>>14244355Selective breeding.
You can inseminate and breed a dog in about 15 months. That will give you a litter of genetically distinct puppies. Then you can breed the smallest dogs and puppies with eachother. In 25 years you can breed 20 generations of dogs, which is significant.
You aren't necessarily looking for gene mutations - just different expressions of basic latent genes that already exist in the dog's gene pool, like those that determine size. If you were trying to develop a new organ from scratch, you'd need a much larger time scale and a good source of radiation to introduce mutations.
