The Biochemistry of the Bond
IN OUR DEALINGS WITH animals, we are a blend of nature and nurture. Many positive responses to animals come naturally to us, and these are the building blocks of the human-animal bond. This instinctive benevolence, just like our instinctive fears, can be encouraged or suppressed by culture. But either way it is forged of strong stuff and explains much of the fascination with animals common to every society.
Some compelling scientific theories and recent studies even point to evidence of a bond in the very biochemistry of mammals. The idea was most recently advanced by Meg Olmert, who has spent twenty years studying the human-animal relationship. Her work brings together the latest scientific evidence that the mammalian hormone oxytocin provides a crucial explanation for the presence of the human-animal bond.
It’s hardly radical to suggest that biochemistry has a strong influence on human and animal behavior. The fear we feel upon encountering a human intruder or a threatening animal derives from a chain reaction of responses, ultimately releasing the hormones adrenaline and cortisol. These, in turn, influence our emotions and trigger glucose production, which prepares the body for a fight-or-flight response. Biochemical changes that are now well understood help explain aggression, panic, and sexual attraction, among many other behaviors. Advances in neurobiology have led to the development of medicines that better control depression and other mental disorders. If biochemical reactions drive aversive responses, it seems plausible that hormones must also affect social behavior, especially for a gregarious species like ours.
Oxytocin is a neuropeptide long known to promote maternal care in animals. It plays a major role in human childbirth, inducing labor contractions and also stimulating lactation. Olmert argues that oxytocin also calms new mothers and intensifies their fascination with their babies. In rodents, oxytocin triggers a mother’s protective aggression against intruders.
But oxytocin does not just circulate in the bloodstream during childbirth and the nursing phase of child rearing. Present in all men and women, it has a broader prosocial, bonding function in human-to-human interactions. It is a social recognition hormone, helping us to identify faces and to exude warmth toward others. It even appears to have stress-relieving effects, such as lowering blood pressure and anxiety. Several researchers have found that administering oxytocin to people encourages trust and empathy, while facilitating better reading of emotions.
Sue Carter, codirector of the Brain-Body Center at the University of Illinois, Chicago and one of the leading oxytocin experts, says much of what she learned about the bonding powers of oxytocin came from studying prairie voles, small burrowing rodents who mate for life. Monogamy is highly unusual for mammals, and rare even among other species of voles. It seems that the reason prairie voles are able to form their powerful social bonds is because their brains make more oxytocin and vasopressin (a closely related hormone) in the regions that release dopamine and serotonin. Together, these pleasure-inducing neurochemicals both initiate and reward social behavior, weaving bonds that last a lifetime.
What holds for prairie voles is also true for us and many other mammals. Researchers are recognizing that common social behaviors trigger the release of these pleasure-inducing hormones. So a smile, a hug, or the smell or laughter of a baby trip the oxytocin switch and stimulate this biochemical cascade, making us want to reach out and approach others and to build more cooperative and nurturing relationships.
Maia Szalavitz and Dr. Bruce Perry, in their book Born for Love, go further, arguing that oxytocin is the basis for familiarity and empathy in mammals. They speculate that its work begins with the mother-child bond but continues throughout life, allowing “mammals to make the connection between a particular individual and pleasure. Without it, many animals can’t even tell each other apart.”
There’s little doubt now that oxytocin plays a critical role in bonding for humans, too. But what about bonding between humans and other species? Two South African researchers, Johannes Odendaal and Roy Meintjes, measured the blood pressure and blood chemistry of eighteen humans and dogs before, during, and after they had friendly interactions. They found that the interactions almost doubled oxytocin concentrations in both the people and the dogs, and that the humans’ blood pressure also dropped dramatically. This finding and others suggest that pets may be “one of the most potent triggers of oxytocin production in humans.”
In 2009, the U.S. Army began pairing service dogs with veterans suffering posttraumatic stress disorder. Just weeks after Iraq war veteran Chris Goehner got a service dog to help him deal with PTSD, he reduced his doses of anxiety and sleep medication by half. Aaron Ellis, another Iraq veteran, ceased his medication and was able to set foot in a grocery store for the first time in three years. Nobody has done the blood work to prove that oxytocin aided the rehabilitation of these veterans, but it’s a decent bet.
A quarter century before Meg Olmert’s synthesis of oxytocin research, the eminent Harvard biologist E. O. Wilson offered his own novel theory to explain the human-animal bond. He argued that humans have “an innate tendency to focus on life and lifelike processes.” “From infancy,” he explained, “we concentrate happily on ourselves and other organisms. We learn to distinguish life from the inanimate and move toward it like moths to a porch light.” This bond between humans and nature is “biologically encoded,” built into us as a result of hundreds of thousands of years of experiences with other living beings. Wilson called his theory “biophilia,” and although the idea was deeply influenced by his love for the natural world, it was grounded in years of study and observation.
