To define what is meant by a dog breed is a little problematical, because this is not in any way a natural distinction; we deal here not with Nature but with the will of Man. Indeed, the whole concept of breeds as we know them is probably a relatively recent notion that only really began to gain headway in the nineteenth century.

The idea probably began as a way to describe what we now call a "landrace," which is a geographical population of animals, often kept by a distinct ethnic group of people, for a particular purpose. Insofar as the individuals of such a landrace were recognisable as a group just from their distinct appearance, people from outside the region began to think of them as a "race" of animals -- what we now term a breed.

To understand properly the present-day concept of a dog breed, it may help to consider a couple examples of populations that might sometimes be thought of as breeds, but that are no such thing. "Labradoodles" might have a distinct (and silly) name, but they are not a breed; they are the fruit of crossbreeding between two breeds, the Labrador Retriever and the Poodle. "Alaskan huskies" are quite often thought of as a breed, but they are not; an Alaskan husky is a dog purpose-bred for dogsled racing (typically) but with no particular requirements for its ancestry or its physical appearance.

From the two preceding examples we can perhaps begin to see what the requirements are for a distinguishable dog breed. A breed must have a recognisable physical appearance (it is defined by typology). It must have a particular purpose -- even if the purpose is only to be a household pet or a showdog. Finally, it must come from a particular definite ancestral group (defined by ancestry); this requirement is known technically as the "pedigree barrier" by cynologists. If a canine population has all three of these defining characteristics, either it is a breed, or else it could easily become one. And when an existing breed is weak on any one of these three axes, that weakens its identity and its status as a breed.