Several years ago I read a book, The Origins of the Irish, by the famed archaeologist J. P. Mallory. Unfortunately, I remember very little of this work, and recall thinking that it was published just a bit too early, as archaeogenetics was clearly going to revolutionize our understanding of the prehistory of Northern Europe, though no clear results were on hand at that moment. In contrast, I recall much more clearly the novels of Irish historical fiction author Morgan Llwelyn, which I read over twenty years ago, Red Branch, a retelling of the legend of Cú Chulainn, and Finn Mac Cool, tales of a semi-legendary hero. Cú Chulainn is a mythical character, resembling Indo-European archetypes of awesome warriors who were inevitably arcing toward a tragic end. I term Fionn mac Cumhaill semi-legendary because his notional descendants intersect with the life of Niall of the Nine Hostages, who most presume to have been a real figure, though cloaked in legend.

The lives of Cú Chulainn and Fionn mac Cumhaill exhibit many dissimilarities despite the fact that both suffer tragic fates, Cú Chulainn in a violent death, and Fionn mac Cumhaill in some infamy. Cú Chulainn is a much more fantastic figure, who seems to have been born of a god and a daughter of the Gael aristocracy. Llwelyn, in keeping with the majority, but not exclusive, tradition, depicts him as physically atypical for a Bronze Age Gael warrior, small, beardless, and very dark haired. In battle though he transforms into a monster. He is a Superman for his age. In contrast Fionn mac Cumhaill is fair haired, and scion of a people conquered by the Gaels, the Fir Bolg. His rise to power occurred as much through his wiles in ascending the ranks of the fianna militia, as much as his martial skills, and despite his pedigree rather than because of it. Fionn mac Cumhaill is perhaps the Batman of ancient Ireland, a dark hero despite exterior appearance.

This rich corpus of myths makes the Irish distinct from the English, as observed by Norman Davies in The Isles. Ireland did not need a J. R. R. Tolkien to create its own epic cycle, it always had one. Not because of the foresight of one man, such as Snorri Sturluson, but the peculiar organic and gradual transformation of Ireland into a Christian nation, where local elites and sub-elites were organically co-opted into the new religion, which lacked the clear patina of Romanitas it took on elsewhere. The later cycles in which the lives of Fionn mac Cumhaill and Cú Chulainn were situated draw upon the world formed by the events of the Lebor Gabála Érenn, the Book of Invasions. Assembled during the medieval period, like Beowulf the Book of Invasions interlaces a world before Christianity and Roman history with a clear understanding of its place within a Christian and Classical historiography. As suggested in Wikipedia one motivation for compiling and creating the Book of Invasions was almost certainly to give the Irish the venerable history which peoples such as the Greeks and Hebrews had.

But these sorts of constructions aren’t created out of whole cloth. Rather, they bring together extant folklore and legend and attempt to create a coherent whole. To create his legendarium Tolkien poured into his world dollops of much of the lore of the European North. Even the geography of Beleriand recapitulates Northwestern Europe. And oral societies can preserve much detail across thousands of years. Doug Jones points out that local Indians in the Pacific Northwest have a cultural memory of the explosion of Mt. Mazama 8,000 years ago, which led to the creation of Crater Lake. Though we need not take the Book of Invasions, and the legends of pre-Christian Ireland literally, nor should we dismiss them as fiction without any historical content. The problem is that we need other avenues of exploring prehistory besides archaeology and myth.

Genetics provides that. Today an open access paper in PNAS dropped, Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome, which makes much concrete about the settlement of Ireland before history. If you read Massive migration from the steppe was a source for Indo-European languages in Europe and Population genomics of Bronze Age Eurasia ,the general results will be unsurprising, and are illustrated above in the PCA. Here’s the abstract:

Modern Europe has been shaped by two episodes in prehistory, the advent of agriculture and later metallurgy. These innovations brought not only massive cultural change but also, in certain parts of the continent, a change in genetic structure. The manner in which these transitions affected the islands of Ireland and Britain on the northwestern edge of the continent remains the subject of debate. The first ancient whole genomes from Ireland, including two at high coverage, demonstrate that large-scale genetic shifts accompanied both transitions. We also observe a strong signal of continuity between modern day Irish populations and the Bronze Age individuals, one of whom is a carrier for the C282Y hemochromatosis mutation, which has its highest frequencies in Ireland today.

