by Rob Dunn
But the most detailed evidence of the role of predators in shaping our identity comes from other primates. For most of our primate history, we would have been about the size of a capuchin monkey and so suffered, many days, a fate like its fate. Several species of New World eagles, such as the Harpy, eat monkeys preferentially. Leopards sneak into trees and take monkeys. A recent study in the Ivory Coast followed two individual leopards and found that although the two individuals had different dietary preferences (one cat’s pangolin is another’s giant rat), almost half of the diet of both was primates, including big monkeys and even chimpanzees.10 In fact, in the few places where primates have been studied over many years and where large predators are still relatively common (if not as common as they once might have been), more individuals die in the mouths of predators or from snakebite than to nearly any other cause. Baboons have been particularly well studied (and eaten), and in those studies one finds evidence of predation by eagles, hyenas, wild dogs, lions, leopards, jackals, cheetahs, and even chimpanzees.
Where predators are common, perhaps three out of a hundred monkeys (or apes for that matter) die each year by being eaten, as was likely our fate for much of our history. For context, in a given year, cancer kills only one out of a thousand Americans, which is to say that if early humans were like modern primates, death by predation would have been 30 times more likely at any moment than is death by cancer today. More to the point, cancer tends to kill us after we have reproduced, whereas predators knew no such forbearance. Regardless of when humans escaped predation by making better tools or being smarter, we began like the other primates, eaten often and nearly inevitably.* To the extent that we were different, it seems possible that we were more rather than less edible. We were potentially easier to track than were other primates, because of our heavy footprints and, at least according to one anthropologist, smellier bodies. Those few primate species, such as vervet monkeys, that have calls with specific meanings, almost inevitably have calls that relate to the threat of predation. The vervet monkeys have three words, “leopard,” “eagle,” and “snake,” which were, in all likelihood among our first words, the most important nouns. Close behind them, one suspects, was the verb “RUN.”
Humans, like other primates, were long the hunted, a situation that shaped how Bakhul and her friends responded but also how they lived and, for that matter, how we respond and live. When predators are around, going to the bathroom and sleeping are among the easiest ways to die (particularly since many primates, not just humans, appear to snore). Some of our responses to such threats relate to specifics of our behaviors, such as the way we (as primates) sleep and build our homes. Monkeys and apes build nests high in trees and sleep together, so that at least one individual is always awake and might alert others of a threat. Chimpanzees build nests, typically above three meters, which is perhaps not coincidentally a little higher than leopards can jump. The only earthbound exception, aside from us, is the gorilla, which when it moved to the ground became big and strong, perhaps as a defense against predators.11 If you cannot climb, you had better be big enough to deal with a leopard on your back, literally.
When we moved to the ground, we were not big enough. As a consequence, we became even easier to eat than we had been before. We may have compensated by moving into caves (as baboons do today) and then, eventually, building houses from which predators could be excluded, houses that we tended to circle, like wagons, when predators were near, doors facing inward. Doors were small and defensible and we nearly always lived in relatively sizable groups of ten or more, even when such groups required us to walk long distances to find food.* The Mbuti pygmies once built huts reinforced like a cage, although it was to keep animals out rather than in. In Bakhul’s town, the houses were clustered, as they may be in yours. The gated subdivision and its cul-de-sacs is a modern version of our earlier villages, in which our front doors face each other and we all keep an eye out for what might lurk in our collective shadows, even though such a design is inefficient and, for a variety of reasons, actually more dangerous than a grid of streets. We feel safest this way because once upon a time we were. So it is that we lock our doors each night and that, in Bakhul’s village, they boarded theirs.
Predators also influence, even today, when we do the things we do. Humans and other primates do very little at night. We sleep in groups but are otherwise inactive, for good reason. Our senses are dulled to night’s realities and dangers. One of the very few things we do at night is give birth. In those few places where human birth is not induced, like Bakhul’s village, most babies are born in the dark hours between dusk and dawn. A recent study of zoo chimpanzees found that roughly nine out of ten were born in the middle of the night, not long after midnight.12 If you are older than fifty, odds are you too were born around 2:00 am. Being born in the middle of the night, when your kin are gathered around, sleeping and, if the need arises, defending, may decrease the odds of the mother and baby being eaten in the process of giving birth.
My wife and I once stumbled upon a black-and-white colobus monkey in the hollow of a tree. In her arms was a pale white newborn baby. It looked fragile and defenseless, like our own newborn daughter and son were. I cannot imagine trying to flee a predator right after my wife gave birth. I suspect all we would have been able to marshal would have been something along the lines of what we told the nurses, “just give us some time.” Newborns and new mothers (and at least this new father) need all the help they can get. Perhaps tellingly, the only monkey known to give birth during the day is the patas monkey. Patas individuals are together during the day but apart at night. These patterns in birthing may or may not be linked to predation. So far, no other possibilities have been suggested.
