Tamed

by Alice Roberts

  The wild horses of Chile seem to belong in that untamed landscape – as much a part of the wild, natural country as the guanacos, pumas, armadillos and condors. And yet the ancestors of the bagual that the gauchos caught in the Chinas Valley could only have been there for a few hundred years. For thousands of years before the Spanish and Portuguese arrived there had been no horses in the Americas. The ancestors of the baguales were domesticated – they are not truly wild horses, but feral.

  And yet, going much further back in time, there were plenty of horses and earlier, horse-like creatures, roaming the Americas. In fact, the origin of this group, and many of its numerous branches, was in North America. The evolutionary history of horses and their ilk includes great proliferation of an ancient family tree, and diversification – as well as a harsh cutting back of many branches, until just a fraction of the splendid, ancient diversity exists today.

  Horses are classified as odd-toed ungulates (hoofed animals). Now, it’s not that their toes are strange, just that they only have one of them, an odd number. Rhinos and tapirs are also odd-toed ungulates, or Perissodactyla – but with three toes. The fossil record of the Equidae, the family which includes modern horses, goes back some 55 million years – starting with the dog-sized Eohippus of North America. These early equids were still in possession of several toes on each foot – three-toed on their front feet; four-toed on their hind legs. Over time, they’d lose them all except one. With plenty of fossils to show the gradual loss of toes, this classic example of evolutionary change in anatomy is enshrined in biology textbooks.

  At times of low sea level, early horse-like creatures could spill out of North America, across the Bering land bridge into Eurasia. There was an early expansion of small, leaf-eating equids out of America into Asia around 52 million years ago – but the descendants of those pioneers later died out. The family tree of horses goes crazy in the Miocene – the geological epoch that lasted from 23 to 5 million years ago. North America filled up with a huge range of horse-like animals of different shapes and sizes: some leaf-eating browsers, some grazers – all fleet of foot. By five million years ago, the fossil record of equids incorporates more than a dozen distinct genera – groups of species – of horse-like creatures, including the three-toed Merychippus, Pliohippus, the earliest one-toed horse, Astrohippus and Dinohippus (the ancestor of modern horses), to name just a few. Again, some – like Sinohippus and Hipparion – spilled out, across Beringia, into Asia.

  At the beginning of the Miocene, North and South America were separated by a large body of water, called the Great American Seaway. In the middle of the Miocene, volcanoes at the bottom of the Seaway created a scatter of islands between the Americas. Sediment gradually accumulated around the islands, until eventually the Isthmus of Panama was created. The emergence of this land bridge allowed plants and animals to spread from North to South America, and vice versa. The migrations peaked around 3 million years ago in what has become known as the ‘great American interchange’. And as part of it, horses expanded down into South America. The first to arrive belonged to the genus Hippidion – a separate, now extinct lineage. They were funny-looking little horses with short legs. By a million years ago, Hippidion would be joined – in South America – by true horses, Equus caballus – essentially the same species as our domesticated horses today.

  The tale of the equid family is one of severe pruning as well as burgeoning proliferation. Of all those diverse genera in the Miocene, only one lineage made it through to the present day: the genus – Equus – to which all the living horse-like animals belong, from actual horses (officially: caballines) to asses, donkeys (the domesticated descendants of the African wild ass) and zebras. Geneticists have been able to extract and sequence DNA from a horse bone preserved in permafrost in the Yukon, dating to 700,000 years ago – the oldest genome yet. Based on the differences between that ancient genome and those of modern equids, the geneticists have concluded that the Equus lineage originated around 4 to 4.5 million years ago. Then the caballine and the zebra–asses lineages diverge away from each other about 3 million years ago.

  Some 2 million years ago, an expansion out of America saw the ancestors of modern asses and zebras arriving in Asia, spreading to Europe and down to Africa. Then, some time after 700,000 years ago, the ancestors of our modern horses also traversed the Bering land bridge from North America into north-east Asia. They quickly expanded across Eurasia. Fossils of two equine species, one an ass, the other an ancient horse, have been found at the early Middle Pleistocene site of Pakefield in Suffolk, dating to at least 450,000 years ago, and at Boxgrove in Sussex, dating to 500,000 years ago.

