How cats and dogs became our best friends

By the time they graduated from the School of Medicine, David Grimm, Ph.D. ’04, and his fiancée, Amy S. Duffield, M.D. ’05, Ph.D. ’05, had wanted a cat for years. After landing in Baltimore—Grimm as a deputy news editor of Science, Duffield as a pathology resident at Johns Hopkins—they felt ready to adopt two kittens. Not long after, one of the kittens spent three days in a veterinary ICU. The bill came to nearly $3,000.

Why, Grimm wondered, had he and his fiancée gone into debt to save the kitten? He decided to explore what he describes as “the evolution of dogs and cats from wild animals to quasi-citizens.” Americans, he soon discovered, spend a lot on their cats and dogs—$55 billion in 2013—and more households have dogs or cats than have children.

His research took him to laboratories, animal shelters, an animal law conference, and a prison. The result is Citizen Canine: Our Evolving Relationship with Cats and Dogs, a broad examination of the history of how humans interact with dogs and cats and how the pets have affected art, religion, law enforcement, public policy, and even the course of epidemics.

Grimm, who studied genetics at Yale, begins by investigating how dogs evolved. The household pet we know as Canis lupus familiaris shares 99.9 percent of its DNA with the gray wolf, Canis lupus. One explanation for the evolution is “pup abduction”—our ancestors may have kidnapped wolf pups and raised them to be gentler than wild wolves. But Grimm doubts that the abductors would have imagined that wolves could be made gentle: people found them terrifying. (Consider Little Red Riding Hood, a tale told by two other Grimms.) Furthermore, early humans had yet to domesticate any animal. As one scientist tells Grimm, “They weren’t thinking, ‘You know, in a century or two, we’ll create this really handy animal, the dog.’ ”

A more likely scenario, Grimm believes, is that wolves evolved somewhere between 15,000 and 30,000 years ago as they followed early humans, scavenging for bones and food scraps. Humans in turn found canines useful for carrying loads and warning of intruders. Cats proved similarly valuable with the advent of agriculture about 12,000 years ago—they killed mice that ate stored grain.

A 20th-century experiment showed how quickly human-animal interactions can lead to genetic changes: the Russian geneticist Dmitri Belyaev began in 1959 to breed caged silver foxes selectively, allowing only the friendliest to reproduce. In just nine years, the foxes’ ears became floppy, their tails curled, and they had lower levels of the stress hormone cortisol. Instead of biting people, they licked their hands. Grimm also notes reversals in the fortunes of dogs and cats—whereas ancient Egyptians venerated felines, in 1233 Pope Gregory linked cats to Satan. Millions of cats were massacred, a boon to the rats that helped spread the plague.

The social standing of cats and dogs has improved markedly since then. Support for medical experimentation on animals is waning. Laws protect animals from harsh treatment, and among Grimm’s field trips was a stint shadowing the anti-cruelty team of the Los Angeles Police Department as they investigated the beheading of two dogs. Americans view their dogs and cats as family members: during Hurricane Katrina in 2005, people risked death rather than leave their pets behind.

Grimm’s account brings us to an era in which canines and felines increasingly look almost like citizens. As Grimm demonstrates, the story of our bond with cats and dogs is still unfolding.