This is what can potentially happen from just one dog. We've used our dog Jools who we adopted from the Pound when she was 6 years old as an example because we've often thought about what happened to all of her offspring. Jools was a well loved dog (an old man's little jewel), but she waited at the Pound for four months because no-one wanted her.
What happens if Jools and her descendants have only one the litter each. Many people want their dog to have one litter and when I was young and idealistic I did too, just the one litter after all. But, now I wonder what happened to all the puppies and what misery did I cause?