First Horse Warriors

PBS Airdate: May 15, 2019

NARRATOR: Horses: powerful, graceful and thunderously fast. No animal has made a greater impact on society or given humans more freedom and mobility than horses.

DAVID ANTHONY (Anthropologist) The thrill that people still get today from riding a horse at top speed, there’s nothing like it. Whereas, if you get on the back of a cow, it’s not that great an experience.

NARRATOR: Centuries before Egyptians built the pyramids, Eurasian nomads unlocked the power of horses and used them to reign supreme over vast territories of the ancient world. But how did they do it?

NIOBE THOMPSON (Anthropologist): (Translated): My name is Niobe.

AUEZ (Kazakh herder): (Translated) And my name is Auez.

NARRATOR: Follow anthropologist Niobe Thompson, as he visits the last of today’s horse riding cultures and explores archaeological sites and genetics labs, seeking to unlock the mysteries of the world’s first riders.

ESKE WILLERSLEV (Evolutionary Biologist): The horse transformed what it means being human. It gave the possibility to explore the world in a way that had never been possible before.

NARRATOR: But horses could also bring terror at the hands of brutal raiders and even pandemic disease. Time-travel back to when prehistoric people began capturing wild horses and rode them like a tide that would forever change the course of human history. First Horse Warriors, right now, on NOVA.

Horses are magnets for our attention. They draw us in, almost demanding we look at them. For most people today, just seeing a horse is a rare sight, perhaps only a couple times a year, watching races like the Kentucky Derby. But not so very long ago, horses were everywhere, woven into the fabric of our daily existence, in the countryside and even in cities.

DAVID ANTHONY: The City of New York had tens of thousands of horses that were doing all the work that trucks do. And they were also doing all of the work that taxis do today.

NARRATOR: We don’t depend on horses anymore, but few animals have been as important to the rise of civilization. For thousands of years, they were our long distance vehicles, the muscle and speed we needed to master the world. But how did this unique partnership form? Who were the first people to unlock the power of horses? And what happened once they did?

Recent discoveries in archaeology and paleontology, genetics and even linguistics are revealing the identity of the world’s first riders, as well as the extraordinary relationship humans forged with horses and how that bond would change the very course of history.

Horses appeared on the scene long before we did, but, surprisingly, looked nothing like the majestic creatures we see today. Fifty-five-million years ago, they are small and move like agile dogs. This “dawn horse” is well-suited to the tropical forests covering much of the earth back then, living and foraging among the dense foliage.

NIOBE THOMPSON: It stayed hot for millions of years, and in all that time, dawn horse hardly changed at all. And then, about 15-million years ago, the earth began to cool.

NARRATOR: And when it does, forested regions, distant from the equator, transform into open plains covered with grasses. And here, the small, dog-like horse evolves to avoid predators, growing sleek, tall, muscled and fast. Although horses first appear in North America, as their numbers grow, they migrate across Beringia, the land bridge that once connected the continents.

More than 100,000 years ago, herds of horses in Europe and Asia prove a rich source of meat for Stone Age hunters.

DAVID ANTHONY: People hunted horses. They are meat on the hoof; they don’t have sharp teeth. It’s not like hunting cave lions, you know?

NARRATOR: And early hunters know how to find migrating horses.

DAVID ANTHONY: Horses are relatively predictable animals, and they tend to follow a regular system of water holes and grazing places.

NARRATOR: At Solutré, in central France, there’s evidence ancient hunters regularly ambushed horses.

SANDRA OLSEN (Zooarchaeologist): At Solutré, for about 20,000 years, people were driving wild horses into a kind of cul-de-sac and then killing them with spears, for food.

NARRATOR: This chunk of earth, excavated at Solutré, is dense with horse bones, revealing just a tiny fraction of the tens of thousands of horses slaughtered here over the centuries.

At Chauvet Cave, in southern France, the importance of the horse to our Stone Age ancestors is on clear display.

NIOBE THOMPSON: When you look at this marvelous wall, you see all of the major animals of the Stone Age world depicted. You’ve got reindeer and mammoths, big cats, but the horse seems to play the most prominent role.

NARRATOR: From their art, many experts believe ancient humans were making a spiritual connection to these animals.

