CHAPTER 1
The Dawn of the Horse
Equine Evolution and Bone Wars
The enticing and seducing whisper of the Wild West was summoning Othniel Charles Marsh. The Civil War had been over for three years, and the vast, windswept prairies and majestic cloud-piercing mountains motioned for American Manifest Destiny. The war-weary nation was licking its wounds and trying to forget four years of unforgiving slaughter that left 750,000 Americans dead but ultimately unshackled 4.2 million human beings from the bondage of chattel slavery. For many like Othniel Marsh, the untamed West was the epitome of freedom and the essence of the rugged frontier spirit.
Born into modest means in Lockport along the Erie Canal in western New York, Marsh, a dour, scraggly bearded thirty-seven-year-old bachelor, had nothing tying him down. He purchased a train ticket to the newly established Wyoming Territory and methodically packed and bundled the bare necessities of a paleontologist: notebooks, pencils, shovels, picks, a well-worn straw boater hat, and, of course, a six-shooter pistol. In short order, restless men and women like Othniel Marsh transformed the West.
The providential opportunities were as endless as the horizon stretching seamlessly beyond the eternal grassland prairies and cascading foothills of the Rocky Mountains, to the sparkling, wave-crested waters of the Pacific. Fortunes awaited in the boomtown gold and silver mines. Fertile and vacant land hungered for the cultivating cleaves of the plow and the ranching hoofbeats of horses and cattle. Ferocious fur-bearing beasts howled from the rogue silhouettes of the snowy peaks. Adventure and amusement beckoned from whiskey-soaked saloons, sweaty bordellos, and dodgy gambling dens west of the Mississippi River.
Within this Gilded Age of upheaval, war, and shifting cultural and economic landscapes, railroads opened the door to westward expansion and, in the process, unlocked a window to our petrified past. The so-called Bone Wars between 1868 and 1892 witnessed a frenzy of trailblazing—and, at times, ruthlessly cutthroat—fossil expeditions and momentous discoveries. Rival fossil hunters and bone collectors scoured and combed the rich beds of (what are now) Wyoming, Colorado, Utah, and Montana.
To climb the professional ladder and attain the accompanying financial windfalls of celebrity status, callous and vindictive American and European paleontologists resorted to bribery, theft, sabotage, violence, and slander. Allegiances were fickle, and alliances fleeting. In this contentious age of embryonic Darwinian evolution, unearthing fossils meant fame, fortune, and academic immortality.
Given the increasing popularity of paleontology, and with successive and seemingly unearthly finds dominating the press and captivating popular imagination, in 1866 the millionaire financier, banker, and philanthropist George Peabody donated $150,000 ($3 million in today’s money) for the construction of the Peabody Museum of Natural History at Yale University.[*1] In a brazen act of nepotism, the institution promptly appointed its benefactor’s nephew, Othniel Charles Marsh, professor of paleontology (the first such academic position in North America) and a trustee of the museum. Marsh was an unlikely candidate to seize the crown of early American paleontology.
Subsidized by his uncle, Marsh had previously studied geology, anatomy, and paleontology at Yale, followed by three years at various institutions in Germany. Although not yet established, he was talented, keen, energetic, and—most importantly, given the sizable expense of research excursions—fully funded. In 1868 Marsh packed his duffle, holstered his pistol, and bought passage (quite ironically as it would turn out) on one of the first “iron horse” trains to chug west on the overland route of the newly constructed Union Pacific Railroad.
During a quick pit stop on the Nebraska-Wyoming border, Marsh took the opportunity to stretch his legs and chat with the locals, explaining in the process the purpose of his trip: he was a fossil hunter. To his surprise, he was presented with fragments of bones that residents had unearthed while digging a well. He quickly assured them that they were not human remains nor, much to their disappointment, those of prehistoric saber-toothed tigers.
Marsh realized, as he later wrote, that they were “many fragments and a number of entire bones, not of man, but of horses, diminutive indeed, but true equine ancestors.” Upon further examination, Marsh had acquired the bones of four separate horse species, including a small, odd-looking horse “scarcely a yard in height, and each of his slender legs was terminated in three toes.” Financed by a $100,000 inheritance from Peabody, who passed away in 1869, Marsh returned to the Wild West on numerous archaeological research trips to dig fossils, hunt bison, and dodge danger.