The paper is open access. You should read it. And the supplements.

Broadly speaking Ireland fits the template for much of Northern Europe. First there were hunter-gatherers. The Mesolithic people were almost certainly part of the same group which expanded rapidly out of refuges along Europe’s southern fringe during the Pleistocene. Hunter-gatherer genomes tend to exhibit indications of low population size, and are quite homogeneous.

Second, there were the Neolithic farmers, who arrived from Anatolia. The modern population which is the best “fit” for this group today are the Sardinians. In Central Europe they began as the LBK, while in southwestern Europe they were the Cardial culture. Like the hunter-gatherers this set of cultures, radiating from a common source in western Anatolia, were genetically homogeneous, with little inter-group divergence. But, unlike the hunter-gatherers their population sizes were large. To varying degrees in various regions and times these people absorbed elements of local hunter-gatherer substrate. Their genetic distance from the European hunter-gatherers was very great, initially settlements in close proximity were as distant as modern Chinese and Northern Europeans in terms of variation. Additionally, they were physically distinct externally. The hunter-gatherers were by and large carriers of alleles which today are strongly correlated with very dark-skinned people, with the exception of mutations around the locus associated with variation in eye color in Europeans. Inexplicably the hunter-gatherers may have had pale eyes set against very dark faces. The farmers had dark eyes, but their skin was certainly much lighter.

Finally you have the third group, which arrives in Northern Europe during the Copper Age with the Corded Ware culture, also known as the “Battle Axe” culture, between 4,500 and 5,000 years ago. There they seem to overwhelm the Neolithic farmer groups, which had overwhelmed the hunter-gatherers earlier. Genetically the Corded Ware were a compound of three groups, one with with deep affinities to the European hunter-gatherers, another with peoples from the Caucasus, and finally lastly a genetic imprint from ancient Siberians. By the time this group began expanding toward peninsular and maritime Europe it has certainly absorbed local genetic substrate. In Ireland the Neolithic culture climaxed in the form of a Megalith building complex of cultures which seemed to be strung out along the Atlantic fringe of Europe. This ceased with the arrival of the Bell Beaker culture around ~4,500 years ago.

Two of the genomes are reasonable coverage, 10x. This might not be “medical grade,” but for population genomics this is pretty good (though I notice they didn’t run PSMC, which I think often requires more coverage). One individual is a female from a farmer culture who died ~5,000 years ago, and the other a male who died around ~4,000 years ago. The PCA above makes it clear that the female farmer is placed very near other early European Farmers (EEF), and the male (along with lower coverage confederates of similar provenance) smack in the middle of Bronze Age Northern Europeans. The admixture plot above confirms these findings.

But there are some wrinkles. PCA, Admixture, and f and D-statistics indicate clearly that the Irish Neolithic female had more hunter-gatherer ancestry than earlier LBK samples. Second, the Irish Bronze Age males had ancestry related to early European framers. At one point they give an estimate of ~40 percent hunter-gatherer ancestry for the Neolithic female. To them this establishes that the arrival of farming to Ireland was a matter of demographics, not cultural diffusion. This aligns with what we’ve seen elsewhere. The transition between the hunter-gather to farmer seems to have been accompanied by a significant demographic rupture all across Europe. As one might have inferred from earlier work, the phylogenomic character of the Irish was roughly established during the Bronze Age.

One of the primary issues with trying to make more precise analyses seems to be that the three root populations which contributed to the ancestry of modern Europeans were genetically rather homogeneous within themselves. That is, there was structure among European hunter-gatherers, but that which was not due to admixture (e.g., the Eastern European hunter-gatherers clearly mixed with a North Eurasian group) was subtle, probably due to rapid expansion from a small founder group after the Ice Age. The two other components had larger effective populations, but they too underwent rapid expansion, almost isotropically in some cases (e.g., along the North European plain), so there was little time to accumulate internal structure not due to admixture with local substrate.

