by Hal Herzog
My neighbor Anne recently broke her shoulder when she fell down a flight of stairs after tripping over her dog. This type of pet-induced accident is surprisingly common. Over a year and a half, sixteen seniors were brought to a Sydney emergency room for the treatment of fractures caused by their pets. Among their injuries were four broken pelvises, two broken hips, three broken arms, two broken wrists, one broken ankle, two broken ribs, a broken nose, and a broken neck. The Centers for Disease Control estimates that over 85,000 Americans are injured each year in accidents caused by tripping over their pets, usually dogs.
Pets can be health hazards in other ways as well. A 1999 survey by the Opinion Research Corporation found that nearly one in six dog owners reported having an automobile accident or a close call caused by their pet jumping around in their car. And 60% of the pathogens that humans are susceptible to are zoonotic, meaning they can be contracted from animals. Humans can pick up a cornucopia of nasty diseases from their pets, among them roundworms, skin mites, Lyme disease, brucellosis, ringworm, giardia, leptospirosis, E. coli, hookworm, and the aptly named cat scratch fever. When I was twelve, I had a pet baby turtle; everyone did. Who knew that 85% of them carried Salmonella? The FDA banned baby turtle sales in 1975, but now snakes, lizards, and other reptiles are popular pets. Predictably, pet-related Salmonella is on the rise, and 75,000 cases of Salmonella infections each year are contracted from reptiles and amphibians living in American homes. Even therapy animals are a potential health hazard. Several research teams have reported that therapy dogs can acquire and spread MSRA, a serious antibiotic-resistant Staphylococcus infection, from patient to patient in hospitals and nursing homes.
IS PET LOVE IN OUR GENES?
Twenty years of anthrozoological research have shown that there are substantial benefits—but also some costs—to living with a pet. These findings, however, do not address the evolutionary mystery of why humans become so attached to animals. Darwinism implies that, directly or indirectly, organisms should act to increase their reproductive fitness—that is, their success in passing down genes to the next generation. But if this is true, why should Joe and his wife pay a thousand dollars a month for chemotherapy to keep their aging golden retriever alive? Wouldn’t their genes be better off if they used the money to pay their children’s (or grandchildren’s) college tuition bills?
On the question of “why pets?” anthrozoologists have offered a wide variety of explanations for the human-animal bond:
Pets teach kindness and responsibility to children.
Pets provide “ontological security” in a postmodern age in which traditional values and social networks have broken down.
Like ornamental gardens, pets are an expression of the human need to dominate nature.
Pets allow the middle class to pretend they are rich.
Pets substitute for human friends.
Pets and people are autonomous beings who gain mutual comfort and enjoyment from their interactions.
All of these could be partially right. But I am most intrigued by a different level of explanation, the evolutionary level. Dan Gilbert of Harvard University claims that every psychologist who puts pen to paper takes a vow to someday write a sentence that begins, “The human being is the only animal that…”
Here is mine: “The human being is the only animal that keeps members of other species for extended periods of time purely for enjoyment.” The question of why we keep pets is an evolutionary mystery, right up there with why humans are the only mammal with complex symbolic languages, moral codes, religious beliefs, and the ability to learn to enjoy the burn of red hot chili peppers (the spice, not the band).
But as with most “humans are the only…” sentences, there are exceptions to mine. There are lots of instances in which a non-human animal has become attached to a member of another species. In the wake of the 2004 Indian Ocean tsunami, an orphaned 600-pound baby hippopotamus named Owen became bonded to Mzee, a 160-year-old giant tortoise in a Kenyan game park. More recently, Tarra, a four-ton Asian elephant at the Elephant Sanctuary in Hohenwald, Tennessee, became fast friends with a rescue dog named Bella. The pair were practically inseparable, and when Bella fell ill, Tarra stood watch for several weeks outside the building where her canine pal was being kept. A comparative psychologist from the University of California at Davis named Bill Mason systematically studied attachments between members of different species by raising young rhesus monkeys with adult dogs. Within a few hours after being introduced, the monkey-dog couples became intensely attached. After a couple of months, each monkey was given a choice between playing with its dog, a strange dog, or another monkey. They chose their dogs. They had become friends.
