Indo-European demic diffusion model, 3rd edition

pca-yamna-corded-ware

I have just uploaded the working draft of the third version of the Indo-European demic diffusion model. Unlike the previous two versions, which were published as essays (fully developed papers), this new version adds more information on human admixture, and probably needs important corrections before a definitive edition can be published.

The third version is available right now on ResearchGate and Academia.edu. I will post the PDF at Academia Prisca, as soon as possible:

pca-map-yamna-corded-ware-bell-beaker
Map overlaid by PCA including Yamna, Corded Ware, Bell Beaker, and other samples

Feel free to comment on the paper here, or (preferably) in our forum.

A working version (needing some corrections) divided by sections, illustrated with up-to-date, high resolution maps, can be found (as always) at the official collaborative Wiki website indo-european.info.

Marija Gimbutas and the expansion of the “Kurgan people” based on tumulus-building cultures

An interesting article that I keep stumbling upon, The tumulus in European prehistory: covering the body, housing the soul, by Anthony Harding (2011):

Finally, in Kurgan IV she saw “continuous waves of expansion or raids[that] touched all of northern Europe, the Aegean area, and the east Mediterranean areas possibly as far south as Egypt”. This was the period of the Catacomb Graves, but also the Early Bronze Age rock-cut tombs of the Mediterranean, Vučedol, Bell Beakers in Hungary, the Single Grave culture of the Nordic region. The Kurgan Culture reached Ireland, she remarked in a paper of 1978 “as early as 3500 B.C.” – by which she presumably referred to megalithic mounds covering passage tombs.

(…)

According to Gimbutas, the “Kurgan people” are evidenced by single graves in deep shafts, often in wooden chests (coffins) or stone cists marked by low earth or stone barrows; the dead lay on their backs with legs contracted; they were buried with flint points or arrowheads, figurines depicting horses’ heads, boars tusk ornaments and animal tooth pendants. Human sacrifice was allegedly performed during the funeral ceremonies,and sometimes ritual graves of cattle and other animals were added. This is said to contrast with what Gimbutas called the culture of Old Europe (i.e. the earlier Neolithic of the Balkans), who “betray a concern for the deification of the dead and the construction of monumental works of architecture visible in mortuary houses,grave markings, tumuli, stone rings or stone stelae, and in the large quantity of weapons found in the graves”.

(…)

single-graves-kurgan
The varying burial traditions of the Early Bronze Age in Central and Eastern Europe (Häusler 1977, fig. 1). Circles: tumuli with the “mound edge principle”. Semicircles: tumuli. Stippling: cremation; other symbols represent inhumation graves, divided according to orientation and sex

Can we really associate the practice of mound-building with a specific people, and assume that the spread of the practice indicates the spread of the people? That is one of the “big questions” of European archaeology, and one which a number of papers in the volume address. My own position is that the practice of tumulus building seems so widespread in time and space that it seems hard to associate it with one particular ethnic group – though I can understand how, in the melting pot that was Early Europe, people could believe this to be the case. There are, however, major arguments against the idea, on archaeological grounds alone – which Häusler’s map indicates very clearly. Burial mode and grave form in Copper and Bronze Age Europe was far too variable for any such simplistic correlation. In any case, what are we to make of the appearance of tumuli in such far-flung places as Japan or North America, where tumuli are very common? It was always unlikely that the megalithic tombs of western Europe were to be associated with movements from the steppe 1000 or 2000 years earlier, and nothing that has happened since Gimbutas was writing has changed that situation

Research has corrected Gimbutas’ opinion on the time of spread of Indo-Europeans, on the role of the horse (see e.g. Anthony 2007) in their expansion, and the unrelatedness of the two main central European Chalcolithic archaeological packages: the Corded Ware package that expanded from the Balkans into north-eastern Europe, and the Yamna package (together with the proto-Beaker package) that evolved into the East Bell Beaker culture.

yamna-migration
Extent of migration of the “Yamna package“, from Heyd 2007

However, the shadow of the “Kurgan people” remains in the outdated body of innumerable writings. It was revived with the first attempts at disentangling Europe’s genetic past (based on the role of R1a in expanding Proto-Indo-European).

