Secrets of the Dead

Captioning made possible by Friends of NCI

NARRATOR

Deep inside a remote cave system in northern Spain, a gruesome investigation is underway. It involves the partial remains of a group of people. They were discovered in March 1994, when cavers exploring the El Sidrn cave system climbed into a small side gallery off of the cave's main tunnel. Hey, I found something. Looks like human bones. The remains are reported to authorities, and partial skeletons of 4 humans are exhumed. The bones are in pieces. Police and cavers note that the bones don't look very old, certainly no older than 60 or 70 years. They believe they are looking at the remains of victims of the Spanish Civil War. They couldn't see yet that there were cut marks on the bones, clear signs of cannibalism. In Madrid, investigators compared the bones to other human remains, but they did not belong to the war victims. These bones came from another time and belonged to another people... Neanderthal. From the cliffs of Gibraltar to the depths of El Sidrn cave, scientists must reach back in time to identify the dead and reconstruct their final days. But can they find enough evidence to crack this prehistoric cold case? Below this valley floor lies the El Sidrn cave system. Here, a forensics investigation has been in progress for more than a decade. The location where the bones were found is now known as the Ossuary Gallery. Every year, more and more relics are exhumed, and the number of dead rises. Scientists across Spain have joined forces. Human fossil expert Dr. Antonio Rosas leads the investigation... Dr. Carles Lalueza-Fox, a world-renowned geneticist from Barcelona, hunts for ancient DNA... and archaeologist Dr. Marco de la Rasilla is in charge of the excavation. He is on his way from the University of Oviedo to the annual dig. He's headed to a river valley in the Asturias region of northern Spain.

Church bells ring

NARRATOR

Most of the young researchers who join the dig are Marco's students. They come every summer to spend up to a month working the site.

Generator engine buzzing

NARRATOR

The Ossuary Gallery is more than 700 feet from the main entrance. The entire tunnel stretches for nearly two and a half miles. The cave can sometimes be an extremely dangerous place to work. Rain from above ground can cause flooding, and a puddle can quickly grow into a raging torrent.

Dripping of water echoing

NARRATOR

The Ossuary Gallery, where the bones are found, is slightly higher than the main gallery. It's safe from flooding, but not from looters. In the first years of the dig, fossils were stolen. A steel cage now keeps the precious remains safe 75 feet below the earth.

Man speaking Spanish

TRANSLATOR

Because we're used to working in caves, this one was just another cave, but it proved more interesting because it was like a container of rather unusual remains.

NARRATOR

Remains that would take years to unearth, transforming the once tiny gallery into a chamber of mazes. The site is cramped and difficult to traverse, but in this confined space, more than a thousand human bone fragments and hundreds of stone tools have been found so far. Every single piece of bone and rock, and the soil from which these items are excavated, is examined, cleaned, and logged. The stone tools are Mousterian, the same as those found in a typical Neanderthal's tool box. But the mystery of their presence here, alongside so many human bones, has haunted the scientists since the very first day of the excavation.

Speaking Spanish

TRANSLATOR

Once we had started the excavation in El Sidrn, the big question was, what were the human remains doing there? We didn't know what it was used for. It could have been a home, a burial ground, or the remains could have come from somewhere else and were in a secondary position. We just didn't know.

NARRATOR

As the bones and stone tools are excavated, and their exact location plotted, it seems they are all in the same layer of ancient soil-- 3 feet deep, 18 feet square-- and they find something else. Random dating reveals the relics are all around the same age-- 49,000 years. It looks as if something, or someone, buried these relics here at the same time. John Hawks is a human evolution expert. He has visited dozens of the world's most important Neanderthal sites and collections. At the Vienna Natural History Museum, a much-awaited human evolution exhibition has just opened its doors to him. As a Neanderthal specialist, he has watched the unfolding investigation at El Sidrn with great interest. The cave is unlike most other Neanderthal sites.

