Cross Breeding
Professional breeder's who choose only the best lines.
There are no two dogs that are good for breeding, they all are, it just depends what you want the end result to be.
Selective breeding for particular traits
Dogs devolved from wolves, and are a separate family in the animal category. In the wild, there is little speciation (as compared to the wild cats say), but their genome seems to be capable of great breeding selection, as evidenced by today's many varieties.
All current types of dog were wild dogs in the distant past. Dog breeding by humans have altered the original dogs appearance to the dogs around today.
They are maintained by reputable breeder's who love a certain breed and produce high quality stock from good blood lines.
Actually vise versa, all dogs alive today are descendants of the wolf. 10,000+ years of selective breeding and domestication have turned the wolf into the dogs we know today.
no certain dog breed HAS to be bow legged. it is all genetics. any dog could have bow legs. like it or not, there is no fix but better breeding... bow leggedness is often a result of poor breeding such as breeding two sibling dogs together, which often results in diseases and bow leggedness.
Dogs can get sick and die.
Separate them
yeah
is dog breeding an example of natural selection