This particular Yukon stallion had a yellowish coat and a long, flowing blond mane and tail. This alone surprised the experts, since it was commonly believed that before domestication all horses had short, bristly manes and stumpy tails.
Olynyk’s horse stood about four feet at the withers and had a disproportionately large skull (by today’s standards). He was a tiny thing, weighing more than the Laetoli mare’s hundred pounds but a lot less than the thousand pounds or so of a well-nourished modern horse. Quite stocky, with thick legs, a clunky head, and a cold-adapted convex nose, he would have been called a hammer-headed horse by the old American cowboys.
DNA testing shows that he is a thoroughly modern Equus.* He is the horse in the backyard barn and in the show ring. He is the horse running loose in the American West and is even, despite his inelegant nose, related to today’s baby-faced Arabian horses. To me, he looks totally practical, a horse born to weather whatever life threw at him. Like Whisper. So it seems my golden-coated Vermont horse came by his survival abilities honestly.
Injuries on the Yukon horse’s body imply that a predator was involved in his death. There are teeth marks on his neck, perhaps made by a wolf. He had horsehair in his stomach. This suggested to the Yukon paleontologist Grant Zazula that he might have been wounded but had tried to heal himself by licking his injury. Maybe he stepped into a muddy wallow that, like quicksand, wouldn’t let him go. I rode Whisper into a mess like that once and I had to get off just so he could pull his single-toed feet out of the bottomless mire without also having to balance me on his back.
Although it’s hard for him to say exactly how the Yukon horse died, Zazula does know a lot about the world the horse enjoyed while he was alive. It was parkland. Pretty as a picture. Dotted with trees—but not forested. Something like an Alpine meadow. Maybe it even looked a bit like the Pryor Mountain peaks Jason Ransom and I visited.
It was a marvelously complex grassland. All kinds of tasty treats grew there for the horse to eat, available from the earliest spring until the dead of winter. A study of well-preserved ground nests left by a variety of critters has found thirty-thousand-year-old pollen and other remains from at least sixty different species of grasses and sedges.
For this horse, there were swaths of bunch grasses, prairie sage, wild rye, poppies, flowering chickweed … and buttercups. Of course, winters were tough, but the horse could still dig down through scattered embankments of windblown snow to find fresh greenery. Even today, scientists sometimes find buried bits of still-green grasses that grew at just about the time the horse died.
It was dry where the Yukon horse lived, almost arid. Precious little snow fell, and what snow did fall was light as flour. Blown by the wind, it piled into drifts. These drifts, too, helped the horse, because when the sun returned in the spring and the drifts melted, some of the meltwater sank into the soil, creating patches of green. The horse could move from patch to patch and find fresh food almost as soon as the dark time was over. These young grasses were full of protein. Jason Ransom has seen modern horses take similar advantage of long-lasting snowbanks: “The horses can move from nutrient-rich spring greens on the south faces of mountains to the same nutrient-rich spring greens on the north faces later in the summer.”
* * *
Though we call this horse’s home the Yukon, geographically it’s considered the easternmost part of a large area called Beringia, a region that extends from the far west of the Canadian Yukon into Siberia. Over the eons, Beringia, like a slowly bobbing apple, has been sometimes partly submerged, as it is today, and sometimes above water. During the above-water periods, the region was massive, almost a thousand miles wide in some places.
In its own unique way Beringia during the ice ages was also a Garden of Eden, albeit much colder, drier, and more challenging than Messel. The Beringian lifestyle required a horse that was quite different from the little dawn horse. Equus was up to the task. Indeed, for the Yukon horse, Beringia may have been downright congenial—at least compared to much of the rest of the northern part of the Northern Hemisphere, where ice sheets more than a mile thick covered the land.
Horses had come a long way since the days of the Eocene, when they needed warmth and rain and grapes. The dark wouldn’t have bothered the Yukon horse, because his eyes had by then evolved into huge orbs that could detect suspicious movements at great distances in very little light. His hearing was exceptional. He depended greatly on his ears, which were controlled by sixteen small muscles that allowed him to rotate them in all directions with great finesse, so that he could focus on even the slightest sounds. He could prick them forward to monitor sounds in front of him as he traveled, or he could lay them back against his head to warn companions of his displeasure. His sense of smell, already developing in the little dawn horses, was by now so well-honed that reading the aromas in the air or in a dung pile left by another horse was for him like reading a book is for us: a font of information about the world around him. His strong social instincts helped him perceive the emotions of the other band members, so that when he saw the ears of another horse pricked forward, he, too, looked up to see what danger might lie far ahead.
We won’t call the Yukon horse the “perfect” horse, because evolution doesn’t work that way, but we can say that his evolutionary heritage had made him a flexible, social, intelligent animal. He needed that intelligence. His pastures of plenty sat in the rain shadow of high coastal mountains, which drained all the moisture from the air. Instead, where the horse lived, there was little snow but a lot of wind. We know this because scientists have found huge drifts of loess. This light dust—like the dust that blew out of the American central plains in the 1930s and the dust that flows like rivers even today in some parts of the American West—piled up high all over Beringia.