HAWKS

When an archaeologist is excavating a site and he finds things that are together in a fairly narrow layer, that still doesn't mean that they were deposited there at the same time. Time is compressing. There could be hundreds, maybe even thousands of years, in that archaeological deposit. It's very rare to come across a place like El Sidrn, where it looks like things might have been deposited at the very same time.

NARRATOR

Neanderthal sites usually contain evidence of everyday life, like the bones of animals they used for food and clothing, but the bones of people are scarce. El Sidrn is just the opposite; it has very few animal bones and a large amount of human remains-- further evidence the remains were deposited in the cave at the same time.

HAWKS

The cave at El Sidrn is a cold place. It doesn't look like it would be a great place to live, especially where you find these bones. It is not typical for where we find Neanderthal occupations.

Birds chirping

NARRATOR

Neanderthal occupation sites were open to fresh air, but also protected. Their real estate ranged from the humble rock shelter by a quiet stream... to cathedral-like rock towers along the Mediterranean. Scientists are studying both of these contrasting environments. But who were the Neanderthals?

HAWKS

The Neanderthals were the people that occupied the western half of Eurasia-- basically central Asia, Europe-- from 300,000 years ago or so up to about 30,000 years ago. They were always a very small population, maybe less than 50,000 people, and they lived in a climate that fluctuated widely from relatively warm periods like today to very cold, glacial conditions.

Wind howling

HAWKS

We used to think of Neanderthals as being basically hunters, and they were eating a very, very high proportion of meat. We've begun to find evidence that they were making use of a wider range of resources. They were masters of knowing what foods were available in their environment. We know from their genetics that Neanderthals are a part of us, but they're not the same as us, and so, when we look at them, we have to make that adjustment that we're looking at somebody very close to ourselves, but maybe not quite like ourselves.

NARRATOR

Inside El Sidrn, investigators work to uncover a time and a people we can scarcely comprehend. The truth behind what happened here can only be deduced from a thorough forensics investigation. The scientists already know El Sidrn was not a typical Neanderthal home, and they know the stone tools and bones were all buried together around 49,000 years ago. But can they find out why they are here, and who or what brought them into this place? The first clue comes from the bones. In Madrid, Antonio Rosas struggles to refit the Neanderthal remains to find out how many people are in the cave. In the process, he discovers what really happened. He's found cut marks in significant places on leg and jaw bones.

Rosas speaking Spanish

TRANSLATOR

This means that parts of the bodies were cut with the intention of ripping away the flesh.

NARRATOR

Some of the bones have been cracked by force.

Rosas speaking Spanish

TRANSLATOR

Here we can see an impact mark on this leg bone fragment. This means that the bone has been struck and broken with a stone in order to reach the bone marrow inside, which is very nutritious.

NARRATOR

Evidence enough for Antonio Rosas to come to a conclusion.

TRANSLATOR

In El Sidrn, there was an incident of cannibalism. It is really some of the strongest evidence that we have from any Neanderthal site that cannibalism was why those bones got there.

NARRATOR

But can we know who cannibalized these Neanderthal people? Was it our Homo sapien ancestors?

HAWKS

Toward the end of their existence, after 40,000 years ago, the Neanderthals declined in numbers, they declined in geographic range. It's obvious we had something to do with it because modern humans show up in Europe at that time. But at the time of El Sidrn, there are no evidences of modern humans being anywhere near the area, so it looks like Neanderthals were responsible, at least as far as the evidence we have right now.

NARRATOR

So why did these people turn to cannibalism?

HAWKS

When we want to understand why Neanderthals would have turned to cannibalism, we have to look at the circumstances in which humans become cannibals. When you look across human cultures, it happens surprisingly often. It happens, in a lot of cases, because of hunger. It's true desperation, where the only food source you have available to you is the bodies of your dead, or maybe not yet dead, comrades. There are other contexts, though. There are ritual contexts, in which you're trying to capture the spirits of dead people who may have been dear to you. There are contexts where you've conquered people, and you want to capture their energy by eating their remains. It is truly culturally complex in humans, and we have no reason to think that in Neanderthals, it would have been less complex.

