I once acquired a dog who had been very finely trained. Whatever I asked that dog to do, he would do. This was fun at first, but ultimately, it was boring. There was nothing coming back from the dog, no emotional reward. After a year in my chaotic household, though, the dog had learned that our relationship was a two-way street. He was still obedient (to a degree), but he was much more of a developed individual. And he was a whole lot more fun to be with.
I suspect that I enjoyed Whisper for the same reason: He was, as I said, the most polite horse I ever had. But he was also very independent, very much his own man. He taught me more than I could ever have taught him. Whisper’s course in why it’s useful to think about the minds of animals has stayed with me for a lifetime and, quite probably, kept me alive in some pretty dicey situations when I found myself on the back of a horse in a place where I definitely should not have been.
But I never expected to get another life lesson from a horse out in the mountains of Wyoming. And yet, there was that old dun mare, High Tail, sending the message that a life well lived may have nothing to do with glamour, power, and drama, and everything to do with just being quietly persistent. Fate had not favored her. Nevertheless, she had lived long and prospered, had several long-term relationships and a number of offspring. Perhaps evolution sometimes favors the nondescript.
* * *
As Ransom and I talked, in the distance we could see the various ranges of the Rocky Mountains, mountains which, ever since they began regrowing 66 million years ago, have dominated the story of horse evolution. As we watched the old mare, the sky darkened over the peaks of those mountains.
For about the umpteenth day in a row, temperatures had stretched up toward 100 degrees, and over in Cody, the sun was relentlessly baking any living thing that dared emerge from under a rock or a roof or a leaf. Walking through the sagebrush from Ransom’s truck to find the horses, we’d worn nothing but light T-shirts, and even those felt too heavy beneath the blazing sun and deep blue sky.
But now, over those ancient mountain peaks, midnight-black clouds rushed in. Up on the nine-thousand-foot-high pinnacles where other bands of horses were munching on summer flowers, we saw bolts of lightning strike the ground at intervals of only a few seconds. Ransom didn’t appear bothered by this sudden change in the weather. I was, though. In New England, where I live, this sort of meteorological misbehavior is frowned upon. A sudden change from a bright blue sky to a sinister jet-black firmament seems to New Englanders to be rather apocalyptic. But out here, folks accept these climatic extremes as just another part of life.
Like Ransom, High Tail seemed not to notice the sudden atmospheric shift. Using her dexterous lips and well-worn front incisors, she just kept picking and choosing which of those sad-looking tufts of brush she would opt for next.
Surely, I thought, this is no place for a horse. I was thinking of the green pastures of New England and of the beautiful meadows higher up in the Pryors.
“Why is she here?” I asked.
“I don’t know,” Ransom answered. “There must be a reason. We just don’t know what it is.”
By this time the storm that had charged over the Rockies had brought swiftly plummeting temperatures. Raindrops the size of jelly beans began to fall. The drops changed to hail. We ran for the truck. High Tail just kept on eating. If the Vogelherd horse is the quintessential stallion, High Tail seemed to me to be the horse as survivor, capable and competent, steady and dependable, and able to adapt no matter what life might throw at her.
* * *
Indeed, wild horses are experts at adaptation, whether within the context of their own individual lives or over the generations, evolutionarily speaking. They don’t care about sudden temperature changes, massive hailstorms, frigid weather, dry heat, or falling snow. Horses can live almost anywhere. It takes a lot to bring them down.
To think about this, all you have to do is consider the plentitude of free-ranging horse bands all around the world. No one knows exactly how many such horses roam our planet or even how many regions have free-ranging horse bands, because these horses often find their way into nooks and crannies where humans, even today, rarely tread. Bands of horses can thrive at ten thousand feet above sea level, or on isolated, hurricane-prone Atlantic islands. They can revel in fields of Kentucky bluegrass, or live in deserts, or make do with a diet of sea peas and beach grass.
When I started researching free-roaming horses, I was astonished at their numbers—in the millions. I was also surprised by the variety of ecosystems where the horses not only live, but thrive. There may be more than a million free-ranging horses in the Australian outback alone, living in conditions so unfathomably harsh that they make High Tail’s grazing grounds seem like paradise. The Down Under horses, called brumbies, are tough—maybe even tougher than High Tail. There’s an old horsemen’s myth that horses do not do well in heat, but that’s certainly not the case in the Australian outback, where temperatures can easily top 100 degrees for days at a time. This is certainly evolution at work.
