A repost from August 2005.
The morphological variation within dogs is pretty extreme.
The picture, above, is of an English Bulldog, a breed with such an overlarge head that almost 100% of all dogs are born caesarian.
This is a breed that would be extinct in 10 years were it not for the regular intervention of veterinarians.
Most people do not realize that almost all dog species, as we know them today, are very recent creations.
In the last 1790s, a farmer by the name of Robert Bakewell realized that by separating males from females -- made easy by the rising number of enclosed fields -- a farmer could choose which stock was allowed to breed. By deliberately inbreeding livestock, and selecting for desirable traits, Bakewell rapidly created new and "improved" breeds of sheep and transformed modern agriculture forever. Bakewell's experiments with sheep quickly spilled over into other farm stock, such as cattle, pigs, and chickens, and eventually into pet stock such as dogs and pigeons.
In 1800, there were only 15 designated breeds of dogs, but by 1865 that number had grown to more than 50 and it exploded fantastically over the course of the next 60 years as Victorian-era dog breeders produced a dizzying array of dogs, most with invented histories and elaborate (and entirely fictional) rationales for their taxonomic differences. To see how rapidly the shape of the Bull Terrier was changed by the Kennel Club show ring >> click here.
Border Collie Skull (above)
Dachshund Skull (above)
Pug Skull (above)
Poodle Skull (above)
Saint Bernard Skull (above)