To avoid inbreeding, our ancestors may have had their own ancient dating networks

One of pre-history’s most eligible bachelors.
One of pre-history’s most eligible bachelors.
Image: Libor Balák
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Though there are notable exceptions—Roman Egypt, for example—incest has been really high on the human scale of moral reprehensibility through most of recorded human history. But what about before then?

When our distant ancestors wandered out of Africa to spread across the world around 50,000 years ago, they did so in small bands of nomadic tribes separated by hundreds, if not thousands, of miles. The great distances between them has long led scholars to believe inbreeding was inevitable. But research published last week, in the journal Science, points to the possibility that our ancient ancestors may have not only understood the dangers of inbreeding, they may have implemented complex systems of mating exchanges—between larger networks of tribes in order to avoid it.

Eske Willerslev, of both the universities of Cambridge and Copenhagen and the closest that the study of ancient genomics gets to a bona-fide rockstar (paywall), was lead author on the study. He and a team of international experts extracted DNA from the graves of four ancients, a man, a woman, a boy, and a girl found at the Sunghir site in Russia, which dates to around 34,000 years ago. The researchers were surprised to find that, genetically speaking, none of the remains analyzed showed a relationship with any of the others at the site closer than that of second cousins; this includes the two children who were buried head to head in the same grave, who were long thought to be siblings.

Genetic sequencing of a Neanderthal from around 50,000 years ago found in the Altai Mountains in 2008 suggests that inbreeding wasn’t avoided in that group, and a lack of genetic variation has been considered as a possible factor in their extinction. But more evidence is needed to determine whether Neanderthals didn’t care enough to avoid the practice, or were forced into it by circumstance.

And so it’s possible that our ancient ancestors understanding of inbreeding may be the reason our species survived and other hominin species died out.

The variety of ritualistic objects found buried with each of the bodies—which Willerslev called “incredible” and “unlike anything found with other archaic humans”—suggests some form of collectivism, which may signify differing tribal affiliations, or who to avoid as a mate, or even the existence of early marriage rituals; this implies the variety that researchers found in the genetic code of those buried was no accident.

Willerslev believes these early humans “must have developed a system for this purpose,” he said in a statement published with the study. “If small hunter-gatherer bands were mixing at random, we would see much greater evidence of inbreeding than we have.” And in global competition for survival, an early rejection of incest may have made all the difference.