During one of these adventures in 1870, Marsh ran into Brigham Young, president of the Church of Jesus Christ of Latter-day Saints, at the theater in Salt Lake City. The Mormon leader immediately set about interrogating him about his equine fossils. Bewildered by the intense probing, Marsh politely answered the questions while his team of Yale paleontology students, in the words of participant C. W. Betts, “flirted with twenty-two daughters of Brigham Young in a box at the theatre.”
Mormon theology posits that the horse was present around 589 BCE, when the prophets arrived in the Americas. According to 1 Nephi 18:25, from the Book of Mormon, “And it came to pass that we did find upon the land of promise, as we journeyed in the wilderness, that there were beasts in the forests of every kind, both the cow and the ox, and the ass, and the horse.” Young’s persistent line of questioning now made sense to Marsh. He was looking for hard scientific evidence to corroborate the spiritual passage.
The seemingly lawless, no-holds-barred competition among bone collectors unfolding on the front lines of American settlement was set against the bloody backdrop of the American Indian Wars. Caught up in this cyclical frontier violence, not to mention the perils posed by rival paleontologists, Marsh and his team carried rock hammers in one hand and, in true Indiana Jones fashion, Colt revolvers or carbine rifles in the other.
During one expedition in 1872 in southwest Wyoming Territory, for example, Edward Drinker Cope, the rival paleontologist, had been spying on Marsh’s team from a craggy outcropping. At dusk, when the team packed up, Cope crept down to the site. Emerging from the skulking shadows, he was elated to find a skull fragment, several teeth, and other assorted bones. The unique combination of anatomical features represented in his looted specimen all pointed to a new, undiscovered dinosaur species. Instant fame and the satisfaction of publicly humiliating his archnemesis Marsh was as good as carved in stone.
What Cope did not know until after he had touted the discovery and published an academic paper on his groundbreaking new fossil was that he had been set up, duped, and played for a fool. Marsh had been aware of Cope’s clumsy espionage and deceptively instructed his diggers to “salt” the ground with the skull, teeth, and bones of miscellaneous fossil species. The credulous Cope arrogantly took the bait. When his blunder was publicly exposed, he had to recant his findings and, in the process, tarnished his reputation. Marsh got the better of his chief adversary in this round of the Bone Wars.
In addition to clashing with Cope, Marsh was often a spectator to the fierce skirmishes between the US Cavalry and mounted Indigenous warriors during the last colonizing campaigns of American progress. On one harrowing expedition near the Bighorn Basin of northwest Wyoming, Marsh hired a young army scout named William Cody as a tracker. Before arriving at their destination, the future Buffalo Bill galloped away to investigate a scuffle with Pawnee warriors. Later in the day, these same Pawnee horsemen became boisterously captivated when Marsh, an influential advocate for Indigenous rights, showed them some ancient fossils of their most prized possession: horses.
On another occasion, Marsh met and chatted cordially with the famed Oglala Lakota (Sioux) leader Red Cloud. Marsh listened with solemn interest as Red Cloud methodically articulated the plight and starvation of his people. The combative atmosphere on the Northern Plains was aggravated by the encroachment of settlers onto unceded Sioux land and the corruption of federal politicians and agents known as the Indian Ring.
Furious with the treatment of Red Cloud and the Sioux, Marsh traveled to Washington and met personally with high-ranking members of the Ring, who brushed him off like an old fossil and stonewalled him at every opportunity. They even tried to discredit Marsh by circulating falsehoods that he was a drunkard who committed scandalous and depraved sexual acts with his “Yale Boys” while excavating fossils out west.
Eventually Marsh secured an audience with President Ulysses S. Grant, alerting him to the frontier tinderbox fueled partially by the corruption of his own cabinet. The Sioux, stressed Marsh, received nothing more than “frayed blankets, rotten beef, and concrete-hard flour.” His humanitarian efforts on behalf of Indigenous peoples did not go unnoticed. “I thought he would do like all of the other white men, and forget me when he went away,” Red Cloud remembered. “But he did not. He told the great father [President Grant] everything just as he promised he would, and I think he is the best white man I ever saw.” By this time, however, Grant had lost control of his own administration, and his subordinates, including those in the Indian Ring, were running roughshod over his policies and his presidency.[*2]
Othniel Marsh, an eccentric and awkward paleontologist, had headed out west to find and catalog equine fossils. In the process, he helped to bring down one of the most infamous and corrupt political rings in American history. In 1875, after Marsh’s tireless petitioning on behalf of Red Cloud and all Indigenous peoples, and a series of scathing newspaper reports, the Indian Ring, or “Trader Post Scandal,” was finally exposed. Numerous members, including prominent politicians, were forced to resign from their positions or faced impeachment trials. Appalled by the brazen embezzlement of the Ring, in the spring of 1876 Lieutenant Colonel George Armstrong Custer even testified on behalf of the Sioux. Three months later, he would die at their hands.
