NEW YORK — Researchers have caught a glimpse into how Neanderthal communities were organized by analyzing the genomes of individuals who lived in the same place and around the same time.
A team led by investigators at the Max Planck Institute (MPI) for Evolutionary Anthropology analyzed the remains of 13 Neanderthal individuals dating back about 50,000 years from two cave sites located close to one another in the Altai Mountains of southern Siberia, at the edge of Neanderthals' range.
Based on the individuals' genetic similarities, the researchers pieced together familial and broader relationships among these samples. As they reported in Nature on Wednesday, the group included close relatives, among them a likely father-daughter pair. Their overall relatedness further suggested that Neanderthals probably lived in small groups of 10 to 20 individuals and that female Neanderthals generally left the group they were born into for another.
"Our study provides a concrete picture of what a Neanderthal community may have looked like," senior author Benjamin Peter, a group leader at the MPI, said in a statement. "It makes Neanderthals seem much more human to me."
Using a hybridization capture approach, the researchers generated genome-wide nuclear genome data for 17 bone or tooth samples that were found either in the Chagyrskaya Cave, which has been posited to have been a short-term hunting camp for Neanderthals, or the nearby Okladnikov Cave. The Chagyrskaya Cave remains were between 51,000 and 59,000 years old, while the Okladnikov Cave remains were at least 44,000 years old, suggesting the samples were largely contemporaneous. The researchers also generated mitochondrial genome and Y chromosome data.
"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," first author Laurits Skov, also a researcher at the MPI, said in a statement.
By delving into the genetic relatedness among the samples, the researchers first found that a handful of them came from the same individual, but also that one of these, dubbed Chagyrskaya D, was related to multiple individuals represented in the sample set.
Chagyrskaya D, an adult male, had a first-degree relationship with Chagyrskaya H, a teenage female. As the two had differing mitochondrial genomes, the researchers concluded that Chagyrskaya H was likely the daughter of Chagyrskaya D, rather than his mother or sister.
At the same time, Chagyrskaya D was also related, albeit more distantly, to at least one other male, Chagyrskaya C. These two shared mitochondrial DNA heteroplasmy at a certain site, suggesting they had a common close maternal relative, especially as heteroplasmy typically only lasts a few generations.
Two other samples, Chagyrskaya A and Chagyrskaya L, were second-degree relatives.
Meanwhile, though the two samples from the Okladnikov Cave were not related to one another, one of them shared mitochondrial DNA with a Chagyrskaya individual, indicating that the two sites had community ties. Mitochondrial DNA, the researchers noted, had much higher genetic diversity than Y chromosomes, suggesting that Neanderthal women migrated between social groups.
These findings, in combination with an analysis of the shared genomic segments of homozygosity among Chagyrskaya individuals, paint a picture of Neanderthals living in small groups of about 10 to 20 related individuals, with female Neanderthals moving between and linking different Neanderthal communities.
In a commentary appearing in Nature, Trinity College Dublin's Lara Cassidy called the finding that Neanderthal women moved between groups "provocative." She cautioned, though, that the Max Planck team's sample size was small.
The MPI researchers additionally noted that the genetic diversity among the Neanderthals they analyzed was low, at about the level of modern endangered species like mountain gorillas. They added that further investigation is needed to determine whether this feature is particular to Chagyrskaya Neanderthals, because they lived at the easternmost edge of the Neanderthals' range, or whether it is common to all Neanderthals.