Yet type is not a fixed and immutable characteristic. Genetic drift and mutation within a species is a normal occurrence and such changes have resulted in the development of breeds such as the Rex, Devon and Cornish. Some mutations confer a biological advantage to a species, and in a natural environment that type will eventually predominate. The change in head shape of Siamese clearly demonstrates this. With current debate in the cat and dog world concerning the health and viability of pedigree animals, it is worth considering how such changes develop in more detail.
Few breeders have an image of how the breed changes.
More often than not, it is the show successes of individual cats or dogs that establish a winning type, which is sought by other breeders. Heart problems have been identified in Boxers, umbilical hernias are common in several breeds of dog. Advisory Councils have an important role in monitoring changes in type, temperament and health within their breed. Their duties should not only be to promote show success, but also to maintain some system of ensuring that a breed remains sound. Perhaps breed policy should consider the effects of population in breeding, which will occur when one or more males dominates a generation.