"Heavily sex-biased" population dispersals into the Indian Subcontinent (Silva et al. 2017)

And so it begins. BMC Evolutionary Biology has a very interesting, but hardly surprising, new paper by Silva et al. on the population history of the Indian Subcontinent. Emphasis is mine:

Background: India is a patchwork of tribal and non-tribal populations that speak many different languages from various language families. Indo-European, spoken across northern and central India, and also in Pakistan and Bangladesh, has been frequently connected to the so-called “Indo-Aryan invasions” from Central Asia ~3.5 ka and the establishment of the caste system, but the extent of immigration at this time remains extremely controversial. South India, on the other hand, is dominated by Dravidian languages. India displays a high level of endogamy due to its strict social boundaries, and high genetic drift as a result of long-term isolation which, together with a very complex history, makes the genetic study of Indian populations challenging.

Results: We have combined a detailed, high-resolution mitogenome analysis with summaries of autosomal data and Y-chromosome lineages to establish a settlement chronology for the Indian Subcontinent. Maternal lineages document the earliest settlement ~55–65 ka (thousand years ago), and major population shifts in the later Pleistocene that explain previous dating discrepancies and neutrality violation. Whilst current genome-wide analyses conflate all dispersals from Southwest and Central Asia, we were able to tease out from the mitogenome data distinct dispersal episodes dating from between the Last Glacial Maximum to the Bronze Age. Moreover, we found an extremely marked sex bias by comparing the different genetic systems.

Conclusions: Maternal lineages primarily reflect earlier, pre-Holocene processes, and paternal lineages predominantly episodes within the last 10 ka. In particular, genetic influx from Central Asia in the Bronze Age was strongly male-driven, consistent with the patriarchal, patrilocal and patrilineal social structure attributed to the inferred pastoralist early Indo-European society. This was part of a much wider process of Indo-European expansion, with an ultimate source in the Pontic-Caspian region, which carried closely related Y-chromosome lineages, a smaller fraction of autosomal genome-wide variation and an even smaller fraction of mitogenomes across a vast swathe of Eurasia between 5 and 3.5 ka.

...

There are now sufficient high-quality Y-chromosome data available (especially Poznik et al. [58]) to be able to draw clear conclusions about the timing and direction of dispersal of R1a (Fig. 5). The indigenous South Asian subclades are too young to signal Early Neolithic dispersals from Iran, and strongly support Bronze Age incursions from Central Asia. The derived R1a-Z93 and the further derived R1a-Z94 subclades harbour the bulk of Central and South Asian R1a lineages [55, 58], as well as including some Russian and European lineages, and have been variously dated to 5.6 [4.0;7.3] ka [55], 4.5-5.3 ka with expansions ~4.0-4.5 ka [58], or 4.7 [4.0;5.5] ka (Yfull tree v4.10 [54]). The South Asian R1a-L657, dated to ~4.2 ka [3.3;5.1] (Yfull tree v4.10 [54]]), is the largest (in the 1KG dataset) of several closely related subclades within R1a-Z94 of very similar time depth. Moreover, not only has R1a been found in all Sintashta and Sintashta-derived Andronovo and Srubnaya remains analysed to date at the genome-wide level (nine in total) [76, 77], and been previously identified in a majority of Andronovo (2/3) and post-Andronovo Iron Age (Tagar and Tachtyk: 6/6) male samples from southern central Siberia tested using microsatellite analysis [101], it has also been identified in other remains across Europe and Central Asia ranging from the Mesolithic up until the Iron Age (Fig. 5).

The other major member of haplogroup R in South Asia, R2, shows a strikingly different pattern. It also has deep non-Subcontinental branches, nesting a South Asian specific subclade. But the deep lineages are mainly seen in the eastern part of the Near East, rather than Central Asia or eastern Europe, and the Subcontinental specific subclade is older, dating to ~8 ka [55].

