppe-related admixture. This is the only sample from Lipson et al. with such an obvious signal of steppe-related input that had enough data to be analyzed individually by me with PCA and D-stats.

For the time being, amongst the best proxies for this signal appear to be Yamnaya_Samara and Samara_Eneolithic. But it's likely that the real source of the admixture is yet to enter the ancient DNA record, or at least my dataset. When it does, it'll probably be an Eneolithic pastoralist population from the North Pontic steppe.

Yamnaya_Samara also gives the best statistical fit as the single source population in qpAdm (see here). It's an important result, because it suggests that steppe peoples very similar to Yamnaya were already expanding on and out of the steppe as far back as ~3500 BCE, and perhaps a few hundred years earlier.

See also...

Migration of the Bell Beakers—but not from Iberia (Olalde et al. 2018)

Thursday, November 9, 2017

Descendants of Greeks in the medieval Himalayas?

Below is an abstract from the upcoming Human Evolution 2017 conference (Cambridge, UK, November 20-22). It'll be interesting to see when the paper comes out how Harney, Patterson et al. uncovered the Greek affinities of some of these individuals; uniparental markers, rare alleles? The accompanying pic is from Wikipedia.

The skeletons of Roopkund Lake: Genomic insights into the mysterious identity of ancient Himalayan travelers

Eadaoin Harney, Niraj Rai, Nick Patterson, Kumarasamy Thangaraj, David Reich

The high-altitude lake of Roopkund, situated over 5000 meters above sea level in the Himalayas, remains frozen for almost 11 months out of the year. When it melts, it reveals the skeletons of several hundred ancient individuals, thought to have died during a massive hail storm during the 8th century, A.D. There has been a great deal of speculation about the possible identity of these individuals, but their origins remain enigmatic. We present genome-wide ancient DNA from 17 individuals from the site of Roopkund. We report that these individuals cluster genetically into two distinct groups-consistent with observed morphological variation. Using population genetic analyses, we determine that one group appears to be composed of individuals with broadly South Asian ancestry, characterized by diffuse clustering along the Indian Cline. The second group appears to be of West Eurasian related ancestry, showing affinities with both Greek and Levantine populations.

See also...

Roopkund Lake dead (preliminary analysis)