The effects of predators on when we give birth and how we build our homes are still a bit speculative. But there are also less ambiguous consequences of having been eaten across most of our generations, for example, our fear modules themselves, built as they are of elements of hormones, blood, adrenal glands, and brain. When the tiger pulled at Bakhul’s foot, a predictable series of things happened in her body and, importantly, in the bodies of her friends, who were watching nearby. The cells in their adrenal glands would have released bursts of adrenaline from specialized “packets.” The adrenaline would have triggered a chain of other chemicals that would have caused their small hearts to beat faster and with more force. Blood flow would have increased, the tracheoles dilated and lungs expanded, allowing more oxygen into the blood. All of this would have triggered a rush of superpowered energy and awareness and, secondarily, a sensation of fear, a sensation meant to trigger a later, more considered, response. For Bakhul, none of this was enough to keep her out of the tiger’s mouth. It still might have saved her from death, though the odds were low. Once tigers catch their prey, they seldom fail to kill it. Bakhul’s friends, on the other hand, escaped, in no small part because of the response of their adrenal systems, which evolved specifically to help us get away from predators or, more rarely, to stay and fight.
In wild primates, when the fear response is triggered, an alarm is often sounded, whether something specific like the vervet monkey version of “leopard,” or a more general scream. Next, the monkeys usually flee, which is probably the most common response. More rarely, when the predator seems weak or there is no other choice, primates will mob and charge it (though usually from a safe distance—better to not tempt fate or leopards too much). Sometimes such mobs are successful, whether in simply chasing away the predator or even killing it. Other times, they are not. When it is an option, the best route remains to, like Bakhul’s friends, run away.
Primates like us are not unique, of course, in having adrenal systems and associated defensive behaviors. Our adrenal system evolved hundreds of millions of years ago. Its basic functioning has remained unchanged across generations, elaborated upon but not replaced. Nearly all vertebrates respond to threats with the same bodily response we experience. What differs from one animal to another
is both how the response is orchestrated and how it is fine-tuned. In reptiles, there is no amygdala and so fear runs directly from perception to the brain stem–perception to barely modulated action. In mammals, the amygdala takes over orchestration. It signals the brain stem. It notifies the conscious brain with a signal that we experience as fear. Among mammals, the twitchiness of the amygdalae of different species differs in their tuning. A cow’s flight response is relatively dulled to external triggers (though it can still be triggered with enough of a stimulus, as it often seems to be on big industrialized farms). This is one of the reasons cows and many other domesticated animals, such as lambs and even genetically modified salmon, are so susceptible to predators.13 Cows and lambs are not just meek. They are actually numbed to the dangers that once haunted them, too tame to flee even when the wolf or the butcher is at the door.
Much of the fine-tuning of the adrenal system from species to species, or from one individual human to another, occurs via changes in the abundance of a single protein. On average, humans have a lot of it, as do nearly all but the very largest, most well-defended species. Cows may have once have had much of it too, but we bred it out of them, as we did with many other domestic animals.*14 Such changes, while not inevitable (horses are still very twitchy), can occur very rapidly. In a Russian experiment that began in the 1960s to domesticate foxes, animals that were friendly toward humans were produced in just three generations of selection. After thirty-five generations, the foxes were not only friendly but also submissive. They wagged their tails and licked their domesticators’ fingers. These offspring had a reduced fear response relative to their ancestors and lower levels of the hormones associated with fear. Evidence suggests that similar transitions occurred in wolves as they made the transition from solitary hunting to hunting in packs (in which twitchiness and rushes of adrenaline and aggression might have been counterproductive to team efforts), with social animals like wolves being docile relative to each other, much in the way that cows are docile to humans.
One could argue that it would be useful for society if humans evolved a less temperamental fight-or-flight response. For the most part though, we appear to have maintained our high responsiveness. If anything, what changed over the most recent years of human evolution is that we became less likely to flee but more likely, with our new tools and bigger brains, to stay and fight. We would even begin to search out fights, as was the case for Jim Corbett, the hunter who was called to Bakhul’s village to find her, the tiger that attacked and maybe killed her, and rescue the villagers from their ancient and overwhelming fear. Corbett would find his quarry (though killing it was another thing entirely), and as a species we would find big animals everywhere, chase them, stab them, tire them, and eat them, one at a time.
10
From Flight to Fight
In the case of Bakhul, the villagers would chase back, but only when Jim Corbett came to town. Corbett was a young man, a boy really, but he came to town to kill a tiger. He wanted to give the village back its peace. With age, Corbett would become the greatest hunter of man-eating cats, but not yet. At this point in his life, he had the wisdom of a young man combined with the bravura of a big gun. With the gun in hand, he turned his fear to rage, flight to fight. He wanted to pursue the tiger, and, once in town, it did not take long for Corbett to find the tracks. At the place near the oak trees, he found blood and the beads of Bakhul’s necklace, and began to follow the fresh trail. He had not walked very far, fear and then also rage welling up in his throat, when he found one of the girl’s legs beside the river in a pool of blood. Bakhul was very definitely dead.
