Secrets of the Sky Tombs

Evidence discovered in the world’s highest tombs reveals ancient rituals and beliefs. Airing February 21, 2018 at 9 pm on PBS Aired February 21, 2018 on PBS

  • Originally aired 01.04.17

Program Description

The towering Himalayas were among the last places on Earth that humanity settled. Scaling sheer cliff sides, a team of daring scientists hunts for clues to how ancient people found their way into this forbidding landscape and adapted to survive the high altitude. They discover rock-cut tombs filled with human bones and enigmatic artifacts, including gold masks and Chinese silk dating back thousands of years, and piece together evidence of strange rituals and beliefs designed to ward off the restless spirits of the dead.




Secrets of the Sky Tombs

PBS Airdate: January 4, 2017

NARRATOR: They came to live in the highest place on Earth; they buried their dead even higher.

MARK ALDENDERFER (University of California, Merced): Check it out.

SUSAN SIMS: Check it.

NARRATOR: Littered among the bones are stunning artifacts.

MARK ALDENDERFER: The part I hate the most is you make a dumb move, you're done.

NARRATOR: Top technical climbers are needed to reach the early human remains.

Somehow, the ancient people adapted to the Himalayan extremes, but life wasn't easy.

JACQUELINE ENG (Western Michigan University): This might be the cause of death for this person. It's hitting right here, kind of, at the occipital temporal mastoid junction.

MARK ALDENDERFER: People are people, there's always conflict and violence.

NARRATOR: Relics are unearthed from sacred death rituals.

CHARLES RAMBLE (Sorbonne University): This is how the vampire firebrand came into being.

NARRATOR: Archaeologists are uncovering the Secrets of the Sky Tombs, up next, on NOVA.

The Himalayan Mountains, Earth's tallest, pierce the clouds. Called the "roof of the world," the terrain is so high, the air so thin, this was one of the last places on Earth humans came to inhabit.

Today, about 6,000 people eke out a living here, in a region called Upper Mustang. Their villages are oases in a high-altitude desert.

Above several of the villages are caves, carved by hand long ago. Many are so hard to reach no one has entered them in recent memory.

But for years, human bones have tumbled out of the caves, tantalizing clues that ancient inhabitants of the Himalaya are buried here. Who were these people? Where did they come from? And what drove them to populate such an extreme environment?

An international team of scientists and climbers are mounting an expedition to explore the caves. Himalayan alpinist, Pete Athans, has climbed Mount Everest seven times.

PETE ATHANS (Explorer): I've been coming to Nepal, now, more than 35 years. The type of skills that I bring to the table is the physical ability to get into the caves, getting our scientists into the caves, more importantly.

NARRATOR: Pete has assembled a team of scientists and the world's best climbers.

PETE ATHANS: Is that pretty much above the big portal, as far as you can tell?

LIESL CLARK (Producer): He can probably make it in from there, but he might have to swing a little bit.

NARRATOR: There are over 10,000 caves here, and they've targeted the most promising.

MATT SEGAL (Professional climber): This one?

LIESL CLARK: You got it.

NARRATOR: The climbers are working with archaeologist, Mark Aldenderfer.

MARK ALDENDERFER: The big question that we're trying to solve with this project is where did people come from that began to live here in these high Himalayas? What were their origins? When did they come here?

NARRATOR: The task is enormous, made ever more difficult by the unforgiving altitude.

The river valley that runs through Upper Mustang is one of the only north-south passages through the Himalayas in Nepal. It's an ancient trade route, connecting India to the south with China's Tibetan Plateau to the north.

For centuries, Mustang served as a cultural crossroads between Tibet and the Indian subcontinent, yet it managed to keep its ancient fortresses and pastoral identity hidden from foreign visitors, until 1992.

The locals are skillful traders. Their cash crop is goats.

What defines the people are their Buddhist beliefs and a traditional way of life. Living at such high altitude is not easy. Of the five babies born in one of Upper Mustang's villages in one year, only three survived.

Could Mustang's modern people be the descendants of those who are buried in the caves? Who were the mysterious people, and why did they carve these sky tombs?

The team treks to one of the highest villages in the region, called Samdzong. It's just 10 kilometers from the Tibetan border. To get there, they have to cross a mountain pass at 14,700 feet.

Pete's children have grown up in the Himalayas, coming to Nepal every year since they were toddlers.

FINN CLARK (Pete's Son): Going up a pretty big pass.

NARRATOR: They're at an altitude where pilots in unpressurized planes must breathe supplemental oxygen.

FINN CLARK: Curse this.

NARRATOR: Low levels of oxygen can cause debilitating symptoms in people who don't live here. The expedition members are among the first foreigners in modern times to visit Samdzong, which means "Earth fortress," named after a stronghold above the village, now a crumbling ruin.

To show respect for local traditions, the expedition holds a "puja," a Buddhist offering to the mountain deities, before scouting cliff-side caves in the area.

Pete's son, seven-year-old Finn, is the first to find a human bone, below some caves. He shows it to bioarchaelogist, Jacqueline Eng.

JACQUELINE ENG: Finn found this humerus of a human. You can see it's a proximal humerus, on the right. Don't know what context this comes from, maybe washed down from somewhere.

NARRATOR: Caves dot the rock face above them. The cliffs have eroded over time, exposing the contents of the tombs, which were likely first accessed by shafts, dug by early people, from above.