While this encounter in June 1876 along the greasy grass of the Little Bighorn River in Montana Territory may have been Custer’s Last Stand, it was also, in a sense, the last stand of Indigenous autonomy and self-determination. The Sioux won the battle, but with their Ghost Dance massacre at Wounded Knee, South Dakota, in 1890 at the hands of the US Cavalry, they lost the war, sealing the fate of Indigenous peoples across the United States.
By 1900, their total population hit its historic nadir at 237,000 survivors, and their land holdings had been reduced to 52 million acres from 155 million only fifteen years earlier. With Indigenous peoples removed, relocated, shattered, and subjugated, the West was open for business for miners, farmers, ranchers, trappers, and fossilists.
As the ongoing Bone Wars intensified, with the aid of Peabody’s money, Marsh bribed the diggers of other paleontologists, including Cope, to reroute the most exotic, complete, and valuable fossils to him at Yale. Ironically, or perhaps hypocritically, like the corrupt Indian Ring he had helped to unmask, Marsh was not above using unscrupulous tactics to further his own financial and professional agendas. “Within a few years, Marsh had so many crates of fossilized bones stored in the attic of Yale’s Peabody Museum,” writes Pulitzer Prize–winning author David Philipps in Wild Horse Country: The History, Myth, and Future of the Mustang, “that he had to prop up the ceiling with extra beams.” Following his death in 1899, it took a team of paleontologists over sixty years to unpack and inventory his enormous collection of fossils.
Lakota leader Red Cloud visits paleontologist Othniel Marsh at Yale University, 1883. (Smithsonian National Portrait Gallery)
Having assembled this vast trove, which included the partial remains of more than thirty ancestral species of the horse, Marsh began the arduous task of trying to piece together the complex puzzle of equine evolution. In doing so, he catapulted British naturalist Charles Darwin’s audacious new theory of evolution forward by cataloging the fossilized ancestral sequence to the modern horse. He started the hereditary branch at one hoof, the most obvious recent relative, and worked backward to those species with multiple toes. “The line of descent appears to be direct,” Marsh announced, “and the remains now known supply every important form.” He labeled his early, small, three-toed Wyoming specimen Eohippus, or “dawn horse.”
Inadvertently, and initially unknowingly, Marsh became entangled in the rancorous and heretical debate surrounding evolution among the British scientific community following Darwin’s 1859 publication of On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. We must remember that in Darwin’s day, evolution was a perverse and profane assault upon the doctrines of Christianity. To many, including academics, it was blasphemous pseudoscientific rubbish.
Equine evolution was originally thought to be an orderly and direct chronological branch, staunchly obedient to the simple, uncomplicated organic laws of natural selection. Distinguishable anatomical modifications and adaptations were easily identified, specifically those amendments to feet and teeth, with successive specimens stacked like Russian nesting dolls. This galloping journey from ancient ancestor to existing Equus was frequently touted as the literal textbook example of unambiguous “straight line” evolutionary progression and the ever-popular exhibit A for museums.
This evolutionary canard is known as orthogenesis: an outmoded theory that variations follow a particular direction and are not merely sporadic or fortuitous. In short, orthogenesis would imply that evolution has a clear objective, a single-minded commitment to a desired end state or biological ambition, and that each extinct relic somehow gave rise to a superior replacement. “The orthogenetic template has…influenced millions of lay people,” concedes distinguished paleontologist at the University of Florida Bruce MacFadden, “many of whom visit natural history museums with turn-of-the-century exhibits that convey 100-year-old ideas.” Naturally, evolution is an interlaced forest of tangled trees, full of branches, twigs, blind turns, and, more often than not, dead ends.
Darwinian natural selection, or “survival of the fittest,” is driven by various external pressures, including changing climate, environmental catastrophes, sustenance variation and accessibility, and reproductive cycles, within ever-shifting and fluctuating local ecosystems.[*3] We tend to forget that evolution is not the engineer of inevitability. According to an orthodox quotation attributed erroneously to Darwin, “It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change.”[*4]
Evolution is driven by immediate survival needs, not the preordained perfection of species over millions of years. Many species existed for millennia before survival pressures condemned them to extinction and an ignominious eternal night at the museum. According to recent estimates, more than fifty billion, or 99.99 percent of all species that once occupied the terrestrial stage, have gone extinct.
