Matter: A History of the Iberian Peninsula, as Told by Its Skeletons Express News

For thousands of years, the Iberian Peninsula — home now to Spain and Portugal — has served as a crossroads.

Phoenicians from the Near East built trading ports there 3,000 years ago, and Romans conquered the region around 200 B.C. Muslim armies sailed from North Africa and took control of Iberia in the 8th century A.D. Some three centuries later, they began losing territory to Christian states.

Along with historical records and archaeological digs, researchers now have a new lens on Iberia’s past: DNA preserved in the region’s ancient skeletons. Archaeologists and geneticists are extracting genetic material spanning not just Iberia’s written history but its prehistory, too.

“We wanted to bridge the ancient populations and the modern populations,” said Iñigo Olalde, a geneticist at Harvard Medical School. Dr. Olalde is the lead author of a paper published on Thursday in Science that analyzes the DNA of 271 ancient Iberians.

In recent years, scientists have created similar chronologies for entire continents, based on hundreds of samples of ancient DNA. Now researchers are starting to narrow their focus to smaller regions.

With a total of 419 ancient human genomes obtained by various laboratories, Iberia offers a rich trove. Scientists have recovered only 174 ancient genomes in Britain, and just eight in Japan.

This dense record shows that Iberia’s genetic profile changed markedly in response to major events in history, such as the Roman conquest. But researchers have also uncovered evidence of migrations that were previously unknown. Iberia, it now seems, was a crossroads long before recorded history, as far back as the last ice age.

The oldest known human DNA in Iberia comes from a 19,000-year-old skeleton found in 2010 in a cave called El Mirón, in northern Spain. The skeleton belonged to a woman, a member of a band of Ice Age hunter-gatherers.

People in Iberia continued to live as hunter-gatherers for thousands of years after that, long after the end of the Ice Age. Dr. Olalde and his colleagues analyzed DNA from four additional hunter-gatherers, while a separate team, based at the Max Planck Institute for the Science of Human History, extracted DNA from 10 more.

Both teams obtained the same striking result: Iberian hunter-gatherers had a remarkable mix of genes, showing that they descended from two profoundly distinct groups of early European hunter-gatherers.

One of these groups can be traced as far back as 35,000 years, thanks to a skeleton discovered at a site in Belgium called Goyet. The Goyet-related people spread across Europe, only to be replaced on much of the continent near the end of the Ice Age by a genetically distinct population.

The earliest sign of the second group appears 14,000 years ago, known to researchers by DNA in a skeleton at an Italian site called Villabruna.

But in Iberia, the new studies find, the Goyet and Villabruna people coexisted. Hunter-gatherers across the peninsula had a mixture of ancestry from the two peoples.

“This is quite amazing, because it’s not happening in other areas,” said Vanessa Villalba-Mouco, the lead author of the Max Planck study, published in Current Biology.

Ms. Villalba-Mouco speculated that the geography of Iberia — located in a far corner of Europe — may have allowed the Goyet people to endure there after they disappeared elsewhere. “Maybe nobody was bothering these hunter-gatherers,” she said.

But whatever solitude Iberia might have offered came to an end about 7,500 years ago, when new people arrived with crops and livestock. These first farmers, originally from Anatolia, brought with them a distinctive genetic signature.

Instead, Dr. Risch suspects “a political process” is the explanation. In their archaeological digs, Dr. Risch and his colleagues have found that Iberian farmers originally lived in egalitarian societies, storing their wealth together and burying their dead in group graves.

But over several centuries, palaces and fortresses began to rise, and power became concentrated in the hands of a few. Dr. Risch speculated that the cultural shift had something to do with the genetic shift found by Dr. Olalde and his colleagues.

The Bronze Age in Iberia was followed by the Iron Age about 2,800 years ago. In skeletons from this period, Dr. Olalde and his colleagues found clues of more arrivals.

Iron Age Iberians could trace some of their ancestry to new waves of people arriving from northern and Central Europe, possibly marking the rise of so-called Celtiberian culture on the peninsula.

In addition, the scientists found a growing amount of North African ancestry in skeletons from the Iron Age. That may reflect trade around the Mediterranean, which brought North Africans to Iberian towns, where they settled down.

North African ancestry increased in Iberia even more after Romans took control. Now the peninsula was part of an empire that thrived on widespread trade. At the same time, people from southern Europe and the Near East also began leaving an imprint.

This shift in ancestry could explain one of the biggest mysteries in Iberian history. Researchers have long puzzled over the distinctive culture of the Basque region in northern Spain.

Up until now, wide swaths of time typically separated genetic studies of living people and those of ancient DNA. But now, in places like Iberia, the gaps are being filled in, creating an unbroken genetic chronology.

“The two worlds are starting to merge,” said Dr. Bycroft.

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