DNA taken from human remains found within a 1,600-year-old burial complex in southeastern Korea reveals that ancient Korean society largely practiced inbreeding and ritual human sacrifice, according to a new study published in Science Advances.

The Imdang-Joyeong burial site in Gyeongsan City is dated to the Three-Kingdoms period (circa 57 BCE to 668 CE), and is known for the high presence of deaths caused by sunjang, the ritualistic sacrifice of servants in order for them to be buried alongside their superiors.

At least 20 tombs at the site contain both a grave owner and one or more individuals believed to have been killed in order to accompany them into death, according to the study.

By analyzing DNA samples from the remains of 78 individuals from 44 different graves, researchers found that they belonged to 13 family trees spread across two separate burial areas within the complex.

Further, the analysis revealed 54 pairs of relatives among the buried individuals, including 11 first-degree pairs (such as parents and children or siblings), 23 second-degree pairs (grandparents, aunts, uncles), and at least 20 more distant connections.

Additionally, researchers found genetic confirmation that entire families had been sacrificed together as part of sunjang, noting at least three different cases where parents and children had been killed and buried together in the same grave.

"Genetic relatedness among sacrificial individuals over generations may suggest the presence of families that served as sacrificial individuals for the grave owner class for consecutive generations," researchers wrote in the study.

Evidence of inbreeding found at site

Even more so, researchers found evidence of inbreeding, or consanguineous marriage, being practiced amongst those buried at Imdang-Joyeong.

Researchers identified five individuals born of closely related parents by measuring long stretches of identical DNA, known as "runs of homozygosity" (ROH). The more closely related one's parents are, the longer these repeated segments tend to be. 

DNA from one person, a woman named by researchers as “IMD003,” showed particularly long runs of homozygosity, indicated that her parents had been been first cousins or closer.

Notably, signs of inbreeding appeared among the sacrificed individuals as well and not only among the more elite grave owners, the study explained, suggesting that "the Imdang-Joyeong society practiced intracommunity marriage, likely within social status."

The findings seem to also challenge assumptions drawn from European archaeology, where it is usually seen in ancient societies that women moving away from their birth families after marriage. 

At Imdang-Joyeong, researchers found that adult women were buried alongside their maternal relatives, meaning that they most likely had stayed close to home.