DNA from closely related Neanderthals in a Siberian cave sheds light on their family structure, but this far-flung population may not have been typical.

An astonishingly rich trove of Neanderthal remains from Chagyrskaya cave in Siberia’s Altai mountains has offered scientists their first insight into Neanderthal family structure. The group was highly inbred, but more surprisingly were patrilocal – with fathers staying close to home while mothers often came from other populations. Whether this was normal for Neanderthals, or a result of this family being from the furthermost edge of Neanderthal’s range remains unsettled.

The sequencing of Neanderthal DNA in 2010 changed how we see ourselves as much as our view of our nearest extinct relatives. We learned that most people on Earth carry a few percent Neanderthal genes within them, and have since discovered some of the benefits and drawbacks of that fact. Yet in the years since, only 16 European Neanderthal genomes have been sequenced and two much older ones from Siberia. These are widely scattered in location and time, revealing almost nothing about their relationships.

So when a team of researchers succeeded in sequencing the genomes of 11 individuals from Chagyrskaya Cave and two from nearby Okladnikov Cave, the 72 percent increase in Neanderthal genomes was bound to matter. In a new paper, the team reveals just how important their find has been, with several of those from Chagyrskaya closely related, including a father and teenage daughter.

A likely first cousin for the father was also found, along with a pair who may have been cousins or grandmother/grandson.

The presence of heteroplasmy, a rare duplication of mitochondrial DNA that tends to disappear within a few generations, is one of several hints they all lived together. Indeed, co-author Professor Richard Roberts of the University of Wollongong told IFLScience it is likely many of them died at the same time, “Possibly in a terrible storm.”

Although Chagyrskaya cave is a few days’ walk from Denisova Cave, where the first Denisovans were found, the Neanderthals sequenced for this study were not closely related to those previously found there, one of whom had a Neanderthal mother and Denisovan father. Instead, they were more closely related to European Neanderthals, suggesting the earlier Altai Neanderthals died out, and were subsequently replaced by some who had made a long migration east.

The cave was occupied for some portion of the period 59,000-51,000 years ago, with dating measurements lacking the precision to refine this further. Roberts told IFLScience that at the time the world had just come out of a particularly cold part of the Ice Age. Even though temperatures were considerably lower than today, the slight warming may have encouraged European Neanderthals to expand.

The Chagyrskaya Cave in Siberia is small, but its attractive location made it home for the first Neanderthal family we have ever found. Image Credit: Bence Viola
The Chagyrskaya Cave in Siberia is small, but its attractive location made it home for the first Neanderthal family we have ever found. Image Credit: Bence Viola

At Chagyrskaya they would have found a particularly enticing residence. The cave is uncomfortably small but sits above a valley through which bison, ibex, and horses migrated, offering a plentiful supply of food. Besides the DNA, the cave contains an unprecedented abundance of Neanderthal stone tools and animal bones.

Comparing the mitochondrial DNA inherited from mothers with the male Neanderthal’s Y chromosomes, the authors found the mitochondrial DNA much more diverse. Although there is a small possibility a few males had managed to dominate reproduction at some point, the more likely explanation is patrilocality. Reversing the practice common in most traditional human communities and near relatives like gorillas, it seems the Neanderthal women moved between communities, while the men stayed put.

Although having one sex move helps maintain genetic diversity, it seems the Chagyrskayans were not doing it enough; their level of inbreeding was similar to that of highly endangered gorillas. “The low genetic diversity probably was not enough on its own to explain their dying out,” Roberts told IFLScience, “but it wouldn’t have helped.” European Neanderthals at the time were less inbred, so it’s possible this was a problem restricted to those who had reached the outermost limits of the Neanderthal range.

No evidence exists for Homo Sapiens family structures at the time since our primary ancestors were restricted to hotter climates where DNA degrades much more quickly.

The paper is published in Nature.

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