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While available evidence now shows that Equus lambei persisted in some far north locations until at least eight thousand years ago, horses in the rest of North America had become extinct by about eleven thousand years ago. In some specific localities, extinction does appear to have occurred abruptly. One such place is the La Brea tar pits in Los Angeles. At this site, a Lagerstätte of southwestern North American coastal life, horses were plentiful about forty thousand years ago. Then, about eleven thousand years ago—they disappear. “First they’re here—and then they’re not,” the paleontologist Eric Scott told me when I visited La Brea. “And after the horses vanish, we don’t see people in this area for another two thousand years.”
The La Brea research site, open to the public, is unique. It’s located right in the center of urban Los Angeles, near the city’s expensive clothing stores, high-end art galleries, and museums. Just a few hundred feet below these buildings is the Salt Lake Oil Field, a subterranean pond of thick, sulfurous oil that slowly seeps up to the surface from the depths of the earth. The upwardly oozing oil from this field creates puddles of thick tar that, on a hot day, are sticky enough to trap someone, or something, foolish enough to walk over it. It’s like nature’s version of flypaper. Even today these puddles, camouflaged by a covering of leaves and dirt, can cause problems. If you’re not careful, you might easily step on what seems like solid earth, only to find your feet immersed in oil. Every once in a while, La Brea staff must rescue some hapless creature, like a squirrel, who has become hopelessly mired.
According to scientists, that’s what happened to a lot of animals beginning about forty thousand years ago. Unlucky horses, bison, and many other species, caught in these traps, were not able to escape, and died there. Some animals, including a lot of dire wolves who preyed on the trapped animals, sank into the seeps and were forever entombed—until paleontologists found them, pulled them out, cleaned them up, and studied them.
When scientists began researching here a century ago, they found so many bones that they established a permanent research laboratory at the site. At first, paleontologists were interested in the larger animals, but now they also study tiny seeds and other bits of plant life, so that today they have a good understanding of the complete ecosystem in which the horses lived.
This is laborious work. I watched one volunteer patiently using a microscope and forceps, examining some of the tar, separating various plant seeds and detritus into individual piles for further study.
“How much time do you spend each day doing this?” I asked.
“About eight hours,” he answered.
“Do you get tired of it?”
“Never,” he answered.
I thought of Chris Beard searching for ten years in poison ivy and kudzu to find one horse tooth, and of Matthew Mihlbachler measuring seven thousand fossilized horse teeth, and realized once again that paleontology is only for the stouthearted.
Evidence from La Brea researchers implies that, at least locally, the disappearance of horses is not connected to the presence of humans. Researchers have discovered only a single human skeleton there. That skeleton dates to about nine thousand years ago, several thousand years after the date of the most recent horse skeleton. Scott, who is an expert in equine paleontology, cannot explain why horses disappear from the local record about eleven thousand years ago. There’s no evidence from the horse skeletons that the horses were suffering in any way, no evidence that they were getting smaller, as in Beringia, or that their bones were brittle because of some new disease. They just vanish.
This extinction event was not limited to horses. Other large animals were also disappearing. Across North America, an estimated 72 percent of the large-bodied mammals died out. During what’s formally called the Quaternary Extinction Event, North American tapirs disappeared, as did short-faced bears and Florida cave bears, giant ground sloths, giant beavers, camels, saber-toothed cats, dire wolves, mammoths, and mastodons, along with plenty of other large mammals.
* * *
Scientists have been unable to pin down the cause of the extinction of horses and other animals. In fact, the issue is surprisingly contentious, even vituperative at times. In the 1960s, the geoscientist Paul Martin asserted that “man and man alone” was responsible for the horses’ disappearance, by overhunting them. Others claimed that climate change was the culprit. While trying to sort out the various points of view, I found myself becoming interested not only in the mystery itself, but in the mystery of why the battle was so bitter.
To better understand, I visited Larry Agenbroad, then director of the Mammoth Site in Hot Springs, South Dakota, where large numbers of young male mammoths fell into a sinkhole twenty-six thousand years ago, died, and were preserved. Other animals, including fish, frogs, birds, rabbits, squirrels, wolves, coyotes, and even a llama, have also been found in this hole.*
Horses are conspicuously absent. Agenbroad told me that horses were too smart to have been trapped this way. I liked the explanation, but had to be honest: Given the young male horse behavior I had seen in Wyoming, I didn’t entirely buy his theory. Young stallion behavior can be pretty risky. Indeed, while Jason Ransom was studying horses in Colorado’s Little Book Cliffs, a band stallion turned up dead at the bottom of a cliff. Tracks at the top of the cliff showed there had been a violent fight. “One of them didn’t judge too well,” Ransom commented.
Agenbroad is on record as firmly believing that humans helped exterminate mammoths from North America, but he disagreed with the theory that humans exterminated the horses.
I asked him why.
“There is no evidence anywhere of humans hunting horses,” Agenbroad replied, referring to North America. He was almost shouting. “We don’t have a good bulletproof theory for their disappearance,” he said. “I think that horses were pretty well gone by the time the people got here.”
But why? I was insistent.