Natural selection is a one-way process of trial and error. Once traits, both detrimental killers and advantageous saviors, have been bestowed and propagated, it is very difficult to reverse course. “In each generation, natural selection can only use the raw materials that previous generations of selection have left it. Thus, over long periods of time, certain branches will prove more successful than others; certain trends will emerge,” recaps historian and author Stephen Budiansky in The Nature of Horses. “But, again, it is always worth remembering that these trends reflect what are in effect the sum total of lucky guesses or accidents. They are the long-term consequences of short-term ‘decisions,’ consequences that could not have been anticipated at the time those choices were made. Most extinct species were victims of their own success—they had the misfortune of being supremely adapted to a niche that did not last.” As Darwin surmised, the adaptable survivors “breed out” those who do not possess favorable traits—simple and uncomplicated survival of the fittest.
As a young naturalist sailing aboard the HMS Beagle on a survey expedition, in 1833 Darwin was “filled with astonishment” to find a horse’s tooth at Santa Fe, Argentina, in the same soil stratum as the fossilized remains of giant armadillos. Upon his return to England three years later, his presumptions were confirmed by Richard Owen, the renowned biologist, anatomist, and paleontologist.
Despite producing a remarkable life’s work on a zoological Noah’s Ark of animals, both extinct and living, and founding the British Museum of Natural History in 1881, Owen is now best remembered for coining the immortal word Dinosauria, from the Greek deinos sauros, or “terrible lizard.” As a rabid disciple of anatomy, Owen had procured right of first refusal to any dead animal or carrion from the London Zoo—an arrangement that vexed and infuriated his wife, who once had the pleasure of entering her front parlor to the cordial reception of a decaying rhinoceros.
Owen recognized that Darwin’s horse tooth belonged to an extinct equine species, noting: “Every point of comparison that could be established proved it to differ from the tooth of the common Equus caballus only in a slight inferiority of size.” Adhering to the undisputed universal doctrine that horses evolved in Eurasia, he went on to state: “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.” This amiable collegiality between the two men was a mirage, however.
Owen would eventually become a harsh critic of Darwin’s theory of evolution, championing instead a philosophy that all living matter was arranged in an “organizing energy,” or life force, that encoded and oversaw the origin, growth, and decay of living tissue. This arrangement determined the anatomical blueprint and life span of individual animals within the larger life cycle and framework of their species. Owen’s concept is eerily similar in construct to Star Wars guru George Lucas’s spiritual canon and metaphysical creed of “The Force” and its energy-binding “midi-chlorians” cellular interface.
Upon the publication of his seminal treatise On the Origin of Species, Darwin courteously sent Owen a complimentary copy, acknowledging that to Owen “it will seem an abomination.” Within the dog-eat-dog world of academia and personal ego, Owen classified Darwin’s work as an “abuse of science” in a scathing review. “The Londoners say he is mad with envy because my book is so talked about,” Darwin responded later. “It is painful to be hated in the intense degree with which Owen hates me.”
Owen’s envious attacks were not limited to Darwin. He also slandered “Darwin’s disciples,” including Joseph Dalton Hooker, Charles Lyell, and the eccentric biologist Thomas Henry Huxley, whom he admonished as an “advocate of man’s origins from a transmuted ape.” Huxley was an evangelical crusader for evolution, which earned him the understated nickname “Darwin’s Bulldog.” His initial response to Darwin’s idea of natural selection was simply “How extremely stupid not to have thought of that!” Huxley successfully recruited converts to Darwinian evolution and was relatively successful in publicly spurning Owen’s persistent attacks.
As an unforeseen appendage to the controversial yet proliferating natural sciences, in the priggish horse-powered society of Victorian England, “fossil hunting” had become a trendy pastime. For upper-crust day-trippers, it offered an adventurous respite from the elysian day in the life of British aristocracy. Fashionable for both noble gentlemen and ladies, these nature walks were purported to be morally elevating and spiritually inspiring by exulting in the breadth of God’s divine handiwork.
In 1839 William Richardson was engaged in just such an outing, foraging for fossils in the famous London Clay beds of Kent County representing the earliest stratigraphic stage of the Eocene period (fifty-six million to thirty-four million years ago). Richardson recalled that he was scavenging with “strong expectation for the evidence of some form of animal life.” His excursion proved fruitful, yielding the front half of a tiny skull, which eventually found its way into the hands of none other than Richard Owen.
