Mesopotamian ancient DNA reveals Iron Age integration of heterogeneous Bronze Age genetic ancestries following resettlement.

The development of complex urban societies in Mesopotamia fundamentally shaped human history, yet the genetic dynamics underlying this process remain poorly understood. Here, we sequence DNA from 17 individuals spanning the Bronze and Iron Ages at Bakr Awa, one of northeastern Iraq's largest ancient settlements located at the border between Mesopotamia and Iran.Genome-wide analyses reveal substantial genetic heterogeneity during the Bronze Age, characterized by influences of Anatolian, Levantine, and Caucasus/Yamnaya-related ancestries on the local background - complementing archaeological and textual reconstructions of a diverse ethnolinguistic presence at Bakr Awa. This Bronze Age ancestry heterogeneity marks a notable shift from the local Pre-Pottery Neolithic composition - represented by previously published samples from Bestansur, which possess a close affinity to Neolithic central Zagros-related ancestry. The integration of ancient DNA with stable-isotope analysis of 12 individuals reveals multigenerational dynamics and identifies the Zagros Mountains as the most parsimonious recent origin for one of the Bronze Age individuals with Caucasus/Yamnaya-related ancestry. Following the Late Bronze Age site abandonment, reoccupation during the Iron Age involves integrating the preceding Bronze Age divergent ancestries rather than a process of population replacement.Our findings reveal that heterogeneous ancestries characterize Bronze Age population structure at Bakr Awa, directly mirroring the diverse cultural landscape observed in historical and archaeological sources. Because the subsequent Iron Age transition integrated, rather than replaced, these divergent ancestries, we demonstrate that cultural transitions need not entail large-scale ancestry transformations. Together, these findings capture Mesopotamia's role as a "melting pot" of ancient Near Eastern ethnolinguistic groups.