Rath on 22 November 2009
If humans stopped interfering dogs would return to a single form over a relatively short period of time. They are still the same species, this is because they are essentially spread over the same range and are able (and willing) to mate with each other and produce viable offspring.
The German Shepard x Chihuahua problem is easily solved by them mating with intermediate dogs.
The only barrier to their reproduction is humanity, which is an artificial barrier.
