Why The Heck Do Animals Live In Our Houses?

How did a dog get on my bed?
Scott Schiller, CC BY-NC

If you own a pet, chances are you’ve found yourself pinned in place by a sleeping furry companion on more than on occasion. Have you ever stopped, for a moment, and wondered just what the heck they’re doing there? Not how you came to be conquered by saucer-like eyes and a wet nose, but rather, how we ended up with animals living in our houses (and sleeping on our laps) to begin with?

Various revolutions in technology have brought forth waves of change that have altered the trajectory of human evolution, but none have changed Homo sapiens as definitively as the domestication of plants and animals and the advent of agriculture 12,000 years ago. The whole basis of modern society and civilization—large nation states and groups of people living together by the thousands and millions— is built upon humanity’s shared interest in avoiding spending the day out looking for food.

Domesticated grains and cereals – crops once collected in the wild that we bred to grow where and how we wanted them – were obviously a big driver in this transition from hunting and gathering. But domesticated animals—that is, livestock—were as well. And it’s easy to see why humans developed such complicated symbiotic relationships with these creatures: it was beneficial for us to do so. Domesticated animals have provided humans with meat, milk products, leather, wool, modes of transport, plowing and military might, and even fertilizer. But how, exactly, did something as impractical as a tuxedo cat come to spend its mornings batting at your face?

What Does It Mean To Be Domesticated?

Before Fluffy could start pooping in a litter box in your closet, her species had to be domesticated. There is a noted difference between an animal that has been domesticated and one that has simply been tamed. A tame animal has been trained to exhibit human-friendly behaviors, but a domesticated animal has had its evolutionary path altered to suit human needs. Countless scores of animals have been, and continue to be, tamed, but far fewer have actually been domesticated. In his pulitzer-prize-winning book Guns, Germs, and Steel, geographer and anthropologist, Jared Diamond describes domestication as such:

That’s a fairly dry way of saying that, essentially, a domesticated animal is genetically different from its wild counterpart; whereas a tame animal has just learned a certain behavior. A tame chimpanzee refrains from slinging its poo around because it’s learned not to. But if that chimp has a child in the wild, you better believe some poop is gonna fly. Without generations of breeding in captivity, traits like following human commands or not flinging poop will fly right out the window as soon as nature takes its course.

Elephants, for example, were used as war machines in ancient times and are still used as work animals in Southeast Asia. But they’re tame, not domesticated. Every elephant you see shlepping people around or dragging logs is, as Diamond puts it, “just [a] wild elephant that was captured and tamed.”

Domesticated animals also stand out in terms of physical appearance. Many species have changed in size, coloring and shape thanks to generations of selective breeding. It makes sense that animals evolve to adapt to their environment – even when that environment is a human’s lap. “A Bichon Frise running wild in Mongolia is not going to do very well.” says biologist Adam Boyko, of Cornell University.

How Does It Happen?

Did an ancient human point to a particularly cute wolf and announce that our two species would be best buds forever? Probably not. But as natural relationships developed between humans and other animals in the wild, our exploitation of their unique skills kickstarted the domestication process. Jean-Denis Vigne, director of research at the French National Centre for Scientific Research in Paris explains the transformation as “a specially strong ecological interaction between humans and the species, subsequently reinforced by human intentionality.”

What this means is that humans and other animals were often crossing paths and symbiotically building livelihoods around each other – as many species often do in the wild. At some point during these relationships, humans realized the benefits of having these creatures around, and took an active role in keeping them there. Thus the giant gears of domestication began to turn. “The pathway to domestication does differ from one species to another, but we can say that the general trends are always the same,” says Vigne.

How It Happened With Cats and Dogs

You may know Scruffy the dog as your slobbering doorman, eagerly awaiting your arrival so he can lick your face clean; or Mr. Horatio as the ambivalent cat that sleeps on top of your keyboard (sometimes causing it to crash); but many pets were not originally domesticated as pets; they did things that either directly or indirectly benefited the people they lived around and were bred to continue to do so.

Eurasian gray wolf walking in the snow

New research led by Boyko suggests that the first dogs originated in Central Asia about 15,000 years ago. Boyko and his colleagues posit that new human hunting techniques, perhaps combined with the effects of climate change, could have taken a toll on gray wolves’ food sources. Some enterprising pups began to tag along with roaming bands of humans in hopes of scavenging meat scraps. Their utility was soon seized upon by humans who bred the dogs as sentinels, hunting companions, sled pullers, camp cleaners, and to fulfill scores of other duties. Eventually, humans had enough resources and downtime to keep animals around for fun and for show, leading us to breed all sorts of strange looking critters.

Cats, unsurprisingly, came to humans more on their own terms. Their arrival in human society occurred a bit later than dogs, approximately 10,000 years ago, with the advent of agriculture. Large, centralized groups of messy humans and grain stocks attracted waves of mice and rats, which in turn attracted cats. Such easy pickings were just too irresistible to hungry felines, who began to lurk around human settlements. Humans, grateful for the merciful relief from rodents, gladly kept them around. Like with dogs, cats’ roles as hunters eventually shifted more to being lovable companions as human society developed and industrialized. Yet in many countries around the globe, cats continue to execute the mercenary role they were originally domesticated to fulfill in ancient times.

Can I Domesticate Anything?

Nope. It’s not as simple as capturing two of any animal, having them go to town, and repeating generationally as needed. Of all the animal and plant species on Earth, very few have, or are able to be, domesticated. To be domesticable, a species must have just the right kinds of traits.

Jared Diamond describes this phenomena by saying “domesticable animals are all alike; every undomesticable animal is undomesticable in its own way.” If a species is missing any one key element required for domestication—like being able to breed in captivity, for example—then efforts to breed it into submission it will be doomed to failure. This explains why, throughout the course of human history, the number of “big mammals” domesticated for livestock purposes is a measly 14.

Now, that number obviously doesn’t include the total number of species that have been domesticated, but it does show the difficulty in actually successfully doing so (new species, however, do continue to be domesticated in the 20th century. Foxes are one particular adorable example). For some animals, domestication is simply impossible. Elephants, as we mentioned earlier, have been employed by humans for millennia, yet to this day they are still not domesticated. That’s largely because they breed poorly in captivity, if they can manage it at all.

No wonder your pup keeps falling asleep on you: The trip from hunting and scavenging in the wilds to lazing around your living room took thousands of years of work. And though not all dogs and cats are slaying mice or raising the alarm on intruders, they are still providing for humans in other ways – even if all they offer are some snuggles.