Thousands of years ago, people learned to perform a surgical operation to open the skull, or trepanation. The BBC Earth columnist talks about the possible purpose of this chilling procedure.
Since ancient times, representatives of different peoples have been practicing trepanation - a gross surgical intervention in which a hole is made in the skull of a living person.
This operation was performed by drilling, cutting or scraping with a sharp instrument.
To date, in the course of archaeological excavations around the world, many skulls with traces of trepanation have been removed from the ground.
Strange, but scientists still cannot come to a consensus as to why our ancestors performed this operation.
Anthropological reports of trepanation performed in Africa and Polynesia in the 20th century suggest that, at least in these cases, the operation was intended to treat headaches, such as those caused by a skull injury or neurological disease.
Probably for the same purpose, trepanation was done in ancient times. Many trepanned turtles showed signs of mechanical damage or neurological disease, often near the trepanation hole.
However, researchers have long suspected that trepanning was performed by ancient people not only for medical purposes, but also as a ritual.
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Painting by the XIV century artist Guido da Vigevano, depicting trepanation
The earliest evidence of skull opening operations date back to around 7,000 years ago. Trepanation was practiced in various parts of the world: in Ancient Greece, North and South America, Africa, Polynesia and the Far East.
Probably, in different regions, people independently developed the trepanation technique.
By the end of the Middle Ages, most peoples abandoned trepanation, but in several parts of Africa and Polynesia that were cut off from civilization, these operations were carried out until the early 1990s.
Since the publication of the very first scientific studies on trepanation (in the 19th century), scientists continue to argue that ancient people sometimes performed trepanation in order to let spirits into the human body or, conversely, expel them.
In addition, trepanation could be part of the initiation rite.
Nevertheless, there is practically no reliable evidence of this. It is almost impossible to exclude the fact that trepanation was performed for medical reasons, since some diseases of the brain do not leave any marks on the skull.
However, in one of the corners of Russia, archaeologists have found one of the most convincing evidence of ritual trepanation.
Trepanned skull of a 20-25-year-old woman. The burr hole only partially healed, from which it can be concluded that she died eight weeks after the operation
This story began in 1997. Archaeologists carried out excavations at an ancient burial site near Rostov-on-Don.
At the site of the excavation, the remains of the skeletons of 35 people were recovered from 20 individual graves. Given the method of burial, archaeologists have determined that they can be attributed to the period from 5000 to 3000 BC. BC, known as the Chalcolithic, or Copper Age.
In one of the graves, the skeletons of five adults were found - two women and three men, as well as a child from one to two years old and a teenage girl.
Scientists have previously discovered several skeletons of ancient people in one grave, but in this case, the find was still unusual: the skulls of two women, two men and a girl were trepanned.
Each of the skulls had one oval hole, several centimeters wide, with signs of scraping along the edges. A depression was found in the skull of the third man, which was clearly the work of a person, but this hole was not through. Only the child's skull was intact.
Elena Batieva, an anthropologist from the Southern Federal University in Rostov-on-Don, took up the study of the remains extracted from the graves. She immediately determined that the holes in the skulls were the result of trepanation, but soon realized that these trepanations were not common.
Trepanning instrument from Germany dating back to the 18th century
They were all made in almost the same place - at a point called obelion. The obelion is located at the top of the skull, closer to the back of the head, approximately in the place where hair is usually collected in a high ponytail.
Less than 1% of all reported trepanations were performed above the obelion. In addition, Batieva knew that the ancient people living on the territory of Russia did such operations even less often.
At that time, she knew only one recorded case of trepanation at this point. The skull was recovered from the ground in 1974 near the site of its current excavation.
It is quite clear that even a single trepanned skull in the obelion area is an outstanding find. But Batieva had five of them, and they all lay in one grave. This case was and still remains unique.
There is a simple explanation for the fact that trepanation in the obelion area is rare: it is very dangerous.
Headache can be unbearable
The obelion is located just above the superior sagittal sinus, where blood from the brain collects before entering the main veins of the brain.
Opening the skull in this place threatens profuse bleeding and death.
This means that people who lived in Russia in the Copper Age must have had good reasons to carry out such operations.
However, none of the skulls showed signs of damage or disease, which would have occurred both before and after trepanation.
In other words, everything looked as if all these people had undergone trepanation, being perfectly healthy. Was this operation associated with any ritual?
This is a very interesting question, but Batieva had to abandon her further search for an answer.
