Facts So Romantic

Love Your Dog? You Should Thank Garbage

scion via Shutterstock

Just south of the equator, thirty miles off the coast of Tanzania, sits a small island called Pemba. The small patch of dry land jutting out from the Indian Ocean is just 30 miles long and 10 miles wide. The quarter million or so people who inhabit Pemba live more or less on the bleeding edge between a traditional hunter-gatherer lifestyle and a more modern agricultural one. Most of the sustenance, for example, comes from hunting and gathering, from fishing in dugout canoes, and from scraping shellfish off the reef that surrounds the island. In the industrialized West, by comparison, we still do a bit of fishing and hunting, but the vast majority of our food comes from farm-raised crops and from domesticated livestock. The Pembans live in huts made of wood, grass, or mud, or occasionally of concrete, and almost all now have roofs made of metal. With one foot in the past and one toe dipping into the present, they would be unable to survive without hunting, but they also keep some domestic livestock around, primarily in the form of chickens. There is even an airstrip that connects Pemba with Dar es Salaam, the nation’s largest city, and Zanzibar, a nearby island. In some sense, the people of Pemba can be thought of as representative of humans undergoing the profound shift to an agricultural, settled-down lifestyle. Oh, and one other notable thing about them: They hate dogs.

In Dogs: A Startling New Understanding of Canine Origin, Behavior, and Evolution, canine scientists Ray and Lorna Coppinger explain that Pembans are Muslims, and Mohammed advised against touching dogs. In their tradition, evil disease-bearing organisms are said to live inside dogs’ noses, which explains their cold, wet, drippiness. It’s a perspective with some medical benefit. At the time of Mohammed, and certainly today in much of Asia and Africa, rabies spreads thanks, in part, to dogs. Coppinger goes on to explain that Pembans also believe that God himself doesn’t like dogs. “If a dog comes into their house, God will not visit them. If a dog comes into the house even uninvited, the house must be cleaned—really cleaned, spiritually cleaned, before God will visit again.” In Pemba, dogs—not wolves, but actual domestic dogs, canis lupus familiaris, just like Fido and Rover and Fluffy—are unwanted. This is decidedly not the picture of man’s best friend, snuggled up against our feet atop our beds.

The usual story of domestication goes something like this: Wolves are distance runners, and so are humans. Wolves hunt cooperatively, and so do humans. At some point, some relatively friendly wolves learned that by working together with humans, they could take down more or bigger prey than they could alone. Thus, man and wolf shared the spoils of the hunt. It’s what Arizona State University psychologist Clive Wynne calls the hunter’s-helper hypothesis. And he thinks it’s wrong.

“Anybody who’s ever been around wolves will tell you that trying to share food with a wolf is a recipe for disaster,” Wynne told me. Wolves don’t share nicely with humans, or even amongst themselves. Feasting on a kill is a moment of conflict for any wolf pack, so “the idea of a puny little human pushing themselves into that is just nonsensical!” Add to that the fact that wolves are equipped to bring down large prey by themselves; they really don’t need our help. And on our own, even with tools, humans would be hopelessly outrun by wolves.

That doesn’t mean you, living in 2013, couldn’t tame a wolf. Nowadays we have chains and cages, collars and leashes. We have a fairly sophisticated understanding of behavioral science. “None of these things,” Wynne points out, “would have been available to our ancestors. It’s just not plausible that they could have made friends with wolves.”

“Anybody who’s ever been around wolves will tell you that trying to share food with a wolf is a recipe for disaster.”

The hunter’s helper sounds like a nice story, but scientists like Wynne are increasingly turning to another hypothesis, one he calls calls the Dumpster-diver hypothesis. Up to around 200 years ago, it was only the richest of the rich who had pet dogs. The rest were village dogs, living in and around human settlements, surviving on garbage and human leftovers, just as other carnivores occasionally do. Today, some 80 percent of the world’s domestic dogs survive by scavenging on garbage, and even a pet dog will go through your garbage can if you aren’t careful.

So how does a wolf rooting through the garbage at the outskirts of human settlements become a dog? To scavenge in a trash dump, a wolf has to be minimally accepting of human presence, which is something wild animals are generally not known for. On average, wolves’ flight distance for humans is 200 meters. In essence, they run away from humans before humans even have a chance to realize there’s a wolf nearby. (In contrast, a study of feral dogs from Ethiopia showed that they tolerate a human’s approach up to a distance of about five meters.) So only wolves who were abnormally tolerant of human presence who would stick around long enough to eat our trash in the first place. Support for this idea comes from a 2010 paper in Nature, which found a small tweak in a gene called WBSCR17 in dogs. The same mutation in humans results in a disorder called Williams–Beuren syndrome, which is characterized by extreme friendliness. According to the Dumpster-diver hypothesis, the trash is itself an evolutionary selection pressure. By becoming more tolerant of other species, including our own, early wolf-dogs could allow our table scraps into their dietary repertoire. That’s part one of the domestication story.

The second part involved the loss of hunting skills, as scavenging took over as the primary mechanism by which they ate. Only then did it become safe to bring them into our homes. That’s when they started to become useful as herders, livestock-guarders, and sled-pullers. That’s also when they finally became useful as hunter’s helpers. And they do provide a lot of help: It turns out that having a hunting dog is equivalent to having a rifle, according to Wynne, in terms of additional pounds of meat procured per year.

“If they could complete the kill, they would complete the kill,” Wynne says. Dingoes in Australia, for example, can hunt on their own. But domestic dogs simply can’t, for the most part. When you hunt with a dog, the dog gives chase to tire out the prey, and then barks so that you can come along with your machete or pistol to finish the job. Only after entering into this sort of symbiotic relationship with humans did our ancestors begin to place value on dogs. Early humans who worked with dogs gave them names and cared for them. When the dogs died, the humans mourned and gave them proper burials. The wolf becomes a scavenger, and the scavenger becomes a partner.

While the Dumpster-diver hypothesis has garnered support, the question is by no means settled. Since we can’t go back in time to investigate the nature of the early relationship between wolf and man, researchers have had to become more creative, by addressing related indicators like flight distance. Mia Cobb, a researcher focused on modern-day working dogs, says, “I think the take-home message is that dogs and people have co-evolved over a long time, opportunistically exploiting each other to various degrees—and [they] still do.”

According to Google n-grams, the phrase “man’s best friend” didn’t appear in a book until after the year 1750. By contrast, the Bible usually refers to dogs much as we refer to pests, like in the first book of Kings, where it says, “[Anyone] who dies in the city the dogs shall eat, and anyone…who dies in the open country the birds of the heavens shall eat.” Coppinger and Coppinger understand this to mean that dogs were thought of as urban vultures, “nasty buzzards prowling the streets at night, ripping apart anything they find lying around, including people.” It’s no wonder that the Pembans think of dogs as a nuisance, not as potential family members. Wolves probably became dogs by first becoming oversized rats, feasting upon our waste. In much of the world, they still are.


Jason G. Goldman received his Ph.D. in developmental psychology at the University of Southern California in Los Angeles and writes a blog called The Thoughtful Animal, hosted at Scientific American. His doctoral research focused on the evolution and architecture of the mind, and how different early experiences might affect innate knowledge systems.

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