Researchers have uncovered a 430,000-year-old human skeleton with fatal skull wounds that may represent the earliest case of murder in history.
The skeleton sits alongside at least 28 others in a cave called Sima de los Huesos - the "pit of bones" - located in the Atapuerca Mountains of northern Spain.
Designated a UNESCO (United Nations Educational, Scientific and Cultural Organization) World Heritage Site, the cave is situated around 13 meters underground, accessible only by a vertical shaft.
To date, it is unclear how the skeletons - estimated to date back more around 430,000 years to the Middle Pleistocene age - arrived at the site in the first place, though theories include accidental falls or intentional accumulation of bodies representing funerary behavior.
In their study, published in the journal PLOS ONE, Nohemi Sala, from Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos in Spain, and colleagues reveal their findings from an analysis of a human skull uncovered from Sima de los Huesos, referred to as Cranium 17 (Cr-17).
According to the researchers, Cr-17 is almost a complete skull, consisting of 52 bone fragments that make up the facial skeleton.
The team was interested in this particular skull because it displayed two fractures on the frontal bone, situated above the left eye.
Fractures caused by two independent blows from the same object
Using 3D imaging to closely analyze the two fractures and assess the contour and trajectory of each wound, Sala and colleagues found that they were likely to have been caused by the same object.
"Furthermore," the team adds, "the fractures show different orientations and different trajectories, implying that each fracture was caused by an independent impact."
Due to the type and the position of the fractures, the authors say they are unlikely to have been caused by a fall down the 13-meter shaft.
"In the case of Cr-17 it is also possible to rule out the injuries as either self-inflicted or resulting from an unintentional hunting accident, mainly because the lesions involve multiple blows," they add. "Based on the absence of cut marks, other potential postmortem manipulations (e.g., cannibalism, ritual manipulations, etc.) seem even less likely and more speculative."
Based on their findings, the team says it is likely the human in question was a victim of "interpersonal aggression" - that is, they were likely to have been murdered by another human.
"The severity of the injuries, with both blows to the head certainly involving penetration of the bone-brain barrier, and the absence of healing via bone remodeling leads us to consider that this individual did not survive these cranial traumatic events," they note, adding:
"Indeed, either of the two traumatic events were likely mortal in and of themselves, and the presence of repeated blows might imply a clear intention to kill. Thus, the most plausible explanation for the perimortem fractures on Cr-17 is as the result of intentional and repeated blows during a lethal act of interpersonal violence.
This represents the earliest clear case of deliberate, lethal interpersonal aggression in the hominin fossil record, demonstrating that this is an ancient human behavior."
Since the individual was likely to have died prior to arrival at Sima de los Huesos, this rules out an accidental fall down the shaft. This means that the individual was likely to have been intentionally dropped down the shaft by other humans, according to the team.
"Thus, the interpretation of the SH [Sima de los Huesos] site as a place where hominins deposited deceased members of their social groups seems to be the most likely scenario to explain the presence of human bodies at the site," they note.
As such, the team believes Middle Pleistocene humans disposed of deceased bodies down the shaft as part of a social practice, which they say may "represent the earliest funerary behavior in the human fossil record."