🧬 3,700-year-old bones reveal the oldest documented case of father-daughter incest

The genetic analysis of 3,500-year-old bones from a Calabrian cave (Italy) yields unexpected revelations about the intimate life of a Bronze Age community. Beyond the expected kinships, researchers have discovered the genetic signature of an extremely rare social practice, offering a disturbing and unique snapshot of human relationships in that remote era.

Advances in paleogenetics now allow entire chapters of human history to be read in ancient DNA. A recent study, published in Communications Biology, applies these methods to a burial site in the Grotta della Monaca in Italy. The initial objective was to understand the composition and origins of a small mountain community from the middle of the second millennium BCE. The meticulous analysis of fourteen individuals' genomes exceeded expectations, revealing not only a family structure but also a singular case that questions prehistoric social norms.

A case of extreme consanguinity revealed by genetics

Researchers identified several direct kinship links among the deceased, including a mother and her daughter. However, attention focused on the remains of a pre-adolescent boy and an adult man buried nearby. Their genetic profile showed an unusual amount of identical genetic material, measured by long runs of homozygosity.

The length and quantity of these segments are clear indicators of the degree of parental relatedness. In this young individual, these values reached a record level in ancient genomic databases, signaling unmistakably that his parents were first-degree relatives.

After ruling out other possibilities, such as a brother-sister union, the scientific team concluded that the genetic configuration corresponded to that of a child born from a father and his own daughter. The remains of the mother, likely the adult man's daughter, were not found at the site, leaving part of the story in the shadows.

Interpretations and limits of an archaeological discovery

This discovery constitutes the oldest direct genetic evidence of such a union, surpassing in antiquity known cases among Egyptian elites or certain Neanderthal populations. The team searched for potential genetic anomalies in the child, often associated with such close consanguinity, but detected none.

The archaeological context does not allow for conclusions regarding the reasons for this union. The community does not appear to have been isolated or small enough to justify such a practice out of demographic necessity. The presence of the adult man, the only one of his sex in this collective burial, might indicate a special social status, without confirming any form of royalty.

As explained by Alissa Mittnik, co-author of the study in Communications Biology, this case could reflect specific cultural behaviors of this group, but its deeper meaning remains uncertain. It underscores how archaeogenetics can shed light on social behaviors that leave no other material trace.

To go further: What is a run of homozygosity (ROH)?

A run of homozygosity (ROH) refers to a DNA sequence where the two copies of a gene, inherited from the mother and father respectively, are genetically identical. This situation occurs when both parents share a relatively recent common ancestor. They then pass on the same genetic version for this specific chromosomal region to their child, instead of different versions which would usually mix.

The length of these segments is a valuable indicator for geneticists. Long and numerous segments suggest a close parental relationship, such as a first-degree link (sibling or parent-child). Conversely, in a population where unions occur between individuals with no known kinship, ROHs are generally shorter and less frequent, because genetic mixing is greater over many generations.

Analyzing ROHs in ancient genomes thus allows for mapping the structure of past populations. It provides information about their effective size, degree of isolation, and marital practices over several centuries. It is thanks to this method that researchers were able to objectively quantify the exceptional level of consanguinity in the child from the Grotta della Monaca.