She had to explore many more skeletons found throughout southern Russia, and she could not be distracted from her main task for the sake of a few skulls, no matter how mysterious they were.
Before retreating, Batieva decided to look through unpublished archaeological data from Russia to find out if other atypical trepanned skulls were found in the obelion area, which for some reason were not registered.
To her surprise, there were two such skulls. They belonged to young women and were found several years ago, one in 1980 and the other in 1992.
Both skulls were recovered from the ground less than 50 km from Rostov-on-Don, and none of them was found to have medical prerequisites for trepanation.
They did it in many regions of the world: a plaster cast of one of the trepanned Peruvian skulls
So, Batieva had eight unusual skulls found in a relatively small area in southern Russia and belonging to people of about the same age.
Several more were discovered ten years later.
In 2011, an international team of archaeologists examined 137 human skeletons excavated from the ground in three separate graves dating back to the Copper Age.
They were all found in Kabardino-Balkaria, in a mountainous area in southern Russia, about 500 km southeast of Rostov-on-Don, near the modern border with Georgia.
Archaeologists did not aim to detect trepanation. Their task was to find out the general health of the ancient people who inhabited this region.
However, they found holes in nine of the 137 skulls.
Five of them were trepanation standard samples. Holes were made at various points in the anterior and lateral parts of the skull, and all skulls showed signs of mechanical damage.
This suggested that trepanation was performed to eliminate the consequences of injuries.
However, none of the remaining four skulls showed signs of injury or disease. Moreover, on each of them, trepanning was carried out directly above the obelion.
Quite by accident, it turned out that the German anthropologist Julia Gresky, who was part of the research group, was familiar with the work of Batieva, describing the unusual trepanned skulls found in the Rostov region.
Then Greski, Batieva and other archaeologists joined forces to describe all 12 skulls from the south of Russia, trepanned in the obelion area.
Their study was published in April 2016 in the American Journal of Physical Antropology.
Regardless of the place of discovery, 12 such skulls are already an extraordinary find. However, the fact that they were all found in one corner of Russia meant that, most likely, they had something in common.
If there was no connection between them, the likelihood that such a number of rare trepanations would occur only in southern Russia would be extremely small.
Gresky, Batieva and their colleagues state that, despite the fact that their conclusions are difficult to prove, the accumulation of such non-standard trepanations suggests that a kind of ritual trepanation center could have been located in southern Russia.
Maria Mednikova, a leading researcher at the Institute of Archeology of the Russian Academy of Sciences, is a specialist in the field of trepanations that took place in Russia.
She is sure that trepanation in certain dangerous areas of the cranium could be carried out to achieve a kind of "transformation".
According to her, people did this, thinking that they would acquire unique abilities that ordinary members of society did not have.
We can only guess why these apparently healthy people had to endure trepanation done in such an unusual and dangerous way.
However, the holes themselves tell us a lot about the fate of people after the operation.
One of the 12 skulls belonged to a woman under the age of 25, whose skeleton was found at a burial site near Rostov-on-Don. It showed no signs of healing, and it can be assumed that she died during or shortly after surgery.
Nevertheless, the rest, apparently, more or less successfully survived trepanation. New bone tissue began to grow along the edges of the trepanation holes, but it did not fill the entire hole.
Trepanned skull of a 30-35 year old man, one of five people buried in a common grave. The hole is partially overgrown - this means that after the operation he lived at least four years
Three of the 12 skulls showed only slight signs of healing along the edges of the burr hole. This means that after the operation, these people lived for only two to eight weeks.
Two of them were women from 20 to 35 years old, and the third was an elderly person from 50 to 70 years old, whose gender could not be determined.
On the rest of the turtles, the holes are much better. Based on modern knowledge about bone tissue regeneration, it can be concluded that after the operation, these people lived for at least four years.
Among the eight survivors were all five from the mass grave near Rostov-on-Don, whose unusual trepanations first attracted Batieva's attention almost 20 years ago.
Two men, two women and one teenage girl were able to live for several years with a hole in the obelion area.
The girl, who, judging by the skeleton, was from 14 to 16 years old, underwent trepanation no later than her 12 years old, or even much earlier.
However, it cannot be ruled out that these 12 people did suffer from diseases or head injuries. If so, trepanning helped at least eight of them.
However, it is also possible that Batieva and her colleagues are right, and these people were trepanned for ritual purposes.
If so, we can only guess what benefit - real or imagined - they got from it.