A young adult unearthed in a Borneo cave is the earliest-known case of a successful major limb amputation.
The hunter-gatherer's skeleton was missing the lower third of their left leg, which appeared to be chopped off by a sharp stone tool when they were a child.
The remains were dated to around 31,000 years old — more than 20,000 years earlier than the previous oldest limb amputation, which was the French discovery of a man who had his left forearm removed 7,000 years ago.
What's more, the person found in the Borneo cave not only survived the operation, but lived up to a decade afterwards too.
Their skeleton was unveiled in the journal Nature today.
Tim Maloney, an archaeologist from Griffith University and study co-author, said the successful amputation strongly suggests early societies, at least those in Borneo, understood advanced medical concepts.
"Not only of the operation itself and negotiating the complexities of removing the lower left [leg] of a child, but there's a very strong case for [their] understanding the need for antiseptic and antimicrobial management to enable the patient, this individual, to survive."
The fact that the child survived into early adulthood also shows ongoing post-operative care and support to negotiate the rocky terrain, Dr Maloney added.
"This individual was a valued member of their community. It's very unlikely that they could have lived without a high degree of community care."
A rare find, made rarer by the amputation
The bones were found in a vast, airy limestone cave called Liang Tebo in eastern Kalimantan, the Indonesian part of the island.
Like many caves in the mountainous region, it is rich in ancient art, such as panels of bright red ochre hand stencils adorning chamber walls, with some in the area dating back as far as 40,000 years.
But who left these compositions is a mystery.
While archaeologists have found artefacts such as stone tools in these caves, human remains are much harder to come by. That's because in the hot, humid, insect-filled tropics, bodies tend to decay and fall apart, or be nibbled before they're preserved.
Even being buried in the cooler, more protected rock shelters isn't an ideal scenario. The soil there can be acidic, thanks to the bats that dwell and poop inside the caves.
So in 2020, when the bones of the young adult, perhaps in their early 20s, were discovered in a deliberate burial pose with a lump of red ochre near their head, Dr Maloney and his colleagues in Australia and Indonesia suspected they'd found someone belonging to this artistic society.
They dated sediments around the skeleton, as well as one of the skeleton's teeth, and calculated the person was buried around 31,000 years ago.
This not only fit with the timing of the artworks in the region, but also made it the oldest-known burial of a modern human on South-East Asian islands.
As the archaeology crew slowly and carefully unearthed the bones, they realised the skeleton was missing their left foot and part of the lower leg.
The ends of the left lower leg bones, the tibia and fibula, looked like they were cut with something sharp, but had healed well.
Those healed sections suggested the leg was lopped off maybe six to eight years before the individual died, which meant they were a child or young teenager when it happened.
The bone looked different to what you'd expect if the foot and leg were bitten off, or crushed under a rock, Dr Maloney said.
"Typically when bone fractures in, say, in a rock fall event or the, I presume, quite powerful jaws of a large reptile like a crocodile or anaconda or any such Borneo critter … [they] do not match the signature we have from the Liang Tebo individual's left leg."
As to what the "surgeon" — or surgeons — used to amputate the limb isn't known, but the "scalpel" was likely a sharpened handheld piece of rock, perhaps something like obsidian, said Renaud Joannes-Boyau, a Southern Cross University geochemist who dated the tooth.
"People have found obsidian blades from prehistory that are still so sharp that you could cut yourself.
"And when you go through cutting ligaments and cutting between bones and so on, you probably would need other tools as well.
"But we have no real clue what they used."
How one person can be a window into society
Piecing together a person's medical history based on ancient bones is a tricky task at the best of times, said Kate Domett, a James Cook University palaeopathologist who was not involved in the study.
"Based on the evidence that I can see [in the study], it certainly could be an amputation.
"It's very unusual, which makes it hard to interpret. You don't come across this sort of thing very often."
Deep dives into one person's skeletal remains — an "osteo-biography" of sorts — can give us an idea of what their wider society was like, Dr Domett said.
"There was obviously a sense of community. They were cared for for a significant amount of time during healing.
"But also, if somebody had this [amputation] done, not only did the community know it was the right thing to do, it does suggest that maybe they've tried it before."
Amputation isn't just a matter of hacking off a bit of the body. Those early surgeons would, for instance, have known to keep a flap of skin to fold over and protect the wound.
The skeleton also had a healed neck bone fracture, but whether that happened at the same time as the injury or infection that forced their leg to be amputated isn't clear.
"It's really difficult to link them to a single event because bone remodelling occurs at such different rates [in different parts of the body]," Dr Domett said.
"Or maybe their mobility was affected, which made them more vulnerable to having other accidents after the amputation."
It's likely the person had a wooden walking stick or similar to help navigate the mountainous terrain, Dr Maloney said. But if it was buried with the person, it's long gone.
More stories to be told
At the time of the Liang Tebo person's life and death, the world was in an ice age. Sea levels were far lower than they are today, connecting many islands in South-East Asia.
Also around this time, on the other side of the planet, people were potentially amputating fingers.
A site in southern Poland called Obłazowa 1 has "a number of fingers without skeletons", said La Trobe University archaeologist Andy Herries, who wasn't involved in the study.
"That has been interpreted by the excavators as potential evidence for fingers that have been lopped off."
But, he said, if that was the case, "they're doing it potentially for a very different reason, in that it is meant to be some form of symbolic thing.
"This [Liang Tebo] situation appears to be life-saving, and is the first evidence we've got for medical intervention of that magnitude."
The researchers are not yet done with the skeleton. Dr Joannes-Boyau is now trying to pin down the exact age of the person at the time of their amputation by examining their teeth more closely.
When we experience physical or emotional trauma, our body changes the trace elements it adds to layers of enamel while our teeth are still in our gums.
This signature, or "stress signal", can be picked up in his lab.
"For instance, birth is traumatic for the baby, and you can actually pick up [being born] as a stress line in teeth," Dr Joannes-Boyau said.
"The amputation would have been an ongoing stress for several months until it healed.
"So we should see a very, very large stress line, or very strong stress period."
Meanwhile, the researchers are going back to Liang Tebo in the hope they strike gold again.
Maxime Aubert, a Griffith University archaeologist and geochemist who is part of the study, said they're heading back early next year to dig more out of the cave floor.
"We're going to go deeper, but also … wider as well, so it's going to be very exciting and we will find new things."