Altogether, therefore, the recently refined Y-chromosome tree strongly suggests that R1a is indeed a highly plausible marker for the long-contested Bronze Age spread of Indo-Aryan speakers into South Asia, although dated aDNA evidence will be needed for a precise estimate of its arrival in various parts of the Subcontinent. aDNA will also be needed to test the hypothesis that there were several streams of Indo-Aryan immigration (each with a different pantheon), for example with the earliest arriving ~3.4 ka and those following the Rigveda several centuries later [12]. Although they are closely related, suggesting they likely spread from a single Central Asian source pool, there do seem to be at least three and probably more R1a founder clades within the Subcontinent [58], consistent with multiple waves of arrival. Genomic Y-chromosome phylogeography is in its infancy compared to mito-genome analysis so it is of course likely that the picture will evolve with sequencing of further South Asian Y-chromosomes, but the picture is already sufficiently clear that we do not expect it to change drastically.

Silva et al., A genetic chronology for the Indian Subcontinent points to heavily sex-biased dispersals, BMC Evolutionary Biology, Published: 23 March 2017, DOI: 10.1186/s12862-017-0936-9

See also...

On the doorstep of India

Indian confirmation bias

The Poltavka outlier

Caste is in the genes

The Medieval pilgrim

Recently at PLoS Neglected Tropical Diseases:

Abstract: We have examined the remains of a Pilgrim burial from St Mary Magdalen, Winchester. The individual was a young adult male, aged around 18–25 years at the time of death. Radiocarbon dating showed the remains dated to the late 11th–early 12th centuries, a time when pilgrimages were at their height in Europe. Several lines of evidence in connection with the burial suggested this was an individual of some means and prestige. Although buried within the leprosarium cemetery, the skeleton showed only minimal skeletal evidence for leprosy, which was confined to the bones of the feet and legs. Nonetheless, molecular testing of several skeletal elements, including uninvolved bones all showed robust evidence of DNA from Mycobacterium leprae, consistent with the lepromatous or multibacillary form of the disease. We infer that in life, this individual almost certainly suffered with multiple soft tissue lesions. Genotyping of the M.leprae strain showed this belonged to the 2F lineage, today associated with cases from South-Central and Western Asia. During osteological examination it was noted that the cranium and facial features displayed atypical morphology for northern European populations. Subsequently, geochemical isotopic analyses carried out on tooth enamel indicated that this individual was indeed not local to the Winchester region, although it was not possible to be more specific about their geographic origin.

...

During analysis, the cranial morphology of the individual was noted as being of an unusual type and unlike other individuals from the cemetery (Fig 4). Therefore, the cranial measurements (S1 Table) were inputted into FORDISC and CRANID, with additional measurements being taken where necessary. The individual was found not to have an affinity with any of the populations contained within the program databases, which do include some from northern Europe, although not Britain. Therefore, the individual could be said not to share a physical affinity with these northern European samples, although this should not be taken as implying anything about their specific identity or origin. Populations that are poorly represented in the database include those from southern Europe and northern Africa (with the exception of Egypt), so there is a possibility that the individual could share physical cranial affinities with such populations, as his cranial morphology does bear similarities to other individuals from British archaeological populations who were also unclassifiable by FORDISC and have been suggested, on isotopic data, to originate from these areas [20]; (Stephany Leach personal communication, 2012).

Citation: Roffey S, Tucker K, Filipek-Ogden K, Montgomery J, Cameron J, O’Connell T, et al. (2017) Investigation of a Medieval Pilgrim Burial Excavated from the Leprosarium of St Mary Magdalen Winchester, UK. PLoS Negl Trop Dis 11(1): e0005186. doi:10.1371/journal.pntd.0005186

Trouble in early Mesolithic Iberia

Humans may have dined on other humans during the Epipalaeolithic-Mesolithic transition in Iberia, according to a new paper at the Journal of Anthropological Archaeology.

If true, I wonder if this had anything to do with the spread of the so called Villabruna cluster across Europe at around that time? I'm not suggesting that Villabruna forager bands ate most of the other European foragers, but rather that they coped best with the stresses associated with the Epipalaeolithic-Mesolithic transition.

The paper is behind a pay wall, but the figures can be viewed here.

