As every schoolboy used to know, the episodes of group migration into the British Isles were remarkably few between the Norman Conquest of 1066 and the beginning of modern mass immigration after 1945: the French Huguenot refugees, the modest flow of Ashkenazi Jews, and a few others. Nevertheless, in recent years the politically-correct elites on both sides of the Atlantic have begun to promote the improbable contention that Britain has always been a land of immigration.

Ironically, just as this has become an article of faith, genetic evidence has begun to pile up about how profoundly wrong it is. Not only did immigration after 1066 play a vanishingly small role in the makeup of the offshore islanders, but even the famous invasions of previous millennia—Normans, Vikings, Anglo-Saxons, and Romans—merely added a fairly minor overlay to the prehistoric gene pool.

Political control and even language varied in the British Isles over time. But the oldest occupants endured, adapted, and flourished. In the words of Oxford University geneticist Bryan Sykes in his new book Saxons, Vikings, and Celts: The Genetic Roots of Britain and Ireland [published in the United Kingdom under the title Blood of the Isles]:

"We are an ancient people …"

The family trees of the English, Scottish, Welsh, and Irish are overwhelmingly indigenous to the British Isles since far back into prehistoric times. The title of Sykes' first chapter, "Twelve Thousand Years of Solitude," summarizes this finding. The "average settlement dates" in the Isles for the ancestors of modern British and Irish people, he estimates, were around 8,000 years ago.

Historical population genetics is an extremely complicated science. It's not uncommon for well-known authorities, such as Sykes and his rival L.L. Cavalli-Sforza of Stanford, to differ. Bearing that in mind, Sykes' recreation of the genetic history of Britain and Ireland appears plausible.

Sykes' team obtained DNA samples from 10,000 individuals in the United Kingdom and Ireland and reviewed genetic records for 40,000 more. They looked at functionally trivial mutations in the Y-chromosome to group each man into clans based on patrilineal lines of descent (e.g., Abraham begat Isaac who begat Jacob who begat …). And they examined mitochondrial DNA to group individuals into matrilineal descent clans. (I reviewed in VDARE.com Sykes' 2001 book The Seven Daughters of Eve , which outlined the initial European-wide genealogical discoveries revealed by mitochondrial DNA. If you are interested in the understanding the technical aspects more, please see that article.)

From his database, Sykes concludes that the majority of the genes of the peoples of the British Isles are descended from the oldest of the modern inhabitants: Mesolithic hunter-gatherers, who began arriving 10,000 years ago from Continental Europe after the end of the last Ice Age, as soon as the islands became habitable again.

Global cooling had pushed modern humans out of northern Europe and down into refuges near the Mediterranean, remixing the early peoples of Europe. (This may be one reason that, as Cavalli-Sforza has noted, Europeans are the most physically homogenous of all the great continental races.)

From the South, big game hunters trekked north again as the ice melted, some getting all the way to Britain. Before the seas fully rose, Britain was connected to Europe by a land bridge, and the Thames was a tributary of the Rhine!

A smaller but still important genetic contribution later came from the Neolithic farmers, who had begun thousands of years before slowly spreading northwest from the Middle East's Fertile Crescent.

Both the hunter-gatherers, who had sought refuge from the ice in Mediterranean lands, and the farmers, who had emerged from the Fertile Crescent, appear to have followed the same two main routes to the British Isles. One was a western oceanic route from Iberia north, primarily settling in Ireland and western Britain. (I would speculate that the somewhat darker coloration of the Welsh reflects this sunnier origin.) The other main path was a central continental route up the great river valleys into northern Europe, and then west to eastern Britain.

In the British Isles, the hunter-gatherer-fishermen presumably stuck to the water's edge, while the farmers cleared the inland forest. This meant there were few incentives for a genocidal clash between them, allowing the genes of both to survive in large numbers. Over time, some of the hunter-gatherers must have learned to farm, permitting them to be fruitful and multiply. The two groups appear to have merged, a happier outcome than typically seen in more recent collisions between farmers and hunter-gatherers.

Sykes writes: "Overall, the genetic structure of the Isles is stubbornly Celtic." (Interestingly, this means that the Irish and the English are largely the same—and Sykes is unable to discern any difference at all between the Ulster Catholics and Protestants, or "Scotch-Irish", as they are known to American immigration history).

Sykes points, out, however, that the term "Celtic" is something of a misnomer:

"The 'Celts' of Ireland and the Western Isles are not, as far as I can see from the genetic evidence, related to the Celts who spread south and east to Italy, Greece and Turkey from the heartlands of Hallstadt and La Tene in the shadows of the Alps during the first millennium BC."