But attachments between animals of different species almost always occur in unnatural circumstances. There is, for instance, no evidence that, in the wild, our closest relative, the chimpanzee, keeps members of other species around to play with. I remain confident in my statement that humans are the only animal to keep pets.
When and why did this phenomenon come to be? On when, we don’t have a clue. Archaeological evidence of pet-keeping goes back 12,000 to 14,000 years for dogs and perhaps 9,000 years for cats. It is possible, however, that some of our Paleolithic ancestors, just like members of some existing tribal societies, captured the occasional parrot or bush pig and brought it home as a pet. The problem is that such early bonds between humans and animals would not leave a trace in the archaeological record. If we were to discover, say, the 25,000-year-old fossil remains of a man cradling a baby monkey, we would not be able to tell if the animal was the dead guy’s pet or if the monkey was placed in his grave as a snack in the afterlife.
Lacking any solid evidence of when bonds between humans and animals first formed, the best we can do is guess. Individuals that looked like us were living in Africa 100,000 years ago. However, many anthropologists believe that the real sea change in human thinking occurred roughly 50,000 years ago as evidenced by an explosion of cultural forms: art, music, weaponry, and tools that were exquisite in form and function. Mike Tomasello of the Max Planck Institute for Evolutionary Anthropology argues that this jump in human creativity was fueled by the appearance of a new and sophisticated mental skill—the ability to infer the mental states of other people. Images inscribed on the walls of caves depicting creatures that were half animal/half human suggest that our ancestors began thinking of animals anthropomorphically 35,000 or 40,000 years ago. James Serpell believes that the ability to think of animals as we would a person opened the door for taming wild creatures and forming bonds with them. Serpell makes a good case, but without a time machine, we may never know when the first person decided that a ball of fur could be a friend rather than a meal.
IS PET-KEEPING AN EVOLVED ADAPTATION?
As creationists gleefully point out, we Darwinists argue a lot. We don’t fight over whether humans evolved from apes or whether the earth is billions of years old. These are facts. Rather, we squabble over the details. The question of why people love pets is related to one of the most contentious debates in evolutionary theory—the issue of adaptation. Advocates of the adaptationist school of thought are convinced that the human mind evolved to give our Stone Age ancestors a leg up in the Darwinian gotcha game of Who Can Pass Down the Most Genes. They believe that the process of natural selection equipped the human brain with specialized modules for skills like learning language, avoiding sex with close relatives, detecting snakes and cheats, and impressing potential mates.
Critics of the adaptationist paradigm argue that some aspects of human nature could have evolved even though they had absolutely no effect on a person’s reproductive success. They think some traits are simply nonfunctional side effects. For example, our bones are white because they are made of calcium, not because women are attracted to men with pallid skeletons. Harvard’s Stephen Jay Gould likened nonfunctional biological traits to spandrels, the leftover spaces in a building that architects integrate into the design for aesthetic rather
than functional reasons.
Consider as an example of this debate, how adaptationists and nonadaptationists explain the evolution of orgasm in human females. Adaptationists (and I was once among their number) have dreamed up nearly two dozen theories to explain why orgasms occur often in human females but rarely, if at all, in other species. Among their more innovative suggestions are that orgasmic contractions suck sperm up into the uterus, that orgasms evolved as a signal to help women tell which men have good genes and which ones are evolutionary losers, and—my favorite—that by making them woozy, the throes of orgasm keeps women lying down after sex so sperm don’t have to swim uphill to reach the egg. Skeptics of adaptationist thinking scoff at these ideas. They explain orgasm in women as the side effect of the fact that orgasm has reproductive benefits for men—just like the presence of nipples on men is the nonfunctional by-product of the fact that nipples evolved so that female mammals can feed their infants.
