In a previous post, I argued that we humans are the only animal to bring members of other species into our lives purely for enjoyment. And I asked -- why don't even intelligent creatures such as chimpanzees sometimes take on a pet? After all, they frequently run across baby animals they could fall in love with. Further, as demonstrated by a group of capuchins in Brazil who adopted a marmoset, at least some non-human primates have the ability to feed and care for members of other species. And, as I pointed out, in captivity, animals readily form bonds with other creatures.
My Theory: Pet-Keeping Requires Cultural Evolution
My tentative explanation of why animals living in the wild don't keep pets is that pet-keeping requires a mix of biological and cultural evolution only found in Homo sapiens. Animals with parental care have the biological part of the equation. It comes in the form of the innate predisposition that causes adults to fall for creatures with big eyes and rounded facial features and functions to prod them into doting on their own infants. But other animals don't posses the cultural part of the nature/nurture mix, the learned social rules that tells you whether it is ok or verboten to love a dog or parrot or a pig and treat is as a friend or even a child.
True, lots of species possess the rudiments of culture. For example, chimp societies differ in their tools and in the brutality of their carnivory. (The chimpanzees of the Cote d'Ivoire are prone to disembowel their prey while Gombe chimps prefer to first rip the limbs off their victims.) But as Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology has shown, a two year old human child far outstrips even the smartest chimp when it comes to soaking up cultural knowledge such as how to read a book, which sneakers are cool, or if a puppy should eat at the dinner table or be eaten for dinner.
Are Pets "Viruses of the Mind"?
It is no accident that the only animal on earth that keeps pets is also the most facile copy cat. I am tossing out the idea that pet-keeping may spread across human cultures by way of the hypothetical entities that the evolutionary biologist Richard Dawkins calls memes. Memes are the mental analogs of genes. They are units of culture transmitted from human mind to human mind via imitation. The philosopher Daniel Dennett compares them to parasitic worms that can take over an animal's nervous system, rewire its brain, and manipulate its behavior. Dennett argues that religions act like mental brain worms. So do snatches of songs you can't get out of your head. Brain-wormish memes operate like computer viruses that commandeer your hard drive and uses it to infect other computers. In fact, Dawkins refers to memes as "viruses of the mind."
But, you ask, what evidence do I have to support the completely non-intuitive idea that our love of pets is the result of thought contagion? First, pet-keeping is not a human universal. Human cultures differ widely in the frequency and form of pet-keeping. My Kenyan anthropologist friend Nyaga Mwaniki tells me that his native language does not even have a word for pet, and, while people in his village keep mongrels around as guard dogs, they never let the dogs come inside their homes or play with them. In a soon to be published study in the journal Anthrozoös Peter Gray and Sharon Young surveyed pet-keeping practices in sixty cultures. Pets existed in most, but not all, of the societies. Dogs were clearly thought of as pets in only twenty-two of them. And in some of the cultures, "pets" were routinely killed and eaten. In others, lactating women would breastfeed their companion animals. (Breastfed pets included pigs, puppies, monkeys, and bear cubs.)
As revealed by the demographics of pet ownership in Sri Lanka, some memes can either facilitate or inhibit infection by other memes, including memes for pet-keeping. In Colombo, the capital city, your chances of being infected by the pet meme depends on your religion; ninety percent of Buddhists homes include a pet but only five percent of Muslim households do.
Most importantly, unlike genes which take a generation to replicate themselves, memes can spread through a culture at warp speed. When I was kid, there was a short-lived craze for pet baby turtles. I had one and so did all my friends. Who knew that most of them carried salmonella? In 19th century Japan, ornamental mice were the hot pets; today the pets of choice for Japanese children include giant stag beetles.
Do Memes Really Exist?
The truth is that I am agnostic on the literal existence of memes and on Dennett's brain worm analogy. While the meme concept itself has "gone viral," most cultural anthropologists (the real experts on cultural change) are not convinced. However, I find that meme-think offers an interesting, novel, and potentially useful perspective on questions like "why do humans - and only humans - love pets?"
Note that my wife Mary Jean is not keen on the idea that our love for our cat Tilly is the result of a brain worm.
That's ok Tilly. I love you even if you are a mental virus, like that song I can't get out of my head - I think it's Patti Paige crooning "How much is that kitty in window...."
Hal Herzog is Professor of Psychology at Western Carolina University. His new book is Some We Love, Some We Hate, Some We Eat: Why It's So Hard To Think Straight About Animals.