I'm mostly comfortable with thinking it's evolution as crazy variety and selective breeding came very late to the party. Most in the last few hundred years - lots of the breeds we know are from the 17th, 18th and 19th centuries.
I would guess that for most of our co-existence breeding was up to the dog to figure out, which might explain the oldest breeds being of a particular region. Task breeds came very much later.
Edit: Also, how do you selectively breed for muscles that didn't previously exist?
I would guess that for most of our co-existence breeding was up to the dog to figure out, which might explain the oldest breeds being of a particular region. Task breeds came very much later.
Edit: Also, how do you selectively breed for muscles that didn't previously exist?