There are over 150 breeds registered with the American Kennel Club, and that doesn't include all breeds in the world. The count is up to over 600 with the new designer breeds such as Labradoodle.
Your pure bred dog isn't as pure as you would like to think. I like to explain it this way. There are "man made" dogs and "God made".
The Boxer "man made" dog was developed in Germany in the 19th century. The Boxer's ancestors were two German mastiff type dogs, the Bullenbeiszer and the Barenbeiszer. They were later crossed with the powerful ancestors of the Mastiff and Bulldog.
The Pharaoh Hound "God made"dog. The Pharaoh hound is one of the oldest domesticated dog breeds in the world. The breed is estimated to have originated around 3000 BC.
Most breeds serve a purpose as a working dog such as retrievers, catch dogs, hounds, guard dogs.. These dogs were bred for a specific job and there for generally have a need to "work".
That is why not all breeds are meant for family type settings. That doesn't mean your family couldn't or shouldn't own a working dog it means to provide the appropriate life and to meet your dogs needs you need to understand what they were bred for.