Genomic analyses of Neanderthals have previously provided insights into their population history and relationship to modern humans, but the social organization of Neanderthal communities remains poorly understood. To explore the social structure of Neanderthals, an international team led by researchers from the Max Planck Institute for Evolutionary Anthropology sequenced multiple individuals from a remote Neanderthal community in Siberia.
According to the researchers, multiple related persons were found among these thirteen people, including a father and his teenage daughter. The thirteen genomes allowed the researchers to gain insight into the social structure of a Neanderthal community. With 10 to twenty members, they seem to have been a small family, and female migration served as the primary means of connecting the groups.
To explore the social structure of Neanderthals, the researchers turned their attention to southern Siberia, a region that has previously been very fruitful for ancient DNA research – including the discovery of Denisovan hominin remains at the famous Denisova Cave. They focused on the Neanderthal remains in Chagyrskaya and Okladnikov Caves, which are within 100 kilometers of Denisova Cave.
Neanderthals used these sites for a brief period around 54,000 years ago, and many possibly contemporaneous Neanderthal remains have been found in their deposits. The 17 Neanderthal remains successfully recovered by the researchers represent the most Neanderthal remains ever sequenced in a single study.
The Neandertals at Chagyrskaya and Okladnikov hunted ibex, horses, bison, and other animals that migrated through the river valleys that the caves overlook. They collected raw materials for their stone tools dozens of kilometers away, and the occurrence of the same raw material at both Chagyrskaya and Okladnikov Caves also supports the genetic data that the groups inhabiting these localities were closely linked.
The 17 fossils come from 13 Neanderthal people: 7 males and six women, 8 of whom were adults and 5 of whom were kids or young teenagers. The researchers discovered many so-called heteroplasmies in people’s mitochondrial DNA that people shared. Heteroplasmies are a unique genetic variation that only lasts for a few generations.
Among these remains were those of a Neanderthal father and his teenage daughter. The researchers also found a pair of second-degree relatives: a young boy and an adult female, perhaps a cousin, aunt, or grandmother. The combination of heteroplasmies and related individuals strongly suggests that the Neandertals in Chagyrskaya Cave must have lived – and died – at around the same time.
Laurits Skov, the first author of this study, said, “The fact that they were living at the same time is very exciting. This means that they likely came from the same social community. So, for the first time, we can use genetics to study the social organization of a Neanderthal community.”
There is incredibly low genetic diversity inside this community of Neanderthals, which is compatible with a group size of 10–20 people, which is another stunning discovery. This compares more favorably to the population sizes of critically endangered species on the edge of extinction and is significantly lower than those observed in any ancient or modern human community.
However, Neanderthals didn’t live in completely isolated communities. By comparing the genetic diversity of the Y-chromosome, which is inherited father-to-son, with the mitochondrial DNA diversity inherited from mothers, the researchers could answer the question: Was it the men or the women who moved between communities? They found that the mitochondrial genetic diversity was much higher than the Y chromosome diversity, which suggests that these Neanderthal communities were primarily linked by female migration.
Despite the proximity to Denisova Cave, these migrations do not appear to have involved Denisovans – the researchers found no evidence of Denisovan gene flow in the Chagyrskaya Neanderthals in the last 20,000 years before these individuals lived.
Benjamin Peter, the last author of the study, said, “Our study provides a concrete picture of what a Neanderthal community may have looked like. It makes Neanderthals seem much more human to me.”