Based on the teeth and the forward-facing position of the eye sockets, Owen, who had studied and cataloged thousands of extinct species, was perplexed, noting, “The teeth, instead of great, ridged, grinding prisms of our present horse, were small, low, and cusped, really more like monkey teeth than horse teeth. The little skull, with its relatively large eyes set about midway from snout to ears…like that of a Hare or other timid Rodentia.” He decided that the contours of the teeth bore striking similarities to existent hyraxes.[*5] Fittingly, Owen called his intriguing new specimen Hyracotherium (“hyrax beast”).
Although Owen categorized the odd-toe ungulate taxonomic order Perissodactyla, he never entered what turned out to be the earliest known ancestor of the horse into this branch. As a reminder, there are seventeen living species of Perissodactyla from three related families: seven Equidae (one horse, three asses, and three zebras), five Rhinocerotidae, and five Tapiridae.
In the meantime, while Owen was pondering hyraxes, Huxley had begun the painstaking process of assembling a vague linear evolution of equine fossils. Key to his findings was that horses came from a small tapir-like animal, with multiple toes and low-crowned teeth. Despite academic scorn and ridicule, Huxley and supportive British and Russian scholars sequenced a partial array of fossils they believed represented the lineage of the horse, acknowledging that it was spotty and missing links between specimens.
What Huxley and his colleagues could not have known at the time is that their mainline evolutionary limb was incomplete, and would always be incomplete, because this anatomical journey took place in the remote continent of North America—not in Eurasia, as was universally and unwaveringly believed. After all, when Europeans first arrived in the Americas, there were no horses to be seen. None. Across the entire Western Hemisphere, the horse was completely absent from the landscape.
A parallel study of equine evolution was taking place in both Europe and the United States independent of each other. The left hoof was not in sync with the right. Getting in step would eventually happen with a meeting of the minds (and fossils) between our resident Englishman, Thomas Huxley, and our American archaeological adventurer, Othniel Marsh, whose forays into the Wild West had produced a brimming collection of ancient horse fossils.
Huxley sailed to the United States during its centennial year of 1876 to embark on a lecture tour promoting Charles Darwin’s controversial new theory by highlighting his evidential fossil record of equine evolution. The first appointment on Huxley’s busy agenda, however, was a visit to Marsh and his museum at Yale. As you might expect, the two scruffy oddballs hit it off immediately.
They analyzed fossils and compared notes by day, continuing their jovial academic banter by horse-drawn carriage at night. After spending a week chatting with Marsh and immersed in his fossils, a giddy Huxley animatedly reported to his wife, “His fossil collection is the most wonderful thing I ever saw.” Huxley’s wife seems a mite better off than that of his archnemesis Owen, who received a decomposing rhino instead of a riveting letter.
Astounded by the breadth of American specimens, Huxley solicited Marsh repeatedly to produce equine fossils exhibiting specific anatomical features. With each request, Marsh turned to his assistant and recited a box number to retrieve from the dusty, and recently reinforced, shelves. This game seemed to last for days until Huxley turned to Marsh and declared, “I believe you are a magician; whatever I want, you just conjure up.” Utilizing Marsh’s technique of working backward from specimens with one toe to three toes, although lacking a fossilized example, they postulated that the original member of the horse family had four toes, which Marsh theoretically named Eohippus. Huxley drew his new friend a satirical cartoon he labeled “Eohippus + Eohomo,” depicting a petite early hominid joyfully riding this ancient multi-toed horse.
Marsh recalled: “He then informed me that this was new to him, and that my facts demonstrated the evolution of the horse beyond question, and for the first time indicated the direct line of descent of an existing animal. With the generosity of true greatness, he gave up his own opinions in the face of new truth and took my conclusions.” Huxley confided in Marsh, “The more I think of it, the more clear it is that your great work is the settlement of the pedigree of the horse.” Huxley rewrote his upcoming lectures to include this new chain of evidence as irrefutable proof of evolution.
These discoveries were also immediately embraced by Darwin, who wrote to Marsh with applauding praise. “Your work on these old birds & on the many fossil animals of N. America,” he extolled, “has afforded the best support to the theory of evolution, which has appeared within the last 20 years.” While buttressing the theory of evolution, the findings of Marsh and Huxley simultaneously refuted the established theory that horses evolved in Eurasia. Overwhelming evidence now pointed to a North American evolutionary origin of the species. European and Asian specimens were episodic immigrants from the main North American epicenter of equine evolution.
