3,000 Years Ago, Britain Got Half Its Genes From … France?

Three years ago in the journal Nature, a vast international research team led in part by Harvard geneticist David Reich shined a torchlight on one of prehistoric Britain’s murkier mysteries.

By analyzing the degraded DNA from the remains of 400 ancient Europeans, the researchers showed that 4,500 years ago nomadic pastoralists from the steppes on the eastern edge of Europe surged into Central Europe and in some areas their progeny replaced around 75 percent of the genetic ancestry of the existing populations.

Descendants of the nomads then moved west into Britain, where they mixed with the Neolithic inhabitants so thoroughly that within a few hundred years the newcomers accounted for more than 90 percent of the island’s gene pool. In effect, the research suggested, Britain was almost completely repopulated by immigrants.

In a paper published Wednesday in Nature, Dr. Reich again targeted the genomic history of Britain, the country from which geneticists have mined more ancient samples than any other. The study, which has 223 co-authors, documents a subsequent and previously unknown major migration into Britain from 1,300 B.C. to 800 B.C.

Analyzing DNA from 793 individuals, the investigators discovered that a massive Late Bronze Age movement displaced around half the ancestry of England and Wales and, possibly solving another longstanding riddle about British history, may have brought early Celtic languages to the island from Europe.

According to the findings, from 1,000 B.C. to 875 B.C. the ancestry of early European farmers increased in southern Britain but not in northern Britain (now Scotland). Dr. Reich proposed that this resulted from an influx of foreigners who arrived at this time and over previous centuries, and who — no doubt to the disbelief of 21st-century British nativists — were genetically most similar to ancient inhabitants of France.

These newcomers accounted for as much as half the genetic makeup of the populace in southern Britain during the Iron Age, which began around 750 B.C. and lasted until the coming of the Romans in A.D. 43. DNA evidence from that period led Dr. Reich to believe that migration to Britain from continental Europe was negligible.

Ian Armit, an archaeologist at the University of York who collaborated on the research, noted that archaeologists had long known about the trade and exchanges across the English Channel during the Middle to Late Bronze Age. “But while we may once have thought that long-distance mobility was restricted to a few individuals, such as traders or small bands of warriors,” he said, “the new DNA evidence shows that considerable numbers of people were moving, across the whole spectrum of society.”

Lara Cassidy, a geneticist at Trinity College Dublin who was not involved in the research, described the study as “a triumph. It takes a step back and considers Bronze Age Britain on the macro scale, charting major movements of people over centuries that likely had profound cultural and linguistic consequences.”

Dr. Reich said the study demonstrated how, in the last few years, archaeologists and ancient DNA researchers have made great strides in coming together to address questions of interest to archaeologists.

“To a huge extent, this is due to the large ancient DNA sample sizes that it is now possible to generate economically,” he said. “These studies are also beginning to address questions that truly matter biologically and culturally.”

A pioneer in the swiftly evolving field of paleogenomics, Dr. Reich is a kind of puzzle master of human origins. By sequencing DNA from ancient skeletal remains and comparing it to the genetic material of individuals alive today, he and his collaborators piece together ancient population patterns that traditional archaeological and paleontological methods fail to identify. By overturning established theories and conventional wisdoms about migrations following the Ice Age, they are illuminating the mongrel nature of humanity.

For all the success of what Dr. Reich calls the “genomic ancient DNA revolution” in transforming our understanding of modern humans, the practice of extracting DNA from ancient human remains has raised ethical issues ranging from access to samples to ownership of cultural heritage. Critics point out that in some parts of the world, the very question of who should be considered Indigenous has the potential to fuel nationalism and xenophobia.

To respond to these concerns, three months ago Dr. Reich and 63 archaeologists, anthropologists, curators and geneticists from 31 countries drafted a set of global standards to handle genetic material, promote data sharing and properly engage Indigenous communities, although the guidelines did little to assuage critics.

Celtic pride

Since languages “typically spread through movements of people,” Dr. Reich said, the wave of migration was a plausible vector for the diffusion of early Celtic dialects into Britain. “Everybody agrees that Celtic branched off from the old Indo-European mother tongue as it spread westward,” said Patrick Sims-Williams, emeritus professor of Celtic studies at Aberystwyth University. “But they have been arguing for years about when and where that branching took place.”

For most of the 20th century, the standard theory, “Celtic from the East,” held that the language started around Austria and southern Germany sometime around 750 B.C. and was taken north and west by Iron Age warriors. An alternative theory, “Celtic from the West,” saw Celtic speakers fanning out from the Atlantic seaboard of Europe, perhaps arising in the Iberian Peninsula or farther north, and settling in Britain by as long ago as 2,500 B.C.

In 2020, Dr. Sims-Williams published a third theory, “Celtic from the Centre,” in the Cambridge Archaeological Journal. His premise was that the Celtic language originated in the general area of France in the Bronze Age, before 1,000 B.C., and then spread across the English Channel to Britain in the Late Bronze Age and Early Iron Age.

“What is exciting for me is that Dr. Reich and his team, using genetic evidence, have reached a compatible conclusion,” Dr. Sims-Williams said. “Their earliest DNA evidence is from Kent, still the easiest place to cross from France.”

Dr. Sims-Williams hypothesizes that Celtic speakers transmitted their language northward and westward from Kent, in southeastern England, until Celtic was spoken in most of Britain, and newer languages reached its shores with later migrations: Latin with the Romans, English with the Anglo-Saxons, Norse with the Vikings and French with the Normans. “The big remaining question is: “Did Celtic reach Ireland via Britain or direct from the continent?” Dr. Sims-Williams said.

The milk of Neolithic kindness

By leveraging their large data set of ancient DNA, Dr. Reich and his colleagues also found that lactase persistence — the ability of adults to digest the sugar lactose in milk — increased 1,000 years earlier in Britain than in Central Europe. At the dawn of the Iron Age, Dr. Reich said, overall lactase persistence on the island was about 50 percent, compared to less than 10 percent in the region stretching from the Baltic Sea to the Adriatic.

Curiously, analysis of the hardened dental plaque coating ancient teeth, and of traces of fat and protein left on ancient pots, showed that dairy products were a dietary staple in Britain thousands of years before lactase persistence became a common genetic trait.

“Either Europeans tolerated stomachaches prior to the genetic changes or, perhaps more likely, they consumed processed dairy products like yogurt or cheese where the lactose content has been significantly reduced through fermentation,” Dr. Reich said.

Paul Pettitt, a Paleolithic archaeologist at Durham University, said, “The results sound fascinating, although in terms of what drink the English adapted to before their continental neighbors, it amazes me that it’s not beer.”