The modern British Bulldog is a Molosser breed, which has been taken far away from its original form. Wynn wrote in his 1886 book that the Bulldog and the English Mastiff evidently had arisen from a common origin. Hugh Dalziel wrote in 1889 that the Mastiff and the Bulldog have the same origin, and tells us that the reason to believe this is the characteristics they still have in common despite so many years of being bred in different directions. The Bulldog from the medieval times to the 1800s was clearly constructed to be used at bullfights, as his name Bull-dog shows. Some say that the Pug, most likely together with the Mastiff, is the foundation of the Bulldog, but we're not so sure of that being true. The Mastiff and other large Molossers were not suited to be pitted against the bull. Therefore, they used the Bulldog, whom with his large head, moves the center of gravity nearer the axis of rotation. When the Bulldog would grab onto the bull's nose, he had a firm grip.

Why is it impossible that the Pug is the ancestor to the Bulldog? Because bull-baiting originated in 1204 and the Pug was first imported from Asia in the mid to late 16th century. The British did not use large Mastiff to fight bulls from 1209 to the 16th century. Smaller and faster dogs were much better suited. It does not make sense either, to cross the already existing bull-fighters, whether it is Mastiffs or Bulldog, with the small Pug that can hardly protect itself. It may have been crossed at one time or another with the Bulldog, but most likely that was after bull-baiting became illegal in 1835.

The muzzle of the Bulldog changed radically over just 45 years. The question is: Is this possible without help from another breed? The Pug has the muzzle needed to produce the Bulldog's changes. Some say that the Bulldog was never a bigger dog, and that the size of the Bulldog today is what they have always been. All old illustrations and descriptions prove that they are wrong. Even today, there is born "throwbacks" of the Bulldog, with a too long muzzle or too long legs. This indicates how the breed looked before the modern-type was bred. Breeders in the 1800's imported Spanish Bulldogs into England and used them in their breeding program. The Bulldog Club of England was, however, founded to prevent the infusion of the Spanish Bulldog blood.

When bull-baiting became illegal in 1835, the Bulldog lost their work and would probably have died out without the transforming to a pet-dog. The aggressive and agile bull-baiters were replaced with a friendlier, but less functional version of the same dog. As a result of this, the modern Bulldogs have lots of medical problems. The aggressive nature was bred out of the former pit fighter, creating a loving family member, although still stubborn and single-minded.