Taxonomically, dogs are classified as Canis familiaris. They are descended from the extinct grey wolf, Canis lupus and likely another wolves, now extinct. This evolution may be overlapping with concurrent evolution from several wolf species according to the project on dog genomes. Although there are varying schools of thought on the evolution of dogs, their genomic typing tells us that they likely began being domesticated around 130, 000 years ago from the now extinct ancestor. There is no distinct point of change from wolves to dogs as their evolution was possibly concurrent and likely hybridized. This was long before the advent of the agrarian human culture around 10,000 years ago.
It is thought that wolves developed a symbiotic relationship with early humans by scavenging the cast-offs of humans. Behavior and survival will always take the easiest route with regards to sustenance. Wolves would have found that garbage of humans too tasty to resist rather than wasting precious energy on a hunt that may or not be successful. In terms of evolution, one must remember that evolution is ongoing. It is the adaptation or mutation of genetic coding. Dogs likely evolved from several different wolf lineages and continue to do so. There are many incidences of wolf remains being found near human habitation sites in England, China, France, Siberia, Asia and throughout the European countries.
In terms of survival, this may be key to the domestication of dogs. The ones who would get closer to human encampments were likely to be rewarded with better meals than their more cautious counter-parts. Operant conditioning is way older than Skinner!
Today, there are more than 150 breeds of dogs, not to mention the mutts and mongrels. If you are wondering, mutts are dogs that you know the mixed ancestry of and mongrels are dogs of unknown ancestry. As for the established dog breeds, they vary in size from 1 pound to 200 pounds. Selective breeding not only changed the outward appearance of the dog but also their temperament and skills. Selective breeding is the method of breeding to achieve the desired traits. This can be size, colour, shape and the specificity of choosing expressed traits of the predation sequence.
Generally, the predation sequence is scenting, tracking, sighting, pursuing, herding, catching, killing and retrieving. Some dogs maintain the entire predation sequence such as terriers whilst others are more specific such as the herding breeds or the retrievers. From working dogs to sporting dogs to lap dogs, they are truly our best friends. We have co-evolved over thousands of years, developing a relationship that is unique and lasting.