[inquest]

The ones closest to wild dogs will be the most likely to survive and breed.

But their descendants will continue to revert, will they not?

There is nothing inconsistent with domestic animals being the result of both selective breeding and mutation.

I didn't say there was. What I was wondering was whether the changes that happen on a timescale necessary to introduce new breeds can realistically come about entirely through mutations, or if they necessarily come about mostly through other factors that might alter the genotype.

[js1138]

What do you mean by mostly? Living thing things differ in their tolerance or variation and mutation. Some species are so tightly wound up that small variations are fatal. Dogs are very plastic, both in the amount of variation carried in recessive traits, and in their tolerance for mutation.

Domestic dogs are even more plastic because they don't have to feed themselves and have medical care. When the welfare system abandons them, most will die or fail to breed. The ones with the fewest handicapping traits will have the most offspring.