20 ways humans have shaped dogs' evolutionary history

The history of dog evolution is often depicted in two stages. First, from an extinct species of wolves to modern-day gray wolves and dogs, and the second from dogs to breeds. A 2017 study published in Nature found that dog ancestors lived 40,000 years ago, who split into the present-day wolves and dogs. The European and Asian groups of dogs divided around 20,000 years ago, according to the same study.

The journey from wild wolves to tail-wagging companions is still marred with mystery with new theories and studies revealing different aspects of a dog’s evolution as man’s best friend. But broadly there are two popular notions. According to Susan Crockford, an anthropologist and zooarchaeologist with University of Victoria in Canada, the first real impact humans had on dogs was during the Stone Age when some curious wolves became comfortable around humans, probably attracted to the food leftovers. Another theory suggests that pre-historic humans adopted wolf pups to help with hunting and guarding. Both theories suggest that the human-dog bond had been established based on mutual benefits.

The association of wolf-dogs and humans began between 10,000 and 30,000 years ago, but there is no single evolutionary chain in dog’s history as a species that can pinpoint to the oldest domestication. From southern China to Mongolia to Europe, genetic studies point to several regions and time when humans found companionship in dogs.

By assessing the genome of 1,346 dogs across 161 breeds, Heidi Parker, a dog geneticist at the U.S. National Institutes of Health found an evolutionary timeline on how humans bred dogs as per their needs, like herding or guarding. She told The Verge, “Each time we come up with different changes into our own sort of society and the way we live, then there’s room for a new kind of dog, or a new shape, a new size.” The human intervention began to shape dogs as we selectively mated animals for desirable characteristics.

Being the oldest domesticated animals, humans and dogs have the longest shared history. A 2013 study published in Nature Communications proved this is true at the genetic level, too; several groups of genes in humans and dogs evolved in parallel for thousands of years. This includes the genes related to digestion, food, neurological process, and diseases.

It is widely believed that ancient dogs traveled with humans across the Bering Strait, to carry things and defend against predators. But with the arrival of the Europeans with their own dogs, the native American dogs disappeared entirely. Dog geneticist Heidi Parker suggests though that the Peruvian hairless dog, the Xolo, and the American hairless terrier have distinct genetic markers that come from this particular ancestor, even if in traces.

A great illustration of the earliest mutually beneficial relationship between dogs and humans and how it evolved with time is the Samoyed bred by the Samoyede. The Samoyede were nomads who had traveled from Asia to Siberia thousands of years ago. The dogs that traveled with them were the Samoyed, the same breed we know today. These dogs were bred specifically to survive in the harsh conditions and provide warmth huddled in the arctic environment as a single human-dog pack. Gradually as the human tribe turned to herd reindeers instead of hunting them, the dog’s duty also changed from a hunting dog to a herding dog.

The earliest traits for which dogs were selectively bred included hunting, herding, and guarding. Two ancient examples of such dogs are greyhounds and mastiffs. In Egypt, greyhounds were revered as much as the pharaohs and used as hunting animals. Mastiffs, on the other hand, have been around for thousands of years in various civilizations across Egypt, Rome, Greece, Tibet, and China, and include the Tibetan mastiff and Neapolitan mastiff. According to AKC, Julius Caesar was so impressed by the ferocity of the British mastiff on the battlefield in the U.K. in 55 B.C., that he brought some back to Rome to fight human gladiators in the arena.

One of the first breeds to emerge after the domestication of dogs began was the East Asian breed chow chow. Chow chows are protective of their owners and have unusual features like a blue tongue and 44 pairs of teeth instead of 42. It is believed that they were bred from native Chinese dogs around 11,000 to 9,000 years ago at the same time as agriculture began to spread near the Yangtze river. They were associated with the Tang dynasty and said to be bred as guard dogs and hunters. Other breeds that have been identified as the basal lineage closest to wolves are the akita, basenji, and later the progeny of the chow chow—spitz and Pomeranian.

The gradual shift of dog breeds from being hunters and herders to working dogs can again be traced to the cold northern regions with the example of the Siberian husky. This tough breed was originally bred as companion dogs by the Chukchi people. But as life became tougher in the sub-zero conditions, the people needed to travel more, and the dogs toughened up to become sled dogs. The isolation of the community ensured that the breed remained pure and produced tough, winter-ready dogs.

According to AKC, the huskies became legendary during the 1990s when they were used by musher Leonhard Seppala to haul critical medicines to Alaska during a diphtheria epidemic traveling 658 miles in only five and a half days.

Pivotal Russian research led by the geneticist Dmitry Belyayev gave vital indications of how wild animals turned into tame domesticated dogs. The 40-year experiment found that physical traits like floppy ears and curly tails that we associate with friendliness in dogs were actually linked to the genes controlling tameness. In other words, as domestication progressed in dogs through human-defined behavioral traits—at first unconscious and later conscious as the researchers note—it changed many morphological, physiological characters of the dog along with the amenability factor that we sought.