But some inferences can be made with various techniques, the details for which you should read the supplements. The Neolithic female seems to be descended from Cardial, and not LBK, early European farmers. That is, the Irish Neolithic is connected to the Atlantic littoral, in keeping with Barry Cunliffe’s thesis in Facing the Ocean. Second, the excess hunter-gatherer ancestry in the Neolithic female exhibits greater affinities with the Loschbour hunter-gatherer from Luxembourg than hunter-gatherers from Central or Eastern Europe. T his indicates that as with the the situation in Spain there was local admixture with hunter-gatherers over time. In Mexico indigenous population structure persists in mixed regional mestizo groups. The same is likely true then in Europe if the above results hold (in the supplements you see a fair amount of evidence that Loschbour-like populations contributed to the ancestry of contemporary Western Europeans more than Eastern Europeans who may have more aggregate hunter-gatherer ancestry).

Naturally this leads one to wonder if the early European farmer ancestry in the Bronze Age Irish samples was from the same group as that of the Neolithic farmer. The surprise is that there isn’t any strong evidence of admixture! Rather, there are better candidates for donor populations on the European continent. The most parsimonious explanation then is that the Bell Beakers mixed with early European farmers, and then rolled over the descendants of the Megalith builders in Ireland. But confidence in this sort of conclusion is weak, as the number of populations is finite, and one should be cautious about making too many inferences from a few samples (though modern Irish are actually a decent proxy for the Bronze Age Irish). The broader point here is again that though there are three broad populations coming together in any given target group, we don’t have a good sampling of all the constituent populations of the three source populations, nor a good grip on the internal substructure across these groups, in part because the structure itself was minimal to begin with due to recent demographic expansion.

Whatever the details may be, the fact that dramatically different peoples were interacting during Irish prehistory should make us reconsider the veracity (or our dismissal) of legends pieced together from folklore and oral history. The Neolithic Irish female likely had a complexion similar to modern Southern Europeans (she was homozygous derived on both SLC24A5 and SLC45A2, so she was likely brunette white, rather than olive or brownish). But she and her descendants were possibly notable darker and physically different in mien from the Bell Beaker people, who were well on their way to becoming truly “fair and delightsome.” And yet it seems plausible that deep into the Neolithic period there were relic hunter-gatherers persisting in out of the way locales, inappropriate for agriculture. They may have looked very different indeed. It is easier to dehumanize when the Other looks different by their nature.

The Greeks in the centuries after the fall of the great kingdoms of their Bronze Age Mycenaean forebears referred to the constructions of that period as cyclopean, as if only creatures of myth could have wrought such architecture. And yet the Greeks knew that the Mycenaeans were their ancestors, and the two groups shared a common language and broader culture! Oral history preserves memory; Troy was real, and it was part of the fringe of the Greek world. But it also distorts and confuses. The men of yore become legends, giants, monsters. What would the Bell Beakers have thought when they arrived to an Ireland where the civilization of the Megalith builders was collapsing, both due to exogenous shocks (the Bell Beakers!) and endogenous forces. In subsequent centuries perhaps the fairy folk had withdrawn to their own world, leaving their coarse but imposing constructions as a testament to their powers in the days of old, as they faded into mythology and legend. And it may be that Cú Chulainn, the son of the god Lugh, who was a Tuatha de Danann, is a recollection of the emergence to maturity of a man who fused the blood of the old people with the new, and whose dark features bore testament to a race whose legacy was fading in the land?

Of course that is all speculation, but it is no longer unfounded. The book of Europe and ancient DNA is coming to a close in regards to outlines of the tapestry. We are in the phase of filling in details, and scholars need to truly become interdisciplinary, and marry what genes are telling us about demographics, with linguistics, archaeology, and folklore. The synthesis may be the closest to a time machine we get.