Males were buried facing one direction, and females another direction. But in the newfound burial, the boys were buried in an unconventional position, facing their parents.
"I think they wanted to reflect a logical relationship, to tell us that these people belong together," Haak said.
In a nearby grave, a boy and girl do not face the female adult buried with them.
Genetic testing showed that those children were siblings but were not related to the adult. "She may have been an aunt, or a stepmother," Haak said.
This study "provides conclusive genetic evidence for the simultaneous burial of a small nuclear family," said Louise Humphrey, a paleontologist with the Natural History Museum in London.
"This suggests that family ties were close and respected even in death," added Humphrey, who was not involved with the research.
Researchers measured the ratio of strontium—a metallic element—in the bones and teeth of the bodies.
The results were compared with the local surroundings, giving an indication of where the people had originated.
The men had stayed within their childhood area, but the women had been raised in different locations, the data showed.
The evidence "implies that the women in the community had migrated to the region from a location at least 60 kilometers [37 miles] away, possibly at the time of their marriage," Humphrey said.
This practice would have reduced the likelihood of inbreeding, she added.
"Sudden and Violent End"
The bodies exhibited evidence of brutality commonly seen in the Neolithic, lead author Haak said.
An arrow lodged in the vertebrae of one adult, as well as skull fractures and defensive wounds among others, point to a "sudden and violent end," Haak said.
Radiocarbon dating showed the burials occurred around the same time, "probably even the same day," Haak said—suggesting the village was attacked. Based on the grave finds, adults older than 30 and children younger than 10 appear to have been the only people killed during the possible attack.
This could mean that the stronger members survived the attackers, or that they were perhaps out hunting for food at the time of the raid, Haak hypothesized.
Whatever happened, the survivors "must have returned to bury [the dead] with that careful treatment that we see today," Haak said.
"Someone must have known what the story was. They wanted to preserve that."
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