Selecting for different traits over hundreds of years of breeding has caused different dog breeds to have distinctive characteristics. (Dog breeds from left to right: top row- Alaskan Malamute, Basset Hound, Llasa Apsa; middle row- Beagle puppy, Shar Pei, Chow; bottom row- Pekinese, Tibetan Terrier, Pug.) Click on image for full size (122) Courtesy of Corel

Dog Breeds: An Example of Artificial Selection

Darwin developed his theory in part because of his study of how dogs and pigeons were bred. He knew several breeders of dogs and asked them how they selected certain traits. According to the American Kennel Club, there are over 150 different dog breeds, from tiny Chihuahuas to giant Great Danes, but they are the same species (Canis familiaris) and all are descendants of wolves.

• A species is a group of individuals that can reproduce with one another, producing offspring that are able to reproduce.
• A breed is a group of domestic animals within a species whose appearance has been determined by artificial selection over many generations. An individual of one breed will be able to successfully reproduce with an individual of another breed, but both breeds’ distinctive characteristics can be lost, this makes a mixed breed animal.

Breeders taught Darwin how they selected certain characteristics and how they ensured that those characteristics made it into the next generation. That’s how different dog breeds are made. If a breeder wanted a dog with a curly coat, he or she would allow curly-coated dogs to breed and not allow them to breed with straight-coated dogs. In nature, the most well-adapted animals are more likely to survive and reproduce, but in dog breeding, the dogs with the desirable characteristics are allowed to reproduce by the breeders.