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Thread: A Genetic Compendium of an Island: Documenting Continuity and Change across Irish Human Prehistory

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    Default A Genetic Compendium of an Island: Documenting Continuity and Change across Irish Human Prehistory

    I'm presently reading this and will add as I go along. The paper can be retrieved from here. By Dr Lara Cassidy.

    http://www.tara.tcd.ie/handle/2262/82960

    Neolithic individuals were found to place overwhelmingly within haplogroup I2a (Electronic Data TableS5-7), one of the dominant lineages of the European Mesolithic and commonly observed in other western Neolithic populations (Haak et al. 2015; Mathieson et al. 2015; Olalde et al. 2017). As expected, Mesolithic samples show more basal lineages with respect to the Neolithic cohort, a significant number of whom placed within the subclade I2a2a1-M284, found almost exclusively in Britain today.
    A near complete turnover is then witnessed in the Chalcolithic and Early Bronze Age, with virtually all samples from this time onwards belonging to the R1b-L151 haplogroup, associated with the Atlantic Modal Haplotype. This lineage forms a downstream branch of R1b-M269, the most prevalent haplogroup in western Europe today (Myres et al. 2011). It was possible to place a further majority of samples (81.8%) into the subclade R1b-L21, a haplogroup whose distribution shows a steep and somewhat restricted peak in modern Ireland, where it accounts for almost half of male lineages (Myres et al. 2011). Only one Y chromosome examined fell outside R1b-M269 after the Neolithic period, belonging to an Early Bronze Age individual from the southwest, Killuragh1, who placed within I2a2a1-M284.
    Irish mesolithic samples are indistinguishable from other European HGs.

    However, a notable exception is the Palaeolithic sample from El Miron in Spain, belonging to the Magdalenian culture, who, within a majority “red” background, possesses a mosaic of components that dominate in diverse modern populations, such as Papuans, East Asians and Indians. This noisy signal is likely to represent deep pre-glacial population structure between Iberian refugia populations and those further east in Italy and the Balkans (Fu et al. 2016). The signature is also seen to a lesser extent in the earliest Mesolithic sample of the region, but disappears in later Spanish samples. Importantly, Irish Mesolithic individuals do not show any detectable level of this ancestry, displaying profiles more similar to Palaeolithic samples from Switzerland and Italy.
    Last edited by Grace O'Malley; 05-23-2020 at 11:24 AM.

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    Possible echoes of the Roman Empire here. Bedouin component present from Italy and the Balkans. Also present in France, Germany and was seen in Britain but absent by the Medieval period. Ireland bypassed as well as Scandinavia and also not seen in the Basque.

    By modern times (Fig. 1.2E), a fourth component of ancestry (beige), found at highest levels in Bedouin populations, has left an impact on European populations, particularly those of Italy and the Balkans. This is most likely an effect of the Mediterranean civilisations that dominated the regions for many centuries, culminating in the Roman empire (27 BC – 395 AD), which saw much of the continent subsumed into this growing hegemony. Indeed, this component penetrates the more isolated northern regions to some degree, including France and Germany. Despite its absence in Medieval individuals, the component is also seen in Britain, where it decreases in scale from Southern England to Scotland. Ireland is bypassed almost entirely, as in Scandinavia. Intriguingly, in Iberia this component is also close to absent in the linguistically divergent Basque region, in sharp contrast to neighbouring populations.

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    Irish Neolithic indistinguishable from Iberian. There is a dramatic eastward shift in the Bronze Age. The Bronze Age populations somewhat resemble present modern-day populations from the same region.

    By the Iron Age (Fig. 1.3E) Irish genetic diversity appears to have homogenised, forming a tight cluster indistinguishable from contemporary British individuals, and placing close to modern populations from both islands.

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    In terms of relationships to earlier hunter-gatherer groups, the Mesolithic Irish appear more similar to Italian and Swiss individuals from the Epigravettian and Azilian cultures, rather than the Iberian Magdalenian and later Mesolithic. This suggests the post-glacial colonisation of the island did not occur from a purely Iberian refugia, although these interpretations, based solely on PCA analysis, will be revisited in greater detail in Chapter Three. Importantly, no early Mesolithic samples from Ireland are available, and the possibility of demographic discontinuity within this period cannot be ruled out.
    Interesting about the Neolithic population and I find this somewhat fascinating. The HG ydna 12a completely replacing the farmer ydna. This is the paragraph. It brings up the possibility of drift but not sure that is the case? Anyway it is very interesting.

    Mitochondrial haplogroup frequencies mirror the autosomal patterns of population replacement with some indigenous input, showing a minority of Mesolithic U5 lineages observed among an abundance of west Asian haplogroups. However, in striking contrast, Y chromosomes show near complete continuity across the transition, with all but two male individuals belonging to the dominant Mesolithic lineage I2a. This may be indicative of unequal contribution by male and female hunter-gatherers to incoming farmer populations, though in a reverse of the usual trend witnessed across episodes of colonisation, that of female continuity and male replacement (Jobling & Tyler-Smith 2003). Alternatively the smaller effective population size and thus increased drift acting on the Y chromosome may be responsible for the differential patterns.
    Apparently there is a lack of British and continental northwestern Neolithic samples to compare to.

