Researchers have identified the origin of cattle, horses, pigs, sheep, camels, ducks, chickens, cats and goats. But the genesis of the domestic dog, our oldest companion and the most varied, numerous and widely distributed domestic animal on the globe? We’re still trying to figure out that one.
The study of patterns of diversity is called systematics, and it is a critical subdivision of evolutionary biology. Systematics researchers (earlier called naturalists and taxonomists) sort out species’ genealogical relationships and estimate the points at which populations diverged from one another. Traditionally, they relied on observations of differences in stable physical traits like teeth, skulls and sometimes fossils. More recently, genome-wide comparisons have been used to provide detailed information about species relationships, including the question of when and where wolves became dogs.
Canis lupus familiaris exhibits the most variability in shape, size, behavior and temperament of any mammal species living on earth. About one billion dogs, a population larger than any other domestic subspecies, roam the globe. Canine fossils, some dating to as long ago as 36,000 years, are found on every continent except Antarctica.
Add to that the unusual phenomenon that extreme variation can occur in as little as one generation—a sort of evolution at hyper speed—and we begin to understand why classifying domestic dogs has challenged many of the taxonomical systems that have been used to make sense of Canidae, a family that includes wolves, jackals, foxes and dogs.
Historically, as far back as the fourth century BCE, theories of the descent of animals were the product of using philosophical approaches to relate organic life to the history of time. At first, fundamental ideas about species-change involved sorting out living beings by means of their common essential properties. Philosophers wanted to know how organic life forms were related, not where they came from.
The Greek philosopher Aristotle (384–322 BCE) endorsed the idea that natural beings were always here and always would be. He commented on the dog’s origin, not in respect to the animal’s continuous chronological past but rather, in terms of breed creation. In his view, the dog that nature created was bred to the fox to make small dogs and to bears to make big ones, perhaps making the point that breeds (although he was mistaken about cross-species hybridization) were created by humans. Still, in the Aristotelian view, dogs always existed.
As time went on, the earliest naturalists came to understand that species were related in more complicated ways, and began to devise orderly classification systems. The bigger picture of life, however, was explained within a theological context: a specific act of an omnipotent creator transformed all living things whole and complete. The revolutionary notion that every animal might not be a singular divine creation didn’t materialize until the late Middle Ages, a contradiction that had to be explored hypothetically to avoid conflict with religious doctrine.
In the late 18th century, France’s leading naturalist and the father of paleontology, Georges Cuvier (1769–1832), introduced a new way of looking at life and death. Although he was firmly in the camp of divine creationism, he theorized that animals eventually went extinct.
Earlier, 16th-century English cleric Edward Topsell (1572–1625), author of The History of Four-footed Beasts, whose worldview was defined by fire-and-brimstone religion, based his categories on morality. This was not as much of a stretch as it might seem from today’s vantage point; during Topsell’s time, people had real reason to fear wolves. For them, the predatory wolf and sagacious, noble dog provided excellent examples of two moral extremes.