There is new evidence to suggest our early ancestors developed surprisingly sophisticated social networks to prevent inbreeding over 34,000 years ago.
A team of international researchers made the discovery after genome sequencing the fossils of four hunter-gatherers from the Upper Palaeolithic period and comparing them to the DNA of modern-day and ancient humans. Their results have been published in the journal Science.
The remains were found at a site in Sanghir, Russia, home to some of the earliest signs of Homo sapien activity in Eurasia. All four bodies were male – one an adult, two children, and the fourth, the incomplete remains of a second adult. Conventional wisdom would suggest the bodies were closely related. However, to the researchers' surprise, they found this was not the case.
The individuals were genetically no closer than second cousins, and the femur of an adult discovered in the children's grave would have belonged to someone no closer than a great-grandfather.
"I think many researchers had assumed that the people of Sunghir were very closely related, especially the two youngsters from the same grave," said senior author Professor Eske Willerslev, a Fellow at St John's College, Cambridge, and the University of Copenhagen, in a statement.
The fact that they were not, suggests that even people in the Upper Palaeolithic period understood the need to avoid inbreeding.
"This means that they must have developed a system for this purpose. If small hunter-gatherer bands were mixing at random, we would see much greater evidence of inbreeding than we have here," Willerslev added.
Current research suggests that like other hominins, including our cousins the Neanderthals, prehistoric humans lived in small family units. This type of living arrangement would make inbreeding likely due to convenience and a lack of alternatives.
Yet, at some as yet unknown point in human history, H sapiens stopped seeking the company of close relatives and looked further afield. The study authors theorize that this could be one reason why H. sapiens have been evolutionarily more successful than other hominin species, though acknowledge that more research needs to be done to support this hypothesis.
The new findings imply Upper Paleolithic groups used social networks incorporating several smaller units to sustain their lifestyle and avoid inbreeding, similar to modern-day hunter-gatherer societies.
"Small family bands are likely to have interconnected with larger networks, facilitating the exchange of people between groups in order to maintain diversity," explained Professor Martin Sikora, from the Centre for GeoGenetics at the University of Copenhagen.
The human remains were found buried alongside jewelry and artifacts, which also suggests a more complex social structure. The researchers say these objects could have been used in ceremonies and rituals involved in the exchange of mates between families – perhaps in an early version of a wedding – or to distinguish between the different groups.
"The ornamentation is incredible and there is no evidence of anything like that with Neanderthals and other archaic humans," said Willerslev.
When you put the evidence together, it seems to be speaking to us about the really big questions; what made these people who they were as a species, and who we are as a result.