by Bryan Sykes
I found, at the end, that out of the 91 Irish Ursulans, 68 had matching sequences elsewhere. Only 23 were unique to Ireland. In many cases I could find their immediate predecessors, in a genetic sense, within Ireland. So a fourth-generation Ursulan sequence, for example, would usually have a third-generation sequence nearby. In these cases I thought it was reasonable to regard that fourth mutation as having happened in Ireland. Counting up these home-grown mutations and factoring in the mutation rate as usual gave me a corrected date for the clan in Ireland of a little over 7,000 years–7,300 to be precise. This was much more reasonable than the 50,000 years which counted all the Ursulan mutations as if they had all happened in Ireland.
Genetic dates, like the 7,300 years for the Irish Ursulans, are not very accurate. They are estimates. We find this concept particularly difficult to grasp because we are accustomed to dates being very precise. The 7,300-year date for the arrival of the Irish Ursulans is an estimate. The date could vary a thousand years either way and still fall within the scope of the estimate. Forgetting the inaccuracies for the moment, what does this date mean? It is an estimate for the length of time it would have taken for all the Ursulan mutations to have accumulated within Ireland. If the ancestors of all 91 Irish Ursulans had arrived at the same time and their mDNA mutations had accumulated since then, the genetic estimate for their arrival would have been 7,300 years ago. Of course, it is very unlikely indeed that they all arrived at once. Some would have come more recently, but in that case, to achieve the average figure, others must have arrived more than 7,300 years ago to balance out the more recent arrivals.
I went through the same procedure with all the other Irish maternal clans, checking to see in each one how many looked as though they had mutated to their final form in Ireland and not elsewhere. From there I calculated the clan arrival times in the same way as I had for the Ursulans. All of them came out between 7,500 and 4,500 years ago. Ursula was still the oldest clan in Ireland and, in common with the rest of Europe, Jasmine was the youngest. It was Jasmine’s clan that Martin Richards and I had linked to the arrival of Neolithic farmers in Europe from the Middle East. The others clustered around the 5,000–6,000-year average. Even bearing in mind the approximate nature of these genetic dates for the settlement of Ireland by the various maternal clans, they are all way before the time, around 200 BC, when the Iron Age Celts were supposed to have arrived. It was beginning to look as if the ancestors of today’s Irish had been there for a lot longer than anybody thought.
But within Ireland, when I looked at the maternal clans in the different provinces of Ulster, Leinster, Munster and Connacht, there was very little noticeable difference between any of them, though the numbers in each were too low to be sure of statistical significance.
If women had been in Ireland for a very long time, what about the men? Just as mitochondrial DNA traces our maternal ancestry, so the Y-chromosome follows paternal genealogies. Like mitochondrial DNA, Y-chromosomes also experience random mutations over the course of time. The precise nature of the mutations might be different between mDNA and Y-chromosomes, as we shall see, but the principles are the same. The accumulation of mutations along paternal genealogies over a very long time means that there are now tens of thousands of slightly different Y-chromosomes which can be distinguished by genetic tests. If two men have the same Y-chromosome fingerprint, then they have usually inherited it from a common patrilineal ancestor. That’s exactly the same principle as saying that if two people have the same mitochondrial DNA sequence they have inherited it from a common maternal ancestor. Although Y-chromosomes are quite different from mitochondrial DNA in the way they change genetically, that doesn’t matter so much when it comes to interpreting the signals they are bringing us from the past.
Just as each of us belongs to one of a small number of maternal clans, so men can be assigned to a paternal clan by the genetic characteristics of their Y-chromosome. From research done throughout the world over the past decade, Y-chromosomes can now be separated into twenty-one paternal clans, eight of which occur in Europe. Of these eight clans only five occur in the Isles to any appreciable extent. Following the tradition of the maternal clans, I have given them names. They are the clans of Oisin, Wodan, Sigurd, Eshu and Re. Like the maternal clans, each founded by a matriarch, the paternal clans must, by the same logical inevitability, also have been started by a single man–the clan father or patriarch. Every man within a clan is a direct paternal descendant of the clan father and has inherited the patriarch’s Y-chromosome, modified by mutations over the intervening millennia.
