“Where does man come from” -article talked about Charles Darwin and evolutionary theory. When animals get babies, they are all different. Then, when these babies grow to adulthood and have their own offspring, some of their properties inherited by their descendants.
Animal breeding means that you look for certain properties in animals, and pick those to reproduce. When you keep doing this over decades, all of that species share the same properties. Take always hens that lay largest eggs and little by little, all the eggs of all hens will be larger.
The dog has been bred from wolf. People have domesticated wolves as their pets and most well behaving ones made puppies together and this went on over and over again. This way the current dog breeds were born.