Despite such reverence, prehistoric humans may have over-hunted horses. And by about 10,000 B.C., when a changing climate may have also depleted their numbers, horse herds became scarce in Europe and disappeared entirely in the Americas, where they would not return until European explorers sailed them back in ships.

But on the grassy steppe lands of central Eurasia, the descendants of horses that migrated from America flourish. And it’s here that many experts believe prehistoric humans eventually discover how to ride them.

The “steppe” refers to this long grasslands plain, stretching over 5,000 miles, from the edge of today’s Europe all the way to Mongolia, in Asia. It’s a harsh environment: cold in the winter, hot in the summer, and in many places, too dry for agriculture. But you can pasture animals. And these Kazakh herders are following in the footsteps of their nomadic ancestors, who may have been among the first people to capture and ride horses.

And Niobe has come here to see what he can learn from them.

NIOBE THOMPSON: (Translated) Peace be with you.

AUEZ: (Translated) And peace to you.

NIOBE THOMPSON: (Translated) My name is Niobe.

AUEZ: (Translated) And my name is Auez.

NARRATOR: Raising sheep, goats and cattle is a rugged, outdoor existence, but horses make herding easier, especially when moving grazing animals to new pasture. And Niobe pitches in.

It was surely a big change to turn wild and wary steppe animals into the working horses we see today. So, who were the first people to tame wild horses? And how did they actually do it?

Fifty-five-thousand years ago, the people who lived at this site in Kazakhstan may have been the first culture to master the horse. The site was discovered 40 years ago, when Russian archeologist Victor Zaibert noticed circles in the earth that turned out to be large houses, belonging to a steppe people anthropologists call the “Botai.”

Prior to creating this village, the Botai are strictly nomadic, living off the land, foraging and hunting and eating what they could find. But then they settle down and change their lifestyle. By the vast number of horse bones uncovered at the site, they began eating horse meat almost exclusively.

But is eating horses the only use the Botai had for these animals? Or could they be riding them as well? That question has roiled the academic community for decades.

Anthropologists David Anthony and his wife Dorcas Brown have long maintained the Botai were among the first people to capture and ride horses. And they’ve pieced together what they believe is convincing evidence, by looking for wear marks a riding bit might make on their teeth.

NIOBE THOMPSON: A bit is part of the bridle, or reins. They can be leather or metal, and they go in the horse’s mouth, just here. So, when I apply pressure through the reins, the bit tells the horse what I want it to do.

NARRATOR: And David Anthony believes he’s found evidence of bit-wear in the jaws of Botai horses.

DAVID ANTHONY: There is a gap between the molar row and the incisors. And if you put a bit in the horse’s mouth, it sits on top of very sensitive tissue. And so, by pulling on the bit on one side, you pull the bit down against the gum, and the horse will turn its head in order to avoid that pressure. You pull the rein on the other side, and the horse will turn its head to avoid that pressure. And that’s how a creature as puny as a human can control an animal the size of a horse.

NARRATOR: But a horse doesn’t want a bit constantly bearing down on its gums.

DAVID ANTHONY: The horse can use its tongue to push the bit up and put it onto these teeth, to get it off of the soft tissue where it can’t hurt them anymore. And then in this position, if the horse grasps the bit very firmly between the lower teeth and the upper teeth, it can keep the bit off of its tongue and gums. So we were looking for wear on the front part of the tooth, here.

NARRATOR: They examined hundreds of samples, looking for evidence of bit-wear…

DORCAS BROWN (Anthropologist): You can see that it’s broken. He chewed all the way through this bit.

NARRATOR: …and feel confident they found it.

DAVID ANTHONY: This is a cast of a tooth, from the site of Botai, that’s 5,000 years old. This is the tooth of a modern horse that’s been bitted, and both of them have wear on this front cusp, right here.

NARRATOR: Despite this apparent evidence, not every expert believed Anthony was correct.

DAVID ANTHONY: There are people who did not believe that the marks that we saw on the teeth were caused by a bit, because those kinds of features can be caused by natural malocclusion in horses.

NARRATOR: Besides refuting the bit evidence, other experts argue that images of humans riding horses or chariots do not appear until about 2,000 B.C., or 1,500 years after the Botai. If the Botai had become riders, surely this would have been depicted in art.