Challenging though these windstorms were, the horse knew how to cope. This we can infer from the vast numbers of horses who lived in the region during that time. Pleistocene horse bones are very, very common. The paleontologist and naturalist Dale Guthrie ranks the horse among the “Big Three” mammals who then lived on these northernmost plains. Horses, bison, and mammoths, Guthrie says, reigned supreme in this cold environment.
So Beringia was a place to call home for many species and not an “interstate highway,” as I’d been led to believe as a child. In the 1930s, scientists posited Beringia as a “land bridge” that allowed animals and people to travel from North America to Asia. The theory was all about migration. I read about the “land bridge” at about the same time I learned about the evolutionary “progress” of horses from small creatures to noble beasts. Pittsburgh, where I grew up, is a city where three major rivers come together, so I knew exactly what a bridge was: an ugly iron structure crossing water. The point of a bridge, I knew, was to get somewhere. You didn’t stay on a bridge. Early scientists imagined Beringia the same way. They never imagined that Beringia could actually have been a focal point of evolution.
They do now, though. The geologist Robert Raynolds suggests that people think of the region not as a land bridge, but as a “food bridge,” where animals found good grazing and where they could make themselves at home. As the modern world warms and the region’s frozen tundra melts, so many Pleistocene carcasses have been pulled out of their burial sites that we now know that Beringia positively teemed with animals. And as those animals stayed there, generation after generation, they became ever more closely adapted to the world in which they lived.
“Evolution didn’t happen in other places and things moved in,” Zazula, a lifelong Yukon citizen, told me. “Evolution happened in Beringia. It was a really nice time to be here.” So Beringia was, in its own way, a land of milk and honey.
Of course, Beringia was not Messel, with all the food a horse would need within easy reach. A horse surviving in the Yukon thirty thousand years ago would have had to be able to travel far distances for food, suggests Christine Janis. He had to have a phenomenal memory and to be able to recall the location of
all water sources. He had to know when the water would be there and when the water hole would dry up. He would have had to know where the overhangs and valleys were that would shelter him from storms. He would have had to be able to flee predators when possible, and to be able to stand and fight valiantly when necessary.
And he had to be highly social. All this knowledge was too much for an individual horse to find out by himself. It had to have been passed down through the generations from the older mares to the youngest foals. If you had friends, and associated with older horses who had long memories and lots of experience, and if you were strong and hardy and cold-adapted, life in the Yukon could have been just the thing.
In the modern world, we underestimate the mind of the horse to a shocking degree. We think that because they accept our bidding and stand cooperatively, there’s not much to them. But when you consider what it took for the Yukon horse to survive those winters without anyone providing grain or hay or shelter from the wind, it brings home the depth of Phyllis Preator’s insight that free-roaming horses “think different.”
We primates generally think of the Arctic as hostile. After all, most of our evolution occurred in the tropics. So it’s not surprising that early paleontologists, who did not live in the Arctic but “heroically explored” that world (where Inuit had been getting along quite well for thousands of years, thank you), assumed that life in the Arctic was miserable. When I was a child, reading Jack London’s stories of dog teams drowning in freezing rivers confirmed my worst nightmares about life up north, and I imagined animals living there as doomed to a kind of relentless Napoleonic march of misery through endless fields of snow, with a constant threat of death from starvation and exposure.
This kind of imagery drives Zazula crazy. The Yukon horse may have lived in the far north near massive ice sheets, but his world was nevertheless, Zazula emphatically believes, quite livable. Beginning about ninety-five thousand years ago, the Laurentide ice sheet began covering much of North America, spanning the continent from New England’s Cape Cod in the east to the Canadian Yukon in the west. It dipped south to stop just short of where the 12-million-year-old Ashfall horses lay hidden. But most of Beringia, running about two thousand miles west of the ice sheet and into Russian Siberia, lay ice-free and above sea level.
For tens of thousands of years, the region was a kind of haven, a refuge from the relentless ice. “This special cold-arid northern grassland was like a monumental ‘inner court,’ surrounded on every side by moisture-blocking features: high mountains, frozen seas, and massive continental glaciers,” wrote the Alaskan paleontologist Dale Guthrie.
* * *
And yet, well suited though he was to his northern world, this northern horse species, the North American Equus lambei, became extinct by about eight thousand years ago. Dale Guthrie wanted to know why. After examining hundreds of horse bones collected in Beringia and stored in New York City’s American Museum of Natural History, he found that, over thousands of years, the northern horse diminished in size. Some scientists had suggested that human hunting had caused the extinction of the horse from North America, but Guthrie’s evidence seems to point another way.
“What role did humans play in the extinction of the horses?” I asked him.
“None,” he replied. “The problem with invoking humans is that you have to have some evidence.” And in North America there’s no evidence that humans hunted horses in large numbers.
The culprit, he proposed, was a change in climate and a subsequent ecosystem shift. When temperatures warmed at the end of the ice ages, formerly frozen landscapes became wet and in some places even swampy. This was fine for cloven-hoofed animals like moose, but not so great for an animal that had evolved to run on a single toe. The warming climate meant that many dry-adapted grasslands disappeared, making the foods the horses relied on harder to find.
