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Deciphering Scotland's Genetic History

Callanish Stones, Isle of Lewis, built by Neolithic farmers, one of the contributors to Scottish genetics

The development of genetic studies has brought on our understanding of human movements in history and prehistory forward by leaps and bounds, as well as that of the relative closeness and distance between different groups of people. While there are still many missing links and questions which remain unanswered, we know enough by this point to be able to tell which modern-day and historical groups of people are descended from whom. We have abundant evidence for Britain in particular, so I am proud to present a more-or-less complete summary of Scotland's genetic history. While such a subject may be intimidating to those unfamiliar with it, I will try my best to keep it understandable and engaging, as there is much to be gained from discovering what genetic studies have to tell us.

One of the benefits of looking at such subjects is because, sadly, national origin myths have often been constructed to suit social or political narratives (which may not even be known to us any more). For example, the Scots have always been held in historical texts (such as the Declaration of Arbroath) to have originated in Scythia (nowadays the southern parts of Russia and Ukraine) and to have come to Ireland via Iberia (before settling in Scotland in post-Roman times). We know based on the genetic studies that the first part of that story is true, but the idea that they came through Iberia is not (the details of which I will explain below). Therefore, the study of ancient DNA (aDNA), or 'archaeogenetics', can help us cut through distortions that have been added to a people's national history using purely scientific means.

The Declaration of Arbroath, in which the Scots argued their unique ethnic origin in Scythia, their journey through the Mediterranean to Spain, then to Ireland and their present home, precluded them being ruled by England

While there are many ways to interpret aDNA, one of the most intriguing and informative are 'haplogroups', which are genetic markers carried by people which trace direct paternal or maternal descent. The former are derived from the Y-chromosomes of men (Y-DNA) and so are only carried by men, while the latter are drawn from mitochondrial DNA (mtDNA) and are carried by everyone. It is on haplogroups specifically that I want to focus here, as they give us the best indications pertaining to direct descent, which is important if you want to study the origins of populations ('autosomal admixture', that is, tracking the relative closeness of population groups, is not as relevant, but still helps us in working out the extent to which populations were replaced by others and will be referred to at points).

Our story begins following the Ice Age, when Britain was colonized by hunter-gatherers (part of the genetic group known as 'Western Hunter-Gatherers' or 'WHGs'). While we now have evidence that Scotland was inhabited during the Palaeolithic, we only have genetic samples from Scotland in the period after the Ice Age. So far, the only Mesolithic sample we have from Scotland is from Cnoc Coig, Isle of Oronsay (next to the Isle of Colonsay), of a woman who carried mtDNA haplogroup V, which is nowadays most common among the Sami of Northern Scandinavia and Russia, followed by the Cantabrians of Northern Spain1. However, most other WHGs typically carried mtDNA haplogroup U, such as other examples from Britain like Cheddar Man.

The most recent reconstruction of Cheddar Man from Somerset, his eye, skin and hair color is based on the presence or absence of genetic markers determining these traits

When it comes to Y-DNA, none of the haplogroups found among hunter-gatherers from England survive today, but a specific related subclade (branch) of Cheddar Man's haplogroup is known as 'I2-M284', which, while it has not yet been found among Mesolithic Britons, is only ever found in Britain from archaeological samples later than the Mesolithic and overwhelmingly in Britain in modern times; this suggests that I2-M284 is indigenous to Britain. Fascinatingly, some of the highest rates of I2-M284 in the world occur in Scotland2. This means that it is likely about 5% of men in Argyll and the Borders (perhaps less in the rest of Scotland) are the direct descendants of her earliest inhabitants3.

I must state at this point that, unfortunately, this article will disproportionally focus on the male lineages, as mtDNA haplogroups are much more dispersed among many population groups and are much more difficult to track. For instance, any given mtDNA haplogroup may be found in two very different places, so it would then be difficult to tell which group it was brought with. In contrast, Y-DNA haplogroups tend to appear in clusters, attesting to the settlement of groups of closely related men, in contrast to women who typically came from a wider variety of lineages. This seems to indicate different patterns of migration between men and women, but for now we must be content mostly with what we can tell from the Y-DNA.

However, one instance in which the information from mtDNA is very clear is that the maternal lineages of the WHGs in Britain were replaced by those of incoming farmers in the Neolithic ('Early European Farmers' or 'EEFs'), whose ultimate origins lay in Anatolia, now Turkey. Interestingly, most of the British EEFs carried haplogroup I2-M284 (an all so far found carried I2), which suggests that the EEF settlement was primarily driven by women and entailed bringing local hunter-gatherer men into their communities (the EEFs carried such mtDNA haplogroups as H, HV0, J, K, T, W and X). The farmers then began to cut down the forests, which the hunter-gatherers had relied upon for their resources, to create arable land for their crops. They were responsible for the great megalithic monuments such as Callanish on Lewis and Maes Howe on Orkney.

Maes Howe, Orkney, a Neolithic chambered cairn

Unfortunately for the farmers on mainland Britain, they appear to have outstripped their resources and their population crashed. A unique culture developed on Orkney which suggests the beginning of hierarchy among British EEFs, which subsequently spread across the east coast of Britain and even as far as Southern England. This potential colonization is characterized by the great 'henge' monuments and the presence of a specific pottery style known as 'Grooved Ware'. However, the stage was set for the most impactful migration, one from whom the majority of Scotsmen today are descended from: that of the Western Steppe Herders ('WSHs'), who introduced the Bronze Age to Britain4.

The WSHs were mainly descended from a group known as 'Eastern Hunter-Gatherers' ('EHGs'), who lived in what is now Western Russia and Ukraine, who picked up the practice of herding animals from their neighbors in the Caucasus (and some of their women too, judging by some of the mtDNA haplogroups and admixture of the WSHs which came from the Caucasus). Maternally-speaking, the EHGs were very similar to the WHGs, also mostly carrying haplogroup U. However, their Y-DNA was very different: most of them carried haplogroup R1. The R1b subclade is most relevant for our story, because not only was it most likely the original WSH haplogroup, but it it is now the most common haplogroup in Western Europe, with 72.5% of Scotsmen carrying it5.

In particular, one culture developed on the steppe that proved crucial to the proliferation of the WSHs, known as 'Yamnaya'. They learned the art of bronzeworking, once again from their Caucasian neighbors, and dominated the steppe. Some folk from the Yamanya culture mixed with EHGs further north (who more typically carried haplogroup R1a, now most common in Eastern Europe and parts of Asia), giving rise to the Corded Ware culture, which began to spread westward into what is now Germany. However, one specific branch of R1b known as 'P312' split from Corded Ware and adopted a type of pottery originating in Iberia, which is known as 'Bell Beaker'. It is specifically the L21 branch of R1b-P312 that is responsible for colonizing the British Isles, which it seems to have done from the Netherlands, bringing with it Bell Beaker pottery and bronze.

The Yamnaya and Corded Ware cultures, R1b (and some R1a) followed the arrow pointing west, while the north-west and eastward expansions represent movements by R1a tribes

L21 is still the most common subclade of R1b in Scotland, Ireland, Wales and Brittany (all historically Celtic-speaking countries), but is nowadays less common in England, where R1b-U106 is more often found (while some has been found in Bronze Age, Iron Age and Roman Britain, this suggests that not all of it arrived in Britain with the Anglo-Saxons and Danes, though most of it likely did, as it was rare in earlier time periods). While the Bronze Age and Iron Age saw migration to other parts of Britain, Scotland largely remained the realm of the descendants of the Beaker folk