So, are Anthony and Brown correct about teeth-wear as evidence for riding? Archaeologists digging at Botai Village have been hoping to find other evidence that the Botai had become riders.

They know the people are smoking, cooking and eating vast quantities of horse meat. And they found large concentrations of horse dung and holes from fence posts, indicating the Botai are keeping horses in corrals, something David Anthony believes makes sense for a culture that had become dependent on horses.

DAVID ANTHONY: It’s easier to kill a horse in a corral than it is to find the horses, go out to the place where you have to ambush them, kill them there and lug it back to your settlement site. It would be a lot more convenient if you just had horses in a corral, and you could go out and get one whenever you wanted a meal.

NARRATOR: Besides serving as a food larder, the corrals could also mean the Botai are breeding and domesticating horses, like other cultures are doing with cattle, sheep and goats: living off these animals for milk, meat, wool and other products.

If the Botai are domesticating horses for the same reasons, this would naturally bring greater interaction and familiarity, making attempts to ride them much easier.

And archaeologist Alan Outram set out to prove the Botai had domesticated horses by focusing on milk.

ALAN OUTRAM (Archaeologist): If people could milk cattle very early on, then people that were living off horse products, why would they not also milk horses? And if you’ve got horse milking, you’ve got a smoking gun for domestication, because no one’s going to argue with you that people are running after wild horses to milk them.

NARRATOR: If the Botai had been milking tame horses, these broken pottery vessels may have once contained their milk. So, Outram brings them to this lab at the University of Bristol. He wants chemist Richard Evershed to use a process called an “isotopic analysis,”…

ALAN OUTRAM: Interesting to know what the blip you found here…

NARRATOR: …to see if he can find residues of milk fat still clinging to the pottery, even after 5,000 years buried in the ground.

RICHARD EVERSHED (Biogeochemist): The basis of what we do is to look at the organic compounds, the fats that have absorbed into the wall of the pot. And actually, they are pretty tough to extract. And we’ve had to develop some methods to actually open up the structure.

NARRATOR: At first, it’s all hand work.

RICHARD EVERSHED: We drill off the surface of the pot to reveal a sort of a fresh ceramic surface, and then we, literally, break off a small piece, about two grams, and put that into a pestle and mortar. And we, literally, grind it to a powder. We pound it to a fine powder. And what that is doing is opening up the pores in the pot.

NARRATOR: This will hopefully free traces of specific chemical fingerprints, called isotopes, of any organic substance the pottery once contained, including milk fat.

The powder is then liquefied and placed into this machine that heats it and analyzes the chemical signature of the gas vapors being released, to see if those signatures match the ones known to come from horse fat.

RICHARD EVERSHED: So, these are the results of the isotope analysis. And you can see these two major peaks. And these are the fatty acids that tell us we’ve got an animal fat.

NARRATOR: A good start, but evidence of fat doesn’t necessarily mean milk fat; it could be carcass fat.

RICHARD EVERSHED: We can’t say from looking at these peaks exactly what type of fat we’ve got.

NARRATOR: And since the Botai are eating horses…

RICHARD EVERSHED: And if you’re cooking meat in a pot you will obviously get the deposition of a lot of fat as the meat is cooked.

So, that didn’t work.

NARRATOR: They go back to the drawing board, realizing they need a way to clearly distinguish milk fat from carcass fat. And the best way to do that would be to go to the original Botai environment, in Kazakhstan, and gather samples of mare’s milk.

The grasses mares eat today should be composed of elements like hydrogen or oxygen that are similar to those their ancient ancestors ate.

RICHARD EVERSHED: It’s the “you are what you eat” principal. So, you’re inheriting the isotope signatures of different foodstuffs that you’re eating.

NARRATOR: In spring, when mares are nursing, their milk absorbs elevated levels of a hydrogen isotope called deuterium that’s in water and grasses. And this elevation will only be in their milk fat, not in their carcass fat.

When the team analyzes the modern milk samples, they find elevated deuterium peaks that match perfectly those from the Botai pottery. This confirms Alan Outram is right: the Botai had been milking domesticated horses.

ALAN OUTRAM: I don’t think that anyone can seriously argue that you haven’t got decent control of animals, if they’re being milked.