For Guthrie, his evidence shows that the northern horses were having trouble surviving in their strange new environs. “The decline in body size that I showed is a piece of evidence that the horses were having a hard time,” he said. “Whatever role humans played, the horses would have become extinct anyway.” Other research supports his view. The molecular biologist Beth Shapiro has looked at DNA evidence that she interprets as suggesting that the northern horses began declining in terms of population numbers as early as thirty-seven thousand years ago.
Zazula agrees. The arrival of humans in Beringia and the disappearance of the horses happened at about the same time, so that they appear, from our distant perspective, to be correlated, but that doesn’t mean that one event caused the other. Most likely the two events are just two symptoms of a changing world, Zazula suggests, adding that the newly arrived humans may have been following the elk and moose, who also arrived in the Yukon at about the same time. All these events are symptoms of a world in flux.
“Things start to really change rapidly up here after fifteen thousand years ago,” he added, referring to changes in climate that were sometimes so abrupt that they occurred within one human lifetime. “The world up here comes apart really fast. That’s when things start to get ugly for the animals.”
All over North America, the story was much the same.
* * *
By fifteen thousand to ten thousand years ago, North America and most of the Northern Hemisphere had become considerably warmer. We know this because, by studying ice taken from ice sheets in Greenland and in several other places, we can read the rise and fall of various isotopes of oxygen, of carbon dioxide, and of methane and other atmospheric compounds that indicate temperature fluctuations. The more methane in the atmosphere at a particular time, for example, the hotter it was.
It turns out that what most of us know as “the Ice Age,” once imagined to be a world eternally encased in a vast field of ice, was not an Ice Age at all—but a series of ice ages that caused the ice sheets to ebb and flow over the Northern Hemisphere with surprising alacrity. Near the end of the Pleistocene epoch, temperatures sometimes rose and fell so abruptly that one team of scientists has likened the climate to a “flickering switch.”
The northern ice cap began melting in earnest about 14,500 years ago, but even this wasn’t one long, smooth process. The ice disappeared slowly in some regions, but more quickly elsewhere. There was no uniformity. Instead, the melting was erratic, occurring in fits and starts. Glaciers would melt back, then another cold spell would occur. Because of this instability, plants that grew in an area might not be able to grow there in following years. Ergo, the animals depending on the plants would not be able to find them where and when they expected them.
The melting also brought a whole new array of insects to harry the animals. Indeed, scientists study temperature fluctuations in part by finding fossils of various species of beetles, which are closely adapted to temperature. This means that beetles, of all things, can provide clues to ancient climate, just as ice cores can. By knowing which beetle species live at which temperatures, the temperature of a particular area can be estimated for a given time frame.
All this evidence points toward a significant climate event that may have contributed to the demise of the North American horses, both in the Yukon itself and throughout the whole continent. About 12,900 years ago a global chill, called the Younger Dryas, dramatically reversed the warming trend. Then about 11,500 years ago the temperature suddenly jumped back up by as much as 8 degrees or so Fahrenheit in some places over the course of only about sixty years. The Younger Dryas was like the Eiffel Tower of Heat that began the Eocene—but in reverse. First it got cold, then it got warm. This warming was not globally uniform. Pollen studies show that the Amazon experienced only minor blips and that, even in the north, temperatures remained stable in some refuges.
Various species were affected differently by this anomaly. At least one species—Homo sapiens—adjusted by making a major lifestyle change: Archaeologists widely attribute the beginning of farming to the warming and drying of parts of the Middle East, where
people had long relied on hunting and gathering. When the number of wild animals began to diminish because the temperatures changed, we had to learn how to domesticate them. We also learned how to raise crops and, to accomplish that goal, began learning how to control the flow of water by digging rudimentary canals. Clearly, the change in temperature was putting a lot of pressure on human beings. The same changes would also have pressured other living things.
The cause of the warming is under debate. One theory with considerable traction suggests that so much freshwater was released from the North Atlantic ice sheet into the northern Atlantic itself that global ocean currents shifted, changing rain and wind patterns. Another theory proposes that the melting ice sheets released large numbers of icebergs that drifted as far south as the Iberian peninsula, disrupting ocean currents. In support of this theory, marine scientists mapping the deep ocean floor have found what seem to be mounds of otherwise unexplained stone rubble. The theory suggests that this rubble dropped onto the ocean floor out of the melting icebergs.
Unfortunately, when considering the Pleistocene extinctions, our very refined data is limited to Greenland and Antarctica and to parts of Europe. We don’t know precisely what happened to temperatures in most parts of North America. We just don’t have enough detail.
We do know that instability was rampant. In The Great Basin, the archaeologist Donald Grayson documented ongoing chaos in the interior of the American West during the millennia between fifteen thousand and ten thousand years ago. The extent of the chaos was biblical. Lakes rose to high levels, causing massive floods. Some, like the Great Salt Lake, rose and fell, and then rose and fell again. At times these regions would have been flower-filled, at other times they would have been inundated. At still other times, they would have been deserts.
The Horse Page 14
