Recent research has shown that this ability may be based in certain areas of the brain, and may be inherited. Our brains have at least five different areas called “face patches,” as explained by the Nobel Prize–winning neuroscientist Eric Kandel in The Age of Insight. These groups of brain cells are dedicated to reading and responding to the facial features and expressions of others, confirming Ekman’s finding that facial expressions are a sort of universal, inherited communication system. Interestingly, at least one of these patches of cells connects directly to the amygdala, the structure that mediates our emotions and social behavior.
Now, research by ethologists and animal behaviorists is confirming that this inherited ability may not be limited to Homo sapiens. Certainly, some dogs are able to do this, and as any horse owner will tell you, horses, too, can read eye and facial expressions.
The Canadian researchers Ian Whishaw and Emilyne Jankunis have found that horses have a universal expression they make when tasting something sour, and that this expression is quite similar to the expression we make when we take a big gulp of pure lemon juice. The two researchers gave forty-four horses sugar water and quinine. The horses who received the sugar water bobbed their heads, perked their ears, and slightly licked their lips. The horses who received the bitter infusion drew their lips back in distaste and stuck their tongues out—much as a child would do when asked to take an unpleasant medicine.
As Ekman showed, we are preprogrammed to read these expressions. Charles Darwin first proposed that we can read the intentions of other animals in this way because that ability helps us survive. Sometimes we do this not because of our experience, but in spite of it. Years ago I was canoeing in Zimbabwe through an area filled with hippopotamuses. My only experience with these animals was in children’s picture books, when the laughing hippo opens his mouth charmingly in the middle of an African lake. In my own canoe, however, when a hippo rose up out of the water and opened his mouth at me, I understood immediately that he meant that as a threat. He was neither laughing nor charming, and I was not amused. I knew instantaneously that I was in danger. No words had to pass between me and my paddling partner. We just both immediately paddled backward.
In The Expression of the Emotions in Man and Animals, Darwin discussed the similarity of emotional expression in the eyes of many different mammals, and theorized that a set of universal emotions coupled to these expressions had evolved over tens of millions of years, just the way skeletons had evolved. Darwin was an excellent rider—his father often chided him for wasting time galloping his horse all over the countryside when he should have been figuring out how he was going to earn a living—and he understood the emotional expressions of horses quite well. As an older man, he once recounted a terribly dangerous ride when his horse encountered an unexpected tarpaulin lying in a field and communicated his terror directly to Darwin: “His eyes and ears were directed intently forward,” Darwin wrote long after the event, “and I could feel through the saddle the palpitations of his heart.” Years after the incident, his writing about it carried a vividness that showed that Darwin himself had never gotten over his own fright at nearly being dumped on the ground.
The clinical psychologist Sandra Wise believes that the dance of communication between horses and humans depends very much on the ability of both horses and humans to exchange information by way of eye contact. “In the eye of a horse, you can see a yin and yang,” she told me. “You can see their genetically based fear, since they’re prey animals, but you can also see their natural curiosity.” Wise runs a program that teaches the finer points of human-human interaction by having students interact with her free-roaming Florida Cracker horses, horses that hark back to the earliest days of Spanish colonization. In her program, Eye of a Horse, students learn to watch the horse’s eyes carefully in order to understand how they themselves are affecting the animal. Her clients include people with autism, people who have experienced personal traumas such as childhood abandonment, and masters- and doctoral-level students in clinical psychology. She believes that people who learn how to bond with a horse by making productive eye contact will have taken an important step toward being able to bond with other people.
Horses’ eyes are huge, larger than even the eyes of elephants. The size of the eye may be related to the horse’s defensive strategy of running from predators. The biologist Christopher Kirk has compared the top running speeds of a number of animals with the size of those animals’ eyes. He theorizes that the horse’s eye is so large because the horse can run forty miles per hour over an open plain in short spurts. Because of this need to see in the distance while running, Kirk suggests, horses have eyes that respond quickly to the world around them.
“How did humans and horses evolve their special relationship? I think it has something to do with their eyesight,” Kirk told me. Of all non-primate mammals, he said, horses have visual abilities that are most similar to our own. “The eye is just a bit smaller than a racquetball,” he said, “and they have tremendous acuity.” By “tremendous” he meant in comparison to most other mammals, and closer to the exceptional acuity of primate vision.
For us, making eye contact is essential to our mental health. We do this persistently even with other animal species. Trained to herd sheep competitively, my border collie was taught not to make eye contact with his shepherd—who ended up being me. I found this very disconcerting, and felt rewarded when he finally made eye contact with me. He’s not as good at herding sheep as he was when I got him, but he’s a much better life companion for me. As a species, we crave eye contact. Psychologists have found that infants need to make eye contact with their caregivers in order to thrive. As adults we retain this fascination. We are, for example, suckers for the wide eyes of infants. We can’t help ourselves. This is our biology. Looking into the eyes of other living things is almost addictive.