Rosas speaking Spanish

TRANSLATOR

What is the real significance of this occurrence of cannibalism? Are they symbolic or cultural reasons? At the moment, we don't have any evidence to show that a ritual occurred here.

NARRATOR

Were all Neanderthals cannibals? We're beginning to find that they were as diverse a group as modern humans. Like us, they lived in different environments and probably had different lifestyles. To place the El Sidrn cannibalism in perspective, scientists are exploring a completely different site at the other end of the Iberian Peninsula. Here, there is a rock cliff that served as a Neanderthal refuge, but no evidence of cannibalism has ever been found. Clive Finlayson is an evolutionary ecologist, and he thinks he's found a Neanderthal Shangri-La.

FINLAYSON

As you come round in a boat and look at this cliff face, you don't just see one cave, Gorham's Cave. You see another cave and another cave, and others going underwater, and they were all occupied by Neanderthals.

Sea gulls crying

FINLAYSON

This was the Neanderthal city.

NARRATOR

El Sidrn is dark and cool, but the path to Gorham's Cave is bright and hot.

FINLAYSON

The Neanderthals had been living in Gibraltar for a long time, probably much longer than 60,000 years ago. The surprising thing here was not when they started, but when they finished. And we found a half a campfire at the top of Gorham's Cave which we excavated, and we took samples for radiocarbon dating, and the surprising result that came back was 28,000 years. That makes them the most recent population of Neanderthals to have survived anywhere on the planet today.

NARRATOR

El Sidrn's story is of a single instance in time. Inside the Gibraltar cave, events that happened over tens of thousands of years are being pieced together. Clive's team has excavated hundreds of stone tools believed to have been made by Neanderthals. His partner, underwater archaeologist Geraldine Finlayson, has been working at the site with Clive since 1997.

GERALDINE FINLAYSON

For a long time, Neanderthals were thought to have mainly been eating meat. But we find, certainly in this part of the world, that they eat a lot of shellfish, and here behind me, we've got different layers like layers in a cake, and scattered among the layers, you can still see the remains of the shells that they have collected. We also find fish bones and fish scales inside the cave. It's very easy to collect fish, so you don't need a rod or a line to catch a fish. Simply just toss a stone at them, you can knock them out, so they can be quite easy to catch.

CLIVE FINLAYSON

They ate all kinds of things, whatever was out there. If you put it together, all that's missing to make a good Mousterian Neanderthal paella is rice. Outside the cave, the view is not the one the Neanderthals would have had for most of the time. The sea level was much lower because the global climate was much cooler. The coast was 4 to 5 kilometers out. The seabed, which is well-submerged now, would have been the landscape where they went out, hunted, and gathered, and then they came back into this cave for shelter and protection.

NARRATOR

Geraldine and her dive buddy, archaeologist Darren Far, are about to visit a site where Neanderthals lived when sea levels were much lower. It is a strange landscape. Large pinnacles, some with freshwater springs at the base, rise up from the seabed. It's a unique and very new investigation.

FAR

We can see valleys, we can see river gullies, and we actually found upwellings of freshwater. So they would have had a lagoon-type system in front of the cave, so you can imagine that would have attracted water birds, a whole bunch of other things. So it was actually quite an idyllic landscape for them to survive in, possibly explaining why they lasted here so long.

