These people almost entirely replaced the earlier farmers. Today, British people trace 90 percent of their ancestry to this immigrant wave.
Were it not for the genetic findings, “nobody would have believed the scale of the turnover,” said Ian Armit, an archaeologist at the University of Bradford who collaborated with Dr. Reich on the research.
“Archaeologists will need to get to grips with this 90 percent replacement, and what this might really mean in human terms,” he added.
A Dramatic Voyage
The Beaker people needed only to cross the English Channel to get to the British Isles. A far more spectacular voyage took place about 3,300 years ago, when humans first sailed to remote islands in the Pacific.
Dr. Reich and his colleagues have shed light on that migration by analyzing ancient DNA from the skeletons of early Pacific voyagers.
“It’s changed the game,” said Matthew Spriggs, an archaeologist at Australian National University, who has collaborated with Dr. Reich.
Until recently, many archaeologists argued that the ancestors of Pacific Islanders were related to the indigenous people of Taiwan. They had sailed south to the islands around New Guinea, the idea went, later mixing with the population, known as Papuans. Only later did their descendants sail east to Pacific islands.
This theory helped account for the kinds of languages spoken in the Pacific, the agriculture, and styles of pottery, as well as the mix of East Asian and New Guinea DNA found in the islanders.
Dr. Spriggs and other archaeologists provided Dr. Reich with bones from Vanuatu and Tonga, and his team succeeded in recovering DNA where others had failed. And what did it say about the prevailing theory?
“We found genetically that wasn’t right at all,” Dr. Reich said. He and his colleagues published their results last month in the journal Current Biology.
Instead, the people who first arrived on Vanuatu and other Pacific islands came directly from Asia — perhaps Taiwan or the Philippines — without ever stopping in New Guinea. Only later did a wave of Papuans arrive.
“We know now when that wave hits — it hits before 2,400 years ago,” said Dr. Reich. “And it’s a total replacement.”
And that second wave actually was made up of at least two migrations. The Papuans who came to what is now Vanuatu probably sailed from the Bismarck Islands. But the Papuans who arrived further east, in Polynesia, came from other islands, possibly New Britain.
As of last month, Dr. Reich’s team has published about three-quarters of all the genome-wide data from ancient human remains in the scientific literature. But the scientists are only getting started.
They also have retrieved DNA from about 3,000 more samples. And the lab refrigerators are filled with bones from 2,000 more denizens of prehistory.
Dr. Reich’s plan is to find ancient DNA from every culture known to archaeology everywhere in the world. Ultimately, he hopes to build a genetic atlas of humanity over the past 50,000 years.
“I try not to think about it all at once, because it’s so overwhelming,” he said.
Correction: March 20, 2018
An earlier version of this article misstated the given name of a mathematician. He is Nick Patterson, not Neil.