> Dog breeding is just a euphemism for eugenics.... Give me ~12,000 years and I'm willing to bet I can give you a breed of super intelligent humans (Border Collies) and a breed dumb dumbs (Bulldogs).

Of course it is a euphemism, but 12 millennia is not enough. First of all dogs can breed at about a year while humans need about 12X the time. Though that alone isn't as bad as you might think; most of the modern breeds are very modern -- less than a couple of hundred years old. And even if you look at older photographs of dogs you'll see that they have changed a lot recently.

However that reflects the second, larger problem, which is that Canidae exhibit an extraordinarily high degree of phenotypic plasticity. You would have a hard time adapting any animal to the degree exhibited by dogs. All our modern food and working plants and animals have been subject to human selection but none show anything close to the degree of specialization that dogs do. Not even parasites; the closest I know if is lice (e.g. pediculus humanus capitis vs pthirus pubis) or the influenza virus.