He answered with a shrug of his shoulders, and then asked his own question. “We’ve gone through worse and better climates and they survived. Why did they die just when a big smorgasbord was being laid out for them?”
So it was back to square one.
When Paul Martin first postulated in 1967 that early humans had engaged in a veritable killing frenzy, he chose the unfortunate, loaded word “blitzkrieg.” Today that word wouldn’t raise many eyebrows, but in the years following World War II, “blitzkrieg” reminded people of the relentless bombing of London and other cities. His word choice implied that the Clovis people, who arrived in the New World with revolutionary hunting technology around twelve thousand or so years ago, coincident with the Younger Dryas, engaged in senseless, bloodthirsty violence. Their advanced killing tools, Martin proposed, made mass slaughter of horses and other animals a likely outcome. This did not sit well with many people, including native North Americans. Discussions quickly became bitter.
Essentially, Martin was starting a rumor. Although he had a clear correlation—humans arrive; large animals disappear—he had no real evidence of direct cause and effect. As I searched the literature, I found that Larry Agenbroad was essentially correct: there are no North American sites showing that humans engaged in large-scale horse slaughter. There are, however, a few sites potentially indicating that people did hunt horses when they found them, but these sites are not widely accepted.
For example, at Oregon’s Paisley Caves, the archaeologist Dennis Jenkins has found what he thinks is evidence—human coprolites (fossilized feces)—that humans may have been there very early, about 14,300 years ago. He’s also found a few horse bones in the area, which would have been marshy wetland at the time, along with what he says are human-made stone tools with horse-protein residue. But Jenkins’s findings are questioned by other scientists who say that his dates may be incorrect.
When I talked with Jenkins about his research, he told me that although the region is dry now, in those days it would have been great horse country: “There would have
been stands of grass. In other places, slightly more elevated, there would have been junipers and ponderosa pines in patches. About a mile away from the cave was the edge of a lake, fairly deep, that likely would not have been frozen over often. There was a marsh where the river dumped in. You’d see all that from the caves. You would certainly have seen mammoth out there. Horses. Camels. The occasional carnivore would have included the American lion.”
Jenkins suggests that these early people, whoever they were, did not stay long. He doesn’t know whether they were hunting the horses or scavenging them. Either way, if you accept his evidence (and again, not all researchers do), it would appear that humans and horses did coexist here for at least a short period of time, several thousands of years before the Clovis people began showing up. Even if that turns out to be the case, though, the small number of horse bones present points toward the theory that horse populations were dwindling long before people became numerous enough to cause the horses’ extinction, since only a few bones have been found.
At another site, Wally’s Beach in the Canadian province of Alberta just north of the Montana border, Brian Kooyman and Len Hills have studied thirteen-thousand-year-old bones from seven horses which, they say, were butchered by humans. These seven skeletons each lay at a distance of several meters from the others, which Kooyman and Hills interpret as indicating seven separate killing events, each of only one horse. The researchers also found what they believe to be tools. Analysis seems to show that horse proteins were on the tools, more clearly than at Paisley Caves. Kooyman and Hills go a step further than the Paisley Caves scientists by suggesting that humans were not just hunting horses, but preferentially choosing horse meat over the meat of other animals. This site has preserved tracks of other animals, but no evidence that any other animals were butchered. Their theory is interesting, but again, other archaeologists are skeptical of the team’s conclusions, citing the difficulty of accurately dating the evidence.
There are several other North American sites like these where horse bones appear to exist in the same layer of time as human artifacts, but all are disputed. One thing is clear, though: no horse-hunting sites in North America have been found that even begin to approach the scale of horse-hunting sites that exist throughout Europe and Asia. If horses were hunted by early North American people, the scale of the hunting doesn’t seem to merit Martin’s “man and man alone” assertion of “blitzkreig.”
Nevertheless, his theory has persisted. I’d heard this idea so often that I’d always assumed it was correct, so when I discovered that it was little more than a myth, I wondered how it got started. I decided that when Martin first proposed his idea, Western civilization was suffering from two crises of confidence—the worldwide economic depression of the 1930s, followed by World War II and the terrifying power of the atomic bomb. The Victorian story of humanity’s onward-and-upward progress had ended with World War I. Then, following World War II, we entered a period of collective self-loathing, so that when Martin suggested that a group of a hundred people arriving in the New World about twelve thousand years ago not only could—but would—lay waste to an entire species, people listened.
Today, views like Martin’s have been moderated by scholars. The word “blitzkrieg” has been dropped. In its place, the commonly heard term is “tipping point.” In this modernized view, which takes into account the accumulating evidence of disastrous climate change following the melting of the ice (information that was not available to Paul Martin when he proposed his theory), humans were not mindlessly committing universal mass slaughter. But, some scientists suggest, humans did play a role as a newly arrived predator.
Humans were “the necessary tipping point,” the archaeologist Stuart Fiedel told me: without humans added to the mix, the animals would have survived. Fiedel’s colleague Gary Haynes believes that long before humans arrived on the scene, the Pleistocene horses had been contracting into ever-smaller ranges, so that small-scale human hunting might have been just enough to push the horses over the edge. Haynes has even taken a stab at guessing how many horses were living in North America when people arrived: only 1.2 million. That’s not very many, given the size of the continent.
