After more than a century of argument and discussion, it is now generally agreed that the single progenitor of all domestic dogs, ancient and modern, was the grey wolf, Canis lupus, but when and where domestication first took place is still much argued about. Was the wolf domesticated in one part of the world or in many regions over its huge range covering the Northern Hemisphere, and what exactly constitutes a domestic dog? The word “domestic” means simply “of the home,” so any tamed animal may be said to be domestic, but if the term is to be used as a scientific descriptive it must have a biological definition, and there must be a clear separation between a wild species and its domestic derivative. A domestic dog is not a tamed wolf but is it a separate species?
To paraphrase the most frequently used definition (see e.g. Lawrence, 1995, p. 551): a species is a population of animals that breeds freely and produces fertile offspring. If the hybrid offspring are infertile then the parents are separate species, for example the horse and the donkey. However, many animals that are normally considered to be separate species will interbreed with fertile offspring, as will all the wild species of the genus Canis, these being the wolf, coyote, and the several species of jackal. A more useful definition is the biological species concept which states that, “species are groups of interbreeding natural populations that are reproductively isolated from other such groups” (Mayr, 1966, p. 19). Using this definition, all fully domesticated animals can be classified as separate species from their wild progenitors, from which they are reproductively isolated. The dog is no longer a tamed wolf but, as a result of selective breeding under human control, it has evolved into a new species, named by Linnaeus, Canis familiaris, which by further reproductive isolation and under the influence of both natural and artificial selection produces new breeds (Clutton-Brock, 2012).
Precursors of the dog
With the increasing care and advanced technology used in the excavation of archaeological sites during the second half of the twentieth century, the bones of wolves have been found in association with those of early hominins from as early as the Middle Pleistocene period.