For centuries inbreeding has been used to refine traits in dogs, making desired traits more hereditary and thereby, different breeds have been invented. Breed standards have been written for each of these breeds, describing in detail the different characteristics of each breed. When humans start to choose which animal to breed from, so called artificial selection, taste is put before function and the laws of nature, the natural selection, cease to apply. During this development, pedigree dogs have gone towards more and more extreme exterior characteristics and the dogs may have inherited various, more or less, severe problems for example compromised vision, impaired ability to move and difficulties to breathe. However they can still survive and reproduce because humans provide them with the conditions to do so.