This was the issue that had perplexed Darwin ever since 1833, when he had stumbled upon the Argentinian horse tooth during the Beagle voyage. “Horses appeared and disappeared in Europe with an absolutely rude abruptness, presenting a kind of magical ‘now-you-see-’em, now-you-don’t’ aspect of which Darwin thoroughly disapproved. It wasn’t just that the horses behaved oddly across the ages. It was that when they reappeared after long absences of millions of years, they were different,” explains Wendy Williams in The Horse. “Darwin was thinking about all this long before we knew about genetics or DNA, and from the European point of view, the evolution of horses flew in the face of logic.”
This intermittent occurrence of horses in the Eurasian fossil strata, with extended interruptions of millions of years—and the glaring specimen gaps in Huxley’s original fossil sequencing—was now easily explained. Only certain North American horse species made the trip to Eurasia, where they eventually died off. Now it all made sense. For Darwin and his disciples, including Huxley and Marsh, evolution prevailed once again, and logic and reason were restored.
Shortly after his return to England, Huxley received a letter from Marsh informing him that he had found their four-toed Eohippus. It had been in the museum all along. Marsh apologized to his colleague, lamenting that he had so many crates of bones pouring in from the western fossil beds that he hadn’t had time to even open, let alone catalog, them properly before Huxley’s visit.
Neither Huxley nor Marsh recognized that the Eohippus was the same creature that Richard Owen had dubbed Hyracotherium some thirty-five years earlier. Separated by the middle passages of the Atlantic, the left hoof was still not quite in sync with the right. The study of equine evolution stumbled on until 1932, when Sir Clive Forster-Cooper of the British Museum finally identified that the European Hyracotherium and the American Eohippus were the same species.
By convention of zoological nomenclature, Owen’s Hyracotherium (1840) is the official designation, since it was the initial taxonomic entry. This tongue-twisting classification, reasoned pioneering equine paleontologist George Gaylord Simpson (1902–1984), was “not likely to win so many friends.” By this time, however, Eohippus (1876), with its endearing translation of “dawn horse,” had already become entrenched in books and museum displays. Although it is a rescinded junior synonym, Eohippus is still used widely today, especially in the United States and Canada. After all, the horse was a gift from North America to the rest of the world.
The dawn of the horse: Anatomical reconstruction and dimensions of Hyracotherium. (Universal Images Group North America LLC / Alamy Stock Photo)
Inhabiting a vast quadrant of the planet roughly fifty-seven million years ago, the Hyracotherium was a small, fox-sized mammal between twenty-five and thirty-five inches in length and between twelve and twenty inches in height (or three to five hands, in horsespeak). Its small, flexible frame, weighing ten to twenty pounds, was supported by four toes on its front feet (the large fifth “thumb-toe” was off the ground) and three on its hind feet (with the fifth and vestigial first toes off the ground), all tipped with padded paws, or soft proto-hooves. Its back legs were longer than its front, allowing it to scamper and bound (like a deer), and browse on fruits, leaves, and other soft foliage with its short snout containing forty-four low-crowned teeth. The fact that its five toes were morphing into three and four toes is an indication, as postulated by Marsh and Huxley, of an earlier evolutionary transfiguration from a five-toed ancestral forerunner.
This progenitor of Hyracotherium remains a mystery, as the post-dinosaur epoch beginning roughly sixty-five million years ago was the transcending shift from reptiles to mammals.[*6] At this embryonic stage, however, the small ratlike mammals that paleontologist at the University of Bristol Christine Janis dubbed “artful dodgers” were still relatively undifferentiated, with a sparse evolutionary tree. Although our skeletons have been pulled in different directions by the survival pressures of natural selection, anatomical vestiges in both horses and humans point to a shared common ancestor, or “stem animal,” somewhere between a hundred million and sixty million years ago.
The global environments these adaptable and burgeoning mammals patrolled would be unrecognizable to us today. The now-desolate, windswept plains and dusty tumbleweed deserts of Wyoming and Colorado where Othniel Marsh’s Hyracotherium scampered fifty-seven million years ago, for example, were a wet, lush, jungle canopy. It was a period of global warming that paleontologists refer to as “Greenhouse Earth,” when crocodiles basked on sunny, breeze-kissed beaches and took leisurely naps under the shade of swaying palm trees—in the Arctic. Landscapes were dominated by forest and jungle, and not by the savannas, prairies, grasslands, steppes, and tundra of today.