CORY RICHARDS (Adventurer): We've rapped into two chambers that are connected, that have lots of what appear to be human remains and animal, as well, as well as more bones on the outside.

NARRATOR: Pete will first map the bones and artifacts, to provide context.

PETE ATHANS: What we want to do is to quickly draw, label and then number, and then get them down to the scientists, so they can start to take a look at these things and give us an idea of what and whom they belong to.

NARRATOR: Human remains have been tumbling out of the cliff-side graves for years. Because the caves are swiftly eroding, this vertical dig for artifacts and bones qualifies as rescue archaeology.

There are 10 cave tombs, in all.

Although he has a fear of heights, Mark has to see the tombs himself, to fully understand the site.

LIESL CLARK: Does it ever get easier?

MARK ALDENDERFER: Unh uh, no. The part I hate the most is actually walking up that trail. It's really narrow, and you just make a dumb move, you're done.

NARRATOR: Pete puts Mark on a double rappel—both ropes clipped into Pete's safety device—so he can stop Mark, if he falls.

It's a 200-foot cliff, with a 40-foot drop into the uppermost caves.

First, excess dirt from collapsed walls is removed from the caves. Then, the dirt is sifted to uncover the smallest artifacts. Each haul bag holds as many as a hundred bones, about half an individual.

Mark believes the caves were carved out intentionally, to entomb the dead.

MARK ALDENDERFER: People carved these caves because this was their cultural pattern on how to deal with the dead. You know, we westerners often put ourselves in cemeteries. These folks, here, created a different kind of cemetery, what I would call a communal tomb.

NARRATOR: The team finds thousands of bones. They'll analyze each one to piece together the story of the unknown people.

MARK ALDENDERFER: Now, the hard part begins, doing the lab work.

NARRATOR: For Jacqueline Eng, studying bones is like reading the personal diaries of the dead.

JACQUELINE ENG: I'm always a little bit in awe, when I do get to handle human remains, because it's one of the last stories that these people can tell: what they experienced in life. "I died young." "I had this infection." Or "I died peacefully."

NARRATOR: Jacqueline determines that a minimum of 105 individuals were buried in the Samdzong cave tombs.

Later, carbon dating of the remains will show the people lived between 400 and 650 A.D.

But there's something unusual about how the ancient people treated their dead.

JACQUELINE ENG: Here's a couple of&hellip

MARK ALDENDERFER: Good god! That's a cut mark.

NARRATOR: Clear cut-marks from a knife are evident on many of the bones. In some instances, multiple cuts are found in one place. This is not the distinctive pattern of cannibalism, but it indicates the Samdzong people were dismembering and de-fleshing their dead.

This bears some resemblance to the local funeral practices today: the Buddhist ritual of sky burial. When a villager dies here, they're not buried underground, but are offered, in a high place, to birds of prey, to ensure the deceased do not return to their bodies.

CHARLES RAMBLE: At the present time, as soon as somebody dies, the first thing that the family will do is to break that person's back, because they have a visceral fear of the dead body becoming a "rolang," which is a term generally translated as "zombie." The idea is that a person dies, and his or her consciousness departs from the body, doesn't realize it's dead, sees the body there and then tries to re-inhabit it.

This is one of the reasons, they say, why they don't bury the dead, because they might rise again.

ANG TEMBA SHERPA (Himalayan Guide): At first, when they bring the dead body here, they tie both hands and both feet on the top of the rocks. And then the lama pray. Then the vultures come. Anybody can cut this dead body, and make pieces and give them to the birds.

NARRATOR: The flesh, and even the bones, are cut into small enough pieces for the vultures to consume. But, unlike the ancient bones preserved in the caves, this Buddhist sky burial is performed to ensure nothing of the body remains. Its purpose is to give the dead a chance of being reincarnated to live another life.

ANG TEMBA SHERPA: So, if we really take care of that man, he will be reborn in a good life, somewhere.

NARRATOR: Buddhism, with its custom of sky burials, is thought to have spread through this part of the Himalayas more than a century after the Samdzong people lived and died here.


NARRATOR: Yet, an artifact found in one of the Samdzong tombs challenges this notion.

MARK ALDENDERFER: There are some interesting Buddhist-era remains in that, that we did not expect whatsoever. It's like a little plaque, made out of clay, and it's got a seated Buddha.

NARRATOR: A Buddha in a cave with human bones seems out of place.

MARK ALDENDERFER: It's a very funny mixture. They're still doing the de-fleshing, but yet, they've got Buddhist elements with them.

MOHAN SINGH LAMA (Excavation Officer, Nepal Department of Archaeology): Yeah.


NARRATOR: Why does a cave holding the de-fleshed bones of a people predating Buddhism by more than a century have an image of the Buddha in it?

MARK ALDENDERFER: Early Buddhism and how it spread is really a big open question. Nobody's really found clear and convincing evidence of their mortuary patterns, so, these findings are pretty exciting.

NARRATOR: This could be the earliest Buddhist relic ever found in the high Himalaya.

MARK ALDENDERFER: Look how fragile.

CHARLES RAMBLE: You have this Buddhist artifact there, which seems to be much earlier than it should be. In theory, it should be no older than the seventh century, but the archaeological evidence seems to suggest it is older. So, we have Buddhism on the edges of the Tibetan Plateau, at least, quite a long time before the official introduction of the religion into the area.