To support his conclusions, Wilson drew upon the behavior of the few hunting-and-gathering cultures that remain. For them, the exploration of nature is not a form of recreation or retreat, as modern societies regard it, but still the central activity of their lives. And a working knowledge of nature, such as the ability to distinguish between poisonous or edible plants, or to understand the habits and behaviors of animals, is a matter of survival. Their whole existence is built around the lives of other creatures and the rhythms of nature, and this outlook affects everything from those individuals’ behavior to their most basic beliefs.
Living in small nomadic bands, early hominids knew how to hunt, but probably ate mostly nuts, plants, and the leftovers from the kills of larger and better equipped predators. For much of prehistory, they maintained stable and relatively low population levels. Population geneticists at the University of Utah guess that one million years ago, there were just fifty-five thousand people “spread across the entire Old World”—half the population of my hometown of New Haven, Connecticut. There is evidence that hominids have been around in various forms for at least two million years, and a few clues trace them back another five million years before that. It was during these innumerable generations that we gained our basic first impressions of animals, impressions that left a permanent mark on our genetic coding.
It was not until the arrival of modern humans, perhaps eighty thousand years ago, with their larger brains, more lethal weapons, and control of fire that our species became a much more dominating predator, able to exert its will over other species and paving the way for steady growth. The human population, scattered across the Old World, expanded from tens of thousands to several million in the years to come. And it was not until about twelve thousand years ago that humans wandered across a Bering Sea ice bridge and first left footprints in the New World.
A few tentative conclusions can be drawn about these diverse hunting-and-gathering peoples. Along with archaeological evidence, we have the records of European explorers who first encountered the natives of the Americas, Australia, and other regions centuries ago. A limited number of these communities still survive and have been studied by anthropologists and ethnographers.
There’s a tendency to think of these preagricultural peoples as “noble savages,” existing in harmony with nature and all its creatures. But this romantic notion does not a
lways square with the evidence. Many archaeologists speculate that about eleven thousand years ago, Clovis people, the first makers of sharp-pointed tools, wiped out many species of large mammals throughout much of the world, including mammoths, mastodons, and giant beavers in the Americas. This “overkill” hypothesis is a contested theory, and other scientists believe that climate change may explain the demise of so many species. But whatever the true causes, there is little doubt that Clovis people were very successful hunters who killed massive numbers of animals and hardly had an ecologically benign impact.
Yet it is still plausible to describe many hunting-and-gathering people as the original naturalists, who depended “on an exact learned knowledge of crucial aspects of natural history,” as E. O. Wilson puts it. Biological anthropologist Jared Diamond of UCLA observes that the hunting-and-gathering societies he’s encountered in Papua New Guinea are “walking encyclopedias of natural history, with individual names (in their local language) for as many as a thousand or more plant and animal species, and with detailed knowledge of those species’ biological characteristics, distribution and potential uses.” Recounting an exchange with a man named Teu, a native of Kulambangra, one of the Solomon Islands in the Pacific, Diamond writes: “For every one of Kulambangra’s eight resident bird species, Teu dictated to me an account consisting of its name…its song, preferred habitat, abundance, size of the group in which it usually foraged, diet, nest construction, clutch size, breeding season, seasonal altitudinal movements, and frequency and group size for over-water dispersal.”
Many tribal communities not only understand other life-forms, but also hold beliefs that acknowledge their complete dependence on other creatures for survival. In their cosmology, “people can turn into animals, and animals turn into people,” according to Dr. James Serpell, an expert on the history of the human-animal bond. The Inuit worry about offending animal spirits and are careful about killing animals, perhaps because in the high Arctic they are so dependent on animal protein for survival. Other communities recognize totem animals—creatures especially revered, and species that are not to be killed. “They are apologetic when they kill animals,” Serpell observes. “It is an interesting moral dilemma. They have to eat animals, but they feel bad about it. They have all sorts of rituals and belief systems to absolve them of the guilt.” Social anthropologist Tim Ingold adds, “The hunter hopes that by being good to animals, they in turn will be good to him. But by the same token, the animals have the power to withhold if any attempt is made to coerce what they are not, of their own volition, prepared to provide…. Animals thus maltreated will desert the hunter, or even cause him to fail.”
It may be that our modern-day appreciation of animals is, in part, an inheritance from tribal peoples who needed these observational skills to survive. Stephen Kellert of the Yale School of Forestry and Environmental Studies says that we are drawn to vistas because that’s the way our ancestors behaved, surveying the landscape for threats or hunting opportunities. And still today we are drawn to the sight and sound of running water because it is clean and drinkable. We especially like to look at waterfalls and find the sound of rushing water soothing. In short, many modern-day behaviors may be partly attributable to the survival benefits they provided to prehistoric hominids.
Pet Keeping Through the Ages
ALMOST EVERYONE WITH A dog or cat notices the daily displays of instinctive action—a cat stalking a toy mouse; a dog chasing a squirrel or rolling on his back in play to expose an open stomach. Dogs or cats who are separated from their mothers at birth behave the same way. It’s in their “wiring,” and while parental teaching or play with others of their kind can perfect it, the core behavior is innate. We domesticated these animals thousands of years ago—the dog at least fifteen thousand years ago, perhaps considerably earlier, and the cat some four thousand years ago—and they have been selectively bred over many hundreds of generations. Yet these predatory or playful behaviors are still there.