Who better to make eye contact with than the horse, the land-based mammal with our planet’s largest eyes? This usually unconscious need has a great deal to do with our natural attraction to horses. Artists know this. Since the days of the Vogelherd horse, they have created horses with large, limpid eyes. In The Arab Tent, the British Victorian artist Edwin Landseer depicted an Arab mare and foal lying together on an elaborate carpet just inside a desert tent. When we see the soulful, huge black eyes of the gentle white mare, our hearts sigh. In Raphael’s Saint George and the Dragon, the wide-eyed horse looks gratefully at his rider after Saint George has slain the predator. In 1769, the British artist Sawrey Gilpin painted Gulliver Taking His Final Leave of the Land of the Houyhnhnms, in which the eyes of horses express disdain for the human, whom they are about to throw off the island because of his lack of intelligence. In George Stubbs’s Mares and Foals, a mare glares a warning at another horse who has come too close to her foal. In the early twentieth century, Franz Marc’s peaceful horses often have their eyes half-closed. The effect is transcendent. Walking through the Viennese early eighteenth-century stables of Prince Eugene of Savoy, a famous warrior skilled at using cavalry in his battles with the Turks, I saw that his favorite horses drank from marble water troughs, and I looked up to see benevolent horses’ heads, also carved of marble, looking down protectively at me.
I wondered what made these horses seem so kind. Then I realized that the horses had been given impossibly enormous eyes, eyes that had been moved so far forward to the fronts of their skulls that their faces looked quite human. They reminded me of the cherubim in the Sistine Chapel. These horses were clearly gifts from the gods. Who wouldn’t love such animals?
* * *
But the eyes of the dawn horses were not at all “kind.” In fact, they were rather rodent-like, located halfway down the skull toward the muzzle. To think more about the evolution of the horse’s eyes, I returned to the American Museum of Natural History, where the paleontologist Matthew Mihlbachler once again patiently pulled bones and more bones out of storage cabinets. The exhibits in the public part of the museum had changed s
everal times since I had last visited Mihlbachler, but these back rooms looked pretty much the same. I sniffed the air. There, once again, was that aroma: dust and eternity.
This time Mihlbachler led me first to the department of modern mammals. He brought out skulls from modern Equus species. These include the horse, the plains zebra, the mountain zebra, the onager (an endangered species who lives in some Asian and Arabian deserts), the donkey, and the Przewalski’s horse—all of whom descended from the original Equus simplicidens of 4 million years ago.
We looked for the location of the eye socket in each of these skulls. At the La Brea tar pits, Eric Scott had shown me a skull that came from a horse pulled out of the tar and compared it to a modern Thoroughbred. The racehorse had very forward-facing eyes that would have provided fairly good binocular vision, but would have handicapped the horse had he lived in the wild, since he would have had difficulty seeing predators sneaking up behind him. The ancient La Brea skull, on the other hand, had eye sockets located well to the sides of the horse’s head. He would not have had very good binocular vision, but would have been able to keep one eye out, looking for danger on the far horizon, while he kept grazing. We were curious about whether we would see such differences from species to species, but they didn’t stand out.
Then we wondered about how the placement of the horses’ eyes had changed over time. We walked back 56 million years by heading over to the paleontological section of the museum. This research facility is monumental. The trek from the Holocene all the way back to the Eocene turned out to be quite a long journey. Traversing halls as long as New York City blocks, we descended cavernous stairwells that smelled of 150 years of scientific research, passed through heavy fire doors, and rode an elevator shaft, until finally we were back where I had first met Mihlbachler, on the sepulchral floor that held the horse fossils.
Once again, Mihlbachler pulled out skulls—this time, of several long-extinct horse species. He laid the skulls down on a long table, the kind you find in a school cafeteria, and formed an evolutionary tree of horse heads.
A lineup of modern Equus skulls at the American Museum of Natural History (Greg Auger)
At the base of the tree were the dawn horses; rising up from that foundation, he created branches to show how many different options horses had chosen over the course of their existence on Earth.
Suddenly, horse evolution was very real. By now, I had seen the horse’s evolutionary tree time and again in scientific papers, but there on the table was the real thing: the change in horse skull shapes over tens of millions of years. While the jawbones of horses, containing mineralized teeth, are common all over the Northern Hemisphere, complete skulls are delicate and rare. Jawbones of animals often survive, Mihlbachler told me, because the teeth in the jawbones are tough and act as a kind of glue that keeps the bone from shattering. The plate bones of the skull, on the other hand, are easily broken and are thus difficult to find.
As I looked at Mihlbachler’s tree of skulls, I thought once again of sickly, anxious Charles Darwin who was so often afraid to publish his books. Chances are good that if Darwin had been able to see what we were looking at that day, his stomach would have bothered him less and he would have saved himself a lot of trips to expensive health spas.
Mihlbachler pointed to a dawn horse skull.
“That animal was probably nocturnal,” he said. “He definitely had large eyes, compared to his size.”
He also pointed out strange indentations in a skull laid out on the table. These indentations sat just below the eye sockets and are called “preorbital fossae.” They are not present in modern Equus.
“What were they for?” I asked.
“We have no idea,” he answered. “It’s kind of a big mystery.”
Some scientists have suggested that the indentations contained scent glands; other researchers, that they were locations for certain muscles.