What you also have is evidence of a type of burial that precedes the Buddhist form of burial that took over in Tibet in the late eighth century. So, the fact that Buddhism is also present does indicate that we're at a transitional stage.

NARRATOR: It's possible Buddhism started earlier here than previously known, and people buried the bones of the dead after removing the flesh. The rite perhaps foreshadowed the sky burial practice of today.

A forensic investigation of Samdzong's artifacts commences, to determine their possible origins.

One cave had a coffin-like bed inside.

MARK ALDENDERFER: Hmm, that's leather.

SUSAN SIMS: That's leather.

NARRATOR: Alongside the bed were the remains of a horse and some horse tack, suggesting the body was that of a prominent individual. Rich artifacts, like a large copper pot, bronze bracelets, iron daggers and glass beads, littered the grave.

Two mysterious pieces of metal were also found in the cave.


PETE ATHANS: I really don't want to flatten it too much. So, that look like a nose?

CLEO CLARK-ATHANS (Production Assistant): That kind of looks like an eye.

MARK ALDENDERFER: We have two masks.

NARRATOR: They are death masks. And there's even a third one.

CLEO CLARK-ATHANS: Please don't break!

MARK ALDENDERFER: Here we go. Check it out. This guy's got more color.

SUSAN SIMS: Check that out.

NARRATOR: They need to determine what metals the masks are composed of and where they were made.

So a sample is sent to University College London, for analysis by metallurgist, Giovanni Massa.

He found there are two layers of precious metals in the masks.

GIOVANNI MASSA (University College London): What you see in this picture is a section of one of the masks, and you can clearly see there are two different colors. The front, in yellow color, which is the gold layer, and the silver, which is the back of the mask.

The technique that they used was hammer welding.

NARRATOR: There are no gold and silver deposits to be found nearby, and the technology needed to hammer gold and silver into death masks indicates the craftsperson who created them was highly skilled.

GIOVANNI MASSA: What is actually very striking is the thinness of the mask—around 50 microns—which is less than the thickness of a human hair. In fact, to make the artifact, you won't need a lot of material. You would need a sphere of about this size for the silver layer and an even less amount of gold.

NARRATOR: Pinholes can be detected on the outer rim of the mask.

GIOVANNI MASSA: The pinholes were used to attach the mask to something else, in order to, actually, have it stable on the face of the person.

MARK ALDENDERFER: I think the mask was actually sewn onto a fabric, and the glass beads were sewn onto that fabric, as well, and formed a fairly elaborate headdress.

The mask covered the face, the fabric covered the head, and then the glass beads were covering that fabric itself, draped down over the shoulders onto the chest; must've been absolutely spectacular.

GIOVANNI MASSA: What you see is an incredibly rich collection of artifacts, pretty much any alloy you could think of. One of the medallions found is stylistically completely different from the rest of the collection.

You have the copper vessels that are just hammered surfaces, very simple. You have the brass bangles that have very simple decorations. And then you have this beautiful medallion. All this shows that these people were connected to a network.

NARRATOR: By the time the Samdzong people were adorning their dead with gold masks, traders from Asia were exchanging goods with Europeans, along an ancient trade route to the north, called the Silk Road.

The cave-buried people might have come from the vast area we know today as China, or are these simply trade goods from the north?

They need more evidence.

A single piece of cloth found in one of the caves could provide a clue. Textile expert, Margarita Gleba, at University College London, made a discovery using a scanning electron microscope that can magnify specimens up to 30,000 times.

MARGARITA GLEBA (University of Cambridge): This textile seemed to be made in what we call plain weave, or also known as tabby.


MARGARITA GLEBA: And that is the simplest type of weave you can create on a loom. So it's one over, one under.

A curious thing with this particular sample is that all the fibers appear to be parallel to each other, but they are not twisted in any way.

NARRATOR: Most thread or yarn is produced by spinning short fibers, like this wool. The twisting action gathers them together into a single long thread.

MARGARITA GLEBA: The only fiber that allows you to produce a thread without a specific twist is silk. And the reason for that is that silk fibers are extremely long. A single silk fiber, when unrolled directly from a silk cocoon, can reach up to two kilometers in length.

We can be quite sure that we are dealing with Chinese silk.

NARRATOR: Since the cloth found in the cave is silk, could this suggest the people came from China?

The Samdzong remains only date to 400 A.D. The earliest known pottery in the region dates back to 800 B.C., so, there must have been people earlier than Samdzong, and Mark wants to find them.

Today's archaeological objective is a cave at 10,000 feet, known as Rhi Rhi. It's a few hours journey from the nearest town. A complete kitchen, cook staff, climbing gear, tents and food make up the loads, which will have to be carried across a river called the Kali Gandaki.

This is the deepest river gorge in the world, carved by the glacial meltwaters of some of the world's highest mountains. Any other time of the year, the river runs so high here it's impassable.

With anchors firmly in place, Pete can rappel down a slope most climbers would avoid altogether. Pete leads another double rappel with Mark.

MARK ALDENDERFER: Hold on a sec.

PETE ATHANS: Okay, and you can just keep lowering yourself in, ‘til you're seated at the edge.

There you go.


