system
Given the following post, respond as if you're commenting on Reddit:
human
How is it that different breeds of Canis lupus familiaris (domesticated dog) can develop to be so different in specific individual populations around the world, yet not be subject to speciation?

Distinct breeds exist that vary in size, shape, and other physical qualities greatly, and have evolved that way in specific populations across the globe. Does the way humans selectively bred the species have something to do with it?
gpt
Dogs have likely only existed as a separate subspecies of Canis lupus for ~ 40,000 yrs at max, which is too short a time for speciation to occur from wolves, much less different breeds of dog, even with geographical or other isolation.  Most dogs are not "purebreds", anyway, so there is little chance for genetic drift. 

Additionally, most breeds the way we think of a dog breed are relatively recent (the last 50 to 200yrs). Breeds are 100% artificial categories, they are not subject to natural selection and the premises of natural selection do not apply.  Dogs have the potential for huge amount of phenotypic variation and few selective pressures which accounts for the wide array of behavior and appearances.  The end result is that genetically similar individuals could end up looking hugely different.