Abstract: The identification of unarticulated human remains with anthropic marks in archaeological contexts normally involves solving two issues: a general one associated with the analysis and description of the anthropic manipulation marks, and another with regard to the interpretation of their purpose. In this paper we present new evidence of anthropophagic behaviour amongst hunter-gatherer groups of the Mediterranean Mesolithic. A total of 30 human remains with anthropic manipulation marks have been found in the Mesolithic layers of Coves de Santa Maira (Castell de Castells, Alicante, Spain), dating from ca. 10.2–9 cal ky BP. We describe the different marks identified on both human and faunal remains at the site (lithic, tooth, percussion and fire marks on bone cortex). As well as describing these marks, and considering that both human and faunal remains at the site present similar depositional and taphonomic features, this paper also contextualizes them within the archaeological context and subsistence patterns described for Mesolithic groups in the region. We cannot entirely rule out the possibility that these practices may be the result of periodic food stress suffered by the human populations. These anthropophagic events at the site coincide with a cultural change at the regional Epipalaeolithic-Mesolithic transition.

Morales-Pérez et al., Funerary practices or food delicatessen? Human remains with anthropic marks from the Western Mediterranean Mesolithic, Journal of Anthropological Archaeology, Volume 45, March 2017, Pages 115–130, http://dx.doi.org/10.1016/j.jaa.2016.11.002

Greek confirmation bias

A new paper at the EJHG claims that Slavic admixture in Peloponnesean Greeks averages a few per cent at best (see abstract below). However, I'd say the authors are making two potentially erroneous assumptions: 1) that Slavic invaders arrived in Greece straight from the Slavic homeland, probably located somewhere in East Central or Eastern Europe, and 2) modern-day Northern Slavs (Belarusians, Poles, Russians and Ukrainians) are accurate proxies for these ancient invaders.

Keep in mind that when the Slavs moved into the Balkans during the Early Middle Ages, they routinely absorbed the natives into their bands as free men and women (excellent paper on the topic here). So their numbers swelled thanks to this more southerly, local input, and, at the same time, their genetic structure shifted in a big way, probably from more or less Northern Slavic to modern-day Southern Slavic. Indeed, it's likely that by the time they arrived in the Peloponnese, they were less like this and more like this, or even this.

So was Fallmerayer correct when he theorized that the Peloponnese was totally re-populated by Slavs during the Medieval period? Probably not, but the population shift may still have been profound, and totaling much more than a few per cent.

I can't wait for more ancient DNA from Greece and Italy, especially from the Bronze and Iron Ages. Based on my experiences with many Greeks and Italians, it's sure to be a big eye opener for them, and a beautiful thing.

Abstract: Peloponnese has been one of the cradles of the Classical European civilization and an important contributor to the ancient European history. It has also been the subject of a controversy about the ancestry of its population. In a theory hotly debated by scholars for over 170 years, the German historian Jacob Philipp Fallmerayer proposed that the medieval Peloponneseans were totally extinguished by Slavic and Avar invaders and replaced by Slavic settlers during the 6th century CE. Here we use 2.5 million single-nucleotide polymorphisms to investigate the genetic structure of Peloponnesean populations in a sample of 241 individuals originating from all districts of the peninsula and to examine predictions of the theory of replacement of the medieval Peloponneseans by Slavs. We find considerable heterogeneity of Peloponnesean populations exemplified by genetically distinct subpopulations and by gene flow gradients within Peloponnese. By principal component analysis (PCA) and ADMIXTURE analysis the Peloponneseans are clearly distinguishable from the populations of the Slavic homeland and are very similar to Sicilians and Italians. Using a novel method of quantitative analysis of ADMIXTURE output we find that the Slavic ancestry of Peloponnesean subpopulations ranges from 0.2 to 14.4%. Subpopulations considered by Fallmerayer to be Slavic tribes or to have Near Eastern origin, have no significant ancestry of either. This study rejects the theory of extinction of medieval Peloponneseans and illustrates how genetics can clarify important aspects of the history of a human population.

Stamatoyannopoulos et al., Genetics of the peloponnesean populations and the theory of extinction of the medieval peloponnesean Greeks, European Journal of Human Genetics advance online publication 8 March 2017; doi: 10.1038/ejhg.2017.18

See also...

Greeks in a Longobard cemetery

Yamnaya X chromosomes

In this analysis I'm using the same qpAdm method and almost the same reference samples as Lazaridis & Reich 2017. However, to improve the resolution, in the right pops (or outgroups) I added European Late Upper Paleolithic forager Villabruna, and dropped the low quality Siberian Late Upper Paleolithic forager AfontovaGora3. Also, I ran tests with and without the allsnps: YES flag.

