Even 34,000 years ago, our ancestors knew incest was a bad idea. Analysis of ancient human remains discovered in Russia has revealed that even among an extremely small society, inbreeding did not take place. This arrangement suggests these early humans mated outside their own clans, instead of risking the problems that arise from having sex with their relatives.
Researchers led by Martin Sikora, from the University of Copenhagen, Denmark, were looking at human remains found at the Sunghir burial site. This Upper Paleolithic archaeological site represents some of the earliest evidence of Homo sapiens in Europe. The four individual males found there lived between 34,600 and 33,600 years ago. Two of them were children and had been buried head to toe.
In their study, published in Science, the team analyzed the genomes of all four, looking at the genetic diversity between them. To the researchers surprise, they found they were unrelated to each other, despite being part of what would have been a very small group of maybe 25 people—humans had only just arrived in western Eurasia, so had not had long to build up a significant population.
The team found the closest relationship the four males could have had was second cousins. As a result, the authors say early humans must have actively sought out partners from outside their own social groups.
“The data that we have suggest that [interbreeding] was being purposely avoided,” senior author Eske Willerslev, from St John’s College, Cambridge and the University of Copenhagen, said in a statement. “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.”
The researchers say small family groups were probably interconnected to wider networks that would have allowed for the exchange of people, thereby maintaining diversity. Artifacts found at the site, including jewelry, add to this hypothesis, indicating people may have developed rituals and rules relating to the exchange of people between groups—potentially a prehistoric proto-wedding.
“Most non-human primate societies are organized around single-sex kin where one of the sexes remains resident and the other migrates to another group, minimizing inbreeding,” said Marta Mirazón Lahr, from the University of Cambridge. “At some point, early human societies changed their mating system into one in which a large number of the individuals that form small hunter-gatherer units are non-kin.
“The results from Sunghir show that Upper Paleolithic human groups could use sophisticated cultural systems to sustain very small group sizes by embedding them in a wide social network of other groups.”
The social structure of these people may have had an impact on the development of cooperation and information transfer, the researchers note. If so, these aspects of their lives could have influenced how human culture evolved, and could therefore be “crucial” to understanding our development as a species.