The genomes of several individuals reveal changes in Bronze Age populations in the south of the peninsula.

The third millennium before our era (ANE) is a very dynamic period in the prehistory of Europe and Western Asia, characterized by large-scale social and political changes.

In the Iberian Peninsula, the Copper Age was in full swing around 2500 BC, with significant population growth, attested to by a great diversity of settlements and fortifications, monumental burial structures, as well as macrovillages of more than 100 hectares. For reasons that are not yet clear, the second half of the millennium has experienced a depopulation and the abandonment of large settlements, fortifications and necropolises.

In the southeast of the Iberian Peninsula, around 2200 BC, one of the most outstanding archeological entities in the European Bronze Age: the culture of “El Argar”, one of the first state societies on the European continent. This society is identified by its large central settlements on hills, differentiated ceramics, specialized weapons and bronze, silver and gold artifacts, in addition to an intramural funerary rite, with graves and habitats integrated in the same space.

A new study led by a research team from the Autonomous University of Barcelona (UAB) and the Max Planck Institutes for the Science of Human History (Jena) and Evolutionary Anthropology (Leipzig), and published in Advances in Science, explored the relationship between large-scale demographic changes and the main social and political changes of the third and second millennium ANE.

The research team analyzed the genomes of 136 Iberian individuals who lived between 3000 and 1500 BC (96 Bronze Age El Argar and other contemporary societies, 34 Copper Age and 6 Late Bronze Age).

Including published genomes from the Iberian Peninsula, the new study encompasses data from nearly 300 prehistoric individuals and focuses specifically on the transition from the Copper Age to the Bronze Age around 2200 BC.

Genetic and population changes

“Although we knew that the so-called ancestry of the steppes, which spread across Europe during the third millennium BCE, eventually reached the north of the Iberian Peninsula around 2400 BCE, we were surprised to see that all prehistoric individuals from the period the argar they carried a part of this ancestry, while in Copper Age individuals it is absent”, says the Max Planck researcher. Wolfgang Haak, lead author and investigator of the study.

O genomic data reveal some of the underlying processes behind this genetic change. While most of the genome shows that Bronze Age individuals are a mixture of local Copper Age ancestry and a small part of continental European ancestry, paternally inherited Y chromosome lineages show a complete shift, linked to movement. steppe descent which is also visible in other parts of Europe.

“The causes of this disappearance of anterior Y chromosome diversity are still very difficult to explain,” he says. Cristina Rihuete Herrada, co-principal author of the study and researcher at UAB.

Substantial new data from the El Argar sites also show that these two components do not fully explain the genetic makeup of early Bronze Age societies.

“We also find signs of ancestry that go back to the central and eastern Mediterranean and western Asia. steppe ancestry, but they were part of the nascent societies of El Argar, which shows that there were continuous contacts with these regions”, adds Vanessa Villalba-Mouco, postdoctoral researcher at the Max Planck Institute and the Institute of Evolutionary Biology (IBE, CSIC-UPF ) and co-principal author of the study.

The UAB researchers were already pointing out possible connections with the Mediterranean when in 2013 they discovered the monumental fortification of the Argaric settlement of La Bastida, in Murcia, to explain the originality of some architectural elements.

“The genetic study supports this hypothesis: the data show that this unprecedented Mediterranean connection would have been sustained over time until the end of the El Argar period, around 1500 BC”, he highlights. Raphael Mico, researcher at UAB and also co-principal author of the study.

Collective burial from the Copper Age of Camino del Molino (Caravaca de la Cruz, Murcia), where around 1,300 individuals were buried between the years 2900-2300 BC.  The image shows the last burial layer, dated between 2500-2300 BC, from which six individuals were analyzed.  / © University of Murcia.  Photograph by Francisco Ramos

Collective burial from the Copper Age of Camino del Molino (Caravaca de la Cruz, Murcia), where around 1,300 individuals were buried between the years 2900-2300 BC. The image shows the last burial layer, dated between 2500-2300 BC, from which six individuals were analyzed. / © University of Murcia. Photograph by Francisco Ramos

social implications

“Whether the genetic change was caused by migratory groups from the north and center of the Iberian Peninsula or by the climatic deterioration that affected the eastern Mediterranean around the year 2200, ANE is a question of a million dollars”, says the Roberto Risch, from UAB, co-investigator and lead author. “It would be absurd to think that everything can be explained with a simple one-factor model. While the timing is surprising, it is likely that many factors were involved.”

One of these factors could be pandemics, as an initial form of Prague, which was evidenced in other regions of Europe at that time. Although it was not found directly among the individuals analyzed in the south of the Iberian Peninsula, it could be a trigger for the population changes observed in the region, the researchers point out.

“In any case, we can now conclude that the population movement that began in the steppe areas of Eastern Europe around 3000 BC was not a single migratory event, but took more than four centuries to reach the Iberian Peninsula and another 200 years to appear in the current Murcia and Alicante“Risch adds.

The archaeological record of the El Argar group shows a clear break with previous traditions of the Copper Age. Funerary rites, for example, went from communal to single and double within villages. Elite burials also indicate the formation of strong social hierarchies.

When testing biological kinship, the study revealed that men are, on average, more closely related to others in the settlement, indicating that the group was likely patrilineally structured. This social organization could explain the marked reduction in the diversity of lineage Y, they point out in the study.

“We observe similar patterns of social organization and stratification growing in other parts of early Bronze Age Europe as well, actually at about the same time and with similar features as early state formations. This suggests a structured restart or reset after some kind of crisis or unstable ​​and highly dynamic times”, summarizes Haak.

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