Particularly strong in that sense is the model set forth by Kristiansen, who was nevertheless aware since his first proposal of the differences between the ‘Kurgan people’ of the steppe and those of the Corded Ware culture, selecting thus an alternative framework of long-lasting human and economic interactions between the “Kurgan people”, the Globular Amphora and Baden cultures with an origin of the culture in the natural region formed between the Upper Dnieper and Vistula rivers.

This idea is continued today, and has been recently linked with the Agricultural Substrate Hypothesis. Originally proposed by Kroonen and linked to the spread of Middle Eastern “R1b1b2” with agriculture, it is now (in Kristiansen et al. 2017 and more recently in Iversen and Kroonen 2017) linked with the expansion of the Corded Ware culture, thus proposing that Pre-Germanic is a branch separated some 6,000 years ago from other branches…

kurgans-corded-ware
Kristiansen’s (1989) schematic presentation of basic principles of burial positions in the Late Neolithic / EBA cultures in northern Eurasia, following to some extent Häusler (1983)

The linguistic proposal is obviously compatible with mainstream archaeological models – which suggest the introduction of Pre-Germanic in Scandinavia with Bell Beaker peoples -, but since the linguistic proposal alone would probably not make such a fuss without the accompanying genetics, I guess this is the right way to publicise it. I doubt linguists really care about genetics, and I really doubt amateur geneticists will read the linguistic proposal, but who cares.

Kristiansen’s traditional model is obviously in contrast with contemporaneous anthropological writings by Anthony, Heyd, or (Gimbutas’ pupil) Mallory, but is nevertheless becoming a resilient tradition in the interpretation of results in studies of human ancestry in Europe.

I doubt that Gimbutas, who was not very fond of tradition, would be proud of this kind of legacy, though…

Featured image: “European dialect” expansion of Proto-Indo-European according to The Indo-Europeans: Archeological Problems, Gimbutas (1963). Observe the similarities of the western European expansion to the recently proposed expansion of R1b lineages with western Yamna and Bell Beaker.

Related:

C.C. Uhlenbeck on the Proto-Indo-European homeland in the 19th century

yamna-expansion-europe

Michiel de Vaan, from the University of Lausanne, has recently uploaded three of his papers published in recent years in the JIES on the works of Dutch linguist C.C. Uhlenbeck:

1. The Early C. C. Uhlenbeck on Indo-European, JIES 44/1-2, 2016, p. 73-80

Christianus Cornelius Uhlenbeck (1866–1951) was one of the leading Dutch linguists between the 1880s and the 1940s. He made his mark on a number of disciplines in descriptive and comparative linguistics, such as Basque, the indigenous languages of North America, Old Germanic and Sanskrit. In 2008, a special issue of the Canadian Journal of Netherlandic Studies (Genee & Hinrichs 2008) was devoted to his memory, the contents of which can be read online.

Uhlenbeck’s work and thinking on the Indo-European language family, and, in particular, on the original habitat of its speakers, have been discussed by Kortlandt 2010, who concluded that Uhlenbeck had remarkably advanced views for his time. The first two journal articles in which Uhlenbeck (1895, 1897) sets forth his views were published in Dutch. During the academic year 2013/14, I had the opportunity to read a number of articles on the question of the Indo-European homeland problem with my students at Leiden University. I provided Uhlenbeck’s Dutch articles from 1895 and 1897 with an English translation which I hereby submit to all colleagues

On Anthony and Haarman:

Anthony focuses on the socioeconomic changes that took place in the fifth and fourth millennium BC, when the Indo-European steppe peoples entered into contact with the sedentary, agricultural population of Southeast-Europe, also termed Old European or Palaeo-European. Importantly, Anthony dismantles the monolithic view of a single “steppe pastoralism”, and instead stresses that the steppe economy itself went through various developmental phases, which might be linked to different periods of expansion of Indo-European into Europe. Haarmann zooms in on the sociocultural effects of the Indo-European expansion(s). Since language contact will often heavily influence the languages which are in contact, he sets out to look for traces of the language of the Old Europeans in the surviving Indo-European languages, first of all, in Ancient Greek. As many scholars before him have also realized, there is a thick layer of non-Indo-European words in Greek in fields such as agriculture, wine production, weaving, metallurgy, religion and mythology, building techniques, and local flora and fauna. Even the Greeks themselves acknowledged the presence of a “Pelasgian” substratum in their own language. Haarmann concludes (2012: 119): “Despite the fact that Indo-Europeans exercised political power and promoted their language as the common vehicle, they were nevertheless impressed by the achievements of the Old Europeans to the extent that the dominant language of the élite absorbed manifold influences from the local language(s).”