NARRATOR

Rocks collected from these pinnacles will be compared with the stone tools found in the Gibraltar cave site. But the real work lies ahead. Using techniques usually seen on land, the team must set up grid lines and meticulously record what they find underwater. If Neanderthals did live here, perhaps their bones are still buried at depth. But because they are now 90 feet below the surface, after only 20 minutes, they have to leave the site or risk the bends. Finding evidence here will be a slow process. And the past does not give up its secrets easily. Deep within El Sidrn, the scientists now know Neanderthals were cannibalized by their own kind, but their task is not over. Finding out how the remains and tools actually got into this cave will require extraordinary detective work. For the scientists, figuring out how the bones and the stones ended up in this place in the cave was really the breakthrough. The discovery comes when Marco and his team are back in their lab at the University of Oviedo and take a closer look at the stone tools. El Sidrn is not a place where Neanderthals lived, but among the many excavated stone pieces, they find proof of the manufacture of stone tools.

de la Rasilla speaking Spanish

TRANSLATOR

We found evidence of the production of what we call lithic flakes.

NARRATOR

These flakes are the by-product of a core rock being struck to make a tool.

Speaking Spanish

TRANSLATOR

With this tool, you can cut meat, make other tools, and even crack bones. It's as sharp as a razor blade.

NARRATOR

Looking closely at the edges of the lithic flakes and what they believe are the core rocks, Marco's team sees a pattern......and attempts to refit the pieces. Here is irrefutable evidence of a moment 49,000 years ago, when someone made stone tools. But these tools were not made inside the El Sidrn cave. If they were, some of the flakes would have been found close to each other when they were excavated. Experiments have shown that flakes don't scatter, but the fitted pieces here were found up to a yard away from one another. It's as if they'd just dropped into the Ossuary Gallery from above. The team finds many more stone flakes, rock cores, and bone in a configuration familiar to scientists. When all the finds at the site are plotted, another pattern emerges-- a cone shape. It's known as a debris flow cone and is a common geological phenomenon.

HAWKS

In El Sidrn, we have a cone of sediment, and it represents something that just fell into the cave.

de la Rasilla speaking Spanish

TRANSLATOR

When this geological phenomena occurred, everything moved inside, so logically, everything appeared together.

NARRATOR

And the stone tools used to take flesh from bone are still as sharp as the day they were made.

de la Rasilla speaking Spanish

TRANSLATOR

The fact that everything appeared together inside the cave means there was a clear activity related to cannibalism, and the stone tools were used for that purpose.

Dripping water echoing

NARRATOR

The El Sidrn investigators find a logical point where the bones and stone tools entered, right above the Ossuary Gallery, but it no longer opens to the surface. The real story of what happened to the people of El Sidrn lies outside the cave. The karst landscape above the cave is constantly reshaping itself. Huge sinkholes appear when acidic rain dissolves the limestone. They will eventually crumble into caverns below. But the collapse in El Sidrn was not a slow process. If it were, the remains would have been scavenged. Wolves and other predators shared the Neanderthal's world.

Rosas speaking Spanish

TRANSLATOR

The fact that there were very few carnivore teeth marks shows us that the bones, the bodies, were only exposed to the air for a short period. The burial process was very fast.

HAWKS

It is amazing how many things had to fall into place in order for all of this evidence to tell us what happened at a moment in time in the Neanderthal life. And that evidence in the archaeological record is so rare, so lucky, that it just-- it blows my mind that we're able to figure out what happened at a particular moment.

NARRATOR

La Cabania is near El Sidrn. The investigators believe a shelter like it could have been directly above the Ossuary Gallery 49,000 years ago.

Water flowing

NARRATOR

In ancient times, there was a stream nearby, similar to the one that runs near La Cabania today. The scientists suspect that a huge storm caused flash flooding, resulting in a sudden collapse that brought the Neanderthal remains into El Sidrn.

Man speaking Spanish

TRANSLATOR

The cave must have been practically like it is now, and in the same way we could live here, they could have done so in the past. There is a roof, water, the basic conditions that they would have needed. There is also silex, the material they used for their tools. They would have lived here very happily.

NARRATOR

But there was death. The El Sidrn investigators believe they know what happened in this ancient cold case. It started with a storm.

Thunder

Water dripping

HAWKS

This is the first time that we have a discovery like this with Neanderthals, where you have a group of individuals that probably knew each other when they were alive.