NARRATOR: It doesn't take long for them to find what they're looking for.

MARK ALDENDERFER: These are all human bones that we're coming up with, at the moment.

NARRATOR: A hand-carved wooden peg is among the first artifacts found.

MARK ALDENDERFER: It looks like one of those little daggers. That's a really cool thing.

NARRATOR: What Mark really wants to find is black pottery that would suggest the burials are around 3,000 years old.

MARK ALDENDERFER: This is some good pottery. Oh, look. Yeah, there's blackware, too, wow. Very nice.

Thank you, Satish.

NARRATOR: The pots are definitely black, with characteristic thick handles.

Carbon dating later confirms the burials are 2,800 years old, among the earliest ever found in the Himalayas.

Mark unearths a deep hole in the cave, where the early people were entombed.

MARK ALDENDERFER: What we're looking at is a pit. And then, at some time, they just bring them up here, open up the pit and put them in, and then go back.

NARRATOR: They ultimately find the bones of about five people.


PETE ATHANS: Yep, you're good.

Okay, nice and easy.

MARK ALDENDERFER: Okay, I'm with you.

NARRATOR: For the local people, finding human bones can be unsettling, because they believe in completely eliminating the remains of a corpse after death.

Molecular anthropologist, Christina Warinner, notices that the bones have been disturbed and altered by visitors to the cave.

CHRISTINA WARINNER (University of Oklahoma): A group went in much, much later, and they applied ocher to the remains. Ocher is this mineral pigment that's naturally occurring.

This red ocher has been rubbed on some of the bones, and in other cases sprinkled on them. We know that it was applied after death, because we find it both on the exterior of the skeletal remains and also on interior surfaces. So, it must've been applied after the body had already decomposed.

NARRATOR: It's possible this was done by Buddhists, long after the initial burials.

CHRISTINA WARINNER: So, they didn't just ignore them or remove them, but, actually, actively engaged with them. That's very unusual for this region.

NARRATOR: Another find from the cave supports this theory. Mixed in with the bones, and broken into pieces, was a one-foot-square ceramic object, marked with strange engravings.

MARK ALDENDERFER: If you look carefully at the surface, you see little daggers. The use of these daggers, like this, is usually some kind of exorcism that's taking place, to get rid of some sort of evil or maleficent spirit that happens to inhabit a place.

CHARLES RAMBLE: "Dagger" describes the object that's called in Tibetan "phurba," a stake, basically, and it's, like any spike, the fundamental purpose is to hold something down, to stab it ritually and make sure it stays down.

NARRATOR: Mark believes the dagger object was left by later visitors to the cave, probably early Buddhists performing an exorcism, in reaction to finding the bones.

MARK ALDENDERFER: They enter these sites at some time in the past, after the people have been buried in them. They encounter the bones, and they become frightened by them.

NARRATOR: If this interpretation is right, the daggers symbolically hold down the bones, like stakes, to prevent them from becoming reanimated.

The remains of the original occupants of the cave are from some of the earliest people yet found. Mark wants to figure out where they came from.

For years, scientists believed these people migrated from the south, what is now India, because it was much more populated than the Tibetan Plateau, and the lands to the north, now China.

A discovery in the early 1990s seemed to confirm the link to India. In a cave complex in Mustang, called Mebrak, German and Nepali archaeologists discovered the Himalaya's first mummies, naturally preserved by cold and dry conditions.

Carbon dating placed the 42 individuals as far back as 400 B.C.

Since their discovery, the mummies have been stored in Kathmandu, until Mark received permission to examine the remains.

FINN CLARK: There's still a little bit of flesh on it.

MARK ALDENDERFER: You've got that right.

NARRATOR: Some are still intact, like this mummified two-month-old baby. Some of the bodies were found on wooden bunk-like beds, in a fetal position, ankles and wrists bound together with cloth. No other burials like this have ever been seen in the Himalayas.

The artifacts look like they originate from the south, from what is now India, and include ornamental gourds, carved wood, a bamboo flute and even glass beads. India has been making glass for over 3,000 years.

This suggests the early people of the Himalaya could've come from India, but it's not that simple. Each cave burial the team uncovers in Mustang is different from the others. Some are de-fleshed, some buried in pits, and others found on bunkbeds.

There are influences from a number of regions, so the settlers could have been from different cultures across Asia.

There's a mystery here that can't be solved by examining artifacts alone.

CHRISTINA WARINNER: Many people proposed different hypotheses about where the people initially came from who colonized the Himalayan Mountains, but none of these lines of evidence was conclusive. What we really needed was D.N.A. from those first people, in order to solve that problem.

NARRATOR: D.N.A. is the double helix strands of chemicals in our cells that carry our genetic information and can reveal what we've inherited from our ancestors. If Mark can procure D.N.A. from the cave burials, he can find clues to their origins.

MARK ALDENDERFER: Upper molar two.

NARRATOR: A tooth's enamel is the hardest tissue we have. It can protect the D.N.A. preserved within the tooth for thousands of years.

Mark extracts teeth from the Mebrak mummies to add to his samples from the other caves.

MARK ALDENDERFER: This one was very hard because it has much flesh keeping it together.

NARRATOR: For the teeth that are difficult to extract, he plays dentist to the dead and uses a rotary tool to free the tooth from the 2,300-year-old mandible.