The different paternal clans are told apart by single DNA changes, just like the mutations in mitochondrial DNA. However, these Y-chromosome sequence changes occur far more slowly than they do in mDNA. There is usually only a single DNA sequence mutation between the Y-chromosomes of one clan and another, even though they have been separated for tens of thousands of years. Luckily for us, the Y-chromosome also experiences a second, much swifter, type of mutation that can split a paternal clan into hundreds, if not thousands of separate paternal lineages. These fast mutations happen, like all DNA changes, when cells divide and there is an error in the usually immaculate copying mechanism.
Along the Y-chromosome are patches of DNA sequence that, when looked at closely, consist of reiterated blocks of short sequences. Treating DNA sequences like a word, these are the genetic equivalent of a bad stammer. It is as if an otherwise smooth read-through just gets stuck. Take the four DNA letters TAGA, an outwardly unremarkable sequence. For some reason, TAGA tends to trip up the DNA copying mechanisms on parts of the Y-chromosome where it is repeated a number of times. Cells can handle a few repeats. The double reiteration TAGATAGA causes no difficulties. Even ten repeats, one after the other, is manageable. But after that the stammering begins. After twelve repeats cells find the blocks of TAGA very difficult to copy accurately and make mistakes much more often than they normally would with regular sequences. What they do wrong is to add an extra TAGA, or forget to copy one. So a Y-chromosome with, let’s say, fourteen TAGA repeats mutates into one with fifteen repeats. Because the cell has such trouble with copying this type of stammering sequence accurately, the rate at which these mutations occur is hundreds of times faster than the regular type of spelling-change mutation, where, for example, a C changes to a T. It is an even faster rate than mDNA, with its comparatively lax error-checking mechanisms.
There are dozens of places along the Y-chromosome where these tricky stammering segments are to be found and they can be used in combination to define tens of thousands of different Y-chromosomes. Because Y-chromosomes, alone among the nuclear chromosomes, are not shuffled at each generation, the combinations can persist for a very long time, changing only when another mutation occurs at one of them. In this respect, the Y-chromosomes can be interpreted just like the mDNA with first-, second- and third-generation mutations changing the Y-chromosome fingerprint of the ‘pure’ patriarch. And, just like mDNA, the number of mutations can be added up to get an idea, again only approximate, of time passing. In reality, because these mutations happen so quickly, in relative terms, it is hard to know what the clan patriarch’s Y-chromosome fingerprint actually was. But as we shall see, this is not really a problem when we look in detail at the Y-chromosome of Ireland.
In my mind’s eye, I collect up the maternal gene-coins from the imaginary map of Ireland, move them to one side and begin to distribute the paternal Y-chromosome equivalents in their place. As soon as I look at the Irish pile, one thing stands out. The vast majority of Irish Y-chromosomes are members of just one clan, the clan of Oisin. It is precisely because of its predominance in Ireland that I gave the clan this name. Oisin was the son of the hero of another of the Irish mythical cycles, Finn mac Cumhaill, sometimes transcribed as Finn mac Cool. Finn is the leader of the Fianna, a band of warriors chosen only after an appropriately gruelling selection process. His son Oisin, meaning Little Deer, is bewitched by Niav of the Golden Hair, the dau
ghter of the Underworld king who reigns over Tir na n’Og, the World of the Forever Young. Oisin goes to this other world to be with Niav and spends his life writing poetry and songs. Eventually he becomes homesick and is eager to visit his own world once more. Niav warns against this, but Oisin is adamant and sets out, though he promises to heed her warning not to set foot on Irish soil. He plans to avoid disobeying Niav’s instructions by riding everywhere on a horse and so not touching the soil. In an extreme version of Back to the Future, Oisin realizes when he returns to Ireland that 300 years have passed while he was relaxing in Tir na n’Og. The shock of this discovery makes him fall from his horse and, as soon as he touches the ground, he instantly ages 300 years and crumbles into dust.