NARRATOR: But it takes practice to milk a horse, as Niobe discovers.

NIOBE THOMPSON: Milking a horse is all about tricking the horse. So, what happens is someone brings a foal in, the foal sucks the milk from the teats, the milk falls, and then they pull the foal away quickly, and someone rushes in and milks the horse. As soon as the mare knows that it’s not the foal or suspects something, something’s different, the milk dries up. The mare sensed that I didn’t really know what I was doing, and as soon as I got a bit of milk out, the teats dried up. They had to bring the foal back in.

It’s really hard…just a little bit.

NARRATOR: Only horses used to a human touch would have allowed the Botai to milk, tame and ride them.

SANDRA OLSEN: And so, by the time you start to pile all of this evidence on, the people living in sedentary villages, milking the mares, eating the horse meat, it’s fairly evident that you have domesticated horses there. And gathering large herds of domesticated horses would be extremely difficult without horse riders to herd them.

DAVID ANTHONY: If you ask people who manage horses today, “How can you manage horse herds without riding horses?” they laugh at you. Of course you have to be on horseback to manage herds of horses.

NARRATOR: So, despite their doubters, all the evidence points to Anthony and Brown being correct. The Botai were riding horses. But how did the Botai convince large, wild animals to let them climb on their backs?

DORCAS BROWN: You choose the docile animals. So, you would approach a horse, and if it ran away, you didn’t get it. But if you approached the horse and it was sort of curious and interested, then you could then begin with that horse and then build on from there, build a whole herd from there.

Oh, I think the first riders were getting bucked off pretty fast. But once they figured it out, why not go long distances, especially on the steppes, you know? You’d always wonder what’s over that next horizon. I think that’s what was going on: they wondered what was past that next horizon.

NARRATOR: Riding! The Botai’s prey has become their companion. Riding this magical creature must have felt like breaking a law of nature. Now the Botai can herd more animals and trade with distant cultures. Their horses prime them to become the most dominant force on the steppe.

DAVID ANTHONY: You would expect the Botai people, with the advantage of horseback riding, to have really thrived, and it looks like they did great. They had these large conglomerations of people living in these big settlements; they were feeding themselves magnificently. But after 3,000 B.C. they pretty much disappeared.

NARRATOR: What became of the Botai and their horses? Archaeologists have found little evidence or even human remains in the village that might help them understand their fate. And that’s what makes this discovery by Alan Outram’s team so important: a fairly intact Botai skeleton.

ALAN OUTRAM: I can’t stress how rare human remains are at this site.

NARRATOR: Their hope is that these bones will yield D.N.A. that geneticists can trace to later populations that may have absorbed the Botai and become their heirs.

Recovering ancient D.N.A. is extremely difficult, but Danish geneticist Eske Willerslev has earned a global reputation for finding and sequencing the genomes of our oldest ancestors. And he’s come to Botai village to see if this rare skeleton looks like it could yield D.N.A. that has survived the ravages of time.

ESKE WILLERSLEV: Hey, guys.

So, you have found a human, huh?

ALAN OUTRAM: Yes.

ESKE WILLERSLEV: But you have no idea how much of the skeleton is there?

ALAN OUTRAM: We don’t yet. There are quite a lot of bone fragments all around. Some of them are horse bones.

ESKE WILLERSLEV: Yeah, yeah.

NARRATOR: Eske is impatient to get specimens back to his lab, but he’ll have to wait for the meticulous process of uncovering fragile bones from the packed earth, and then hope for the best.

ESKE WILLERSLEV: We are getting D.N.A. out of a lot of specimens that we, six, seven years ago, didn’t think you could get anything out of whatsoever, right? And now they’re working. So, I mean, it’s really hard to predict whether this specimen will work or not. But I’m pretty optimistic.

When you have cleared the head, can we, kind of, remove the lower jaw to get a tooth?

ALAN OUTRAM: I don’t think the lower jaw will come away.

ESKE WILLERSLEV: Not by itself, huh?

NARRATOR: Eske wants a tooth, because the D.N.A. inside is protected by an outer coating of enamel.

The team gives him one.

ESKE WILLERSLEV: Wow! Okay, this is beautiful!

MAN: This is beautiful.

ESKE WILLERSLEV: This is beautiful.