In the left pops, apart from test group Steppe_EMBA (Early Middle Bronze Age steppe conglomerate made up of closely related Afanasievo, Poltavka and Yamnaya samples), we have the putative ancestral populations: Eastern European Hunter-Gatherers (EHG), Caucasus Hunter-Gatherers (CHG), Kura-Araxes (Armenia_EBA), a Chalcolithic Anatolian (Anatolia_ChL), Chalcolithic Armenians (Armenia_ChL), and/or Chalcolithic farmers from Iran (Iran_ChL).

As far as I can tell, these are the best statistical fits with the X chromosome and genome-wide data, respectively. Feel free to set me straight; the full output is in a zip file here.

Outgroups
Mota
GoyetQ116-1
Kostenki14
Levant_Neolithic
MA1
Ust_Ishim
Vestonice16
Villabruna

Steppe_EMBA X
CHG 0.617±0.178
EHG 0.383±0.178
chisq 1.868 taildiff 0.93139015
allsnps: YES

Steppe_EMBA
Anatolia_ChL 0.139±0.050
CHG 0.356±0.063
EHG 0.505±0.025
chisq 5.084 taildiff 0.405658017
allsnps: YES

In my opinion, despite the relatively low resolution of the X chromosome analysis, the Steppe_EMBA X chromosomes show a strong southern, in particular CHG, character, which suggests that CHG admixture into Steppe_EMBA was mediated largely via female gene flow.

Interestingly, in one of the models, the Steppe_EMBA X chromosomes are fitted successfully as a two-way mixture of CHG and Iran_ChL (see here). It's impossible to model Steppe_EMBA in such a way with genome-wide data (for instance, see here and here).

Failure to replicate

Just in at bioRxiv:

We fail to replicate a genetic signal for sex bias in the steppe migration to central Europe after ~5,000 years proposed by Goldberg et al. PNAS 114(10):2657-2662. Estimation of X-chromosome steppe ancestry in the Bronze Age central European population with the qpAdm method (Haak et al. Nature 522, 207-11) does not indicate lower steppe ancestry on the X-chromosome than in the autosomes. We perform a simulation which indicates presence of estimation bias of -19.5% in the inference of X-chromosome admixture proportions using the method used by Goldberg et al., largely eliminating the observed sex bias.

Iosif Lazaridis, David Reich, Failure to Replicate a Genetic Signal for Sex Bias in the Steppe Migration into Central Europe, bioRxiv, Posted March 14, 2017, doi: https://doi.org/10.1101/114124

Update 04/04/2017: Goldberg et al. reply:

Comparing the sex-specifically inherited X chromosome to the autosomes in ancient genetic samples, we (1) studied sex-specific admixture for two prehistoric migrations. For each migration, we used several admixture estimation procedures, including ADMIXTURE model-based clustering (2), comparing X-chromosomal and autosomal ancestry in contemporaneous Central Europeans, interpreting greater admixture from the migrating population on the autosomes as male-biased migration. For migration into late Neolithic/Bronze Age Central Europeans (BA) from the Pontic-Caspian steppe (SP), we inferred male-biased admixture at 5-14 males per migrating female. Lazaridis & Reich (3) contest this male-biased migration claim. For simulated individuals, they claim that ADMIXTURE provides biased X-chromosomal ancestry estimates. They argue that if the bias is taken into account, then X-chromosomal steppe ancestry is similar to our autosomal ancestry estimate, and that hence, steppe male and female contributions are similar. We conduct simulations of ancient and modern data under a range of conditions. We conclude that our inference of male-biased Pontic-Caspian steppe migration, seen using ADMIXTURE, STRUCTURE, mechanistic simulations, and X/autosomal FST, is robust. Our analysis further illuminates the impact of small haploid reference samples on ADMIXTURE; we look forward to refining sex-specific migration estimates as larger, higher-coverage ancient samples become available.

Goldberg et al., Reply To Lazaridis And Reich: Robust Model-Based Inference Of Male-Biased Admixture During Bronze Age Migration From The Pontic-Caspian Steppe, bioRxiv, Posted April 3, 2017, doi: https://doi.org/10.1101/122218

Epic fail

This is the somewhat dubious conclusion from a new paper by Balanovsky et al. at Human Genetics dealing with, amongst other things, the Y-chromosomes of the Early Bronze Age Yamnaya people:

The currently available dataset does not contradict the hypothesis that R-GG400 marks a link between the East European steppe dwellers and West Asians, though the route and even direction of this migration is disputable. It does, however, demonstrate that present-day West European R1b chromosomes do not originate from the Yamnaya populations analyzed in (Haak et al. 2015; Mathieson et al. 2015) and raises the question of their origin. A Bronze Age origin is more likely than a Neolithic one (Balaresque et al. 2010), but further ancient DNA studies may be necessary to identify this source.