It’s probably not so different for us—the connections to animals and to the physical features of the natural world are still with us, ready to be expressed with the proper cues. We have not shed these inclinations or instincts in the last ten thousand years. As Kellert notes,
The various expressions of biophilia hardly constitute “hard-wired” instincts like breathing or eating. In fact, the human affinity for nature represents a collection of relatively weak biological tendencies. All the various strains of biophilia depend on adequate learning and experience.
Even in our era, with meat at supermarkets in every neighborhood, hunting still preoccupies a portion of the male population. It is practiced throughout the world, and thirteen million Americans go hunting every year. Some reasonably argue that hunting behavior is still encoded within us. There is something atavistic in men. Yet it is also clear that hunting is a learned behavior, with fathers or grandfathers passing on the tradition to the young—the sort of “weak” tendency that without cultural support would fall away. But once triggered, the thrill of stalking and killing a living creature is addictive for some hunters, providing an adrenaline rush. Many hunters speak of “buck fever”—the physical reaction that occurs when an animal comes into shooting range. As one hunting blogger writes,
It is the severe case of the jitters. It’s the adrenaline rush associated with the sight of your target. It’s the nervous system on overdrive. Crazy things such as the shakes, sweats, increased blood pressure and just plain poor shooting can occur when Buck Fever overtakes you.
Hunting animals can become a mania. Some well-heeled trophy hunters travel the world in search of big game and have killed three hundred different species and subspecies of animals, making it almost a full-time avocation. They will tell you they consider their rapacious pursuits a “God-given right.”
It’s also true that more than 90 percent of men in industrialized societies choose not to hunt at all, and demographic trends show the practice is in a gradual but steady decline. Social scientists speculate that other activities now provide an outlet for this biological impulse. “Humans are not hardwired to hunt, but they are hardwired to engage in physical activities that resemble hunting,” argues James Serpell. “Most sports have to do with chasing and catching and hitting small objects that are traveling fast.”
Although hunting is a long-standing, biologically based human behavior, other, gentler behaviors better demonstrate the human-animal bond. Generally, we think of pet keeping as a modern Western practice. But people have been drawn to pets throughout human history, and even prehistory. Prior to the last two centuries, it was more a custom of elites than the underclass. The British monarchs, for instance, displayed a particular affection for small dogs. The ancient Egyptians had an incredible affinity for animals, even mummifying them as a demonstration of respect. And in ancient China, Serpell notes, “the ancestors of the modern Pekingese enjoyed a privileged status unrivaled by any other variety of pet before or since. They were given the titles of princes and princesses, and huge personal stipends were set apart for their benefit.”
Serpell’s most surprising revelation, however, is that pet keeping was also a social activity among tribal societies. “The practice of capturing and taming wild animals is widespread and incredibly common, especially in South America and Southeast Asia,” he writes. This seems counterintuitive, given the popular perception that hunting-and-gathering peoples engaged in an unyielding struggle for survival, and that pet keeping would be an unaffordable luxury for people living on the edge. Nevertheless, it’s true that our remote ancestors found a place in their lives for the care of animals. It may be that some of these pets were the orphaned young of animals killed in the hunt. The same people who killed the mothers of these creatures felt pity at their bleats and cries—an early expression of our conflicting impulses toward animals.
Early Native Americans, for instance, kept tame raccoons, moose, bison, wolves, and even bears as pets, and they treated their dogs affectionately. S
erpell cites the Norwegian explorer Carl Lumholtz who observed that Australian Aborigines treated their pet dingoes “with greater care than they bestow on their children,” kissing the animal on the snout and even grooming them. Occasionally, tamed wild animals were used for food, but often they were just companions. “In the New Guinea villages where I work,” Jared Diamond relates, “I often see people with pet kangaroos, possums, and birds ranging from flycatchers to ospreys.” According to Serpell, Spanish explorers reported that South American Indian women kept wild animals in their huts. The women would never eat or sell them; when strangers killed one, the women would shriek, dissolve into tears and wring their hands “as if it had been an only son.”
There is also evidence that native peoples took things a step further than pet keeping. The cries of baby animals may have drawn empathetic responses from women in native communities. Women suckled animals, whether wolf puppies or other baby animals, as a sign of kinship and affection, in one of the first steps toward domestication. These experiences remind us that the human-animal bond is not a modern-day invention, but just the latest expression of it.
Domesticated Animals: “Bonded to the House”
AT SOME POINT, PROBABLY in the latter half of the twentieth century, we crossed a divide in the animal kingdom: the planet became home to more large domesticated mammals than wild ones. Cows, pigs, horses, goats, and others of their kind outnumbered the great herds of caribou in the Arctic, the wildebeest and zebra and Cape buffalo who migrate across the plains of East Africa, and all the bison, bighorn sheep, deer, elk, and other large mammals in the world.
The Bond Page 4