The Y-chromosome might be decaying fast, and well on its way to sharing Oisin’s fate, but for the moment his clan’s Y-chromosome is doing extremely well in Ireland. Almost 80 per cent of Irish Y-chromosomes belong to the clan of Oisin. Within Ireland there was very little difference to be seen in the geographical distribution of the maternal clans in different parts of the island. However, with Y-chromosomes there certainly is. Dividing Ireland into the four ancient provinces, each roughly occupying a quadrant of the Irish rectangle, the differences between them are very striking indeed. In the south-east quadrant of Leinster, 73 per cent of Y-chromosomes are in the clan of Oisin. In Ulster, in the north-east, this rises to 81 per cent. The clan reaches an even higher frequency in the province of Munster, in the south-west, where 95 per cent of men are in the clan. However, in Connacht, occupying the north-west quadrant, the proportion of Y-chromosomes in the clan of Oisin reaches an astonishing 98 per cent. This was one of the first results from Dan Bradley’s genetic survey of Ireland, which he undertook in this instance with graduate student Emmeline Hill. But, rather than just leaving it at that, Dan took their analysis one stage further to look for an explanation. Recalling the twelfth-century Anglo-Norman invasion of Ireland, it occurred to them that one reason for the difference in Oisin Y-chromosome frequency between the provinces might have something to do with this invasion and the subsequent occupation. The invasion began in Leinster, in the south-east, and that was where the Oisin clan was in its lowest proportion.
The vehicle for testing this idea was to use surnames which, like Y-chromosomes, are also passed down the paternal line. There have been inherited surnames in Ireland for as long as anywhere in Europe. They were first adopted in about AD 950, a good 200 years earlier than in England. The Gaelic origin of many Irish surnames is evident from the prefix ‘Mc’ or ‘O’, meaning ‘son of’, as in McCarthy or O’Neill, but there are plenty more whose Gaelic origins required a little research. Fortunately, the enormous interest in genealogy over the last hundred years has led to the compilation of comprehensive surname dictionaries where the origin of almost any name can be found. Sure enough, when Y-chromosomes were compared to surname origins, Gaelic or Anglo-Norman, the correspondence was clear. Even in Leinster, the proportion of Oisin clan members was higher among the men with Gaelic names than among the men whose surname could be traced to Anglo-Norman origins. You will recall that, in his survey of blood groups, Professor Dawson explains the higher frequency of blood group A in Leinster by the Anglo-Norman invasion.
The comparison with the mitochondrial results is striking. All of the seven major maternal European clans, and most of the minor ones, were to be found in Ireland and there was not much difference in their proportions in the four provinces. Very obviously, in Ireland anyway, the version of history told by men and women was not the same. To explore this further, I want to look in more detail at the Irish Y-chromosomes, in particular the detail among the members of the clan of Oisin. A Y-chromosome fingerprint, or signature, consists of a set of ten numbers. Each of these is the number of stammering DNA repeats at the ten places on the Y-chromosome that we test. If there are 10 repeats at the first marker and 22 at the second one, the fingerprint starts off as 10–22. If there are 13 repeats at the third marker, the fingerprint continues as 10–22–13 and so on. When I am checking through 10 marker signatures from the DNA analyser, if there are Irish men among the batch it isn’t long before I find this particular signature: 11–24–13–13–12–14–12–12–10–16. It is very familiar indeed. This is the quintessential Oisin Y-chromosome and huge numbers of Irish men carry it. I am not the only person to have noticed this particular Y-chromosome combination. Dan Bradley certainly knows about it, and it has also been spotted by Jim Wilson, who worked for a time at University College London. Jim is a native of the Orkney Islands, just off the north coast of Scotland, and he had noticed this same combination among his fellow Orcadians. It also cropped up, interestingly, in surveys of Y-chromosomes among the Basques of north-eastern Spain and among the people of Galicia in the north-west of Spain. Its oceanic affinities led it to be christened, not Poseidon or Neptune, but the far more prosaic Atlantic Modal Haplotype, or AMH for short. I prefer to call it the ‘Atlantis’ chromosome. In the Isles it is by far the commonest Y-chromosome signature within the clan of Oisin, or any other for that matter.
