Genetically, domestic cats are far less variable than domestic dogs. For example, the range in the size of domestic dogs is far greater than that of domestic cats. There is an historical reason for this. Dogs have been required to carry out a wide variety of tasks in their partnership with mankind for up to 20,000 years compared to about 10,000 years of domestication for domestic cats. The many utility roles that domestic dogs have been involved in must include: hunting partners, fighting dogs, dogs of war, guard dogs, retrievers, setters, pointers, terriers, sight-hounds, scent-hounds, racers, herders and lap dogs.
For around 10,000 years, the domestic cat had one utility role and it still applies in some households today, namely, as a pest-controller. However, the usual role for domestic cats nowadays is to be an entertaining and reliable companion. As a good rodent-destroyer the domestic cat already had the anatomy to carry out that task highly efficiently. There was no need to evolve a different anatomy or for breeders to make anatomical modifications. The domestic cat is a supreme carnivore and the domestic ancestor of the North African wildcat which is a highly efficient, specialised Hunter. There was therefore no pressure to change its shape.
The only issue for the domestic cat was to become less shy because the North African wildcat is a shy, secretive animal. In general, people want a confident cat able to interact freely and be lap cats. Therefore, over the eons, people selected individuals who were more confident with humans and friendly but also more juvenile in their behaviour even when adult. This allowed the cat to become a perpetual kitten towards its new human companion while at the same time remain a committed predator towards rodents.
The last stage in modification of the domestic cat was to change its coat in terms of colours and markings. Over thousands of years the domestic cat became a companion of many coats and colours.
P.S. Cat breeders have created a range of cat sizes from the Maine Coon (the largest) to the Singapura (the smallest) but the differences are small compared to dogs and purebred cats are relatively rare compared to dogs which are more commonly dog breeds rather than radom bred.
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