  Having originated in North America, before spreading to South America and to the Old World, Equus would ultimately go extinct in its homeland. Some 30,000 years ago, as the ice sheets were descending over North America, the endemic, ‘stilt-legged’ horses disappeared from the landscape. In South America, Hippidion and caballine horses clung on longer, until after the last glacial maximum. If I’d been able to travel back to the Las Chinas Valley, perhaps 15,000 years ago, I may have seen truly wild horses – and perhaps species of both Equus and Hippidion – there. But they wouldn’t be around for much longer. And it wasn’t only the climate that was against them.

  Around the peak of the last Ice Age, sea level was low and human hunters would have been able to cross Beringia into the northernmost reaches of North America. Butchered horse bones have been found in the Bluefish Caves in the Yukon, dating to around 24,000 years ago. But access to the land further south was blocked by vast ice sheets. By 17,000 years ago, the ice sheets were melting at the edges – enough to allow human colonisers to migrate from Beringia and the north-east tip of North America, down into the rest of the continent. By 14,000 years ago, there’s plenty of evidence for human occupation right across North America, and down into South America too. And these humans carried some formidable hunting weapons.

  Horse bones turn up occasionally in North American archaeological sites, associated with human occupation or activity. At Wally’s Beach, above the St Mary River in south-western Alberta, Canada, wind erosion has helpfully exposed ancient sediments from the very end of the Ice Age. And pressed into the ancient mud are the preserved footprints and trackways of extinct American mammals – this was clearly a well-used game trail. But alongside the tracks of these long-gone animals, there were bones too – of horse, musk oxen, extinct bison and caribou or reindeer. Some of the horse and camel bones had clearly been butchered. The site has also yielded human artefacts, in the form of stone flakes, which were probably the tools used on the carcasses. The evidence at Wally’s Beach includes eight separate butchering localities.

  Archaeologists have suggested that these localities were almost contemporaneous – it’s possible that animals were being butchered at these separate sites during the same year, the same season, possibly even during the same hunting trip. But are they really evidence of hunting, or could those ancient Paleoindians simply have been scavenging carcasses that had been killed by other predators? No hunting weapons were found at the butchering sites themselves, but a few stone points or spearheads were discovered nearby. And when archaeologists tested these points, they found two bearing traces of horse protein.

  The stone points – which are beautiful, carefully flaked spearheads – are of the Clovis type. The oldest firm dates for Clovis culture in North America place its emergence around 13,000 years ago. The Wally’s Beach stone points were ‘out of context’ – it’s impossible to get a direct date on these spearheads. They were found some distance away from the bones at the butchering site, which were themselves dated to 13,300 years ago. So this leaves two possibilities: either the spearpoints, bearing horse protein, represent slightly later hunting of horses by Clovis people, after 13,000 years ago; or Clovis culture emerged a century or two earlier than previously thought. Whether the finds from Wally’s Beach represent at least two events, separated by a few centuries, or a single event, m
ay be a question that remains impossible to resolve. Nevertheless, the points do provide unequivocal evidence – the Stone Age equivalent of a smoking gun – of the hunting of horses by ancient people in North America.

  The last specimens of Hippidion – found in Patagonia – date to 11,000 years ago. Caballine horses in both North and South America may have clung on a little longer – but their days were numbered. The last trace of truly wild horses in North America comes not from bones, but from DNA preserved in sediment in Alaska – dating to 10,500 years ago. The debate rumbles on about whether it was climate or humans that finished off the indigenous American horses. There was an overlap of several thousand years between the arrival of humans in the Americas and the disappearance of the horses. So human hunters certainly weren’t rampaging across the land on some sort of violent, overkilling spree. On the other hand, we can be sure that they were hunting these animals, even if only occasionally, and that would have had some impact on the already dwindling population. Although climate and changing environments are probably mostly to blame, humans may have helped to speed the extinction of American horses.