The British "Celts" have been in the British Isles long before the emergence of Central European Celts known to anthropology and the military history of the Roman Republic. These British "Celts" adopted the Celtic language, but otherwise their relationship with the continental Celts, if any, remains unknown.

Sykes guesses that the proliferation of La Tene-style handicrafts in Britain was not the result of mass immigration from Central Europe, as anthropologists have long presumed, but simply of British Isle goldsmiths learning to copy the latest style from the Continent. (Similarly, the recent mass-production in China of knick-knacks emblazoned with the Celtic Cross for Dublin tourist traps doesn't mean that Guangdong is suddenly filling up with Irishmen.)

Sykes observes:

"It seems to me that the constant tendency to interpret past events in terms of movements is completely the wrong assumption. Surely the correct starting point is to assume that our ancestors were sufficiently resourceful and skillful to pick up virtually any skill."

The half of modern British/Irish DNA that comes from female ancestors is especially native to the Isles.

Sykes points out that after the arrival of the agriculturalists in Britain:

"The genetic bedrock on the maternal side was in place. By about 6,000 years ago, the pattern was set for the rest of the history of the Isles and very little has disturbed it since."

The one region where there was subsequent large-scale female immigration was the northern islands of Shetland and Orkney. Some 30-40 percent of today's inhabitants trace their maternal ancestry to Viking women.

There was also a limited immigration during historic times of women into eastern and northern England, accounting for 10 percent of the maternal genes in the east and 5 percent in the north.

Whether these women were Saxons, Vikings, or Normans is hard to say because they are all so similar genetically. The Angles, Saxons, and Jutes, who invaded England after the Roman evacuation in 410 A.D., were from southern Scandinavia and northern Germany. The Vikings, who sacked the monastery of Lindisfarne as early as 793, were centered merely a little farther north and west. The Normans were simply Vikings who had conquered Normandy and adopted the French language.

Sykes' guessed, based on sketchy historical evidence: most of this newer maternal-side DNA was introduced by the Vikings.

The Vikings/Normans were incredibly dangerous—their conquests ranged from the Volga to North America, from Greenland to Sicily—for the paradoxical reason that during the Dark Ages they cooperated with each other better than their less ferocious victims did. (To defend against Viking raids, Europeans eventually evolved feudalism, the fundamental institution of the Middle Ages, to support the expensive knights in shining armor needed to rapidly mobilize and defeat a Viking raid.)

Yet, despite their taste for rapine and pillage, the supremely opportunistic Vikings were not averse to family outings either, apparently bringing their womenfolk with them to farm in Orkney and East Anglia.

The Romans appear to have imported almost no women into Britain. Sykes found only a "tiny number" of examples of exotic mitochondrial DNA that might represent female slaves imported by the Romans from Syria or black Africa.

The famous historic invasions left a larger, but still limited, mark on the male Y-chromosome.

Roman soldiers no doubt left children behind, but it's hard to pick them out because, as the Empire matured, fewer Legionnaires were recruited from increasingly decadent Italy, and more from the northern reaches of the mainland Empire, where the men were genetically closer to the British.

All together, the Saxons, Vikings, and Normans account for the ancestors of about 10 percent of Englishmen living south of the old Danelaw line between London and Chester, and 15 percent north of it, "reaching 20 per cent in East Anglia."

(Remarkably, this ancient ethnic palimpsest can be seen to this day in the United States. As David Hackett Fischer pointed out in his great history of British settlers in America, Albion's Seed, the American Puritans tended to originate in East Anglia and other once-heavily Danish regions of England. In turn, the American states founded by Puritans and their descendents feature the most famous colleges and the highest NAEP school achievement test scores.)

That the people of the British Isles, whose offspring founded and still profoundly shape the American nation, have been a homogenous racial group for 6,000 years has many implications.

For one thing, it offers an important perspective on the current obsession with the supposed educational blessings of racial diversity. Virtually every college president in America publicly denounces the mentally-stultifying effects of a non-diverse student body. (Diversity of opinion, of course, is somehow much less fashionable on campus.)

And yet, William Shakespeare, who likely never left homogenous England in his life, sketched what is perhaps the most diverse array of personalities in world literature. Nor have the British Isles—home to Samuel Johnson and John Lennon, Oscar Wilde and the Duke of Wellington—been grievously lacking in real life individuality.

This is not to say that the close observation of racial diversity doesn't add interest to our understanding of humanity … or Shakespeare wouldn't have made Othello, the Moor of Venice, the tragic hero of one of his greatest plays.

What it does show, however, is that even in the most superficially uniform racial groups, there is almost endless human richness to be found.

[Steve Sailer [email him] is founder of the Human Biodiversity Institute and movie critic for The American Conservative. His website www.iSteve.blogspot.com features his daily blog.]