The teeth go to Christina Warinner's lab at the University of Oklahoma. It's a highly sterile workplace, built to protect ancient samples from the modern D.N.A. that surrounds us.

CHRISTINA WARINNER: There is D.N.A. everywhere. Every time you cough or sneeze, you're putting D.N.A. into the air. So, if we want to be able to recover this very ancient and degraded material, we have to get rid of all of that extraneous D.N.A., as much as possible. So, we conduct this work in special laboratories that have highly filtered air; we have ultraviolet radiation built into the ceiling to sterilize the room in between uses; and we wear these Tyvek suits, which help keep our D.N.A. in. Most people, when they see them, they're used to seeing them in context of people in epidemics trying to protect themselves from disease. We wear them for the reverse reason. We're trying to protect our samples from our D.N.A.

We clean the teeth with bleach to remove and destroy any D.N.A. on the surface. In a way, it's almost like getting a very belated dental cleaning. We use an abrasive tool to remove the outer layer, to really scrape off these contaminants. And then we use ultraviolet radiation that causes damage in any D.N.A. that's still remaining on the surface. We can then liberate the D.N.A. from the tooth itself.

NARRATOR: Tina's meticulous cleaning methods pay off. She's found some of the best preserved ancient D.N.A. ever sequenced.

CHRISTINA WARINNER: That is extraordinary and likely resulted because the region is so cold and dry.

NARRATOR: One hundred milligrams of tooth material, about the size of a pea, is all that's needed to fully sequence a single human genome, the genetic blueprint, unique to each of us, that contains traces of our ancestors' D.N.A.

CHRISTINA WARINNER: We can take these pieces of D.N.A., from that, we can painstakingly reconstruct the genome of that person and learn all sorts of things about them: what they looked like; if they're male or female; we can learn where their ancestors came from.

NARRATOR: Geneticists can find out clues to our origins by looking closely at small variations in our D.N.A. and comparing them to other groups.

Population geneticist Anna Di Rienzo found that the genomes of all the samples collected in Mustang, even those from different caves, are very similar.

ANNA DI RIENZO (University of Chicago): One of the major findings of our study is that the gene pool of these populations hasn't changed in a major way over the period of time that we have sampled, which is roughly 3,000 years.

NARRATOR: After comparing the samples from the cave people with each other, Anna then compared the genomes with different present day populations around the world.

She's looking at small sections of their D.N.A. for similarities and differences in the order of D.N.A.'s four chemical bases, abbreviated as A, C, T and G.

ANNA DI RIENZO: We can ask with this analysis, "Who are the populations that are closest, genetically, to our samples?"

NARRATOR: Surprisingly, there was no match with people from any part of India today. The results indicated the Himalayan peoples are most closely related to East Asians, including today's Japanese, Han Chinese, Tibetans, and the Sherpas, who live near Mount Everest.

So, the earliest Himalayan people came from the north, from East Asia and the Tibetan Plateau.

Although their burial customs differed from one group to another, and some had artifacts from India, and lived at different times, genetically, all the cave people were very close.

CHRISTINA WARINNER: The genetics were incredibly stable through time. This was fascinating to us, because we saw big changes, for example, between the Mebrak and the Samdzong period. We suddenly see de-fleshing. That's a new thing, that's a religious change; and yet we don't see any change in the underlying genetics of the population.

NARRATOR: But researchers have spotted one genetic change, specific to high-altitude peoples of the Himalaya. It's an ancient mutation, or gene variation, a change in the order of the chemical bases, the As, Ts, Cs and Gs that make up the gene. The variant prevents people from getting sick at high altitude, where the available oxygen is low.

CHRISTINA WARINNER: There are a few places in the genome, a few traits, in which we have experienced very recent evolution. So, one of these would be the adaptation to high altitude. There's only a handful of these genes that are very, very recently undergoing selection, and this is one of them.

NARRATOR: Most of the Himalayan people that live here now have this variant. The team wants to know if the ancient people buried in the caves also had this mutated version of the gene.

To gather even more D.N.A. samples, the team heads to another burial site, in a region called Nar-Phu, where there are reportedly hundreds of bones.

Although it's only 30 miles away, as the crow flies, due east, getting there takes three days of driving and another three days on foot. It'll take 10 hours to hike to 12,000 feet in a day, a rapid 4,000-foot gain in elevation, not enough time for most people to acclimatize, or adjust, to the altitude.

PETE ATHANS: You'll see, as we're walking uphill, steadily gaining elevation, we have to breathe a lot heavier, might just feel like our performance is really down. Now, a lot of the locals don't really feel that, because they have that special makeup in their D.N.A., and it allows them to acclimatize very quickly. Meanwhile, we're out of breath. We're definitely feeling a lack of performance. We might feel like we have a little bit of a headache, a little dizziness.

NARRATOR: There's about 35 percent less oxygen available here than at sea level, so the team keeps track of how much oxygen is getting into their bloodstream, as their bodies adapt.

PETE ATHANS: We're at Meta, which is at about 11,700 feet, and we're just going to be checking the level of oxygen concentration in the bloodstream with a pulse oximeter.

The lower number is the pulse rate and the upper number is the percentage of oxygen that's being carried by the blood.

