Don,
Oh, where to start?
Approximately 150 years ago, an english hunting parson, the Rev. John Russell, developed a breed of terrier that would enter the fox's den and either drive the fox out or engage it. This took a tremendous amount of courage from a dog about 10-15 lbs. in weight.
Over the years, Jack Russells have hunted everything from foxes to badgers to raccoon to groundhogs, etc. There is a whole world of Jack Russell hunting enthusiasts out there and the breed has garnered a place in both the English Kennel Clubs and the American Kennel Club.
There are numerous books about the breed and the Internet possesses literally thousands (1,000's) of websites devoted to this unique little working terrier. Energy, alertness and courage are typical traits.
This is only the tip of the iceberg, if you wish to know more - please research the Internet or write me at rooson@earthlink.net
Take care,
RB