As the temperature and ecosystems of the Earth fluctuated, Hyracotherium was forced to adjust, and through an assortment of evolutionary offspring—and many more dead ends—gradually transitioned into modern Equus. These adaptations allowed the modern horse to not only survive but also, eventually, with human intervention, thrive. It is important to consider, as paleontologist Richard Hulbert at the Florida Museum of Natural History stresses, that the evolutionary journey of the horse is a “web of hypotheses and theories, with many points of contention and controversy. No two paleontologists interpret the fossil record exactly alike, and this is certainly true in the case of horses…. Nevertheless, because of our long-term relationship with horses, their fossil record will always have special significance.”
For our purposes, however, we must condense the fascinating and complex bloodlines of equine evolution and corresponding anatomical adaptations. Only those vital and exploitable anatomical, biological, and behavioral attributes (and events) on the evolutionary ladder that allowed humans to harness the unrivaled potential and historical influence of the horse will be detailed. Without these critical steps and traits, our dominant, earth-shattering relationship would have been untenable. To initiate this evolutionary sequence, we must travel back to the dawn of the horse.
Although the supercontinent Pangea, encompassing almost all the Earth’s land mass, slowly began to break apart 175 million years ago, most cross-continental land routes were still accessible. A high-altitude land bridge connecting North America to Europe via the Arctic islands of Canada, Greenland, and Scandinavia allowed for the extensive migration of animals across current continental divides. By fifty-five million years ago, Hyracotherium was established throughout Europe, Asia, India, and North America, particularly in Wyoming, Colorado, and New Mexico.
Around fifty million years ago, the Earth began to cool, and humidity levels dropped. As jungles and forests retreated slowly, grasses filled the ecological vacuum. Hyracotherium became extinct between thirty-four million and twenty-three million years ago, save for North America, where they continued to evolve. According to archaeologists David Webb and Andrew Hemmings, during this middle Eocene period, “North America became isolated from other northern landmasses. In Europe the family…diverged from the true Equidae, which persisted only in North America. Thereafter North America had hegemony over equid evolution.” By thirty-two million years ago, North America was producing equines that, although much smaller in stature, had a similar silhouette to modern-day horses. The 120-pound Miohippus, for example, which lived roughly thirty-two million to twenty-five million years ago, would be easily recognized today as a miniature horse.
Throughout these evolutionary trails, equine species would emigrate from North America across Beringia to Eurasia and begin a separate evolutionary path, only to become extinct, while the main American line continued its own progression. “This pattern of global radiation and Old World extinction would occur repeatedly,” explains anthropologist Pita Kelekna, “before modern Equus finally evolved in North America.” For example, eleven million years ago, a remarkably successful globetrotting species known as Hipparion fanned out from North America across the Arctic, Asia, Europe, the Middle East, and the Indian subcontinent. These animals persevered in Africa until four hundred thousand years ago, long after the extinction of their kin across Eurasia and North America.
At Laetoli, Tanzania, roughly thirty miles south of the infamous Olduvai Gorge, a surface known as Footprint Tuff records the earliest known interaction between the ancient ancestors of horses and humans. Among the numerous footprints excavated between 1976 and 1978 by renowned archaeologist Mary Leakey are the side-by-side, juxtaposed steps of Australopithecus and Hipparion. As they walked across, and imprinted their mark upon, this muddy, ashen surface some 3.6 million years ago, these progenitors could not have imagined that the eventual dynamic union of their offspring would irrevocably change the world. “Wherever man has left his footprint in the long ascent from barbarism to civilization,” acknowledged late-nineteenth-century historian and author John Trotwood Moore, “we will find the hoofprint of the horse alongside.”[*7]
The most significant global equine dispersion involved an early species of the modern genus Equus, which DNA research suggests evolved in North America some 4.5 million to 4 million years ago.[*8] Traversing the newly formed Panamanian land bridge, or Isthmus of Darien, about 2.7 million years ago, these horses were among the first mammals to enter South America during a wave of accelerated migration known as the Great American Interchange, which included the ancestors of the heavyweight Arctotherium, a hulking four-thousand-pound short-faced bear!
