First one dog barks, then another four doors away joins in. Soon a whole suburban neighborhood rings with the seemingly endless racket. What are the dogs discussing in such strident tones? Raymond Coppinger and Mark Feinstein, of Hampshire College in Amherst Massachusetts, think the dogs are being a bit childish.
Most members of the dog family yip, growl and howl. And they share a number of similar facial and body-posture communications. A fully bared set of teeth sends a pretty universal signal, even to humans. But the bark truly sets dogs apart. Wolves and coyotes—and some dog breeds, such as the so-called barkless basenji—bark only rarely. Most dogs bark incessantly. Coppinger and Feinstein once clocked a dog barking continuously for seven hours. Another scientist recorded 907 barks in a ten-minute period. Coppinger and Feinstein asked why.
Another habit of domestic dogs gives the tip-off as to why domestic dogs bark, and perhaps to why we have domestic dogs at all. That habit is rooting through garbage. Few dog owners have missed the experience of finding the kitchen garbage strewn across the floor, or the outdoor garbage can upended. Dog fossils occur along with those of humans in sites about 10,000 years old, and Coppinger and Feinstein suggest these dogs were scavenging among the humans’ garbage. The humans may well have killed and eaten some of these dogs, but the researchers find it highly unlikely that humans domesticated dogs deliberately. Instead the dogs found an available ecological niche, hanging around human encampments.
The puzzle of the dog’s bark comes from comparing it to other animal vocalizations. Low, noisy grating sounds, which we call growls, almost universally indicate adult animals. To human ears, growls sound dangerous. And this assumption is borne out with all members of the dog family. A dog’s or wolf’s low menacing growl communicates threat. On the other hand, a clear, high-pitched whine or yip indicates unthreatening babyhood. A dog whines to come in if it’s outside and (sometimes immediately afterward) to go out if it’s in. We hear no threat in a whine.
But a bark appears to combine both kinds of sounds, Coppinger and Feinstein found, as if the bark conveyed an adult message, harsh and low, along with a youthful keening. The researchers think this fits well with their proposal of domestic dog evolution. Dogs least afraid of humans fared better in and near human settlements. But such tameness is a juvenile trait. Humans can safely handle many baby animals, whereas the adults of most nondomesticated species are too dangerous to approach. The environment around human encampments selected for tameness. A fearful dog would have a harder time reaching the choicest bits of garbage; a tame one, brave enough to approach the garbage pile, would “fit in.”
As the tamer dogs bred, they passed on more of the genes for tameness to subsequent generations, and along with tameness came other juvenile characteristics, Coppinger and Feinstein argue. Most dogs never develop a fully adult hunting instinct. Mother dogs nurse puppies, but rarely provide solid food for them. Even dogs’ variable colors and sizes, and the fact that they come into heat twice a year (instead of once as is common in wild canines) relate to a juvenilization.
Along with this package of changes came barking, a mixture of juvenile and adult sounds. The barks may make no more sense in the life of a dog than playfulness or floppy ears. They just do it.