Those horses too fragile to handle life in the outback die young, leaving no offspring. Only the most rugged, independent, and intelligent make it through this purgatory and survive to create the next generation. (Whisper, my street genius, would probably have made it. Gray, maybe not. Or maybe he would have bonded with a buddy as smart as Whisper and thus survived.) The Australian brumbies differ from domestic horses particularly when it comes to their feet. Over the century or so that they have lived in the outback (there were no horses in Australia until a stallion, four mares, a colt, and a filly arrived along with a shipload of English convicts in 1788), they have evolved exceptionally strong hoofs that can cope with constant walking over some very abrasive surfaces. One Australian researcher followed a band that traveled for two days to water where the horses drank their fill, then traveled back for two days to where grazing was available. The researcher saw a newcomer, an escaped domestic horse, join up with this band. He didn’t last long. Unable to keep up the pace, he suffered greatly and died. Evolution sometimes happens this way. The horse probably had many great qualities—but he didn’t have the right qualities to succeed in that particular environment. After Darwin published his theory of evolution in the middle of the nineteenth century, many people interpreted him as having said that only the strong survive. Darwin’s thinking was much more nuanced. While he believed that the “struggle for existence” sometimes involved what he called “warfare” between species, he also understood that, like the poor domestic horse who couldn’t survive in the world of the brumbies, animals not well suited to specific environments simply would not leave offspring. Consequently, a species, given enough time, would change.
It turns out that horses are quite talented at changing as the world around them changes. There are a few other places where horses have adapted to live in exceptionally dry areas. In the Namibian desert in southwest Africa (another place where modern horses did not live until they were brought there by humans), free-roaming horses have thrived in harsh conditions for almost a century. Researchers think they may descend from horses used by German soldiers when the region was a German colony.
All over the American West, free-ranging horses roam in small bands. They even seem to do well in areas around Death Valley, one of the hottest and driest places on Earth. You would think that a species that can live in Death Valley would have trouble living in swamps and wetlands, but it turns out that they don’t. A little south of the Namibian desert, another population of horses lives in the Bot River delta of South Africa. And along the Atlantic coast of North America, from Cumberland Island National Seashore in Georgia north into Canada, horses live on numerous sea islands, including those of North Carolina’s Rachel Carson Reserve and Currituck Banks Reserve, and on Assateague and Chincoteague Islands in Maryland and Virginia. Local lore claims that the ancestors of these horses swam to these islands after the many Spanish shipwrecks that occurred in the region during the 1500s. The equine genetic
ist Gus Cothran has shown that there is indeed a genetic connection between these island horses and those in Galicia studied by Lagos and Bárcena.
However the horses got to their islands, local people over the centuries let them stay. Such abandonments happen frequently. It’s expensive to keep horses in barns and in paddocks and to feed them; those same horses, left to their own devices, can feed themselves quite adequately. In recent years, in areas of the American West that have experienced economic decline, domestic horses have been abandoned to fend for themselves—a tradition that’s as old as horsemanship itself. In Europe, when the Soviet bloc broke up in 1989 and 1990, before leaving the collective farms where they’d been forced to live, Romanian farmers released their workhorses onto the Danube River Delta, to give the animals a fighting chance at survival. They did much more than just survive. Twenty-five years later, those horses, possibly the world’s newest population of free-roaming horses, now number in the hundreds, and various local factions and international animal welfare groups are fighting with each other over how to manage them.*
* * *
The evolutionary resilience of horses is still manifest in our world today. Fifteen hundred miles west of the Danube River Delta are the famous white horses of France’s Camargue wetlands, widely believed to be one of the world’s oldest free-roaming populations. Some people say these coastal Mediterranean horses derive from Roman stock, but others say the horses have “always” been there, perhaps since the days when Egypt reigned. (Or maybe even longer.)
The Camargue delta is hot, humid, and filled with all kinds of disease-bearing insects. It’s the kind of world where horses shouldn’t be able to live. But they do. What’s even more unexpected is the fact that the Camargue horses are white. Their coloring puts them at greater risk for diseases associated with sunlight, such as skin cancer. (This vulnerability is one reason why European royalty kept white horses: their coat color spoke of the wealth of their owners, who could afford to pamper their horses indoors and feed them, rather than putting them out to graze.)
Scientists who study evolution have long wondered why these horses are white. Wouldn’t evolution have weeded out animals with delicate skin? A hypothesis that white horses are less visible to predators in open marshland than dark-coated horses turned out to be wrong, as did a hypothesis that white coat color kept the horses cooler by reflecting more sunlight.
The answer lay in the presence in the Camargue of immense numbers of very large flies, insects that in great enough numbers can kill a horse. Carriers of infectious diseases, horseflies in great quantity may suck so much blood from a horse that the animal becomes ill. In large enough numbers, horseflies can literally annoy horses to death by preventing them from eating.
The Hungarian researcher Gábor Horváth and his colleagues have found that, in this situation, white horses have an advantage: flies attack white horses substantially less often than dark horses. Horseflies target their prey by following polarized light, in which the photons oscillate up and down in the same direction rather than every which way. Darker horse hairs polarize sunlight more efficiently than lighter horse hairs, so the signal the flies are looking for is stronger when the horses are darker colored. White horse hair polarizes almost no light. Ergo, horseflies bother white horses less.
So why aren’t most free-ranging horses white? In most parts of the world, horses enjoy a number of options when it comes to avoiding horseflies. They can stand on ridgelines where the wind blows, discouraging the insects. They can graze in drier regions during horsefly season. (Dehydration kills the flies.) Or they can stand in cooler areas, also discouraging the flies. But in the Camargue, there are no options. The delta is horsefly paradise, with its perfect trifecta of conditions—the right amount of humidity, the right amount of heat, the lack of wind. Consequently, here the white coat color is an advantage rather than a disadvantage and is, therefore, selected for.