Corbett bent to her leg, tenderly. As he stood there bowed and saddened, he began to feel as though he had made a mistake. The feeling he had was very specific. The hairs on his arms rose. His skin tingled. A chill ran through him, and he had an overwhelming urge to run. Each of these responses was innate and unconscious, triggered by the sound of falling dirt that he heard coming from the hill above him. It was the tiger, looking down, its heavy paws crumbing the hill’s loose soil. Corbett’s body released adrenaline, which flooded his blood and he began to feel, for lack of a more perfect word, explosive. His heart leaped at his ribs as though trying to find a way out. Some part of his body was sure that he, like Bakhul, was about to die, and that part of him was urging him, imploring him, to run.
The tiger turned from Corbett and moved on, up the hill. Fighting to control his body’s urgings, Corbett got a better grip on his gun. He went after the tiger and as he did, he was suddenly aware of thousands of sounds. He could hear leaves bending back and forth in the wind, insects moving, and then as he got closer, the tiger’s low snarl. He was alert with adrenaline. Corbett followed the pad of footfalls and a kind of pounding that might have been his heart, or maybe even hers. He pursued all afternoon until his mind was overwhelmed with the accumulated hormones and blood. He could not make out where he was relative to the village or the tiger, and so he started to panic. He ran over rocks, through blackberry thorns and giant ferns until the sky was dark blue, then black. He had no light, so although the tiger could undoubtedly see him, he could not see her. He was in a narrow crevasse, closed on one end. He had a gun, but he was in this moment as naked and vulnerable as any human had ever been. He could hear her now, again. He backed away, slowly, out of the forest, retracing his steps and listening for the tiger he could no longer hear over his breathing, the tiger that he was sure would follow him home.
Somehow, Corbett was spared and made it back to the village. There, he composed himself. Tomorrow he would try something new, something different. Meanwhile, up in the ravine, among the vines, thorns, and hills, the tiger roared.
No one knows when humans began to hunt on a regular basis. Of course, we long hunted insects, snails, and the occasional rodent in a hole. But what about bigger prey? The answer is mixed in among the messy piles of ungulate and human bones excavated across Africa, Europe, and Asia on the basis of which the question is debated vehemently by anthropologists. They wield pens and pencils in hands that once held spears. They brandish them and grumble, but consensus seems far off. What one can say is that before we invented tools, hunting was likely to have been rare and clumsy.
Even once we had tools, they would not have helped much, not at first. For the first 500,000 years of our human history, we had nothing more than stones sharp enough to break the marrow free of scavenged bones. With these first tools, we were like hyenas, though less dangerous and far less effective. Eventually, early stone tools were combined with sticks to produce spears. Spears were combined with running and calling back and forth, to chase, at first, smaller herding animals. This appears to have occurred at about the time that wolves too started to become more social. We would have hunted side by side with wolves during the day, and hidden from them at night. The transition was slow, but progressive. In at least two well-documented study sites, archaeologists have shown that humans moved from eating slow-reproducing, slow-moving prey, such as tortoises and limpets, to faster-moving, faster-reproducing prey, such as rabbits and eventually birds.1 As the tortoises and limpets became scarce and the rabbits were chased away, the hunting of deer and other larger herbivores became more important. In some places, such as the cold regions where little in the way of plant food was available during the winter, it may even have become necessary.
The shifts toward hunting caused our bodies to change. Look at your hand. As we began to pick up sticks and stones, our hand bones literally evolved to be better able to handle such weapons. The ways you grip a baseball bat or ball are vestiges of the way your ancestors once picked up sticks and stones, respectively. Homo erectus or Ardipithecus ramidus would have sucked at baseball, as would our even more distant ancestors. The only way individuals with better abilities to grip would have been favored is if holding a stick or a ball improved their chances of survival or mating.2 In other words, tools and their use were eventually necessary for survival. Our legs became longer and our lungs
relatively bigger. We became better at long-distance running. All of these things changed together. We were still weak and fleshy. We were still among the most edible of vertebrates, but we could work together using sticks and calls.
Jim Corbett, in the context of this long history, had an idea. He would use the villagers to chase the tiger from the wide, uphill part of the valley down through the valley to the only opening on its narrow end, where he could shoot it. In doing so, Corbett would be reenacting thousands of earlier hunts in which, like wolves or African wild dogs, humans had called back and forth to each other, even signaled, as they chased their prey. Just a few years earlier, archaeologists had documented a place where Native Americans had once chased a herd of buffalo down a ravine and off a cliff, whereupon they butchered them. That night he traced the plan in his head, as though he were sketching out a cave painting. In the image was the tiger, hundreds of villagers raising their arms, and then one man lower down, with a gun. The tiger in this sketch, like the predators in hundreds of cave paintings, still looked as though it stood a fair chance.
When the villagers went to help Corbett chase the tiger, they did so with bodies like those that had long chased animals. Corbett’s plan was that they would gather what they could—rocks, cans, and sticks—and stand at the top of the ravine. When Corbett and the headman signaled from the bottom of the ravine, everyone was to begin beating their instruments, so that they might drum the beast out of the woods down toward Corbett’s aimed gun. In acting out this plan, they were reenacting the imperfect transition of humans from hunted to hunters.*