More to the point, the authors are trying to argue the following two rather far-fetched and tenuous positions:

- R1b-GG400, the most common Y-haplogroup in Yamnaya samples sequenced to date, moved into Eastern Europe from West Asia, and therefore the Indo-European homeland was in West Asia

- there was no massive Kurgan expansion deep into Europe from the Pontic-Caspian Steppe, because the most common type of R1b in much of Europe is R1b-L51 and not R1b-GG400.

What they're ignoring is that a wide range of European Upper Paleolithic and Mesolithic foragers, mostly from Eastern Europe, belong to R1b, including R1b-P297, the ancestral lineage to both R1b-GG400 and R1b-L51 (see here and here). On the other hand, not a single West Asian forager or even Neolithic farmer as yet belongs to R1b (see here).

Hence, even though it's still possible that R1b-GG400 moved into Eastern Europe from West Asia, it's no longer a parsimonious or convincing theory because it's contradicted by direct evidence from currently available ancient DNA.

The authors are also ignoring very solid evidence from genome-wide data that Yamnaya, or closely related populations from the Pontic-Caspian Steppe, contributed in a big way to the ethnogenesis of modern-day Europeans. Considering that R1b-L51 is a sister clade of R1b-GG400, it's only logical to think that it could have been one of the main Y-chromosome haplogroups associated with this event.

The paper has some nice data and maps, but it's an epic fail as a whole, because it's basically an exercise in confirmation bias.

Citation...

Balanovsky, O., Chukhryaeva, M., Zaporozhchenko, V. et al., Genetic differentiation between upland and lowland populations shapes the Y-chromosomal landscape of West Asia, Hum Genet (2017). doi:10.1007/s00439-017-1770-2

Eastern Scythians = Steppe_MLBA + East Eurasians

OK, I said I wasn't going to make any bold statements in regards to this issue until we see more ancient genomes from Central Asia, but I'm pretty sure now that the steppe ancestry in the eastern Scythians from Unterländer et al. is mostly of the Steppe Middle Late Bronze Age (Steppe_MLBA) kind, rather than the Steppe Early Middle Bronze Age (Steppe_EMBA) kind.

For background info, refer to the discussion in the comments here. Now, check out the graph below (based on the datasheet here). I see four things when I look at this model:

- Steppe_MLBA and Steppe_EMBA are different because the former show excess Central European Middle Neolithic (Central_MN) affinity, and thus cluster at the top of the graph and above the line of best fit, while the latter show excess Caucasus Hunter-Gatherer (Caucasus_HG) affinity, and so cluster at the top of the graph but below the line of best fit

- Indo-Aryan-speaking South Asians fall below the line of best fit, which suggests that they don't have much, if any, Central_MN ancestry, so they're probably largely of Steppe_EMBA origin (though their Iran Neolithic-related farmer ancestry might be skewing things to some extent here, because it's more closely related to Caucasus_HG than to Central_MN)

- Both the ancient and most modern-day Eastern Iranian-speakers (Sarmatians and Pamir Tajiks, respectively) more or less hug the line of best fit, suggesting that they're a mixture of Steppe_MLBA and Steppe_EMBA

- all of the Scythians fall above the line of best fit, suggesting that their steppe ancestry largely derives from Steppe_MLBA.

As per point 2, it's possible that the outcomes for the South and also Central Asians are skewed by their Iran Neolithic-related farmer ancestry, but this shouldn't be much of an issue for the eastern Scythians, and if it is, then in fact their Central_MN/Steppe_MLBA affinity is being underestimated here.

Moreover, word around the campfire is that the R1a-Z93 in the eastern Scythian bam files is of the same type as in the Sintashta samples (Z2124+). Not 100% sure if that's true, but it might well be, because it lines up very nicely with the above graph.

Citation...