MAN: This is fantastic; amazing, yes.

ESKE WILLERSLEV: Thank you, very much.

WOMAN: You’re very welcome.

NARRATOR: And there’s something else.

ESKE WILLERSLEV: Oh hey, there’s a petrous there, right? Wow!

NARRATOR: The petrous, a small bone that’s part of the skull near the inner ear, is a fortuitous find.

ESKE WILLERSLEV: So, the petrous bone is the most dense bone in the human body. Therefore the D.N.A. preservation is better than in other parts of, you can say, the skeleton material.

NARRATOR: After months of work, Eske and his team identified the genetic signature of the Botai villager. They expected to find traces of his genome in later steppe cultures, but, stunningly, they couldn’t find it.

ESKE WILLERSLEV: The Botai people, if you want, as far as we know, haven’t left any direct descendants.

NARRATOR: Despite their resources and well-established community, the Botai somehow died out.

ESKE WILLERSLEV: It’s kind of tragic irony that they do something extremely challenging, they domesticated the horse, probably one of the most influential events in human history, but they don’t take over the world with this new, major power they have. I mean, they become a dead end, right? They don’t have any impact.

NARRATOR: As it turns out, we know more about the fate of Botai horses than the Botai people.

French geneticist Ludovic Orlando has also come to Botai village to collect bones for D.N.A. sampling, in his case, horse bones, not human ones. If these are indeed the remains of the world’s first domesticated horses, then, Orlando believes, it’s very likely their genetic signature will have passed on to all domesticated horses living today.

He took samples back to his lab to see if his theory was correct.

LUDOVIC ORLANDO (Molecular Archaeologist): I was expecting that the first population of domestic horses to have been the source of all and every possible domestic horse that lives on the planet today.

NARRATOR: But when he ran the tests, the results came as a shock.

LUDOVIC ORLANDO: I have no way to express how wrong I’ve been, actually.

NARRATOR: When Orlando sequenced the Botai horse genome and looked for its signature in modern horses, he couldn’t find it, as if the Botai horses, like their masters, had disappeared. But then, in a surprising twist, he found them in the least-likely horses imaginable.

LUDOVIC ORLANDO: The big surprise is that it’s the Przewalski horse.

NARRATOR: The Przewalski horse: for centuries, these unique-looking horses were thought to be the last and only wild horses on Earth, living in a remote area of Mongolia. As it turns out, they are the genetic descendants of Botai horses that returned to the wild when their masters disappeared. So, these last of the wild horses are actually descendants of the first domesticated horses, a living legacy of their Botai masters.

Although the Botai fade away, another steppe culture seizes the mantle of “horse kings.” They are called the Yamnaya, bands of nomads who roamed a territory north of the Black and Caspian seas at the start of what’s called the Bronze Age. By about 3000 B.C., they become the greatest horse culture of the ancient world.

DAVID ANTHONY: The most important thing about the Yamnaya culture is that they were the first culture to take advantage of both horseback riding, plus wagons.

NARRATOR: Although the first wagons are heavy and crude-looking, they are a breakthrough technology. Wagons stocked with food and supplies, accompanied by horse-herded flocks, allow the Yamnaya to easily move to the best pasturelands. And in no time, the Yamnaya are out-competing other steppe cultures.

DORCAS BROWN: The horses helped them increase their herds. And so, they could get more sheep, more cattle and more meat, and so, they became wealthier. Horse herders could, could beat everybody out.

NARRATOR: And if anyone dares to resist the Yamnaya, here, too, the horse gives them the upper hand, literally.

DAVID ANTHONY: It was an advantage to ride up to somebody on a horse and use the horse as a platform. The height advantage is a real advantage.

SANDRA OLSEN: I think we find it hard to imagine how thoroughly they could overcome other populations who are just sitting there, and unfortunately, very, very vulnerable.

NARRATOR: Over time, the Yamnaya and other cultures they influence develop weapons, like battle axes, that are lethal on or off a horse.

FLEMMING KAHL (Nationalmuseet, Denmark): This battle axe was a very important piece. The edge is not sharp; it’s not very good for cutting wood. But used in battle for, well, breaking skulls, it’s very efficient. All over Europe, we find, actually, skulls which has been, well, broken by ax blows.