NARRATOR

Now, the greatest challenge facing the scientists is to give these people back their identities. The bone fragments don't fit together to make even one whole person. In Madrid, Dr. Rosas and his team have spent a decade trying to get to know the Neanderthals of El Sidrn better. He has led a meticulous forensics investigation to find the age, sex, and health of the victims. Each year, more evidence is exhumed and the death toll rises. It started at 4 and is now much higher. For scientist Almudena Estalrrich, the teeth hold the key to identifying each of the bodies.

Estalrrich speaking Spanish

TRANSLATOR

We know that the teeth belong to a certain kind of individual for many reasons. In the first place, the wear is the same. In other words, all the teeth are in the same state-- eroded or not eroded-- and mainly because of the marks on the sides of the teeth, caused by friction, so they serve as a kind of fingerprint. They're the same now as when the teeth were together.

NARRATOR

In this way, they discover a much higher death toll than expected.

Rosas speaking Spanish

TRANSLATOR

There are 12 individuals represented-- 6 adults and 6 children. Among the children, there are 3 teenagers close to maturity. There is one child around 5 years of age, another approximately 8 years old, and a very young one of around two years of age.

NARRATOR

The investigators know the Neanderthals' age and sex. They know they were cannibalized and how they ended up inside the cave. But there is one more thing they hope to find, something that may offer the ghosts of El Sidrn a type of immortality-- their ancient DNA. Genetics. The new wave of Neanderthal research is about to take the investigation into another realm. In Barcelona, Carles Lalueza-Fox wants to give ancient peoples an identity.

LALUEZA-FOX

I wanted to try to provide an image of the Neanderthals that could be not just genetic Neanderthals, but persons with their own traits, like just in modern humans.

NARRATOR

At the Institute of Evolutionary Biology, Dr. Lalueza-Fox specializes in the extraction and analysis of ancient DNA.

LALUEZA-FOX

Because we are alone, and we know for sure that we have been alone for thousands of years in this planet, we don't have the concept of what different human species would be. For us, it's very difficult to imagine someone who would be, at the same time, very similar to us, but also at the same time fundamentally different to us, and that is what the Neanderthal would be.

Dripping of water echoing

LALUEZA-FOX

Going into the cave, I discover that was a very special site, probably a unique site because the temperature was so stable all along the year, and it has been stable during at least 50,000 years. And I thought we are going to find DNA preserved in Neanderthals. It's going to be there. I was given a tour first to check if there was Neanderthal DNA in it. After several weeks, I was able to retrieve Neanderthal DNA from that particular tooth, but I also discovered that the tooth was plagued with Homo sapiens' DNA.

NARRATOR

Our human DNA is very similar to Neanderthal DNA, which makes separating the two difficult. The moment El Sidrn was discovered, cavers, police, and even scientists contaminated the remnants of the Neanderthals' DNA with their own.

LALUEZA-FOX

It's difficult to believe, but if you breathe over the bones or you touch a particular bone fragment or a Neanderthal tooth, your DNA can go from the outside into the inside of the specimen.

NARRATOR

Carles knew he could not waste this extraordinary opportunity.

LALUEZA-FOX

I decided to implement an anti- contamination protocol at the excavation itself. I put my lab into the excavation.

NARRATOR

Now, a bone to be tested is not exposed until the dig is stopped, the site is locked down, and the excavator suits up in sterile gear. Carles also ensured that the DNA of everyone who comes close to the remains is recorded, so he can eliminate their DNA signature from his results.

LALUEZA-FOX

We were able to know exactly who was contaminating the remains, and we were also able to compare the Neanderthal sequences with all the sequences of the people that had been not just touching the remains, but close to the remains, into the excavation itself.

NARRATOR

The El Sidrn protocol will change the way ancient DNA is collected and tested throughout the world. In his hands, Carles may hold clues to identifying some of the El Sidrn victims.