Successive waves of Equus also wandered across the Bering Bridge to Siberia and Asia and eventually established themselves across Europe and the Indian subcontinent by 2.6 million years ago. These multiple migratory populations created a deep genetic rift and deviation among modern horses, asses, and zebras. Equus found its way down to Africa, displaced the resident Hipparion, and, in time, gave rise to various groups of zebras. At roughly the same time, the Equus subgenus Asinus (asses) evolved and scattered across Eurasia and the Middle East.
According to a recent archaeological study by Peter Mitchell from the University of Oxford, the common ancestor of both zebras and asses “likely coexisted with the earliest horses in North America before dispersing into the Old World a little before 2 million years ago. A recent whole-genome study (as opposed to ones targeting only some parts of an individual’s DNA) places the separation of zebras and asses at 1.99–1.69 million years ago.” Both zebras and asses continued to diverge into subspecies until roughly 150,000 years ago.
During the Pleistocene epoch (roughly 2.6 million to 12,000 years ago) no fewer than fifty-eight species of Equus are present in the North American fossil record, with dozens living simultaneously. This is certainly not “straight-line” evolution at play. The direct descendant of modern caballine horses showed up in North America loaded with genetic adaptations around 1.2 million years ago and its offspring in Europe as early as 1 million years ago. With the advent of DNA testing, genomic analyses of the seven living species of the genus Equus have revealed a more composite schematic blueprint of equine evolution than thought previously.
Shadowing and interwoven within the fabric of these migrations and extinctions was a series of successive adaptations fashioned by the gradual climatic and ecological transition from jungle and forest to grasslands and tundra, or what influential nineteenth-century poet Walt Whitman called the “vast, trackless spaces” within North America. Natural selection is not all that complicated. It has one superseding prerequisite: the need to eat and not be eaten. This simple equation dictated most equine evolutionary modifications from Hyracotherium to horse spanning a period of roughly thirty-five million years.
An era of global warming beginning roughly twenty million years ago kicked off an evolutionary explosion. This “Great Transformation” produced numerous competing equine species in North America. While most were evolutionary dead ends, those inheriting specialized genetic mutations to teeth, the digestive tract, feet, legs, and brain survived and thrived in a capricious ecosystem being overrun by grass. “The evolutionary saga of the horse is a kind of cast-out-of-Eden story,” writes Philipps. “The horse started in a lush paradise that it lost as the global climate changed…. That evolution helps explain why the animal made such a tight bond with humans, and why it was able to spread all over the world in the modern era when so many other animals disappeared.”
It is precisely these biological features, developed within an adapt-or-die evolutionary arms race with grass, that set the horse apart from all other animals and engineered its matchless potential as a living machine that would eventually come to dominate our planet and our shared history.
From Hyracotherium to horse: The global evolution and dispersion of Equus. Note the survival pressure shift from browsers to grazers. (American Association for the Advancement of Science)
*1 Having no legitimate heir to his vast business enterprise, Peabody partnered with Junius Spencer Morgan in 1854. Their joint venture would eventually become J. P. Morgan & Co., the predecessor to three of the largest banking institutions in the world: JPMorgan Chase, Morgan Stanley, and Deutsche Bank. Peabody is also considered the first modern philanthropist.
*2 The seventeenth-century term “running roughshod” described a horse that wore shoes with projecting nailheads. This gave the horse better traction while also creating a more lethal trampling weapon. Over time the term evolved to mean “attaining one’s goals or desires by completely ignoring the opinions, rights, or feelings of others.”
*3 The expression “survival of the fittest” is commonly, but mistakenly, attributed to Darwin. The English biologist and anthropologist Herbert Spencer coined the catchphrase in his 1864 book Principles of Biology after reading Darwin’s On the Origin of Species. Darwin then borrowed the term from Spencer for the fifth edition of his book, published in 1869.
*4 This often-referenced quotation does not appear in any of Darwin’s published writings, journals, or letters.
*5 These rather unassuming, chubby, furry critters—weighing five to ten pounds and resembling a marmot or a groundhog—are found only in Africa and a small swath of the Middle East. Quite unexpectedly, given their rodent-like appearance, hyraxes are closely related to elephants, aardvarks, and manatees. Evolution works in mysterious ways.
*6 Dinosaurs ruled the Earth for an astounding 165 million years—six hundred times longer than our own hubris-driven reign as Homo sapiens.
*7 While Moore was a prolific writer and journalist, and the state librarian and archivist for Tennessee, he was also an unabashed racist and apologist for the Old South and Confederacy.
*8 Some argue Equus is as old as seven million to eight million years.