NARRATOR: When we breathe, oxygen enters our bloodstream and provides our cells the fuel they need to carry out their jobs. At sea level, a healthy person should have at least 95 percent oxygen saturating their blood cells. But at 12,000 feet, lowlanders who first arrive will only have between 80 and 90 percent.

PETE ATHANS: There is about an 82 percent carrying capacity of O2, percentage of oxygen in the bloodstream, currently. And their pulse is at about 108, 109. These are fairly common numbers, actually, for arrival at altitude.

MARK ALDENDERFER: …for unacclimatized folks.

PETE ATHANS: …for an unacclimatized person.


NARRATOR: If Mark were at sea level, 82 percent would be a low blood oxygen saturation, called hypoxia, and he'd be given bottled oxygen to breathe, but at altitude this figure is normal. In contrast, Himalayan people can tolerate low levels of oxygen, thanks to a genetic trait.

MARK ALDENDERFER: Somebody who lives at altitude that's got the appropriate genetic adaptations, I'd expect their pulse rate to be lower. I'd also expect their oxygen saturation to be significantly higher than folks like me. I guess we'll test that now.

Temba, where were you born?

ANG TEMBA SHERPA (Himalayan Guide): I was born in the Everest region, which is the elevation about 12,600 feet.

MARK ALDENDERFER: My expectation is, is that Temba will have a relatively low pulse rate, and he'll also have a relatively high oxygen saturation in his blood, because he's adapted to high-elevation life, genetically.

Your saturation is what? I can't see it very well. It's 92, 91? And his pulse rate is 78. You know, pretty typical for folks that are adapted to this kind of life.

NARRATOR: If most of the people living here today have this genetic variant, the question is when and where did this adaptation begin to appear?

The team moves ever-higher, into the cold and arid alpine zone at 13,000 feet. It's a wonder people came to settle here at all.

The villages are abandoned, as locals have gone to higher pastures for foraging. Life is hard here, which is why the Himalayas were settled so late.

MARK ALDENDERFER: If you look at the pattern of human migration over the last 2,000,000 years, mountains are one of the last places on the planet to, in fact, be occupied. Deserts come earlier. Polar extremes, like around the Arctic Circle, come somewhat earlier, as well. Mountains come somewhat later. These are difficult places for people to live.

NARRATOR: They've reached their destination of Kyang. The village feels like a ghost town.

PETE ATHANS: There's really nobody around. I walked through, just trying to talk with some people, but it didn't look like, I mean, there were a few donkey people, just around the corner, but they left about 15, 20 minutes ago.

NARRATOR: These are the same pastures the early inhabitants used for their animals, thousands of years ago.

MARK ALDENDERFER: Somebody lived here some long time ago, built the site and buried their dead somewhere around here, on these relatively fertile pieces of ground, surrounded by these incredible vertical environments.

We will have to find out what the dates are and if there are any associated artifacts that give us a sense of what this group of people might be related to, because, right now, they are essentially unknown to us, except for the fact that they exist.

NARRATOR: The team is anxious to see if Pete can get inside the cave.

FINN CLARK: We can watch the GoPro, what Dad's doing, filming, on here, live.

NARRATOR: About 800 vertical feet above the village is the naturally occurring cave, with manmade walls stacked above it.

PETE ATHANS: Work our way up, like, from the right, and up and around the cleft.

NARRATOR: Pete's objective is to get safely inside, to photograph the interior.

PETE ATHANS: We're at the base of the big crack now.

It's just that it's exposed, and there's a lot of loose rock stacked up on the ledges. If you grab the wrong handhold or foothold, you could send a big rock down, or you could fall.

NARRATOR: Pete free-climbs the large crack leading deep into the cave. He'll place an anchor above him, for a safety rope if he falls.

PETE ATHANS: Going up into the cleft and way back into the dark, wearing a respirator mask and a headlamp, it can be very narrow. I can certainly get very claustrophobic moving in there.

It's very dusty inside. There's a lot of remains from birds and bats and every manner of rodent in there.

You're just inching your way up through this crevice, and then you enter this very spacious bone room. It was very much crypt-like.

Hey, Mark, you guys copy?

MARK ALDENDERFER: Yes, we copy, Pete.

PETE ATHANS: I have a couple of jaws here, couple of femora, and then a few other human pieces, a piece of wood that's pretty interesting, that are all in a bag, right here, we'll collect on the way down. Break.

NARRATOR: The climb is too technical for the scientists to get inside, so, Pete maps out sections of the cave on a grid, and all bones and artifacts are bagged according to their location.

PETE ATHANS: The process with the grid that we're lining out is really just to try to give the archaeologists an idea of where, in the cave, these materials were actually taken from.

NARRATOR: The original burials have been disturbed, most likely by looters looking for valuable funerary goods.

PETE ATHANS: There's a real scattering of materials. It looks like someone had actually been doing some digging, right down in this area, to my left. So, we're looking at a context that's more disturbed than I had anticipated.

NARRATOR: It takes three days to fully excavate every bone and artifact from the cave.

MARK ALDENDERFER: Okay, I've got the bag, if you guys pull.

NARRATOR: The next step is to look for signs of death rituals.

FINN CLARK: People's heads.

MARK ALDENDERFER: People's heads, yes.

NARRATOR: The presence of animal bones suggests they were sacrificed to bury with their human owners.

