Original sentence: According to the "Four Foundations" theory, the evolution of the horse ultimately produced horses of four basic body types, adapted to different environments.Beginning with the domestication of the horse, horses of different body types were and still are cross bred until a desired characteristic is achieved and breeds true, at which point the type is declared a breed or a purebred.Certain horse breeds, such as the Andalusian horse and the [{Arabian horse]], are claimed by afficionados of the respective breeds to be ancient, near-pure descendants from one or the other of the original four wild prototypes, though absent a full mapping of the horse genome and other DNA research, such claims are difficult to prove or disprove.Written and oral histories of various animals or pedigrees of certain types of horses have been kept throughout history, though breed registry stud books trace only to about the 13th century
Edited sentence: Horses were and are cross bred until a desired characteristic is achieved and then that type is declared a breed or a purebred.In simplistic terms, the Thoroughbred is a larger version of the Arabian and the Quarter Horse is a stockier version of the Thoroughbred.Some horse enthusiasts will assert that the only purebred horse is the Arabian, but this is not so.The Arabian horse is a combination and an evolution of horse breeding through the ages and is a very refined breed which has influenced virtually every modern breed