“Man’s best friend” has had a close relationship with humans for thousands of years, which has resulted in the amazing diversity of breeds present today. The first animal domesticated by humans, dogs have been selectively bred for countless generations to fill many different roles in our daily lives, leading to the over 400 breeds which exist today, 163 of which are recognized by the American Kennel Association. In fact, domestic dogs are the most diverse mammal species alive, whose members can have over a hundred-fold weight difference.
Recent studies have revealed that, amazingly, domestic dogs (Canis lupus familiaris) all share a common ancestor: the gray wolf (Canis lupus). This was confirmed by comparing the DNA of many different modern domestic dog breeds to wolves, coyotes, and jackals (which all belong to the genus Canis); dog DNA is most similar to that of the gray wolf.
Exactly when and where the first wolves became domesticated remains under debate, but their ancient history with humans can be gleaned from fossil records. The oldest domestic dog remains date to 14,000 years ago; these were found in the Ukraine and Germany. Twelve thousand years ago, many smaller dogs lived closely with humans in the Middle East, as evidenced by the oldest discovered burial of a dog with a human. Domestic dogs quickly spread, with humans, throughout the rest of the world, and many dog remains have been found throughout Asia and Europe dating 10,000 to 8,000 years ago. The earliest fossils in East Asia and North America date to around 8,500 years ago. In addition to fossil evidence, a variety of different dog breeds are also depicted in the art of very early human civilizations across the globe.
As the oldest discovered domestic dog remains date to 14,000 years ago, dogs must have diverged from wolves before this. Remains of a 32,000-year-old canine that was not a domestic dog, but was more similar to a dog than a wolf, were discovered in the Goyet cave in Belgium, suggesting that ancestors of the dog had already diverged evolutionarily from wolves by this point. Some researchers theorize that predecessors of modern dogs were already becoming a different wolf subspecies before humans influenced them; such wolves may have, for example, been changing their diet to become more omnivorous and less carnivorous, and later became domesticated by humans.
There are many ways in which people may have initially domesticated wolves. Many humans were expanding their territories 14,000 years ago, developing agriculture, and creating settlements. Permanent dwellings generated food waste that may have attracted local wolves (which are, like humans, omnivores). It is also quite possible that orphaned wolves were adopted by humans. The less wary and aggressive wolves may have stayed, their traits selected for over generations. Because wolves are pack animals with complex social behaviors and a social hierarchy, they can be quite trainable and playful, and fit well into human social structures. Dogs’ expressive body language has always been quite appealing to humans.
Domesticated dogs and humans formed a mutually beneficial relationship from the start. While humans supplied dogs with a reliable food source, they could also benefit from dogs’ hunting abilities. Even though wolves are quite fierce, humans using tools and weapons offered additional protection from mutual enemies. Humans could also use dogs for hauling, and as a source of food and fur. Additionally, humans allowed dogs to breed earlier and more often, including those that may not have reproduced at all in the wild, due to low social standing in their pack.
Humans selected for certain traits in dogs. Over many generations, domestic dogs became less wary, although this led to them becoming less responsive to environmental stimuli and less active. Human breeding of dogs also increased their sociality, changed they way of being trained, and increased their sexual behaviors. Overall, dogs have undergone juvenilization, or “neoteny,” which is especially seen in the head: Domestic dogs similar in size to the gray wolf have smaller paws and teeth, and a smaller head, muzzle, and brain.
While it is unclear where the first dog domestication events occurred, there are several well-founded theories. Based on genetic evidence, a handful of domestication events may have occurred. Fourteen thousand years ago, the gray wolf was widespread, living throughout much of Eurasia and North America (although its territory is now much diminished). Asia is the most likely suspect for the origination of dogs, as early dog remains most resemble a small Asian gray wolf. Additionally, genetic evidence has revealed that the oldest dog breeds, those most similar to wolves, are Asian breeds.
However, based on the oldest fossil findings, early domestication events may have occurred in the Middle East and/or Europe. Genetic evidence also implicates European wolves as having been involved, though maybe later in time; some domestic dogs have interbred with wild wolves.
Findings published in 2004 by Dr. Elaine Ostrander’s laboratory, at the National Human Genome Research Institute of the National Institutes of Health, grouped modern domestic dog breeds according to their genetic similarity to each other and gray wolves. Using 85 dog breeds and several wolves, researchers grouped breeds of dogs according to how genetically similar they are to the gray wolf. The oldest group of dog breeds—those most similar to their wolf ancestors—contains Asian breeds: the Shar-Pei, Shiba Inu, Akita, and Chow Chow. The second oldest group consists of the Basenji, an African breed. The third oldest group includes two Arctic breeds, Alaskan Malamutes and Siberian Huskies. Lastly, two Middle Eastern sighthounds make up a fourth group: Afghans and Salukis. Surprisingly, some breeds thought to be ancient, such as the Pharaoh Hound and Ibizan Hound, were revealed to have much more modern roots, probably due to efforts to recreate ancient appearances.
Aside from these four ancient-rooted dog groups, sometimes referred to as “old-world dogs,” the other, newer breeds analyzed had less genetically in common, but some groupings were still apparent: “Mastiff”-types (which included Mastiffs, Boxers, Bulldogs, Bernese Mountain Dogs, German Shepherds surprisingly; and others), herding-types (Shetland Sheepdogs, Collies, Greyhounds, Saint Bernards, and Irish Wolfhounds), and more modern European breeds and hunting dogs (terriers, spaniels, pointers, and retrievers).
Amazingly, most of the diversity of familiar dog breeds familiar today only came about during the last few centuries. For most of our shared history, there were only a few distinct dog breeds. However, as humankind began to understand genetics, many breeds were quickly generated; a variety of breed clubs were created in Europe in the 1800s.
Dogs today vary greatly in size: The smallest known dog, a Yorkshire terrier, weighed a quarter of a pound, while the most massive, an English Mastiff, was 343 pounds, and the tallest, a Great Dane, was three and a half feet at the shoulder. Breeds come in an astounding array of head shapes as well as coat colors, lengths, and textures. Dogs have been bred to serve a variety of purposes, from hunting, guarding property, herding livestock, and hauling, to physical and psychological therapy and—most commonly—companionship. Although rarely thought of as physical laborers today, 12,000 years ago sled dogs may have enabled humans to cross the Bering Straight and enter North America. Even with this astonishing diversity, numerous dog breeds have gone extinct in famines, depressions, and wars.
We must be sure to take care of our “best friend,” who’s been by our side for so many thousands of years. Three to four million dogs and cats are euthanized every year in the United States by shelters, according to the Humane Society of the United States. Only through proper planning, spaying, and neutering, and adopting animals from local shelters, can this ancient relationship be properly honored.
For more on the history of the domestic dog, see Heidi G. Parker et al.’s “Genetic Structure of the Purebred Domestic Dog,” P. Jensen’s “The Behavior of Dogs,” Mietje Germonpré et al.’s “Fossil dogs and wolves from Palaeolithic sites in Belgium, the Ukraine and Russia: osteometry, ancient DNA and stable isotopes,” K. Kris Hirst’s article on “Dog History: How were dogs domesticated?,” the website for “The Humane Society of the United States,” Wikipedia’s “Gray Wolf,” Wikipedia’s “Origin of the domestic dog,” and Wikipedia’s “Dog.”
Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at firstname.lastname@example.org.