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    Like what was known previously the Chalcolithic and Early Bronze Age was what brought the biggest change. Ydna changed to R1b-L21 with Rathlin 1 showing inflated sharing to modern populations Irish, Scots and Welsh with somewhat lesser affinity to the English most likely due to Anglo-Saxon migrations. `

    Interestingly:

    Forthcoming research on the fine-scale population structure of modern Ireland, based on haplotypic analyses, also supports these conclusions. This demonstrates that, while some introgression of European and British haplotypes into Ireland is apparent at horizons of known historical migrations, it is more ancient Celtic population structure that remains the defining characteristic of the Irishpopulation (Byrne et al. submitted).
    However, it must be noted that substantial prehistoric migration to the island post-dating the Early Bronze Age from closely related populations of similar genetic makeup, particularly those of Celtic Britain or indeed historic Gaul, may not be detectable. Indeed, the presence of shared tribe names across the various regions in Ptolemy's Geography, hint at such a possibility. Substantial demographic upheavals in Britain and the continent, such as those linked to the spread of Latin and Germanic languages, may have worked to reduce signals of haplotypic and Y chromosomal continuity with Early Bronze Age Ireland, that could have otherwise extended the affinities of Rathlin1 across a much wider region of western Europe. Indeed, for the population of England, as noted above, this is demonstrably the case.

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    Regarding migration of Celts. Possibly from some closely related populations but obviously not answered here.

    The only exception may be mass migration from a closely related group, as noted above. Indeed, the most recent expansions of Goidelic from Ireland to Scotland and Brittonic from Cornwall to Brittany, both involving some population migration, are a testament to how regularly such phenomena could occur. Future contributions of ancient genomics to linguistic models will involve the demonstration or disqualification of such events across the Bronze and Iron Ages, a task which demands both denser regional sampling and deeper genome sequencing of ancient individuals.

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    Apparently R-M222 was found in Iron Age NW Ireland, although I guess that was expected.

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    Still getting to the Iron Age. Was reading about the HGs and then just skipped over a lot of it. (Not greatly interested). Taking a lot of breaks reading.

    Northeastern France (Calais-Picardy) provides the most popular candidate homeland for Ireland andBritain’s first farmers (Cunliffe 2013; Mallory 2013). Strong parallels are seen between the Neolithic of southeastern Britain and the continental Michelsberg and Chasséen cultures across the channel (Fig. 3.1C), which share similar round-bottom Carinated Bowl pottery, domesticated faunal assemblages and flint leaf-shaped arrowheads (Whittle 2007; Cunliffe 2013). Carinated Bowls are most abundant along the eastern seaboard of Britain, though they are ubiquitous across the Neolithic of both islands, as are the characteristic arrowheads. Another component of the Neolithic package in Britain and Ireland that has clear connections with northern continental traditions are the large rectangular timber houses that first appear a few generations after pottery and domesticates in southeast England (Sheridan 2013; Cummings 2017). In Ireland, this so-called ‘housing horizon’ begins no earlier than 3,720–3,680 cal BC (Whitehouse et al. 2014; McLaughlin et al. 2016), accompanied by the appearance of cereals. Together, such material culture has been grouped under the the blanket term ‘Carinated Bowl Neolithic’ (Sheridan 2010), and is proposed to have spread along the east coast of Britain, before penetrating into Scotland and crossing over to Northern Ireland, where it travelled southwards down the east and west coasts.
    Second strand of Neolithisation from Brittany.

    Importantly, later Iberian samples show increased haplotypic and allelic input from the Spanish EN, relative to Irish individuals. This, together with the clear lack of Spanish HG ancestry in the Irish Neolithic (though again potential outliers, such as MillinBay6 exist) argues against any large-scale direct contribution from Iberian populations to the island, via the Atlantic. From an archaeological perspective it is more likely that the Mediterranean-type ancestry within the Irish Neolithic diverged from Spanish groups at the Golfe du Lion, where it spread both inland via the Rhône and westwards toward the coast. Furthermore, admixture with LBK and derivative groups in the north most probably took place,
    suggested by the increased haplotype and allele sharing seen with LBK individuals for some Irish samples. The extent of such admixture cannot at present be estimated, but it may be partially responsible for the overall dilution of Cardial ancestry in Irish samples relative to Iberians.
    Last edited by Grace O'Malley; 05-23-2020 at 02:30 PM.

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    The demographic effects of historical and proto-historical migrations on the modern populations of Ireland and Britain have recently been explored using novel haplotypic methods (Leslie et al. 2015, Byrne et al. submitted), revealing the impact of both continental movements into the islands (Anglo-Saxons, Viking, Normans) and movements between the islands, which have have left particularly strong signatures in the east and north of Ireland, as well as in Scotland. Furthermore, Byrne et al. (submitted) have demonstrated that haplotypic clustering methods loosely separate the modern Irish population on the basis of the historical provinces of Ireland (Ulster in the north, Leinster in the east, Munster in the south and Connacht in the west), whose boundaries, typically incorporating geographical barriers such as the Shannon river, have existed in some form since the very beginning of Irish written history. These records also indicate a society which was feudal and dynastic in nature, with great emphasis put male line descent. Indeed, patronyms are still the most common surname type in Ireland, and emerged early in Medieval records. Warfare was common between kingdoms, of which cattle-raiding constituted a key part, given their value as a key economic and sustenance source (O’Connell et al. 2016). It is perhaps remarkable that the modern Irish population has some of the highest incidences of lactase persistence in the world (Gerbault et al. 2011), alongside other variants with possible selective advantages, including mutations involved in iron-retention (Distante et al. 2004) and skin pigmentation (Rajeevan et al. 2012).

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    "Byrne et al. (submitted)" - which study is that?

    Quote Originally Posted by Grace O'Malley View Post
    Irish Neolithic indistinguishable from Iberian.
    This is what I was telling long ago, that Irish (and British in general) Neolithic was more like Iberian Neolithic than like Italian Neolithic.

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