MARK ALDENDERFER: This is a very common pattern in this part of the world is to inter the dead with domesticated animals of one kind or another. Here in Kyang, the only ones that we've seen so far are sheep or goat.

CHARLES RAMBLE: If you find animals in a grave, like that, there's got to be a reason for it. It's most likely that the animals were sacrificed and placed with the dead person, for one of two reasons: either to be food in the next life, to constitute part of his or her herd; or, as the animal that guided the dead in the afterworld.

NARRATOR: Every scrap of evidence is analyzed.

MARK ALDENDERFER: It's definitely been imprinted on there, somehow. Good eye, Finn. I bet if we wet it in water,…

Oh, yeah, check it out. There it is. Can you see it more clearly? Very nice artifact.

NARRATOR: It's a simple bamboo stick, but the woven pattern on it suggests it was once part of a basket.

Later, carbon dating reveals the people of Kyang lived around 200 B.C., the same time as the Mebrak mummies. Their artifacts appear to be locally made, indicating the people were self-sufficient and lived off the land. The bamboo and wood could've come from nearby.

MARK ALDENDERFER: This is a very nice, um, wooden bowl, soft wood. It has a really lovely little base on it that's been made, and it imitates a bowl that's been made on a wheel. So, it's been carved to look like that.

NARRATOR: Jacqueline determines 23 people were buried in the Kyang cave, with no cut-marks, and the presence of flesh on the joints suggests they were buried whole, but the ages of the dead are surprising.

JACQUELINE ENG: Several of these individuals are younger than 20. Several of the adult remains are also younger adults, so, below the age of 30 to 35, and that suggests that people did die of something that shortened their lives—could be starvation, could be an infectious disease—that, you know, moved really rapidly.

NARRATOR: An enigmatic object found in the cave hints at ritual practices that may be connected to these premature deaths.

MARK ALDENDERFER: One of the most interesting things we found during this work here at Kyang is this special stick. You can see it's well-carved. It's thin at the bottom, widens out. Clearly it's been meant to either be put in the earth or maybe in a socket of some kind.

The first thing that jumps out, when you look at this under the microscope that we have here in the field, is those are little tiny pebbles that have been placed inside little tiny divots. And the divots are holding, um, glue, some kind of cement that hold these things in place. But if you look at this image, it's the image of a person.

What I really think this person is doing is holding something we found in the archaeological site, what I've been calling "fire sticks."

They're little sticks. They might be four or five inches long, and usually one end is burned. You can see the wavy or sinuous line, which I would interpret as smoke coming out of the end of that fire stick.

NARRATOR: Cultural artifacts open a window on a people's long-vanished beliefs. The humanoid figure on the stick is so unusual, Mark travels to France, to see if anthropologist, Charles Ramble, can make sense of it.

Charles specializes in the ritual practices of Himalayan peoples.

CHARLES RAMBLE: What's the material? This is not just discoloration from water or something?

MARK ALDENDERFER: No. Not at all. That's actually…what they've done to highlight, they've ground up some dark stone into very fine particles and then literally pushed it into the outline of this, to kind of emphasize and bring out the contrast.

CHARLES RAMBLE: So, all this was intended?

MARK ALDENDERFER: All of this was very much intended.

NARRATOR: Charles has recently discovered an ancient text that describes a death ritual using sticks called "firebrands," much like the ones Mark found.

CHARLES RAMBLE: Tibetans believed that people died because their souls were taken away by death demons. And these are known variously as "shi" or as "shay." "Shi" is commonly translated as vampire. And rituals had to be performed afterwards, in order to separate the soul from the demons who had taken it.

(Reading from text) I am Taklamembar, and this is how the vampire-killing firebrand, the emanation of my mind, came into being. The demon of bad death among males was killed with the firebrands. The demoness of bad death among women was killed with the firebrands.

There is one text: its title translates as The Origin Tale of the Firebrands for Killing Vampires. These firebrands, in this text, are being used as a means of killing vampires, and vampires are the agents that are responsible for death. They are serial killers.

So, if people of a certain age, between 20 and 30, die in a series, that's the effect of vampires. So, the vampires are something that steal vitality and, eventually, life. And they latch themselves onto a family, and they will continue to affect that family until they are got rid of.

NARRATOR: This may explain why the fire stick was found in the Kyang cave with young adults who died prematurely.

CHARLES RAMBLE: It's unusual that we can find textual evidence to support archaeological evidence.

(Reading from text) The killing of vampires with the firebrand is over. May there be good fortune, good luck, blessings and virtue.

Stakes of this sort are very ancient. They've been found in many parts of central Tibet and also at the foot of the Great Wall. And they date back to the third century B.C.

NARRATOR: The discovery of stick effigies at the foot of China's Great Wall is another piece of evidence confirming these people could've come from there.

With D.N.A. recovered from each cave population, the scientists can see, over a 3,000-year timespan, which of them was adapted to survive at altitude and when the adaptation appeared.

ANNA DI RIENZO: An important feature of the study is that it provides ancient D.N.A. samples and data from different time points in the past. We can see how the data changes over time. And this is what we call watching evolution in action.

NARRATOR: Anna finds that all of the people buried in the caves have the high-altitude adaptation. But the study of their D.N.A. reveals there's a second adaptation that also enables people to live at altitude. The earliest of the cave people have the first genetic variant, but the most recent burials, the Samdzong people, acquired a second variant. Both variants are seen in the people of the region today.