2. Where was the Indo-European proto-language spoken?, by C.C. Uhlenbeck (1895), translation by Michiel de Vaan, JIES 44/1-2, 2016, p. 181-185.

It cannot be objected that the eastern and the western Iranians differed much in their dialects, for the PIE language itself must have been split in a number of fairly different dialects. There has never been in the world a language without dialect differences, larger or smaller, depending on the geographic distance. That is why, in the beginning of this piece, I spoke not of one original language, but of a group of closely cognate dialects. Since the linguistic area of PIE was probably very large, it is certainly possible that part of it lay in the steppes, another part in the mountains, and yet another part in the fertile plains. If so, the fauna and the flora of the homeland cannot have been the same in different areas. And this is an argument, which the linguistic prehistorician must not lose sight of!

On the necessary natural (geographic and stage) division of PIE, he made apparently a dialectal division into a European group (including Greek?), a Balkan-Balto-Slavic group, and Indo-Iranian.

3. The prehistory of the Indo-European peoples, by C.C. Uhlenbeck (1897), translation by Michiel de Vaan, JIES 44/1-2, 2016, 186-212.

The following excerpt is probably not the most interesting one (check out the different aspect of prehistoric life described through linguistics), but it is fun to be able to support the same arguments today:

Does linguistics provide us with the means to indicate a smaller region as the center of expansion of the Indo-European languages and peoples? Hardly. After all, it is far from certain that the people who speak Indo-European languages are also ethnologically more closely related to each other than to peoples with languages very different from ours. If the homeland of the Indo-European languages does not coincide with that of the Indo-European peoples, it becomes impossible to determine either one. In reality, if the Indo-European speaking peoples do not form an ethnological unity, we have not the slightest reason to suppose that they all hail from a single region. The use of a common language can just as well be explained by a powerful, prehistoric cultural influence, as by common ancestry. The unknown, unknowable origin of that cultural force is then, in a certain sense, the homeland of our language family. Searching a homeland of the Indo-Europeans or of the Indo-European dialects is like taking a wild stab, something which all who understand history must abhor. If Schrader regards as the homeland the Pontic steppes, if Hirt regards the coasts of Lithuania as such, this is based on insufficient and partially judged data. Still, the large agreement in vocabulary between Indo-European and Egypto-Semitic remains a remarkable fact, which Friedrich Delitzsch first illustrated in a truly scientific way.

(…)

If we stick to the facts, and refrain from bottomless speculations, we will find no other homeland than the area indicated above, which encompasses half of Europe and a part of Asia.

Iberian Peninsula: Discontinuity in mtDNA between hunter-gatherers and farmers, not so much during the Chalcolithic and EBA

iberia-mtdna

A new preprint paper at BioRxiv, The maternal genetic make-up of the Iberian Peninsula between the Neolithic and the Early Bronze Age, by Szécsényi-Nagy et al. (2017).

Abstract:

Agriculture first reached the Iberian Peninsula around 5700 BCE. However, little is known about the genetic structure and changes of prehistoric populations in different geographic areas of Iberia. In our study, we focused on the maternal genetic makeup of the Neolithic (~ 5500-3000 BCE), Chalcolithic (~ 3000-2200 BCE) and Early Bronze Age (~ 2200-1500 BCE). We report ancient mitochondrial DNA results of 213 individuals (151 HVS-I sequences) from the northeast, central, southeast and southwest regions and thus on the largest archaeogenetic dataset from the Peninsula to date. Similar to other parts of Europe, we observe a discontinuity between hunter-gatherers and the first farmers of the Neolithic. During the subsequent periods, we detect regional continuity of Early Neolithic lineages across Iberia, however the genetic contribution of hunter-gatherers is generally higher than in other parts of Europe and varies regionally. In contrast to ancient DNA findings from Central Europe, we do not observe a major turnover in the mtDNA record of the Iberian Late Chalcolithic and Early Bronze Age, suggesting that the population history of the Iberian Peninsula is distinct in character.

