Genomics of the Log Coffin culture in Thailand

The Iron Age of highland Pang Mapha, northwestern Thailand, is characterized by a unique mortuary practice known as Log Coffin culture. Dating to 2,300-1,000 years ago, archaeological surveys and excavations have identified over 40 natural caves and rock shelters where large coffins carved from individual teak trees were mounted on stilts. While numerous multidisciplinary studies have been carried out to investigate the cultural development and of the Log Coffin-associated sites, the origins of the practice, connections with other wooden coffin-using groups in Southeast Asia and social structure within the region remains understudied. Here, we present ancient DNA from 33 individuals from four Log Coffin culture sites to study genetic ancestry profiles and genetic interconnectedness within and between Log Coffin-associated sites. We successfully model the Log Coffin-associated genomes as an admixture between Hòabìnhian hunter-gatherer-, Yangtze River farmer- and Yellow River farmer-related ancestry. Bronze and Iron Age from Ban Chiang, northeastern Thailand show no evidence of this Yellow River farmer-related component, indicating different influence spheres also reflected by cultural practises. Our analyses also identify seven close genetic relationships between individuals from the same site and more distant connections between sites in the same river valley. In combination with high mitochondrial haplogroup diversity and genome-wide homogeneity, the Log Coffin-associated groups from northwestern Thailand seem to have been a large, well-connected community, where kin groups played a significant role in the mortuary ritual.