Proceedings of the National Academy of Sciences.Specifically, the scientists were interested in whether the individuals buried closest to each other were also close relatives. The 13 victims were found in four separate graves. Each contained at least one adult, along with anywhere from one to three children. As a result, some scientists have speculated that each grave might represent a separate family killed in the attack. DNA analysis, they argue, would allow them to fill the gaps surrounding the identities of the deceased.Scientists extracted DNA from the teeth of all 13 individuals. They focused on the mitochondrial DNA (mtDNA), which is passed down from mother to child, the Y-chromosome, which is passed down from father to son, and small segments of the remaining chromosomes, which are passed down from both parents to their children. Even though ancient DNA is notoriously difficult to work with, the authors were able to extract usable DNA from nine of the 13 individuals.The results from one of the four burials, Grave 99, were especially intriguing. The grave contained the remains of an adult male, an adult female, and two male children. DNA analysis revealed that the adult female had the same mtDNA type as the two male children (K1b). Analysis also revealed that the adult male had the same Y-chromosome DNA type as the two male children (R1a). Due to the ways that mtDNA and Y-chromosome DNA are passed from one generation to the next, these results suggest that the two adults in Grave 99 were husband and wife, and that the two male children were their offspring. Indeed, the authors had originally hypothesized some sort of connection between these four individuals, because while the two adults adhere to normal burial patterns for the time period (lying toe-to-toe facing south), the two children face north, toward their parents.The notion of these four individuals being buried together, as a family, raises many questions on the origins of the nuclear family in ancient times. Even the authors admit that “our image of past family life and structure is still dominated by 19th century ideals, and reconstruction of prehistoric families even now adhere to these orthodox schemes.” Indeed, there has been little evidence to precisely date the origins of the nuclear family, and this example hardly closes the book on how and when such a social unit developed. However, it does show that using ancient DNA can be quite useful in determining ancient biological relationships. Indeed, the results from Grave 99 reveal how important the nuclear family must have been to these villagers; that they chose to bury these four victims not as individuals but as a social unit, huddled together in a single grave.