iberian-mtdna-samples
Iberian mtDNA samples

Detailed conclusions of their work,

The present study, based on 213 new and 125 published mtDNA data of prehistoric Iberian individuals suggests a more complex mode of interaction between local hunter-gatherers and incoming early farmers during the Early and Middle Neolithic of the Iberian Peninsula, as compared to Central Europe. A characteristic of Iberian population dynamics is the proportion of autochthonous hunter-gatherer haplogroups, which increased in relation to the distance to the Mediterranean coast. In contrast, the early farmers in Central Europe showed comparatively little admixture of contemporaneous hunter-gatherer groups. Already during the first centuries of Neolithic transition in Iberia, we observe a mix of female DNA lineages of different origins. Earlier hunter-gatherer haplogroups were found together with a variety of new lineages, which ultimately derive from Near Eastern farming groups. On the other hand, some early Neolithic sites in northeast Iberia, especially the early group from the cave site of Els Trocs in the central Pyrenees, seem to exhibit affinities to Central European LBK communities. The diversity of female lineages in the Iberian communities continued even during the Chalcolithic, when populations became more homogeneous, indicating higher mobility and admixture across different geographic regions. Even though the sample size available for Early Bronze Age populations is still limited, especially with regards to El Argar groups, we observe no significant changes to the mitochondrial DNA pool until the end of our time transect (1500 BCE). The expansion of groups from the eastern steppe, which profoundly impacted Late Neolithic and EBA groups of Central and North Europe, cannot (yet) be seen in the contemporaneous population substrate of the Iberian Peninsula at the present level of genetic resolution. This highlights the distinct character of the Neolithic transition both in the Iberian Peninsula and elsewhere and emphasizes the need for further in depth archaeogenetic studies for reconstructing the close reciprocal relationship of genetic and cultural processes on the population level.

So it seems more and more likely that the North-West Indo-European invasion during the Copper Age (signaled by changes in Y-DNA lineages) was not, as in central Europe, accompanied by much mtDNA turnover. What that means – either a male-dominated invasion, or a longer internal evolution of invasive Y-DNA subclades – remains to bee seen, but I am still more inclined to see the former as the most likely interpretation, in spite of admixture results.

Related:

Featured images: from the article, licensed BY-NC-ND.

Spread of Indo-European folktale traditions related to cultural and demic diffusion (using genomic data)

folktale-genomics

New article at PNAS, Inferring patterns of folktale diffusion using genomic data, by Bortoloni et al. (2017).

Abstract:

Observable patterns of cultural variation are consistently intertwined with demic movements, cultural diffusion, and adaptation to different ecological contexts [Cavalli-Sforza and Feldman (1981) Cultural Transmission and Evolution: A Quantitative Approach; Boyd and Richerson (1985) Culture and the Evolutionary Process]. The quantitative study of gene–culture coevolution has focused in particular on the mechanisms responsible for change in frequency and attributes of cultural traits, the spread of cultural information through demic and cultural diffusion, and detecting relationships between genetic and cultural lineages. Here, we make use of worldwide whole-genome sequences [Pagani et al. (2016) Nature 538:238–242] to assess the impact of processes involving population movement and replacement on cultural diversity, focusing on the variability observed in folktale traditions (n = 596) [Uther (2004) The Types of International Folktales: A Classification and Bibliography. Based on the System of Antti Aarne and Stith Thompson] in Eurasia. We find that a model of cultural diffusion predicted by isolation-by-distance alone is not sufficient to explain the observed patterns, especially at small spatial scales (up to ~4,000 km). We also provide an empirical approach to infer presence and impact of ethnolinguistic barriers preventing the unbiased transmission of both genetic and cultural information. After correcting for the effect of ethnolinguistic boundaries, we show that, of the alternative models that we propose, the one entailing cultural diffusion biased by linguistic differences is the most plausible. Additionally, we identify 15 tales that are more likely to be predominantly transmitted through population movement and replacement and locate putative focal areas for a set of tales that are spread worldwide.

I am very interested in folktales and their origins within Proto-Indo-European culture, so the title alone was an immediate click-bait for me. It did, as always, disappoint in its methods and conclusions, but just the idea it proposes is of great interest for future studies.

There are gross limitations in assessing folktales using simply the Aarne-Thompson-Uther Classification without further analysis or explanation, apart from a summary of tales in the supplementary materials.