Electric drill buzzing

NARRATOR

The bone powder drilled from inside the sample will need to go through many processes before Carles will know if his protocol has been successful. And if DNA is found, it will be in fragments that will have to be magnified, replicated, and reconstructed. He's looking for nuclear DNA, which is responsible for an individual's traits and is passed down from both parents. The El Sidrn bones will help create a new vision of Neanderthals.

LALUEZA-FOX

We had an image of what Neanderthals could look like, and what we could say is that Neanderthals had, likely, red hair... they were O blood group...

Heart beating

LALUEZA-FOX

they were able to have this bitter taste perception, and they probably had language abilities like us.

NARRATOR

This is the first model of a Neanderthal created using genetic evidence. Carles has given physical traits to a female from El Sidrn... but he still wants to know if members of her group were related. To find out, he must look for another type of DNA. Mitochondrial DNA is passed down from mothers to their children. Because it changes at a very predictable rate over generations, it can be used to trace lineage back to ancestors who lived hundreds of thousands of years ago. Finding it will establish whether this group of 12 were related. The people of El Sidrn, they were family-related. We don't know exactly which were the relationships, but we know they were family-related. All the 3 adult males had exactly the same mitochondrial DNA, while the 3 adult females had different mitochondrial DNA, which is shown in modern hunter-gatherer groups where the females move from one group to other, while the males stay in their paternal family group. Two of the women were directly related to children from the group, and could have been their mothers. Here is the first real proof of a Neanderthal social structure. Here's a case where we have maternal relatives. That does tell us something about the way that ancient human groups may have begun to be composed. For this set of Neanderthals, what looks like happened is that the women were going from one group to another, probably at the time that they began to mate, and so that tells us how the genes are moving across Neanderthal populations. They're moving with women. Marco de la Rasilla has found proof that groups did exist in the area and that they were on the move.

de la Rasilla speaking Spanish

TRANSLATOR

The silex we have discovered here was used by these groups, but it can also be found in other areas near and far. Therefore, we can conclude that they moved around and took raw materials from one place to another-- for hunting or for work-- for what they needed on their journeys to different places.

HAWKS

When you start losing little groups because things become harsher, then you have a situation that puts the entire population genetically at risk. They can't maintain their adaptability to new circumstances.

NARRATOR

The death of a family could have isolated the surrounding groups even further. The distances to exchange females would eventually be too great. Over time, the resulting inbreeding would halt the vital flow of genes that leads to evolution.

HAWKS

We can see an event here where we had people that were very hungry, where they were not able to survive without turning to cannibalism, and that puts the entire survival of this broad population into a very interesting context.

NARRATOR

So why did populations of Neanderthals begin to shrink? Some say our arrival in Eurasia was the beginning of the end. Clive Finlayson believes climate was the killer.

CLIVE FINLAYSON

Climate change affected the environments that these people occupied across central parts of Europe and even central parts of Asia and even northern Europe.

NARRATOR

Ice core data shows that between 50,000 and 30,000 years ago, the climate see-sawed between warm, wet periods and cold, dry periods. The El Sidrn act of cannibalism coincides with the latter.

CLIVE FINLAYSON

As that climate changed their landscape, their environment-- which was a wooded environment where they would ambush-hunt animals-- began to shrink. Gradually the population was being pushed back, back, back into these strongholds like the one we find here. They were becoming like pandas or tigers. The populations were isolated from each other, and there was very little gene flow between them, and therefore they were suffering from inbreeding and all the kinds of effects that small populations have. They were there, but their days were numbered. Those Neanderthals were living dead.

NARRATOR

So far, there is no evidence pointing to climate as the killer at El Sidrn, but these Neanderthals would have needed to consume a huge amount of food. Getting enough energy to survive even an ordinary winter would have been a challenge.

Rosas speaking Spanish

TRANSLATOR

It is thought that the composition of the Neanderthal body-- not only because of its size, but also due to the muscular thickness of the limbs and torso-- needed a large amount of daily energy for its metabolism. This means that an individual's daily consumption of calories, proteins, and other nutrients must have been very high. Thus, certain unfavorable environmental conditions could have led to physiological stress brought on by food shortages.

