Since as early as 15,000 years ago, humans have played a part in the species differentiation between dogs and wolves. Dogs, or canis familiaris was the first species to be domesticated, at least several thousands years before any other animal or plant species (Leonard, Vila and Wayne). From centuries of selective breeding more than 400 distinct breeds of dogs have been produced that differ greatly in morphology (form and structure, such as body size, coat length and color), behavior, and disease susceptibility. (Parker, Sutter, and Ostrander). The holding of dog shows and the later establishment of the kennel clubs in Britain, America, and France in the late 19th and early 20th century have had a generative effect on pedigree dog breeding and showing throughout the world (Sampson and Binns). These breeds have developed not from natural selection, but from selection by humans for various uses in different societies, leading to different proclivities for certain behaviors like retrieving, herding, and guarding, between breeds. Natural selection and geographic separation may have also contributed to genetic differentiation, resulting in additional breeds. Even within a breed exists variability between individual dogs in their suitability as pets or working dogs, which reflects the heterogenic background of dog breeds (Giger, Sargan, & McNiegel).