The most surprising aspect of this variant is that scientists have seen it before.

In 2008, the tiny pinky bone of an extinct human ancestor was discovered in a cave in the Altai Mountains of Siberia, called Denisova.

The 41,000-year-old pinky bone had just enough D.N.A. in it to be sequenced. The individual was female, young and had that second adaptation.

ANNA DI RIENZO: This Denisovan population that had a relatively wide geographic distribution in Asia, maybe they already had adapted to high altitude. That's part of the history that we would like to dissect.

NARRATOR: At some point in pre-history, Homo sapiens, our modern human species, must have mated with the now-extinct Denisovans. It's likely the only way humans could have obtained the second high-altitude gene adaptation.

ANNA DI RIENZO: We don't know exactly where the encounter between this Denisovan-like population and the modern human populations occurred.

It's possible that this mutation was present in the Denisovan-like population but was not advantageous, yet after the mixing between these two, and the modern human population moved to high altitude, it became advantageous.

NARRATOR: This important D.N.A. variant, or allele, from an extinct human ancestor is part of the genetic inheritance of Himalayan people today.

ANNA DI RIENZO: The finding was very exciting. It's telling us something more than just the fact that modern humans and Denisovans mixed, but, also, that Denisovans gave modern humans an allele that allowed them to conquer this so-called "Third Pole," and to adapt to these very harsh conditions of high altitude and hypoxia.

NARRATOR: Genetics and the study of ancient D.N.A. allow us to see modern human evolution in action.

CHRISTINA WARINNER: This new ability that we have to actually sequence ancient genomes is teaching us so much we didn't know about human history and pre-history. So, already, we're rewriting the storybook of humanity.

JACQUELINE ENG: We're definitely still evolving. The point at which we stop evolving is when we're an extinct species; that's the end of evolution, right there. Those slight changes give us the ability to adapt to changing environmental conditions.

NARRATOR: Here in the Himalayas, we can trace how we evolve over time. That the people here can thrive at altitude shows just how adaptable we, as a species, can be. We now know more about the early cave peoples' beliefs and how they endured one of the toughest places on Earth.

And the knowledge gained by recovering ancient D.N.A., and deciphering death rituals, provides a clearer picture of the unique heritage of the mountain peoples who live at the roof of the world.

Broadcast Credits

Liesl Clark
Edited by
Jean Dunoyer
Liesl Clark
Jake Norton
Pete Athans
Cory Richards
Ted Hesser
Ang Tshering Lama
Renan Ozturk
Mark McKnight
Pierre de Parscau
Piers Leigh
Jay O. Sanders
Associate Producer
Crescent Moegling
Production Manager
Pete Athans
Sound Recordists
Jyoti L. Rana
Pete Athans
Bryn Clark
Jason Alberts
Ben Marcus
Chris Syner
Assistant Camera and Drone Operator
Finn Clark
Mitch Butler Explain-O-Graphics, LLC
Assistant Editor
James Dunoyer
Online Editor and Colorist
David Bigelow
Audio Mix
Heartpunch Studio
Danya Gordin
Production Assistant
Cleo Clark-Athans
Archival Material
Angela Simons
Institute of Archaeology and Ethnography of the Siberian Branch of the Russian Academy of Sciences
Jean-Marc Mandonnet
Stef Hoffer/Pond5
Special Thanks
Nepal’s Department of Archaeology
Village of Samdzong, Upper Mustang
Shangri-La Nepal
Sienna Craig
Robert Schoene
National Science Foundation
The North Face
Petzl USA
Marcos Martin-Torres
Dr. Laure Dussubieux
The Field Museum
National Geographic Society
Henry Luce Foundation
yU + co.
Walter Werzowa
John Luker
Musikvergnuegen, Inc.
Ray Loring
Rob Morsberger
The Caption Center
Spencer Gentry
Jennifer Welsh
Eileen Campion
Eddie Ward
Ana Aceves
Caitlin Saks
Anne Barleon
Linda Callahan
Sarah Erlandson
Janice Flood
Susan Rosen
Kristine Allington
Tim De Chant
Lauren Aguirre
Lauren Miller
Ariam McCrary
Brittany Flynn
Kevin Young
Michael H. Amundson
Nathan Gunner
Elizabeth Benjes
David Condon
Pamela Rosenstein
Laurie Cahalane
Evan Hadingham
Chris Schmidt
Melanie Wallace
Julia Cort
Paula S. Apsell

A NOVA Production by Sky Door Films for WGBH Boston in association with Sky Vision Productions, National Geographic and France Televisions  

© 2017 Sky Door Films

All rights reserved

This program was produced by WGBH, which is solely responsible for its content.

Original funding for this program was provided by Cancer Treatment Centers of America, the David H. Koch Fund for Science, and the Corporation for Public Broadcasting.


Image: (Upper Mustang, Nepal)
© Liesl Clark


Mark Aldenderfer
University of California, Merced
Pete Athans
Anna Di Rienzo
University of Chicago
Jacqueline Eng
Western Michigan University
Margarita Gleba
University of Cambridge
Giovanni Massa
University College London
Charles Ramble
Sorbonne University
Ang Temba Sherpa
Himalayan Guide
Christina Warinner
University of Oklahoma

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