A mass migration of males transformed the genetic composition of people in Spain during the Bronze Age, reveals a study
DNA evidence shows that migrants flowed through the Pyrenees, replacing existing male lines in the whole region within a space of 400 years.
It is unclear whether there was a violent invasion or whether a male social structure played an important role.
The result derives from the largest study of its kind.
Researchers have reconstructed the history of the population of Iberia (modern Spain and Portugal) over 8000 years ̵
Their study is published in Science journal.
They extracted and analyzed the DNA from 403 Iberians who lived between 6000 BC and AD 1.600.
Male migrants of the Bronze Age traced some of their ancestors to Neolithic (Stone Age) farmers throughout Europe – including Spain – while the rest of their genetic heritage was similar to that of the people who lived at the time in the Russian steppe.
This lineage of steppes was introduced into Europe by nomadic shepherds who migrated west from Asia and the eastern fronds of Europe.
The ancient British "replaced" by the newcomers
Crisis of the stone age
One of the triggers could have been was a crisis that precipitated the population in Europe towards the end of Neolithic period (which preceded the Bronze Age). Recent studies suggest that the plague may have played a role.
As the steppes moved westward, they gathered elements of culture from the people with whom they mixed along the way. In Central Europe, such a mixed culture was formed known as the Bell Beaker tradition. The Bechers and their descendants may have established highly stratified (unequal) societies in Europe, including Iberia, where they begin to increase from 2,500 BC.
The researchers examined the Y chromosome – a DNA packet handed down more or less unchanged from father to son. It can be used to trace the inheritance of the male line. Around 2000 BC, the local Y chromosomal lineages had been eliminated from the Iberian gene pool, in favor of those transported by the newcomers.
When the team analyzed the DNA of the entire genome – the complete complement of genetic material found in cell nuclei – they discovered that the Iberians later tracked 40% of their ancestors to the new population.
The newcomers – of Bell Beaker origin – brought innovations such as bronze working (including the manufacture of bronze weapons) and probably rode horses. These may have given them a military advantage over stone-age agricultural societies, but they probably also conferred a higher social status to incoming males.
Patterns of inheritance
Coauthor Iñigo Olalde, of Harvard Medical School, USA, said: "It would be a mistake to jump to the conclusion that Iberian men were killed or forcibly displaced." He added: "The archaeological documentation does not provide any clear proof of an explosion of violence in this period".
Instead, the high social status of new arrivals may have been linked to greater reproductive success. "Their male descendants would inherit wealth and social status, and they too had a much higher reproductive success," Dr. Olalde told BBC News.
A system that emphasized male power and legacy could have been the key: "A patrilineal and possibly patriarchal social structure would further expand the patterns observed, since probably only the firstborn son would inherit the properties of the clan, while the other sons would move out and try to found their own clans, further spreading their Y lineages on new territories, "he
An even more extreme replacement model occurred more or less at the same time in Britain, where the Beakers they replaced 90% of the descendants who were there before they arrived.
"At least in the east and south-east, we see a change in the settlement patterns … which lasts until the arrival of the Romans," co-author Dr Carles Lalueza-Fox, of the University of Barcelona.
In this r egion, the Iberian culture of the Iron Age established fortified settlements on a hill.
"The Iberians lived in hill settlements and were a violent society, structured along tribal lines, something clearly changes the social structure existing in the late Neolithic."
Looking at the human remains of an earlier period, the study found that the hunter-gatherers of the stone age who traced a significant percentage of their ancestors in some of the first European settlers, survived in southern Spain until diffusion of agriculture 6,000 years ago  The team also studied genome data from Moorish Spain (711-1492 AD), when parts of the peninsula were under the control of Muslim emirs of North African origin.
The North African influence was present in Iberia at least from the Bronze Age. But the researchers found a radical change in the genetic composition of people from regions controlled by the Moors after the medieval "Reconquista", when Christian armies regained control of the peninsula. The conquerors expelled many Muslims, although some were allowed to stay if they converted to Christianity.
While many Moorish individuals analyzed in the study appear to have been a 50:50 mix of North African and Iberian ancestors, North African ancestry in the peninsula now averages just 5%.
Modern Iberians derive about 50% of their ancestors from the Neolithic peasants, 25% from ancient hunter-gatherers and 20% from the steppe.
Faces of the past of Iberia
The people of the Iberian civilization of the iron age of the east coast of Spain generally cremated their dead. The cremation process prevented scientists from extracting DNA from these remains. While culture was responsible for great works of art, such as the sculpture of Dama de Elche, even the Iberians had a violent side. They hammered large nails through the severed heads of enemies killed in combat and exposed them in public spaces as war trophies. About 40 of these heads were found in the Iberian settlement of Ullastret, allowing scientists to analyze DNA from them.
Two burials in the study revealed high levels of black African ancestry. Both individuals came from Granada, in the south-west of Spain, where the last Muslim emirate resisted until it was conquered by the Christians in 1492. One of the people came from a 10th-century cemetery where the bodies were buried in the tradition Islamic – oriented in the direction of Mecca. The other individual is from the 16th century, after the Christian conquest of Granada. They are thought to come from the Morisco community – former Muslims converted to Christianity (only to be expelled from Spain later).
After the fall of the Roman Empire, wandering tribes from northern and eastern Europe poured into Iberia. The Visigoths, who spoke a language related to Swedish, German and English, took control of the region. They founded the Spanish monarchy that continues today and introduced laws that formed the basis of those used by the later Christian kingdoms. The burials of Pla de Horta, in the north-east of Spain, include a mother and a daughter of Visigoth origin. Their genomes suggest that they had recent ancestors from Eastern Europe, while DNA from cell batteries, or mitochondria – which passed more or less unchanged from mother to child – is of a type associated with populations of East Asia. It is a sign of the genetic complexity of the eastern steppe region, where their roots lie.
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