Pets are a relatively recent invention. Most date the pethood concept to the eighteenth and nineteenth centuries. Of course, human beings lived with animals for much longer—dogs have been domesticated at least 30,000 years—but pets are a very special category. The pet, says Marc Shell, is the “one essentially inedible animal,” the ultimate indulgence in the long history of using animals for food and/or work.

The OED’s first reference for “pet” is from 1539, meaning a baby lamb raised by hand. Another old meaning: the pet as a favored or indulged person, as in the still-current “teacher’s pet.” Ingrid H. Tague argues that both these definitions merge into the modern usage, a pet being a tame animal much-indulged in the home. Since the nineteenth century there has been a particular split between domesticated farm animals and domesticated house animals. Today, few Westerners have daily contact with working animals or those destined to be eaten. The richer parts of the world have the most pets: there are an estimated 163.6 million dogs and cats in the U.S. (compared to some 73 million children under 18) and Americans spend more than $60 billion a year on them.

“Once most animals were moved away from intimate human contact, it became possible for some to be marked out as special by virtue of their sharing the same domestic space as their human owners,” writes Tague. She analyzes eighteenth-century literary works in Britain. Among the hundred plus British epitaphs or elegies for pets in that century, she finds 6 for monkeys, 12 for canaries, 17 for cats, and 53 for dogs. As is often the case when people write about animals, the subject was really “the ways people used animals to think about humans’ place in the world.” By the end of the period, “pet keeping could come to symbolize all that was best in the human spirit, and mourning a pet could be seen as praiseworthy rather than ridiculous.”

Marc Shell delves further into the “sexual, familiar, and finally social role that the institution of pethood plays in contemporary politics and ideology.” His thought-provoking essay includes discussion of kin (family) and kind (species), Penthouse Pets, petting (both senses), snugglebunnies, the bestiality and incest taboos, the Animal Groom Story (“Beauty and the Beast” is the best known) in which the hero or heroine marries an animal, and Christianity as an omnivorous ideology, including even cannibalism (via the Eucharist). You may never look at Fido again in the same way, much less a cat named Bob—Catholicism once highly frowned on pet-keeping and particularly the giving of “Christian” names to pets.

According to Shell, pets now fill the lacuna left by the absence of “slaves, housemaids, servants, mistresses and domestic working animals.” He calls family pets “generally mythological beings on the line between human kind and animal kind,” and concludes “if there were no such thing as pets, we would breed them, for ourselves, in the imagination.”

That’s quite a bone to gnaw on.