But their maps and simplistic hypothesized waves of diffusion (‘African origin’, ‘northern Eurasian’, ‘Eastern European’, or ‘Middle-Eastern/Caucasian’) seem to me as if they try to swim with the tide of the current literature regarding the identification of Proto-Indo-European demic diffusion with “steppe admixture” distribution (and ancient language family diffusion in general through admixture), and as such it can only be wrong.

If you just look at actual folktale distribution (black dots) and compare them with prehistoric cultures and ancient Y-DNA distribution, you realize their maps don’t make much sense, and more complex methods (and a clearer idea of what admixture represents) are needed.

If their intention was to get published in a journal of high impact factor, they succeeded, so good for them. I am glad this subject gets more attention. Of course, their conclusions are kept formally in line with the many limitations of their methods, and are the most interesting aspect of the article:

By correcting for the presence of ethnolinguistic barriers, we find that the null model of cultural diffusion predicted by IBD alone cannot explain the observed distribution of folktales across Eurasia. Instead, beyond ~4,000 km, cultural diffusion biased by linguistic barriers exhibits the highest correlation at all geographic bins. At small geographic bins (<4,000 km), population movements and linguistic barriers may be more relevant than geographic proximity, pointing once again at the possible importance of small-scale processes of cultural transmission for testing more specific hypotheses when using genetic evidence. In addition, processes other than simple cultural diffusion may be more relevant for a smaller group of tales shared by pairs of populations that are genetically closer than populations not exhibiting those tales. Looking for smaller packages of tales or individual tales and their variants can be useful to shed light on the formation process of this vast body of popular knowledge. The long-range patterns detected by our analyses may complement this picture by suggesting a more ancient origin of some of these folktales (SI Appendix). On a broader level, these results can be used in the future to infer directional trends of cultural dispersal as well as to test for the emergence of systematic social biases [such as prestige bias, conformism/anticonformism, heterophily, and content-dependent biases] or cultural barriers different from linguistic ones, which have a chronology that may be independently ascertained.

If you are interested in studies about folktales, and especially those related to Indo-European traditions, you can check out the following articles I found interesting in the past:

Related:

Featured image (featured also in the article): Possible focal area and dispersion pattern for tale ATU313 “The Magic Flight,” one the most popular folktales in this dataset, which may have been additionally spread through population movement and replacement. It is interesting to note how this tale reached locations that are far from its putative origin (such as Japan and southeastern Africa), whereas it was not retained by many populations located in between (gray dots).

Analysis of R1b-DF27 haplogroups in modern populations adds new information that contrasts with ‘steppe admixture’ results

R1b-DF27-iberia

New open access article published in Scientific Reports, Analysis of the R1b-DF27 haplogroup shows that a large fraction of Iberian Y-chromosome lineages originated recently in situ, by Solé-Morata et al. (2017).

Abstract

Haplogroup R1b-M269 comprises most Western European Y chromosomes; of its main branches, R1b-DF27 is by far the least known, and it appears to be highly prevalent only in Iberia. We have genotyped 1072 R1b-DF27 chromosomes for six additional SNPs and 17 Y-STRs in population samples from Spain, Portugal and France in order to further characterize this lineage and, in particular, to ascertain the time and place where it originated, as well as its subsequent dynamics. We found that R1b-DF27 is present in frequencies ~40% in Iberian populations and up to 70% in Basques, but it drops quickly to 6–20% in France. Overall, the age of R1b-DF27 is estimated at ~4,200 years ago, at the transition between the Neolithic and the Bronze Age, when the Y chromosome landscape of W Europe was thoroughly remodeled. In spite of its high frequency in Basques, Y-STR internal diversity of R1b-DF27 is lower there, and results in more recent age estimates; NE Iberia is the most likely place of origin of DF27. Subhaplogroup frequencies within R1b-DF27 are geographically structured, and show domains that are reminiscent of the pre-Roman Celtic/Iberian division, or of the medieval Christian kingdoms.

Some people like to say that Y-DNA haplogroup analysis, or phylogeography in general, is of no use anymore (especially modern phylogeography), and they are content to see how ‘steppe admixture’ was (or even is) distributed in Europe to draw conclusions about ancient languages and their expansion. With each new paper, we are seeing the advantages of analysing ancient and modern haplogroups in ascertaining population movements.

