Of the 85 skulls studied from in and around the 5,000-year-old tomb, at least 20 per cent — but potentially as many as 40 per cent — were found to have evidence of trauma.
Orkney-based archaeologist David Lawrence, who led the investigation and revealed preliminary findings last week, said the skulls — both male and female, children and adults — showed injuries consistent with violent attacks.
“These wounds are too common and varied to be the result of accidents. Some blows went straight through the skull, and the wounds were certainly caused with intent.”
He said there were “clear cases” of skulls being “caved in” with a hard, blunt object, some by sharp-edged weapons and others where a thin pointed instrument had penetrated the bone — stones, stone maces, stone axes, antler picks and bone-pointed arrows were all possible weapons that were around at the time.
“I think it is very likely that some of the head injuries were suffered during face-to-face fights, because of the wound sites. I can’t say who they were fighting though – each other or different groups.”
The findings go against the long-held belief that the people who lived in the north in the New Stone Age were peaceful farmers.
He said: “The level of cranial trauma at the Tomb of the Eagles was quite astounding. By checking if the wounds were healed or not, we can see if someone suffered the trauma at around the time of death.
“To say with absolute certainty whether they actually died from a particular wound is very hard, but certainly many of them show no signs of healing. Some attacks were so severe that the whole skull split in two.
“Other wounds are very subtle, and are most easily observed inside the skull, where splinters have been bent inwards.
But not everyone died of their injuries, Mr Lawrence continued, with several cases where the lesions had healed.
“Some wounds did heal. There is a skull of a woman that has three healed wounds, which were caused by blows from a blunt object to different parts of the head. She also had a dislocated jaw which was badly healed.”
Others do not display any trauma, so all this cranial damage was probably not related to funerary rituals.
This finding — that the early settlers were not the friendly farmers that historians had thought them — is in line with recent results from studies elsewhere in Britain, and finds in Europe.
“For a long time it was thought Neolithic people were friendly farmers, but in recent years it has been proven that this was not necessarily the case,” Mr Lawrence said.
“My study shows this again, but this time on an apparently remote island. Perhaps it shows that Orkney was on a major trade route, or that there was particularly great competition for resources.”
Mr Lawrence is convinced that the people in the Tomb of the Eagles were not ritually killed.
He said: “There was a great variety in the places where people were hit and the instruments used. There is no simple pattern. This variety makes it very unlikely that they were killed in some kind of ritual.”
He believes that particular people were selected to go into the tomb.
“There were so many strange things appearing on the bones of these people, I think it must be related to the selection process.”
He explained that “a significant number of the people had had some disability in life, and some probably had neurological problems as a result of cranial deformity. Instances of particular deformities were much higher than would be expected.
“There were, for instance, four examples of a hip abnormality that nowadays affects one in 25,000 people, numerous cases of a cranial deformity that affects about four in every 1,000 people, and so forth.”
“But,” he said, “the presence of only 85 burials at Isbister, over possibly 1,000 years, also means that it is unlikely that it was used for general burial. The patterns of disease and demography suggest that these people were not a hereditary elite either, although inbreeding is possible.”
He continued: “One theory is that the tomb was a grave for people who had suffered ‘unaccepted’ deaths — people who were murdered, died by accident or who were from other tribes. Would an elaborate tomb have been built for such people, though?
“It seems more likely that disease and deformity marked them out as somehow special: perhaps chosen by the Gods or possessed of some supernatural attribute. In that case, these tombs might be a focus for ritual activity.
“Where are the bodies of the other people, then? They must have been disposed of in some way that is difficult for archaeologists to recognise.
“It is ironic that the Tomb of the Eagles has been held up as an example of the redepositing of defleshed bodies, which it was not, but that it is likely that the bodies of most people, during its period of use, actually were disposed of in some such manner.”
Mr Lawrence undertook the research in a collaborative project between Orkney Museum and the University of Bradford, funded by the Arts and Humanities Research Council.
Chemical testing has also led the archaeologist to believe that the men and women may have enjoyed different foodstuffs according to sex.
He aims to continue his research, in the short term, with a programme of radiocarbon dating to examine the time scale of the deaths.
The Isbister chambered cairn, better known as the Tomb of the Eagles, in South Ronaldsay, was littered with around 16,000 human bones, and 70 talons from the white-tailed sea eagle, among many other animal bones.
The tomb is 2.5 metres high, and consists of a rectangular main chamber divided into stalls, with additional side cells.
It was accidentally discovered in 1958 by farmer Ronnie Simison, whose digging led him to a chamber containing around 30 human skulls.
Coming back to the site almost 20 years later, Mr Simison exposed the rest of the chamber and recovered the largest and best-preserved collection of Neolithic human bones to have been discovered in the UK.