So the question remains: Why would horse numbers have been so severely diminished?
* * *
When thinking about cause and effect, philosophers often use the terms “proximal” and “distal.” The proximal cause of a forest fire, for example, might be human behavior: a campfire left burning. But the distal cause of that same forest fire might be a longer-term factor or factors, such as drought. Likewise, the proximal cause of the catastrophic floods in Colorado in 2013, which rose all the way up to the edge of Jason Ransom’s family homestead, was obviously an unusual deluge lasting for days. A distal cause might be that ongoing drought had killed vegetation that might have encouraged some of that moisture to soak into the ground rather than run down the mountainside. And an even more distal cause might be that our shifting climate has caused changes in global wind patterns, which brought Gulf of Mexico moisture all the way up to High Country desert.
Your interpretation depends on how far back you want to follow the chain of cause and effect. Given our improved understanding of late Pleistocene temperature and climate, the list of proximal and distal causes for the great extinction mystery is growing on an almost daily basis. For example, the plant paleontologist Jacquelyn Gill has found that, after a system of plants becomes fundamentally degraded, it will likely take hundreds of years for a different ecosystem to become firmly established. In the meantime, there may well be a comparative paucity of vegetation varieties.
The smaller mammals might be able to find their way through the morass, but, suggests the evolutionary biologist John Tyler Bonner: “Size matters.” Bonner explained the extinction of large mammals to me this way: “Most evolutionary biologists would say that this [occurs more easily] because there are fewer of them. There are many more rodents than there are elephants. The chances of becoming extinct because of a natural event is more likely with large mammals. All you have to do is knock out a few elephants. Remember: size limits the abundance of species. If you have fewer around, then it’s easier to make them extinct.”
I suggested that this might be particularly true of an animal like Equus, which only reproduces once a year. A large animal with limited reproductive abilities would certainly be vulnerable to quick shifts in vegetation and climate. And a large nonmigrating animal would have been even more vulnerable. We don’t know for sure whether Pleistocene horses migrated or not, but we do know that most modern horses stay within a home range. Perhaps this affinity for a home range also made them more vulnerable to ecosystem changes. And perhaps as the world changed, each of the isolated populations of horses became smaller and smaller, until Equus simply vanished from the continent where he and his ancestors had lived for 56 million years. Like dust in the wind.
INTERMEZZO
One spring Vermont day when I still had Whisper, the weather was glorious. Windmill Hill, the dirt road leading to my house and barn, was knee-deep in mud. A few piles of snow still dotted my yard, but the sky was an inviting soft blue. A tempting smell of warmth wafted through the air. Tender young leaves were budding on the sugar maples, and patches of grass and curlicues of young ferns pushed up along the road’s shoulders. It was the kind of day that made any heart glad.
Whisper’s gladdened heart got the urge for going. I never saw him leave, or Gray follow him. But yielding to some gnawing sixth sense, I got up from my piano and looked out at the paddock for the horses. Nothing. They could have been standing in their barn, since I’d left the barn door open for them. But I doubted that. It was just too nice a day, the kind of day that Whisper was likely to be very pleased about.
I walked down the hill to check. Nothing. I walked over to my neighbor’s front yard. Nothing. I checked all the usual places, walking about a mile down the road. No horses. But then I saw their tracks. It looked as if the two were
headed all the way down the hill to the school yard. Their tracks were quite directed. They were not meandering. They had a definite goal in mind.
I panicked. Who knew what these guys were up to? In those days, I didn’t know that horses rarely go far. I imagined them ending up in New Hampshire, or even Maine. At a fork in the dirt road, the tracks changed direction, turning right. Now they were heading away from the school and down an overgrown cart path, abandoned for more than a century, since the Green Mountain hill farmers headed west looking for better wheatlands. Vermont has an awful lot of forest laced with these old roads. If you know them, you can travel all the way from the state’s border with Massachusetts up to Canada. Great for riding. Not so great if you’re chasing horses on the move.
To find a horse, ask a horse. I borrowed one of my neighbor’s horses, threw a bridle on her, and let her decide. She moved with purpose. She, too, knew just where she wanted to go. She chose yet another old cart road, one that quickly became little more than a footpath, but I knew we weren’t just wandering in the wilderness because the path ran along one of the state’s ubiquitous tumbledown rock walls, evidence of long-abandoned farms. I wasn’t on a road to nowhere. I was going somewhere. I just didn’t know where. It was a nice day for a ride, but as we moved ever more deep into the forest, my anxiety increased.
Then, suddenly, there they were. Muzzles down, lips pulling away at the nicest patch of grass a horse could imagine. Perfect grass. Grass that must have been as sweet to them as Dutch chocolate is to us.
The golden palomino and the gray Percheron stood in rays of bright spring sunshine. My Tom-and-Huck duo looked angelic, almost as though they were surrounded by a halo in the midst of the dark evergreen forest. Beatific. Innocent. Not at all like criminals.
Above them was that soft blue sky.
The Horse Page 15