Soon, dogs were being bred based on what humans desired. Cindy Vogels, a breeder-judge from Littleton, Colorado, and an AKC expert adviser gives the example of a terrier from Ireland that once had color variations like blonde, red, and blue. The coat also varied from wavy, straight, and curly. Gradually, three breeds evolved from this original terrier: Irish, Kerry blue, and soft-coated Wheaten terriers. They can be differentiated based on their color and coats. The Labrador retriever color variations of black, brown, and fawn are also the result of a similar practice of breeding based on physical characteristics.

Bulldogs were popular in Britain in the 13th century for bull-baiting when they were turned loose on a staked bull. When bloodsports were banned in the 1830s, according to AKC, the gruesome sport turned into underground dogfighting pits using the same breed. But bulldogs were slow and that is where cross-breeding with terriers began to create bull terriers. The bulldogs’ stability and tenacity were used to create other breeds, too, like the bullmastiff.

More often than not, breeding in human-induced environments has aggravated health issues in different breeds. Deafness has been linked to the same genes that give Dalmatians their spots. Golden retrievers are predisposed to diabetes. Bone conditions in the case of Labrador retrievers and breathing issues in flat-faced dogs like bulldogs and pugs are common. While it is generally assumed that such health issues arose only in pure breeds, mixed breeds also have had negative health impacts owing to their genetic mix. AKC’s Cindy Vogels points to the case of breeding of pointers with Dalmatians that upped the health and life risks instead of reducing them.

Dalmatians were at one time known as carriage dogs because they ran alongside carriages in 17th-century England to ward off any accidents with highwaymen on the road. Their watchfulness and coaching instincts were then used by firefighters with the dogs helping clear out the streets as the fire carriages arrived. As horse carriages became obsolete, their athleticism and sense of humor were honed through selective breeding to turn them into circus dogs in later decades.

Bulldogs, chow chow, retrievers, mastiffs—almost all breeds have changed with time through selective breeding to suit the temperament of the humans they live with and also because of the transformation from nomadic life to apartment dwellings. The evolution of the English cocker spaniel to American cocker spaniel also shows how new breeds came up through successive selective breeding.

With the rise of the elites in every society across the world, a dog also evolved as a status symbol—one that could also be carried easily. While many believe that toy dogs like the Chihuahua and the pug are modern-day fascinations created to accommodate pet lovers with restricted spaces, these are actually ancient breeds. The pug’s history can be traced back to 2,000 years ago in China, while the Chihuahua can be traced to Mexico and to the Aztecs even before that.

What qualifies as a modern toy breed is the miniature American shepherd, a progeny of Australian shepherd, and was recognized as a new breed by AKC in 2015.

The external changes occurring in dog breeds due to selective breeding like color, coat, agility, friendliness, or aloof nature are commonly visible. But research has also shown how the dog brain structure has modified internally because of this isolation of selective traits. Erin Hecht and colleagues through MRI scans of 33 breeds found that variation in brain structure was not just related to the size or shape of a dog. The researcher mapped six varying brain networks that showed variations resulting from at least one behavioral variation in a breed.

A significant development that has occurred in all these decades of selective breeding of dogs is the disappearance of cooperation among the dog clan for food. Per Smithsonian magazine, domestication has made dogs less cooperative than wild wolves. Sarah Marshall-Pescini of the University of Vienna tested dogs and wolves at the Wolf Science Center in Austria. She found that wolves instantly cooperated to get a plate of food tied to a rope but dogs did not. An effect of bonding with humans has been losing their pack lifestyle.

Of the 400 odd dog breeds that have been bred in the last 200 years, there have also been some unusual ones like the catalburun, which is a Turkish pointer with a distinct double nose. Though not known much outside of Turkey, the breed has distant cousins with the same kind of double nose structure—the pachon Navarro and Andean tiger-hound. Needless to say, these remarkable traits are a rarity and might have also been the result of inbreeding over generations, though that is uncertain.

Humans have domesticated a number of animals from horses to cats, fish, and hamsters, but what is it about dogs that makes them become part of the human family so willingly over any other animals? A study by Miho Nagasawa, a researcher at Japan's Azabu University finds that dogs have actually adapted over the course of history to hijack humans' maternal bonding systems. This means, when a dog gazes into your eyes, you are experiencing the same bonding feeling that a mother and a child experience. The researcher found that dogs had increased oxytocin levels when gazing at their owners, and the owners, too, experienced the same oxytocin surge. This kind of interspecies maternal bonding has been found only between dogs and humans over such a vast course of time.