NARRATOR: With their horses, wagons and weapons, the Yamnaya and other cultures they combine with, begin to range ever farther from the central steppe, moving as far east as Mongolia and west into the heart of Europe.

And David Anthony contends these aggressive nomads dominate almost every population they encounter, because many people begin speaking Yamnaya.

DAVID ANTHONY: Language is connected to power or to wealth. People drop the language they’re speaking and adopt a new language, because that language gives them advantages.

NARRATOR: But the Yamnaya left no written record of their language, so how could Anthony or anyone possibly know what their language looked like or sounded like?

ANDREW BYRD (Linguist): (Translated from Yamnaya) He formed creatures of the air and animals, both wild and tame...

NARRATOR: Andrew Byrd believes these words…

ANDREW BYRD: (Translated from Yamnaya) …from it, horses were born and cows were born...

NARRATOR: …are close to those spoken by the Yamnaya. He’s made up the story...

ANDREW BYRD: (Translated from Yamnaya) …from it, goats.

NARRATOR: …but can trace the words back to the time they were first spoken, and then reconstruct the language they came from.

ANDREW BYRD: (Translated from Yamnaya) He formed creatures of the air.

NARRATOR: Linguists have long maintained that many languages in Europe and Asia, including ancient Greek and Roman, romance languages, like French and Spanish, Germanic languages, including English and the Scandinavian languages, even Russian and Indian Sanskrit all derive from a common language source.

ANDREW BYRD: If you look at languages like English and Latin and Greek, Sanskrit and Russian, and you start to see these words looking very, very similar to one another. For example, if you look at the word for brother: within English it’s “brother;” if you jump down to ancient Rome, it’s “frater” as in our word fraternity; if you go to ancient India, it’s “bratar;” and if you go to ancient Greece, you have “pratar.”

And you could see that these words look so overwhelmingly similar: they have Rs after some sort of B- or P-like element; they have a T sort of thing in the middle of the word. They all end in R. And, and the fact that all of these things look alike, can’t be by chance, leading us to the only sensible conclusion is to say that these all were inherited from an ancient language.

NARRATOR: Linguists call this source language “Proto-Indo-European.” They can take a word like “is” and trace its spelling and sound pattern back through past languages to approximately when the word first appeared. They can do this with many words, like “father,” and most seem to originate in the period of Yamnaya expansion. And some words, like “wheel,” connect directly with the Yamnaya and only appear after the Yamnaya become dominant.

DAVID ANTHONY: You can establish that the later Indo-European languages all expanded after 3500 B.C. because they have the wheel and wagon vocabulary. And wheels and wagons didn’t exist; they had to be invented first. It’s very much like the word “hard disk.” It shows up in dictionaries in 1978. And dictionaries before 1978 didn’t have the word “hard disk” in them, because it hadn’t been invented yet. And so Proto-Indo-European must have been spoken after wheels were invented.

ANDREW BYRD: Therefore, we assume that there was some ancestral language, which we can call the Yamnaya, which was the source of all of these languages.

NARRATOR: But how did these bands of nomads overwhelm other cultures so completely that people began speaking their language? Shouldn’t there be some indication they had become conquerors?

JOHANNES KRAUSE (Archaeologist): There is very little evidence that what happened 4,800 years ago is related to violence, that there was a massive amount of warriors coming in and just like stabbing and killing everybody, because we don’t find evidence for that.

NARRATOR: So, how did Yamnaya language and culture spread across Europe and Asia? Is there something more tangible than language to account for their dominant presence? Back in Copenhagen, Eske Willerslev had long puzzled over the question, “Which ancient cultures were most responsible for the ancestry of people living today?”

ESKE WILLERSLEV: Our history, far back in time, is actually written, still, in our genes. And that means you can, you can follow human history by analyzing the genome of these ancient individuals.

NARRATOR: He was especially curious about the Yamnaya. If they had dominated large parts of Europe and Asia, then their D.N.A. should have passed on to future generations, down to the present.

His team began by sequencing ancient remains from across Eurasia and then comparing them to a Yamnaya genome, to see how widely the Yamnaya genes had spread. They then compared this data to the genomes of modern populations and put the results on what are called P.C.A. plots.