The argument over evolutionary adaptation also applies to explanations of the human-animal bond. I suspect that most people—including many anthrozoologists—want to believe that love of pets is an attribute of human nature that evolved because it helped our ancestors survive and reproduce. Evolutionary psychologists argue that if a trait is an evolved adaptation, it should be common, widespread, and perhaps, like language, universal. This is not the case with pets. The anthropologist Donald Brown of the University of California at Santa Barbara compiled a list of nearly 400 human universals that ranged from thumb-sucking to beliefs about death. “Interest in bioforms” makes the list, but pet-keeping is conspicuously absent. In many parts of the world most people do not form close bonds with animals. This is particularly true in Africa. My anthropologist friend Nyaga Mwaniki is from rural Kenya. In the village where he was born, people never become attached to individual animals. Indeed, there is no word for pet in Kiambu, his native language. The villagers do keep dogs to guard against intruders and to chase elephants from their gardens. But they never allow dogs in the house, they do not think of them as companions, and they would be horrified at the idea of letting one sleep in their bed.
The argument that pet-keeping is an evolved trait would be strengthened if we had evidence that love for animals has a genetic basis. But we don’t. Behavior geneticists use twins to determine the relative influence of genes and environment on a trait. Identical twin pairs will be more alike than pairs of fraternal twins if a trait is strongly affected by genes. By comparing the two types of twins, scientists have discovered that genes are responsible for 90% of the differences between people in height, 50% of differences in how happy they are, and 35% of differences in how often women have orgasms. No one, however, has investigated whether identical twins are more similar than fraternal twins in their attachment to pets. In fact, the role of genes in any aspect of our relationships with animals remains an open question. (The exception is our desire to eat their flesh.)
Finally, if pet-keeping is an evolved adaptation, at some point in human history, people bonded to individual animals must have been better at passing on their genes than their less pet-o-philic peers. Your final score in the game of Darwinism is measured in terms of reproductive success. The fact that your cat makes you happier, healthier, or even helps you live longer is irrelevant. Could living with a pet increase your reproductive fitness? Perhaps girls who grow up with pets are more successful at raising offspring in adulthood because they learn parenting skills by taking care of the family dog. Or maybe early humans who kept pets were more apt to survive the hard times because they could eat their companion animals. I suppose it is remotely possible that some women are turned on by macho guys with big dogs and others by kinder and gentler men who demonstrate their sincerity by cuddling puppies. (Recall that Antoine, the handsome Frenchman, got more dates when he had a dog with him.) But I am skeptical that the possible reproductive advantages our ancestors accrued by falling in love with an animal outweighed the costs in time and resources.
PETS ARE PARASITES?
If pet-keeping does not have an evolutionary function, why do we form such close bonds with animals and invest so much money and emotional energy in them? One possibility is that love of pets is, like the color of our bones, an evolutionary side effect. Consider Harvard evolutionary psychologist Steven Pinker’s theory of music. Pinker is an adaptationist when it comes to language and fear of snakes, but he believes that our love of music is a biologically useless consequence of the way that our brains are wired. Could Pinker’s view that music has no adaptive value also apply to our love of pets?
Consider the most common claim that Americans make about their pets: “They are my children.” Humans are instinctively drawn to animals that remind them of infants—creatures with big eyes, large heads, and soft features. These traits hook our parental instincts and serve to help us pass down our genes by eliciting care for creatures with whom we do share genes: our offspring. But because instincts operate automatically, they can be hijacked. Take, for example, nest parasitism, a reproductive strategy used by dozens of species of birds. A brown-headed cowbird will lay an egg in the nest of an Eastern phoebe. The hapless phoebe will blithely brood the cowbird’s egg and then feed the parasitic nestling until it fledges and flies off. Ironically, the phoebe probably gets great emotional satisfaction by raising her faux offspring, not realizing that she has been the victim of a Darwinian sting operation.
