Ancient genomes from the Imdang-Joyeong burial complex reveal an extensive kinship network in a Three-Kingdoms period society in Korea

The burial complex of the Imdang-Joyeong site at Gyeongsan, Republic of Korea, is notable for the large number of tombs constructed for a short period of late 4th to early 6th centuries CE as well as frequent presence of burials with sacrificed individuals co-buried with the grave owner. To characterize this Three-Kingdoms period society from a genetic perspective, I conducted ancient DNA analysis on 182 skeletal elements, resulting in a successful retrieval of genome-wide data from 78 individuals buried at the burial complex. Using genome-wide data, I detected 11, 23, 20 pairs of the first, second, and three-or-more-distant relatives, respectively, providing rich information on the kinship network in the Imdang-Joyeong society. I found that the Imdang and Joyeong burial site does not represent distinct families; I find continuous kinship connections between the two burial sites. I also found 5 individuals whose parents were close relatives of each other, coinciding with historical records of consanguineous marriage in this region during the Three-Kingdoms period. Within the reconstructed pedigrees, I observed adult female descendants buried together with their kin, unlike several recent archaeogenetic studies in Europe reporting a strict pattern of female exogamy. By comparing the sharing of IBD (Identity-By-Descent) segments longer than 12 cM between Imdang-Joyeong ancients, I reconfirm that adult females and adult males share similar number of kinship connections with other buried relatives. These findings suggest an endogamous mortuary practice within the Imdang-Joyeong burial site. I also observed no difference in the genetic profiles between the grave owners and the sacrificed individuals, suggesting the overall homogeneity of the Three-Kingdoms period populations ancestral to modern Koreans. My analysis sheds light on the burial customs and social structure at the Imdang-Joyeong site and provides a new perspective on the Three-Kingdoms period society in Korea.