I've just been reading these two books, which tackle a fascinating subject: the genetic origins of the peoples of the British Isles.
Written by English authors—Stephen Oppenheimer and Bryan Sykes—both books were published in 2006. Curiously, each of the two authors gives the impression that he ignores the work of the other… even though they are both associated with the University of Oxford. They use both maternal (mitochondrial DNA) and paternal (Y-chromosome) data to reach their conclusions, which are rather similar. Basically, the people of Great Britain (England, Scotland and Wales) and Ireland are the descendants of settlers from the Iberian Peninsula (today's Spain and Portugal) who migrated up to the British Isles at the end of the Ice Age, some 15 millennia ago. In other words, our most ancient ancestors were the indigenous Cro-Magnons, rather than relatively recent colonists from the east. Among other things, this means that our indigenous European ancestors evolved spontaneously from being hunters and food-gatherers into the state of graziers and farmers. They were not simply replaced by eastern invaders who brought this know-how with them. As for legendary cultural phenomena such as the Celticism of the Gaelic-speaking lands, and the alleged Anglo-Saxon roots of the English, these must be thought of, genetically, as relatively-recent minor modifications, imported into the British Isles from the European continent, and limited largely to language.
I regret that both authors have resorted to nicknames for the various mtDNA and Y-chromosome haplogroups at the base of their vast research. For example, my personal DNA testing has placed me in a precise paternal haplogroup designated as R1b1b2a1b5. For Oppenheimer, on the other hand, I'm a member of the Ruisko tribe, which Sykes prefers to label the Oisin tribe. For serious adepts of DNA testing, the official haplogroup terminology is both necessary and sufficient, and the silly nicknames introduced by Oppenheimer and Sykes serve no useful purpose.
The existence of interesting in-depth studies such as those of Oppenheimer and Sykes evokes a common criticism that is often raised by people who are wary of the validity of all kinds of genealogical research, be it strictly personal (as when I explain with pride that my Skyvington patriarch in England came over with William the Conqueror, or that I've established another ancestral line running back up to this same Norman invader) or applied to the peoples of vast regions such as the British Isles. To get the gist of this criticism, look at the following pedigree chart (so-called because all the T-shaped signs can be imagined as goose tracks), in which my paternal ancestors are designated by blue dots, and my maternal ancestors by pink dots:
Now, it's all very well to determine the paternal tribe of the most ancient blue dot in our pedigree, and the maternal tribe of the earliest pink dot. But what about the respective tribes of the "infinite" (well, almost) horde of ancestors who aren't even apparent in my pedigree, let alone designated by any kind of dot? Surely, it's a grotesque over-simplification to allege that I belong to the Ruisko/Oisin tribe merely because of the blue dots in my pedigree. For example, let's imagine that one of my female ancestors happened to be a daughter of Boadicea, or that another had married Attila the Hun. Wouldn't perfectly-plausible family-history events such as these put a few gigantic flies in the ointment associated with the tidy little system of blue and pink dots? To put things in a more recent context, if I were suddenly to discover that one of my ancestors was a hitherto-unidentified offspring of Jack the Ripper, then my personal genetic package would owe no less to Jack and his clan than to any other distinguished tribe of Prehistory or Antiquity, and my inherited characteristics would certainly be more closely linked to those of the Ripper than to those of the Conqueror. Now, every serious researcher in genealogy should be perfectly aware of this common-sense situation. We describe the rare ancestral lines that we've been able to unearth, whereas we have nothing whatsoever to say (at least for the moment) about the vast network of untraced lines up into the mysterious past.
Getting back to the kind of research conducted by Oppenheimer and Sykes, isn't it a huge weakness to draw conclusions based merely upon the Y-chromosome and mtDNA profiles of present-day residents of the British Isles? If they had tested, say, a (fictive) London chap named George Skyvington and found that he (like me) was a descendant of the Ruisko/Oisin tribe, wouldn't they be drawing hasty and unsound conclusions by ignoring, as it were, that George might have had lots of other ancestors from quite remote tribes: Eskimos, American Red Indians, Chinese, Pacific Islanders, Tasmanian Aborigines, etc? Doesn't the absence of such perfectly-real ancestors cast a dark cloud of incompleteness or imperfection upon the global outcome of the research carried out by Oppenheimer and Sykes?
No, not at all. Don't forget that these researchers have been performing DNA tests upon large groups of people living in the British Isles. Consequently, if indeed our George Skyvington had ancestors belonging to "tribes" such as Eskimos, American Red Indians, etc, then it's possible that the existence of these ancestors will show up in the Y-chromosome and mtDNA data obtained from some of George's "genetic cousins"… about whom he probably knows nothing (and never will). Statistically, if the tested population is large enough (a criterion that can be determined mathematically), everything should come out in the wash, as it were. George's Eskimo and Red Indian ancestors won't be totally forgotten. They'll merely be associated with other tested individuals. And George won't even be tempted to complain about "his" ancestors being associated with total strangers, because he simply won't know that this has happened. Maybe George might even look at research results and say to himself: "My God, to think that, here in my native England, I'm living alongside descendants of Eskimos, American Red Indians, Chinese, Pacific Islanders, Tasmanian Aborigines, etc!"