* * *
Like other scientists interested in understanding how systems change over time, Charles Darwin spent much of his life contemplating the adaptability of horses over millions of years, but it’s only recently that science has shown us how evolution has helped horses in the modern era by giving them such flexible genomes. The same species that evolved to live on cold, dry Ice Age plains, like the Vogelherd horse, has also evolved to live on the shores of the Mediterranean in the hot and humid Camargue.
Or consider the case of the sea-island horses who live on Canada’s Sable Island, a small harborless sandbar of an island located far out in the North Atlantic, about a ninety-minute plane flight east from Halifax, Nova Scotia. This tiny island, shaped like a crescent moon, is about thirty miles long and very narrow. Buffeted constantly by violent North Atlantic storms, this island seems an unlikely home for free-roaming horses, yet as many as 450 graze here, surviving by eating beach grass and sea peas. This sounds like a meager diet, but the horses, abandoned there by a Boston entrepreneur before the American Revolution, have endured for more than 250 years.
Predator-free, their numbers rise and fall according to environmental conditions. No one feeds them or takes care of them. Since the 1960s, their numbers have not been culled. The Sable Island horses, in fact, may be the modern world’s only genuinely free-roaming, entirely unmanaged horse population.
The horses are dependent on whatever gifts the sea provides, yet in recent years their numbers have increased. When I met him at the Vienna conference, the Canadian researcher Philip McLoughlin told me, surprisingly, that he suspects that the population explosion of horses may be due to an explosion in seal numbers. It seems that following a global prohibition against seal hunting, several hundred thousand seals now give birth on Sable Island yearly. This pupping, McLoughlin theorizes, with its accompanying deposition of an awful lot of fecal matter, has increased what he calls “sea-to-land nutrient transfer.” In other words, all those seals leave behind a whole lot of nitrogen-rich manure. The manure feeds the plants. The plants feed the horses.
The only non-marine mammals on the island, the horses serve as a real-world laboratory of evolution. Over the centuries, they have become unique. Their pasterns are now so short that, from a distance, their lower legs look something like the legs of mountain goats. The pasterns of most horses are long and angled, allowing for plenty of spring in the horse’s step, which in turn allows for greater speed and stamina when a horse gallops at high speeds over an open plain. Long pasterns evolved as a survival strategy. But longer pasterns also carry an important disadvantage: the pastern’s fragile bones and vulnerable tendons can easily break or strain, laming the horse. Many a racehorse has ended his career because of this vulnerability. But on Sable Island, the horse does not have to run fast to escape predators. Instead, their enemy is deep sand and their worst “predators” are steep, treacherous sand dunes, some almost a thousand feet high, which the horses must climb in order to eat. These dunes provide some pretty dangerous footing for horses. On Sable Island a horse is much more likely to injure a leg while descending these steep dunes than by running along the island’s beaches. Still, a hungry horse must ascend and descend these obstacles.
Consequently, evolution has made a clear choice, just as in the Camargue region. Sable Island horses have shorter, less vulnerable pasterns, giving them that goatlike look. Over 250 years, natural selection has opted for shorter pasterns, improving the horses’ ability to graze, thus improving the horses’ ability to live longer and produce more offspring. We often think of evolution as complicated, but in this case, the process is pretty easy to grasp.
The Sable Island horses are also behaviorally unusual. Worldwide, many horse bands share their home ranges with other bands. Although the bands don’t travel together, their ranges often overlap, leading to the squabbling Ransom and I watched in the Pryor Mountains. While the horses constantly argue and fuss with each other, normally they don’t drive the other bands away from specific grazing areas. They are not territorial.
On Sable Island,
however, they are very territorial. Island resources are limited. Under these conditions, the horses stake out territories which they defend from other bands. Rather than sharing grazing opportunities, McLoughlin has found, the horses divide the island into three distinct territories: the western end, with its rich grazing and year-round freshwater pond; the middle area, with poorer grazing and ponds that are often full; and the eastern end, with very poor grazing and almost no surface water. The horses on the eastern end must use their hoofs to dig holes into the sand to reach freshwater. The horses on the island’s western end do not allow the horses from the eastern end into their territory. In effect, the horse bands have formed hierarchies, giving new meaning to the concept of a stratified population of upper, middle, and lower classes.
Elsewhere in the world, other populations of horses have evolved other unusual environment-dependent survival strategies. Siberian horses living in the Yana River region, near the Arctic Circle, sometimes called Yakut horses, are said to enter a kind of quiescence in the winter. During the summer, the horses graze constantly on steppe grasses, storing up calories in a subcutaneous fat layer. In the winter, the horses survive by slowly burning this fat, by breathing only half as much as they do in the summertime, it is said, and by standing quietly without exerting themselves whenever possible. Villagers think of this as a kind of semi-hibernation.
Innovation is a never-ending process. Around the world, wherever they live, given enough time, horse bands tend to become distinct entities, well-honed to the world they inhabit. Watching them is an invitation to fall in love with their backstories—not just of individual animals, but also of their long-term evolution.
The Horse Page 4