Unterländer et al., Ancestry and demography and descendants of Iron Age nomads of the Eurasian Steppe, Nature Communications 8, Article number: 14615 (2017), doi:10.1038/ncomms14615

North Pontic Steppe Scythians: heirs of the Srubnaya people

Open access at Scientific Reports. Emphasis is mine:

Abstract: Scythians were nomadic and semi-nomadic people that ruled the Eurasian steppe during much of the first millennium BCE. While having been extensively studied by archaeology, very little is known about their genetic identity. To fill this gap, we analyzed ancient mitochondrial DNA (mtDNA) from Scythians of the North Pontic Region (NPR) and successfully retrieved 19 whole mtDNA genomes. We have identified three potential mtDNA lineage ancestries of the NPR Scythians tracing back to hunter-gatherer and nomadic populations of east and west Eurasia as well as the Neolithic farming expansion into Europe. One third of all mt lineages in our dataset belonged to subdivisions of mt haplogroup U5. A comparison of NPR Scythian mtDNA linages with other contemporaneous Scythian groups, the Saka and the Pazyryks, reveals a common mtDNA package comprised of haplogroups H/H5, U5a, A, D/D4, and F1/F2. Of these, west Eurasian lineages show a downward cline in the west-east direction while east Eurasian haplogroups display the opposite trajectory. An overall similarity in mtDNA lineages of the NPR Scythians was found with the late Bronze Age Srubnaya population of the Northern Black Sea region which supports the archaeological hypothesis suggesting Srubnaya people as ancestors of the NPR Scythians.

...

Mitochondrial lineages in the NPR Scythians analyzed in this study appear to consist of a mixture of west and east Eurasian haplogroups. West Eurasian lineages were represented by subdivisions of haplogroup U5 (U5a2a1, U5a1a1, U5a1a2b, U5a2b, U5a1b, U5b2a1a2, six individuals total, 31.6%), H (H and H5b, three individuals total, 15.8%), J (J1c2 and J2b1a6, two individuals, 10.5%), as well as haplogroups N1b1a, W3a and T2b (one individual each, 5.3% each specimen). East Eurasian mt lineages were represented by haplogroups A, D4j2, F1b, M10a1a1a, and H8c (represented by a single individual), in total, comprising 26.3% of our sample set.

Juras, A. et al. Diverse origin of mitochondrial lineages in Iron Age Black Sea Scythians. Sci. Rep. 7, 43950; doi: 10.1038/srep43950 (2017).

See also...

Cimmerians, Scythians and Sarmatians came from...

Genetic origins and legacy of the Scythians and Sarmatians

Neolithic Europe: it's complicated (Lipson et al. 2017 preprint)

The dam is breaking. Just in at bioRxiv:

Abstract: Ancient DNA studies have established that European Neolithic populations were descended from Anatolian migrants who received a limited amount of admixture from resident hunter-gatherers. Many open questions remain, however, about the spatial and temporal dynamics of population interactions and admixture during the Neolithic period. Using the highest-resolution genome-wide ancient DNA data set assembled to date---a total of 177 samples, 127 newly reported here, from the Neolithic and Chalcolithic of Hungary (6000-2900 BCE, n = 98), Germany (5500-3000 BCE, n = 42), and Spain (5500-2200 BCE, n = 37)---we investigate the population dynamics of Neolithization across Europe. We find that genetic diversity was shaped predominantly by local processes, with varied sources and proportions of hunter-gatherer ancestry among the three regions and through time. Admixture between groups with different ancestry profiles was pervasive and resulted in observable population transformation across almost all cultural transitions. Our results shed new light on the ways that gene flow reshaped European populations throughout the Neolithic period and demonstrate the potential of time-series-based sampling and modeling approaches to elucidate multiple dimensions of historical population interactions.

Lipson et al., Parallel ancient genomic transects reveal complex population history of early European farmers, bioRxiv, Posted March 6, 2017, doi: https://doi.org/10.1101/114488

Update 08/03/2017: In fact, there's nothing overly complicated in this manuscript. The table below says it all: Neolithic farmers across space and time in most of Europe were very closely related, and only differed in their levels of Western Hunter-Gatherer (HG) admixture. Admittedly, things would look a lot simpler if not for that somewhat unexpected R, R1 and R1b1 in Middle Neolithic Germany, but this doesn't appear to be a game changer, and is not flagged as such in the preprint.