A Dog looks like Dogs because they are dogs!
Every dog looks different.
Most exotic breeds of dogs : Grey Hound Chihuahua Labrador German Shephard Pug Dashund Pomeranian Doberman Dalmatian Chow Chow Brussels Griffon Shih tzu Other: Golden Retriever Alaskan Malimute...
You can buy a dog at a humane society or a pet store. I would not suggest purchasing a dog at a pet store because many of these dogs come from Puppymills. You don't really know what type of facility...
Er... because that's how they were made? Evolution.