English Bulldogs are my personal poster child for how breeding for appearance rather than ability ruins dogs.
The below section in quotes is all taken directly from http://bandogmastiffs.blogspot.com/
"Three varieties of “ Alauntz ” are mentioned in The Mayster of Game, written in the fourteen century: “ The which men clepyn Alauntz gentil. Other there byn that men clepyn Alauntz ventreres. Other byn Alauntz of the bocherie.”
The first variety is so “gentil ” that Edmund de Langley, in giving a list of the animals which it would attack, mentions oxen, sheep and swine, “ or to men or to other hounds, for men have seen Alauntz sle her mayster.”
Evidently a nice pet to leave with the children. This variety was shaped like a “ greyhounde ” except the head, “ which shuld be greet and short.”
The second and third varieties were evidently more heavily built, and “ Thei holde fast of here nature.”
They were used for bull-baiting and boar-hunting in company with greyhounds.
Edmund de Langley alludes to mastiffs in addition, but it is fairly clear that they and bulldogs descend from the same parent strain.
In old pictures of bull- and bear-baiting the dogs shown are like small, active mastiffs. They were magnificent specimens physically and, necessarily, brave to a fault.
The shows did the dogs more harm than the bulls, bears of Bill Sikes. Lest I be accused of prejudice, I will quote the Natural History Museum : “ Other characteristics are the short, wide skull, the small loins and hind limbs and the strength of the forequarters. These features are exaggerated in the present breed, which is useless for fighting. The skull for instance (as shown by the specimen in the table case), is so broad and underhung as to be a monstrosity, while the outward bending of the legs is excessive.”
It may be noted that the specimen alluded to (a show champion whelped in 1901) is far less of a monstrosity than present-day champions.
The present-day bulldog is born old ; he is a wheezy amiable creature, useless for any purpose, but, usually still retains the indomitable courage of his ancestors.
Doubtless, if a club were formed to revive the old breed it could be done. It would only be necessary to pick out and breed from the least deformed puppies produced by parents themselves not too inbred.
The rapidity with which dogs will throw back to ancestral and natural type is proved by the Brancaster Basset hounds Q. V.
I have been accused by no less a person than the secretary of the London Bulldog Society: he said that I had tried to discredit the National Dog.
I replied that my regret was that the national dog is extinct, or almost so, and has been replaced by a useless, wheezing monstrosity. Underslinging of chassis may improve motor-cars, but it does not improve dogs."
Additionally: (all from bulldoginformation.com) Most English Bulldogs are delivered via cesarean section due to the bitch's small hips and birth canal as compared to the large heads of the pups. "Most Bulldogs cannot successfully consummate a mating without assistance[...] If natural breeding is chosen, the bulldog will need assistance and even the natural breeding will have to be planned, guided and supervised more carefully than with any other dog breed, for a variety of reasons. One of the problems with natural breeding is that the morphology of the bulldog does not allow the stud to easily mount the bitch." I don't think Mother Nature can speak much louder than that.