Dogs original jobs

Question
I'm currently researching for a book on dogs.

While watching the Westminster Kennel Club dog show, I noticed that they usually discussed the breed's former occupation (examples: The Bulldog was a bait dog, to bait a bull for the matador; The Dalmatian walked beneath a carriage, maybe for protection?; and one dog even went down holes to get badgers.)

Since most of the dogs were breed for different activities than how they're used today, could a dog be retrained to perform the activities of their past?  

Thank you,
Nancy

Answer
Absolutely and it is still being done.  The Earth dog trials for terriers is training for what they were meant to do.
The Alaskan sled dog races are the same.  The field trials for sporting dogs are also going with the heritage.  It is easier to train them for what they were meant to do that what they weren't meant to do.
Nancy