So I am a raving evolutionist who happens to believe that the Bible can also be historically true. If I put a sequence of letters in a computer, a fast computer, and allow the locations to be mutated. And if I only allow 4 letters in the game, A,T,C,G, then any sequence I start with can be mutated to any sequence I want. If mutation is really random the computer can mimick it. There is no limit.
Lets do it simply.
There are only 256 different possibilities. DNA is merely a sequence. Some sequences do not allow a living being to survive. But as long as there is a path through the sequence space from one sequence to another in which all sequences allow a living being to exist and reproduce, then mutation can move from one species to another. Considering that a new phylum was found two years ago, would suggest that this may not be the case.