Quite recently there was a suggestion based on steppe admixture that Basque-speaking Iberians resisted the invasion from the steppe. Observing the results of this article (dates of expansion and demographic data) we see a clear expansion of Y-DNA haplogroups precisely by the time of Bell Beaker expansion from the east. Y-DNA haplogroups of ancient samples from Portugal point exactly to the same conclusion.

The situation of R1b-DF27 in Basques, as I have pointed out elsewhere, is probably then similar to the genetic drift of Finns, mainly of N1c lineages, speaking today a Uralic language that expaned with Corded Ware and R1a subclades.

The recent article on Mycenaean and Minoan genetics also showed that, when it comes to Europe, most of the demographic patterns we see in admixture are reminiscent of the previous situation, only rarely can we see a clear change in admixture (which would mean an important, sudden replacement of the previous population).

Equating the so-called steppe admixture with Indo-European languages is wrong. Period.

The following are excerpts from the article (emphasis is mine):

Dates and expansions

The average STR variance of DF27 and each subhaplogroup is presented in Suppl. Table 2. As expected, internal diversity was higher in the deeper, older branches of the phylogeny. If the same diversity was divided by population, the most salient finding is that native Basques (Table 2) have a lower diversity than other populations, which contrasts with the fact that DF27 is notably more frequent in Basques than elsewhere in Iberia (Suppl. Table 1). Diversity can also be measured as pairwise differences distributions (Fig. 5). The distribution of mean pairwise differences within Z195 sits practically on top of that of DF27; L176.2 and Z220 have similar distributions, as M167 and Z278 have as well; finally, M153 shows the lowest pairwise distribution values. This pattern is likely to reflect the respective ages of the haplogroups, which we have estimated by a modified, weighted version of the ρ statistic (see Methods).

Z195 seems to have appeared almost simultaneously within DF27, since its estimated age is actually older (4570 ± 140 ya). Of the two branches stemming from Z195, L176.2 seems to be slightly younger than Z220 (2960 ± 230 ya vs. 3320 ± 200 ya), although the confidence intervals slightly overlap. M167 is clearly younger, at 2600 ± 250 ya, a similar age to that of Z278 (2740 ± 270 ya). Finally, M153 is estimated to have appeared just 1930 ± 470 ya.

Haplogroup ages can also be estimated within each population, although they should be interpreted with caution (see Discussion). For the whole of DF27, (Table 3), the highest estimate was in Aragon (4530 ± 700 ya), and the lowest in France (3430 ± 520 ya); it was 3930 ± 310 ya in Basques. Z195 was apparently oldest in Catalonia (4580 ± 240 ya), and with France (3450 ± 269 ya) and the Basques (3260 ± 198 ya) having lower estimates. On the contrary, in the Z220 branch, the oldest estimates appear in North-Central Spain (3720 ± 313 ya for Z220, 3420 ± 349 ya for Z278). The Basques always produce lower estimates, even for M153, which is almost absent elsewhere.

R1b-DF27-tree
Simplified phylogenetic tree of the R1b-M269 haplogroup. SNPs in italics were not analyzed in this manuscript.

Demography

The median value for Tstart has been estimated at 103 generations (Table 4), with a 95% highest probability density (HPD) range of 50–287 generations; effective population size increased from 131 (95% HPD: 100–370) to 72,811 (95% HPD: 52,522–95,334). Considering patrilineal generation times of 30–35 years, our results indicate that R1b-DF27 started its expansion ~3,000–3,500 ya, shortly after its TMRCA.

As a reference, we applied the same analysis to the whole of R1b-S116, as well as to other common haplogroups such as G2a, I2, and J2a. Interestingly, all four haplogroups showed clear evidence of an expansion (p > 0.99 in all cases), all of them starting at the same time, ~50 generations ago (Table 4), and with similar estimated initial and final populations. Thus, these four haplogroups point to a common population expansion, even though I2 (TMRCA, weighted ρ, 7,800 ya) and J2a (TMRCA, 5,500 ya) are older than R1b-DF27. It is worth noting that the expansion of these haplogroups happened after the TMRCA of R1b-DF27.

R1b-DF27-PCA
Principal component analysis of STR haplotypes. (a) Colored by subhaplogroup, (b) colored by population. Larger squares represent subhaplogroup or population centroids.