Among the Oisin clan in Ireland, it certainly isn’t the only Y-chromosome fingerprint, but most of the others can be linked to it by one or two mutations. This gives us an opportunity to get an Irish date for the Oisin clan, rather as we did with the Ursulans and other maternal clans. The mutation rate of these Y-chromosome fingerprints is roughly one change per 1,500 years, much faster than the mDNA rate of one for every 20,000 years. By following exactly the same procedure for the Oisin clan as we did for the first Irish Ursulan calculation, we get a date of 4,200 years. This lies well within the time frame of human settlement in Ireland and, since it is still prey to the wide approximations of genetic dates, and thus quite close to the 5–6,000-year estimate for mDNA, it would be tempting to imagine we have solved the origins of the Irish.
However, we have done nothing of the sort, because we have overlooked the Martian factor. Remember that the original Irish Ursulan date was 50,000 years ago–older than Ursula herself and far too early to be a plausible date for the settlement of Ireland–assuming that all the mutations among Irish Ursulans had happened after the first ones reached Ireland. To get round this we had to decide which of the mutations happened on Irish soil, and which had already occurred before the clan reached Ireland. When we did this it made a huge difference to the date, bringing it forward to the much more plausible 7,300 years ago. Applying the same correction to the Irish Y-chromosome data brought the date forward to just 1,200 years in the past. This is far too recent to be plausible, even given the approximations involved. Something else must be going on. And it was, but it took me a while to realize the explanation. And it didn’t happen until I had done a lot more work. Not in Ireland, but in Scotland. Only then was I able to make sense of the strange behaviour of the Irish Y-chromosomes.
Nevertheless, we have made a good start. In Ireland, the maternal lineages are diverse and very old, while the Y-chromosomes are unexpectedly homogeneous, and at first glance look comparatively young. We have seen a difference between different regions of the island, a difference that may be an echo of the Anglo-Norman invasion of Ireland beginning in the twelfth century. We have seen some evidence of a genetic link between Ireland and Spain along the Atlantic fringe of Europe, which archaeologists are now beginning to realize was a much busier seaway than was once thought. What we don’t yet know is how the Irish results will fit with the rest of the Isles, and to begin to do that we shall travel across the shallow sea to Scotland.
10
SCOTLAND
It is barely 12 miles across the sea from Fair Head on the north-western tip of Ulster to the cliffs of the Mull of Kintyre, rising above the waves of the North Channel. Scotland is bounded on three sides by the sea: by the wild Atlantic to the west and north and by the temperamental North Sea beyond the eastern coastline. Across its historically fluctuating southern land boundary lies England, at different times enemy and friend, but never indifferent ne
ighbour. The western sea boundary is fringed with several large, inhabited islands and hundreds of small ones deprived of inhabitants. Off the north coast lie the Orkney Islands, and 60 miles further to the north-east and halfway to Norway are the Shetlands. The total land area, including the islands, is just over 30,400 square miles, only slightly smaller than Ireland. Mountains dominate the mainland, with the rugged Scottish Highlands reaching to over 1,300 metres. Ben Macdui (1,309 metres), highest of the Cairngorms in the north-east, and Ben Nevis (1,344 metres) in the west are the highest mountains in the whole of the Isles.
The mountains continue all the way to the northern coast of Scotland, especially on the west side, where millions of years of erosion, compounded by the gouging action of the glaciers, which covered the whole of Scotland in the last Ice Age, have left a dramatic landscape. In the far north-west, Old Red Sandstone peaks like Suilven and Stac Pollaidh stand isolated above featureless country of bog and lochan. In the extreme north, the mountains relent, leaving a fertile coastal strip where the thin, acidic soil of the Highlands is invigorated by calcium-rich limestones and sandstones.