In 2005, Mary Jean and I were victims of this scam. The parasite was none other than our cat, Tilly, and the perp was the savvy mother cat who deposited a baby at our door, never to be seen again. Our yellow Lab, Tsali, had died the year before, but we were not looking for a new pet. When I came home from work one afternoon, Mary Jean greeted me with a big smile. That’s when I heard a plaintive meow coming from the living room. She had found a kitten under our deck. The little sad-sack of a cat had the full complement of baby releasers. With those big eyes and soft fur, she was irresistible. It was a done deal.
The idea that the human-animal bond is caused by a misfiring of our parental instincts appeals to me. The problem is that it does not explain the large cultural differences that exist in the frequency and styles of pet-keeping. Perhaps a different type of evolution—cultural evolution—provides a better perspective on why we love our pets than does Darwin’s theory.
PET-KEEPING AS A MENTAL VIRUS
The high point of my intellectual career may have been in 1979, when I found myself sitting next to Richard Dawkins on a bus filled with ethologists who were headed for the Vancouver Aquarium. I had just finished his book The Selfish Gene and was star-struck. The book was important for a lot of reasons, but it was chapter 11 that spun my head around. In it, Dawkins argued that evolutionary change does not require either genes or organisms. All you need are replicators—gizmos that can make copies of themselves and have the attributes of longevity, fecundity, and copying fidelity. In biological evolution, the gizmos are the molecular spiral staircases that we call genes that use our bodies to reproduce themselves. Dawkins’s insight was that cultural evolution works in the same way. Only with culture, the gizmos are bits of information that are transmitted by imitation and that use our minds to reproduce themselves. The term gizmo does not have much scientific gravitas, so he called his hypothetical units of cultural transmission memes, a term he coined because it rhymed with genes and harked back to the Greek word for memory.
Memes are everywhere. Some are trivial (wearing baseball hats with their brims pointed backward), some are tragic (a short-lived fad in Japan for strangers to commit suicide together by igniting a charcoal brazier in a sealed minivan), some are transcendent (the arts). Snatches of songs you can’t get out of your head are memes. So are cool sneakers and political ideologies. Our ancestors spread memes by copying each other’s actions. But memes became a much bigger factor in human evolution with the development of symbolic language. Now, memes spread around the globe at warp speed via radio and television, and, of course, the Internet. The new
est mode of mimetic transmission is text-speak, a language I find impenetrable—plz!
The term meme is itself an extraordinarily successful meme. When I Googled “meme” ten minutes ago, I got 350 million hits. The word has made it into the Oxford English Dictionary. Last night, a TV commentator described a nasty political smear campaign as a meme. But while nerdish techies, edgy hipsters, and a few philosophers have embraced Dawkins’s idea, anthropologists, the real experts in cultural evolution, are lukewarm at best. They claim the definition of memes is too loosey-goosey, that—unlike genes—memes are not discrete units. They argue that human cultures march along just fine without the assistance of imaginary replicators.
I am agnostic as to whether memes exist as actual entities. But there is no doubt that ideas and behaviors are contagious, and I find that memes are a useful metaphor for thinking about the role culture plays in our relationships with other species. From the meme’s-eye view, pet-keeping is a mental virus spread by imitation. This idea sounds far-fetched, but the evidence for this perverse hypothesis is surprisingly strong.
First, because memes are transmitted by learning, they tend to run in families. Catholic parents usually have Catholic children and circumcised fathers usually have circumcised sons. Similarly, pets run in families; children raised with pets usually grow up to be pet-owning adults. Further, cat kids usually become cat adults, and dog kids, dog adults.
Second, consistent with the meme hypothesis of pet-keeping, societies differ widely in their attitudes toward and treatment of companion animals. Darryn Knobel of the University of Edinburgh studied patterns of dog ownership on the island of Sri Lanka, a culturally diverse society that has one of the highest densities of dogs in the world. In Sri Lanka, your religion determines whether you have a pet dog. In the capital city of Columbo, 89% of Buddhist homes include a dog, as opposed to 4% of Muslim households. The fact that a Sri Lankan Buddhist is twenty times more likely than a Muslim to own a dog suggests that Islam inoculates believers from infection by puppy-love memes, while Buddhism makes people more susceptible.