NARRATOR

But we do know what some of the family ate during their lives at El Sidrn. The teeth of 5 family members have been analyzed, and calcified dental plaque removed.

HAWKS

On the surfaces of teeth of any kind of human, we sometimes will find calcified plaque. Your dentist scrapes that off. You know, it's hard work to get it off of there, but what it's doing is it's capturing little particles of the food that you eat, and those little particles include micro-fossils. From that, you can tell what kinds of plant foods were being eaten.

NARRATOR

Molecules of cooked grains and also traces of bitter green plants were found. The presence of bitter plants has led to speculation that these people were using plants as medicines.

HAWKS

El Sidrn puts this really interesting perspective on this new evidence about plant utilization because when we look at those people, we would initially look at them and say, "Look at the breadth of resources that they're using. They're masters of knowing what's in the landscape." But at the same time, we know that they're in a population that has times of real desperation, and so when we look at the evidence of these bitter plants on their teeth, what we begin to think is, "Oh, maybe they're really stretching to the limit, trying to get every possible food that they can," and at the end, it just didn't go well for this small group of people.

NARRATOR

A family was wiped out in El Sidrn, eaten by their own kind, perhaps in an act of desperate hunger.

HAWKS

When we look across Neanderthal sites all over Europe, we see clear signs of stress. We see their teeth are having problems when they're forming, which represents, you know, times of hardship when they're growing up. We see evidence of hard lives all over their skeleton, and El Sidrn is one piece of evidence that's really consistent with the entire picture. Neanderthal lives were, in many cases, hard.

NARRATOR

Eventually, that population was whittled down to one person. That last Neanderthal may have lived in a place where food was always plentiful.

CLIVE FINLAYSON

At the time of the people living in El Sidrn-- in that more cold, northerly climate, they're really having it hard, to the point that they're eating each other--the Neanderthals down here carry on doing what they've always done. For a quarter of a million years, there's very little change in this part of the world. The climate is fairly mild. It gets slightly dry and slightly wetter. But then, at 28,000 years, the cores tell us there were a series of droughts. There was a period which got really harsh-- not cold, but dry--and not only did the Neanderthals disappear from here, but nobody else lived in here, and that is quite telling, I think, that Neanderthals survived for a quarter of a million years, and we suddenly lose their signal when we get the worst climactic conditions registered by the marine cores outside this cave.

GERALDINE FINLAYSON

It must have been really very sad for the last few people to stay here and maybe realize that they didn't come into contact with other groups like they had been used to. There must have been the last one, and I always feel quite emotional when I think about them.

NARRATOR

1,800 bones and 400 stone relics have been recovered. But this is not the end of the story. There may be more bodies in the cave. Antonio Rosas and Marco de la Rasilla will soon take this year's finds back to their laboratories for analysis.

Speaking Spanish

TRANSLATOR

Until now, there has been no archaeological site in the world that has produced a greater number of bones than in El Sidrn. It is an exceptional site on all counts. Finding a hundred well-preserved Neanderthal remains at the same site every year is highly unusual. The extraordinary level of fossil preservation also makes this place absolutely unique. There is nothing to add. It's just unique.

HAWKS

There's no limit to what we will discover as we get more and more methods of looking at this evidence. What a hard life these people led, and what a terrible way to go. We still can appreciate their lives and really begin to understand how they fit into this long term of existence of a very mysterious group of people.

NARRATOR

They have been in the dark for 49,000 years... and have only just begun to tell their secrets. Captioning made possible by Friends of NCI Captioned by the National Captioning Institute --www.ncicap.org--

ANNOUNCER

The "Secrets of the Dead"investigation continues online. For more in-depth analysis and streaming video of this and other episodes, visit pbs.org. This "Secrets of the Dead" episode is available on DVD for $24.99 plus shipping. To order, call 1-800-336-1917.