I've been reading "Why Does My Dog?" recently and I found
this passage pretty interesting:

"If you took the offspring of two different breeds and mated
them with the offspring of two more breeds, then repeated
this procedure again and again, before long -- except for its
size -- the dog would start to revert to type. The ears would
be erect, the tail carried low, and the animal would become
far more independent and not as easily trained. The type
to which it is reverting is the wolf..."

Par...