The eyes of the dawn horses were located well to the sides of the skull and nearer to the muzzle than the eyes of Equus. The dawn horses’ eyes sat just above their teeth. As we looked at the change in horse skulls over time, we could track the spread of grasslands by the change in eye socket location.
“As the horses’ teeth got larger,” Mihlbachler explained, “the eyes had to move closer to the ears to make room.” Relocating the eye sockets allowed for heftier molars that could consume more silica-laden grass.
So, I realized, the evolution of the horse’s eye is connected to the evolution of the horse’s teeth, and the evolution of the teeth is connected to the evolution of grass, and the evolution of grass is connected to changes in global temperatures, and the changes in temperature are connected to tectonic movements and changing ocean currents and the tendency of Antarctica to go it alone by reigning over the South Pole.
What we see by looking into the eyes of the horse is that we are all members of one constantly seething energy system.
* * *
So we understand now the truth that Darwin struggled with: our world is about change, and the corollary that not all change is equally successful. Some ideas—the colossal cecum of the horse, for example—turn out to have long-term staying power, while other ideas may work at one time, but turn out to have dire long-term consequences. Too much change too fast may create highly specialized animals who can’t make ecological shifts when the world around them shifts in a major way, such as a sharp rise or fall in temperature. They may have simply become too highly specialized to survive. On the other hand, not changing at all has its own drawbacks. To illustrate that evolution is about synchrony with the natural world, Mihlbachler laid out on the tabletop a whole separate branch of the evolutionary tree of horses—one that also evolved large, fabulous animals every bit as exciting as modern horses, but one that ultimately disappeared from our world. Eventually, they didn’t fit in anymore. There are many such branches in horse evolution, like the outstandingly successful Hipparion, who spread worldwide and then disappeared entirely.
Among the skulls on the tabletop was one from Merychippus, the horse that appeared somewhere around 17 million years ago and the horse from which Equus would eventually emerge. There was also a skull of Megahippus, a member of the dead-end branch we were thinking about. “If you saw this animal in a zoo,” Mihlbachler said, pointing to Merychippus, “you’d say that it was some kind of weird horse. But if you saw this”—he pointed to Megahippus—“you wouldn’t know what it was.”
And he was right. I could see the future of the horse in that little Merychippus skull, but Megahippus, who lived only 10 million years ago, just before Equus appeared, was one bizarre guy.
He was large, like a modern horse, but he never evolved the rest of the horse package—long legs, or single-toed hoofs. He remained three-toed, which limited his opportunities in a world about to become very cold. His teeth never modernized, so he would have been stuck with browsing rather than grazing. Nor did the shape of his muzzle evolve to a wide form suitable for grass grazing. Instead, it stayed delicate and narrow, like the muzzle of a deer. Unlike the Yukon horse, Megahippus would not have been able to nuzzle through snow to pick at hidden bits of greenery. Nor would he have been able to see across wide grasslands. His eyes stayed halfway down his skull rather than moving closer to his ears.
Suited for forest life rather than open steppes, Megahippus died out. Some people call this “survival of the fittest,” but that’s just a popular perversion of what Charles Darwin meant: Megahippus fit the world in which he lived—but that world disappeared. It was really a matter of bad luck, more than anything else. Indeed, if Megahippus’s world hadn’t contracted and the world of Equus hadn’t expanded, we might be riding Megahippus today—although, given the odd shape of his backbone, we would need a different saddle.
* * *
Interestingly, while the eyes of the dawn horses showed only a bit of promise of what was to come, the eyes of the Polecat Bench primate already looked something like our own eyes. As Phil Gingerich told me,
this primate’s eyes had moved forward to the front of his face, and he probably already had fairly good binocular vision.
We needed all this binocular vision. It provides depth perception. Who wants to jump from treetop to treetop without knowing exactly how thick our destination branch is? Or precisely how far away it is? One mistake and we’re down on the forest floor.
Our ability to see more colors than other placental mammals also aids depth perception. Seeing colors is a way to perceive specificity. When we evolved a third color cone, some time around 35 million years ago, a whole new world opened to us: we were suddenly able to distinguish “red.” For those of us who can see red (some people are colorblind and cannot distinguish this color), it’s hard to imagine not seeing it. But most mammals cannot.
This includes horses, who never evolved this third cone. When they look at a red object, they see color—but not the distinct red that we perceive. Most likely, researchers believe, our “red” is a yellowish-greenish hue to them. If we look at a red ball lying on green grass, the ball will stand out because of its color. If a horse looks at the same ball, the ball will not stand out. That’s one reason why you may notice the ball at a distance, but your horse may only notice that ball when he is much nearer. And when he does notice it, it may startle him.
Our ability to see color is a key component of our ability to perceive the world around us, so that the fewer colors we are able to recognize, the less distinct our perceptions—so it’s important to consider the world of color in which the horse lives. But just what is that world like? When I was a child, I was taught that dogs and horses see only in tones of black and white, but today we know that isn’t true. It’s likely that the range of color detection in horses and dogs is quite similar.
The Horse Page 22