  By the nineteenth century, the memory of ancient horses in the Americas had completely faded. As far as everybody was concerned, horses were firmly Old World animals, introduced to the Americas by the Spanish. And then, on 10 October 1833, a ship’s naturalist from Britain was exploring the coast near Santa Fe, recording the geology and any fossils he came across. He was investigating a fossil of an extinct, giant armadillo, when he found what appeared to be a horse’s tooth in the same layer of reddish sediment. It looked a bit weird compared with modern horses’ teeth, but definitely horse-like, nonetheless.

  The naturalist – none other than Charles Darwin – pondered in his field notebook as to whether the tooth might have washed down from a much later layer, but he concluded that this was unlikely. The tooth was extremely old. Darwin had found the first evidence of an indigenous, ancient horse in the Americas.

  When he returned home, Darwin wrote up his discoveries in the Journal of researches into the geology and natural history of the various countries visited by H.M.S. Beagle – the book which would later be rebranded as The Voyage of the Beagle. And he returned to that horse’s tooth in his Origin of Species, writing: ‘When I found … the tooth of a horse embedded with the remains of Mastodon, Megatherium, Toxodon, and other extinct monsters … I was filled with astonishment.’

  The eminent nineteenth-century anatomist Richard Owen (who later became – I think it’s fair to say – the closest thing Darwin ever had to an arch-enemy) wrote up the fossil mammal remains collected during the voyage of the Beagle. He looked at the tooth from Argentina and had to admit that Darwin was right. He wrote that the tooth ‘… from the red argillaceous earth of the Pampas at Bajada de Santa Fe … agreed so closely in colour and condition with the remains of the Mastodon and Toxodon from the same locality, that I have no doubt respecting the contemporaneous existence of the individual horse, of which it once formed part.’ Then, he continued, begrudgingly: ‘This evidence of the former existence of a genus, which, as regards South America, had become extinct, and has a second time been introduced into that Continent, is not one of the least interesting fruits of Mr. Darwin’s palaeontological discoveries.’

  It was an interesting fruit. No wonder Darwin had been ‘filled with astonishment’. It was a real revelation: when the Spanish brought horses with them to the Americas on the cusp of the sixteenth century, they were reintroducing a lineage which had existed for thousands of years in the New World – and which had in fact originated there. Darwin went on to use his fossil horse’s tooth from Santa Fe to illustrate his ideas about extinction in the Origin – proving that ancient horses had once galloped across South America, and then disappeared, long before Columbus made his voyage of discovery.

  Horses in the Old World

  While horse populations were dwindling, eventually to disappear completely, in the Americas, their relatives – horses, asses and zebras – survived in the Old World. Large herds of wild horses continued to roam across northern Siberia and Europe while their American cousins were facing extinction.

  It seems odd that horses went extinct in the Americas at the end of the Pleistocene, whilst surviving in Eurasia. They were facing similar pressures in both places – climate change and human predation. And horses had been feeling the sharp end of human hunting weapons for much longer in Eurasia than in the Americas. Our own species, Homo sapiens – originating in Africa some 300,000 years ago – had expanded into both Europe and Siberia by at least 40,000 years ago. But way before that, horses had been predated by earlier populations of humans, going back hundreds of thousands of years. At Boxgrove in Sussex, a 500,000-year-old horse scapula with spear damage shows that early humans – probably Homo heidelbergensis – were hunting horses. At the last glacial maximum, the horse population of north-west Europe would have plummeted, under attack from both the icy conditions and the lethal spears of the Palaeolithic hunters.

