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Ancient Genomes Reveal Genetic Diversity Among Neolithic Upper Mesopotamians

NEW YORK — During the Neolithic Period, the population of Upper Mesopotamia was genetically diverse and shaped by migration into the area, a new ancient DNA analysis has found.

Upper Mesopotamia, falling between the Tigris and Euphrates rivers, was involved in the Neolithic Transition, a shift from hunter-gatherer lifestyles to agricultural ones and related cultural changes. While genomic analyses of other early settlement sites like those in the South Levant, Central Zagros, and Central Anatolia have recently been conducted, studies of Neolithic Upper Mesopotamian populations have been hampered by low levels of DNA preservation in the region.

But researchers from Turkey and elsewhere have generated about a dozen ancient genomes from Pre-Pottery Neolithic Çayönü Tepesi individuals who lived in the Tigris Basin in what is now southeastern Turkey. As they reported in Science Advances on Friday, the researchers compared the genomes of these individuals to each other and to other ancient populations to gain insight into the demographics of the region and their effect on cultural change.

"The question has remained as to whether this cultural dynamism was driven by large-scale population circulation at the site, especially through connections with distant regions of the Fertile Crescent, or whether it purely reflected the local community's ingenuity," first author Ezgi Altınışık from Hacettepe University in Ankara, Turkey, said in a statement. "Our 13 ancient genomes, the largest sample produced yet from this region, allowed us to finally address this."

The researchers examined the skeletal remains of 33 individuals from Çayönü, who lived about 8,500 to 7,500 BCE, and generated sequencing libraries for 14 individuals. They determined that two samples either came from the same person or came from identical twins, leading them to merge that data and to have, in total, 13 samples representing six adult women, two adult men, three female children, and two male children.

When they compared the genomes they generated for the Çayönü individuals to other individuals who lived in the Fertile Crescent or surrounding areas between 15,000 BCE and 5,500 BCE using multidimensional scaling analysis, the researchers noted that the Çayönü individuals occupied their own spot within the range of Southwest Asian genetic diversity. They were bordered by early Holocene individuals from South Levant, Central Zagros and South Caucasus, and Central Anatolia, with further analyses suggesting a genetic blend from across the eastern and western Fertile Crescent.

Broadly, the researchers found that Çayönü individuals were three-way admixtures of Central Anatolia-, South Levant-, and Central Zagros-related ancestries.

However, one Çayönü individual — a female toddler — was an outlier and more closely related to Zagros/Caucasus individuals. This finding suggested that there was migration into Upper Mesopotamia and other historical or demographic ties between this population and nearby ones.

The researchers further noted that one of the individuals with whom the toddler was buried was likely her paternal great-aunt, suggesting both that burial practices reflected family ties and that immigrants moved into the region.

"Her maternal lineage is probably from the east, while her paternal lineage was likely local," Altınışık said, adding that "we find people moving and integrating, and these small-scale movements could be among the factors shaping cultural dynamism in Çayönü."

The toddler further exhibited evidence of having experienced intentional head-shaping as well as evidence of cranial cauterization, which may have been performed to treat endocranial lesions and anemia the child appeared to have.

The researchers additionally found that Upper Mesopotamia was the likely source of eastern gene flow into Anatolia that occurred after 7,000 BCE, which they noted tracks with material culture findings.

Overall, the researchers hypothesized that Çayönü was a "lively hub" that exhibited cultural dynamism not only because of its fertile land but also because of its demographic connections across the wider region.