Having a deep interest in both dogs and evolutionary biology (I failed Creation 101 in university), I recently started thinking about the evolution of the dog. There is much variation within the species, Canis familiaris (i.e., there is a huge number of dog breeds and yet all belong to the same species). Studies suggest that the wolf ancestors of dogs diverged from other wolves around 100,000 years ago, and that domestication occurred sometime around 15,000 years ago. Studies of mitochondrial DNA date the evolution of humans at around 150,000 years ago. It is easy to imagine that dogs (or their ancestors) have been with us, evolved right along with us, for many thousands of years. Not only did we contribute to their evolution (especially recently), but they may have shaped a part of ours.
Though it may be difficult to train a Yorkshire Terrier to herd a flock of sheep, he is still constrained by his genes to behave like a dog. An English Bulldog may be constrained by his stature (and a lack of a thick coat) to pull a sled in the Arctic, though this (or similar) behaviour may still be elegantly encoded in his genes.
Recent DNA analysis has led to the identification of 14 ancient dog breeds, excluding a few breeds previously thought to be the most ancient. While some of these dogs exhibit a phenotype (physical appearance essentially) that is similar to wild dogs (i.e., wolves), I was shocked to see a few of the smaller breeds included in this group of 14. I'm not shocked to see this breed on the list:
The Siberian Husky.
But this one?
The Shi Tzu: an ancient breed. Incredible.
This very fact underscores my long-standing view that 1) these dogs are constrained by their genes (and look how far back the Shih Tzu goes!), and 2) their genetic similarities require us (pet owners) to treat them as equals.