  The Ice Age inhabitants of western Europe were very familiar with horses, and these animals formed the subjects for some cave paintings – images that would be discovered and wondered at millennia later. At the famous cave of Lascaux, near the town of Montignac in the Vézère Valley, in south-west France, small, pot-bellied horses run along the walls, alongside bulls and reindeer. They’re thought to have been painted around 17,000 years ago. My favourite Ice Age painting of horses comes from another cave, however, about 100 kilometres to the south of Lascaux – Pech Merle. The paintings inside this cave are believed to be even more ancient, perhaps around 25,000 years old. I was lucky enough to visit the cave in 2008, with just a few other people, and I wrote about what I saw there:

  A flight of stone stairs led down … I passed [through a door] to emerge into a limestone cave deep within the hillside. I walked through magnificent chambers with huge flowstone creations, enormous stalagmites and stalactites, some of which had met between ceiling and floor to form massive pillars. The cave opened into a great chamber … there, on one rare, smooth part of the cave wall to my left, were two beautiful horses outlined in black, facing away from each other, their hindquarters partly superimposed. They were covered in black spots which also flowed on to the background around them, as though they were somehow camouflaged. There were red ochre spots, too, on the belly of the horse on the left, and on the flanks of the other. I noticed that the flat wall of rock had a strange contour where it ended on the left – almost like a horse’s head. It was as though the artist had taken this suggestion from the natural shape of the rocky canvas … The horses were stylised rather than naturalistic representations. They had great curving necks and small heads, rounded bodies and slender legs. Were they artistic representations of real horses or mythical beasts?

  Whatever those images represented – imaginative riffs on real horses, or horse-spirits, or even horse-gods – we can be sure that the Palaeolithic hunter-gatherers of Europe not only knew what horses looked like, they knew what they tasted like, too. There are plenty of Ice Age archaeological sites with butchered horse bones. In fact, horse – together with bison – is the most common large mammal in archaeological assemblages. Around 60 per cent of late Ice Age archaeological sites in Europe and Siberia contain horse bones.

  After the peak of the Ice Age, the climate began to improve and the potential range for horses increased, with plenty of pasture rolling out – but their numbers kept falling. The continued pressure on the Eurasian population of horses must surely have been exerted by human hunting. And by this time, of course, the hunters of Siberia and Europe were accompanied by dogs.

  The world kept warming up, and the environment kept changing: grasslands were shrinking, as Europe became increasingly forested. The cold snap of the Younger Dryas interrupted the trend, with the forests of western Europe reverting briefly to glacial tundra – but then warmth returned. By 12,000 years ago, the open, Ice Age grasslands known as the ‘Mammoth steppe
’ had all but disappeared from Europe – together with the mammoths themselves. Instead, there was now extensive woodland – mainly birch in the north, pine in the south. From around 10,000 years ago, the central European lowlands were colonised by much denser, mixed deciduous forest, with oak as the predominant species. Warm-loving, forest-dwelling animals such as deer and brown bears were suddenly in their element; they spread north from refugia in southern Europe. Horses, however, were facing habitat loss, and by 8,000 years ago they’d disappeared from central Europe. But there were other areas where much more widespread, suitable habitat existed, on into the middle of the Holocene. These were the grasslands of Iberia, and the Great Steppe or Eurasian Steppe, stretching from north of the Black Sea, as the Pontic-Caspian Steppe, through Russia and Kazakhstan to Mongolia and Manchuria. Plenty of grazing, then, in those grasslands – but also plenty of hunters.

  Even in Europe, there appear to have been some refugia – pockets of suitable habitat – where small numbers of horses could cling on. There are over 200 archaeological sites, dating to between 12,000 and 6,000 years ago, ranging from Britain and Scandinavia to Poland, which preserve evidence of wild horses. This suggests that – although the new forests were too dense for animals like mammoths and giant deer, which then faced extinction – there were enough woodland groves for horses to graze in, even if their populations were now small and fragmented. Forest fires – common in pine forests – could have helped to create clearings. Along the course of large rivers, regular flooding could also have kept woodland at bay, creating river meadows suitable for large, grazing mammals.

  And there was something else that helped to create habitat for wild horses. Around 7,500 years ago (5500 BCE), the frequency of horse remains found in archaeological sites across Europe increases. This upsurge in horses seems to coincide with the arrival of a new way of life in Europe: farming – and the beginning of the Neolithic. When early farmers began to fell trees to clear space for agriculture, cattle and sheep, they were inadvertently making room for wild horses too.