Neanderthal genetics study shows that our closest human cousins probably lived in small groups

New research is bringing to life for the first time a description of the social organisation and small community dynamics of Neanderthals.

Neanderthals were our closest human cousins, but up until now we’ve not known much about how they lived and their social relations.

The research published in Nature and led by the Max Planck Institute for Evolutionary Anthropology in Germany, is based on DNA analysis of 13 Neanderthal individuals from two caves in Russia.

Neanderthals lived in western Eurasia from around 430,000 years ago before going extinct around 40,000 years ago, not long after Homo sapiens (modern humans) arrived in Europe from Africa. There is still debate about what exactly caused the extinction of Neanderthals, but new theories appear to counter the old idea that direct confrontation between Neanderthals and our modern human ancestors led to their demise.

While DNA sequencing has given us a better understanding of some aspects of Neanderthal evolution and physiology, their social organisation has remained a mystery until now.

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The Max Planck researchers’ findings shed light on the social organisation of Neanderthals, and despite being only 13 individuals, is one of the largest genetic study of these hominids reported to date.

Eleven of the Neanderthal individuals’ remains were found in the Chagyrskaya Cave and two from Okladnikov Cave. Both caves are in the Altai Mountains of southern Siberia, Russia.

The Chagysrkaya Cave is believed to have been occupied by Neanderthals between 59,000 and 51,000 years ago. The Okladnikov remains are at least 44,000 years old.

Of the Chagyrskaya individuals, the results show some were closely related and lived around the same time. Genetic diversity in the Y chromosomes (passed down from father to son) is much lower than the mitochondrial DNA passed down from mothers. This suggests more widespread migration of females than males between tribes.

Homozygosity – possessing two identical forms of a particular gene inherited from each parent – was found to be high in the Neanderthal individuals, at levels similar to those found in mountain gorillas.

The authors suggest such findings are best explained by small communities of around 20 individuals. At least 60% of the females in these groups most likely migrated from another troop to join new mates’ families while the males were fixed.

The findings corroborate earlier research based on fossilized footprints and spatial analysis which also suggested small communities of Neanderthals.

Comparing their new Neanderthal genomes with previously sequenced genomes, the researchers were able to determine that these populations fit into the broader Neanderthal picture.

“All 13 newly sequenced individuals shared most variants with the high-coverage genome from Chagyrskaya Cave and were more similar to the around 50,000-year-old Neanderthal genome from Vindija Cave in Croatia than to the 91,000-130,000-year-old Altai Neanderthal from Denisova Cave. Therefore, although the communities from Chagyrskaya and Okladnikov caves were genetically distinct, they all appear equally related to European Neanderthals and were part of the same Neanderthal population; no individual showed evidence of recent gene flow from other Neanderthal populations,” the authors write.

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The authors note the important advance represented in their large-scale genetic study of a Neanderthal population.

“For the first time, to our knowledge, we document familial relationships between Neanderthals, including a father-and-daughter pair,” they write.

But they note that their sample size is small and may not represent the social organisation and group size of Neanderthals across the continent.

“Our findings raise questions as to whether the characteristics of the Altai communities are related to their isolated geographical location at the easternmost extremity of the known range of Neanderthals (especially because the population size at Vindija Cave was probably larger), or whether they are characteristic of Neanderthal communities more broadly,” the authors comment.

“Future studies should, therefore, when possible, aim to sample multiple individuals from additional Neanderthal communities in other parts of Eurasia to shed further light on the social organization of our closest evolutionary relatives.”