Sum up and discussion

We have characterized the geographical distribution and phylogenetic structure of haplogroup R1b-DF27 in W. Europe, particularly in Iberia, where it reaches its highest frequencies (40–70%). The age of this haplogroup appears clear: with independent samples (our samples vs. the 1000 genome project dataset) and independent methods (variation in 15 STRs vs. whole Y-chromosome sequences), the age of R1b-DF27 is firmly grounded around 4000–4500 ya, which coincides with the population upheaval in W. Europe at the transition between the Neolithic and the Bronze Age. Before this period, R1b-M269 was rare in the ancient DNA record, and during it the current frequencies were rapidly reached. It is also one of the haplogroups (along with its daughter clades, R1b-U106 and R1b-S116) with a sequence structure that shows signs of a population explosion or burst. STR diversity in our dataset is much more compatible with population growth than with stationarity, as shown by the ABC results, but, contrary to other haplogroups such as the whole of R1b-S116, G2a, I2 or J2a, the start of this growth is closer to the TMRCA of the haplogroup. Although the median time for the start of the expansion is older in R1b-DF27 than in other haplogroups, and could suggest the action of a different demographic process, all HPD intervals broadly overlap, and thus, a common demographic history may have affected the whole of the Y chromosome diversity in Iberia. The HPD intervals encompass a broad timeframe, and could reflect the post-Neolithic population expansions from the Bronze Age to the Roman Empire.

While when R1b-DF27 appeared seems clear, where it originated may be more difficult to pinpoint. If we extrapolated directly from haplogroup frequencies, then R1b-DF27 would have originated in the Basque Country; however, for R1b-DF27 and most of its subhaplogroups, internal diversity measures and age estimates are lower in Basques than in any other population. Then, the high frequencies of R1b-DF27 among Basques could be better explained by drift rather than by a local origin (except for the case of M153; see below), which could also have decreased the internal diversity of R1b-DF27 among Basques. An origin of R1b-DF27 outside the Iberian Peninsula could also be contemplated, and could mirror the external origin of R1b-M269, even if it reaches there its highest frequencies. However, the search for an external origin would be limited to France and Great Britain; R1b-DF27 seems to be rare or absent elsewhere: Y-STR data are available only for France, and point to a lower diversity and more recent ages than in Iberia (Table 3). Unlike in Basques, drift in a traditionally closed population seems an unlikely explanation for this pattern, and therefore, it does not seem probable that R1b-DF27 originated in France. Then, a local origin in Iberia seems the most plausible hypothesis. Within Iberia, Aragon shows the highest diversity and age estimates for R1b-DF27, Z195, and the L176.2 branch, although, given the small sample size, any conclusion should be taken cautiously. On the contrary, Z220 and Z278 are estimated to be older in North Central Spain (N Castile, Cantabria and Asturias). Finally, M153 is almost restricted to the Basque Country: it is rarely present at frequencies >1% elsewhere in Spain (although see the cases of Alacant, Andalusia and Madrid, Suppl. Table 1), and it was found at higher frequencies (10–17%) in several Basque regions; a local origin seems plausible, but, given the scarcity of M153 chromosomes outside of the Basque Country, the diversity and age values cannot be compared.

Within its range, R1b-DF27 shows same geographical differentiation: Western Iberia (particularly, Asturias and Portugal), with low frequencies of R1b-Z195 derived chromosomes and relatively high values of R1b-DF27* (xZ195); North Central Spain is characterized by relatively high frequencies of the Z220 branch compared to the L176.2 branch; the latter is more abundant in Eastern Iberia. Taken together, these observations seem to match the East-West patterning that has occurred at least twice in the history of Iberia: i) in pre-Roman times, with Celtic-speaking peoples occupying the center and west of the Iberian Peninsula, while the non-Indoeuropean eponymous Iberians settled the Mediterranean coast and hinterland; and ii) in the Middle Ages, when Christian kingdoms in the North expanded gradually southwards and occupied territories held by Muslim fiefs.

DF27-iberia-france
Contour maps of the derived allele frequencies of the SNPs analyzed in this manuscript. Population abbreviations as in Table 1. Maps were drawn with SURFER v. 12 (Golden Software, Golden CO, USA).

I wouldn’t trust the absence of R1b-DF27 outside France as a proof that its origin must be in Western Europe – especially since we have ancient DNA, and that assertion might prove quite wrong – but aside from that the article seems solid in its analysis of modern populations.

Related:

Text and figures from the article, licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.