VAGHEESH NARASIMHAN (Population Geneticist): P.C.A. is a way of understanding, very simply and visually, the differences in genetic ancestry between populations. For example, you put a bunch of people from Europe on a P.C.A. and you’ll notice that the people in northern and southern Europe separate. The second thing you want to do on this is to overlay ancient populations on top of the modern populations and see where they lie.

NARRATOR: These two plots show modern population groups as gray dots in Europe and Central Asia. When we overlay the genomes of people who lived 10,000 and 8,000 years ago, we see almost no overlap, indicating little genetic connection to people living today. But in this plot, representing the approximately 5,000-year-old Yamnaya expansion, the dots overlap significantly, meaning today, millions of people of European and Asian descent owe their ancestry to Yamnaya nomads of the Eurasian steppe.

VAGHEESH NARASIMHAN: What we didn’t understand from the archaeology is the extent of the movement and the impact that the Yamnaya had on genetic ancestry. But now we know that up to 50 percent and 30 percent respectively of the genetics of Europe and South Asia are directly descended from that of the Yamnaya. So, the impact is huge, as much as any genetic ancestry that we have.

NARRATOR: And the Yamnaya could not have made such a massive and wide-ranging genetic impact without their horses and wagons.

ESKE WILLERSLEV: Anthropologists, like Anthony, were right that the early Bronze Age is characterized by this very significant movement of the Yamnaya peoples, on horses that are very speedy, very fast, into northwestern Europe and central Asia, and bringing with them, of course, the genes, the culture and the language. But the majority of archaeologists, you know, didn’t believe this was the case.

NARRATOR: For Anthony and Brown, this was vindication: the Yamnaya had been masters of their universe.

DORCAS BROWN: We were very happy. We were smiling and laughing and going, “Oh, my god, I can’t believe it’s that big. But I was pretty sure these guys were roaming all over the place.

NARRATOR: But a big question remained. It appears Yamnaya numbers are small, compared to the size of the populations they encountered. So, despite the advantage their horses gave them, Eske wondered if there could be other factors that weakened the populations they dominated.

ESKE WILLERSLEV: And first we thought maybe it’s some kind of climatic changes. And we went through the climate records, and we couldn’t really see anything very dramatically. And then there was one of the archeologists on the team said “What about diseases?” So, we thought, “Well, let’s look for pestis.”

NARRATOR: “Yersinia pestis:” the plague. During the Middle Ages, this lethal pandemic killed over half the population of Europe. If it had struck during the Yamnaya times, it might have decimated local populations, clearing a path for a Yamnaya takeover. Eske decided to see if he could find traces of the plague in the bones of the Yamnaya and the people they encountered. But he would need lots of human samples to test.

Remarkably, in St. Petersburg, Russia, a rather unique anthropology museum had just what he needed. Some of the museum’s displays have a Ripley’s Believe It or Not® feel to them, but the real treasures are in storage, as Niobe finds out firsthand.

NIOBE THOMPSON: If you’re after D.N.A. from any part of the former Soviet Union, this is the place to come: the museum of anthropology that Peter the Great founded over 300 years ago, the Kunstkamera. For centuries, Russian archaeologists have been coming back to these storerooms with their discoveries. And today, well, the collection of human remains is astounding.

There are hundreds of skulls and skeletal remains from different time periods and throughout Asia and Europe.

ESKE WILLERSLEV: Okay, this is the last collection.

NARRATOR: And Eske has convinced the museum’s archaeologist, Slava Moiseyev, to let him take back scores of teeth and petrous bones to analyze in his lab.

The two men work for days, cutting samples...

ESKE WILLERSLEV: Nothing like the smell of fresh bone in the morning.

NARRATOR: …carefully documenting each specimen and, literally, pulling teeth.

Moiseyev has one group of Yamnaya samples he knows Eske will want.

SLAVA MOISEYEV (Anthropologist): This is rather strange burial, because mostly people had just single burials, and this consists of seven individuals. It’s quite unusual.

ESKE WILLERSLEV: Oh, wow.

NARRATOR: Group graves became common for later-era plague victims, so these samples will go to the top of the stack.

In the end, the museum, like the Tooth Fairy, bequeaths Eske a goldmine of samples. And sure enough, many contained genetic evidence of the plague.

ESKE WILLERSLEV: We start screening. And you know, bang, it just jumped out, right? I mean, so we saw fragments of it and then we said, “wow! This is basically evidence of pestis and plague epidemics 3,000 years before any written record,” so it was an amazing result.

NARRATOR: The evidence shows the plague begins in the steppe, possibly in Yamnaya communities and including the family of seven, buried together in a single grave. So clearly, at some point, the Yamnaya themselves are suffering horribly.

But those that do survive probably develop immunity. And as they expand their reach, they become like the Grim Reaper on horseback, carrying plague germs with them.

JOHANNES KRAUSE: The plague is spreading with those people. Those people actually bring the plague into the regions that they move into.

NARRATOR: And where people have no previous exposure, only a few survive. And what happens to those survivors is an age-old story.

DAVID ANTHONY: The Yamnaya brought really deadly disease with them. That could have been responsible for a large part of the population replacement. There are other ways though, of course, to replace a population, other than disease. You can directly kill them.

And it does look like the survival of males was much less than the survival of females. You find Yamnaya tribes that regularly engaged in raiding, killing the men and taking local women.

NARRATOR: And using those women to produce Yamnaya offspring. The ancient world could be a very unpleasant place.

ESKE WILLERSLEV: When I started this project, I had this very romantic view of, of the whole thing and, and kind of, you know, dreamt about, you know, living myself during the Yamnaya time, right? I have changed that conception. I am happy to live now.

NARRATOR: The full impact of the Yamnaya’s culture, language and genetic dominance would take centuries passing down to other cultures they combined with.

VAGHEESH NARASIMHAN: It’s sort of a slow rolling process. It’s not like one group of people is just packing up their bags and moving off to Iberia or England or South Asia or India or wherever you want to go. But they’re meeting large groups of people who are farming and, you know, doing their thing. And then there’s a hybrid culture that evolves and a hybrid genetic ancestry that evolves, and these people then, subsequently, move to other parts of the world.

NARRATOR: But back on the steppe, the Yamnaya continue their nomadic ways and inspire later steppe people to take horsemanship to a whole other level.

DAVID ANTHONY: If we go back to the steppes where Yamnaya came from, horses continued to be extremely important, and in fact, a new form of military vehicle was probably invented by the people in the steppes, around 2000 B.C.: the chariot.

NARRATOR: Pulled by swift horses, the chariot is the first high-speed vehicle. And many ancient cultures begin using it in battle, especially on level ground, like deserts. But the most significant developments come when the great horse cavalries of first the Huns and then the Mongols begin thundering across the steppe.

These skilled horsemen could ride and shoot at the same time and become the most lethal military force the world had ever seen, capable of bringing armies and whole cities across Asia, Europe and the Mediterranean to their knees. Although these steppe warriors emerged centuries after the Botai and Yamnaya, their roots go back to those first riders and their mastery of horses.

SANDRA OLSEN: If you just think of some of the great empire leaders in history, for example, Genghis Khan or Alexander the Great, so many of them built their empire on the backs of horses. And that, of course, led to the spread of civilization and the spread of all kinds of technologies, the Silk Road, various trade routes. Everything hinged on having horses.

NARRATOR: The reverence ancient people had for horses, revealed first in early cave paintings, would continue for thousands of years. This bronze and gold Sun Chariot, discovered in Denmark, perhaps expresses this best and is one of the most important symbols of the Bronze Age. Here the horse is god’s partner, helping pull the sun across the heavens.

FLEMMING KAHL: We could wonder why the horse became the most prominent helpers of the sun, but I think the reason is that the horse was and is, even today, perhaps the most aristocratic animal that you can find, a natural choice for a divine being, the very symbol of movement.

ESKE WILLERSLEV: Getting the first time on a horseback, and being able to just feel the speed and the distance you can cover, you can see the whole possibility of exchanging knowledge, understanding the world you are in. It’s a game changer, right? It’s a game changer in human history.

NARRATOR: For nearly 6,000 years, horses have been the human race’s special companion, our extra muscle, our overland vehicles and symbols of power.

NIOBE THOMPSON: Horses gave us the freedom to move, and that freedom changed the very nature of human life. For all we puny humans lack, horse power made up for it. It’s hard to imagine where we’d be, what our world would look like, without horses.