Genetics follows the environment

Quantaq Magazine describes a puzzle, how does evolution select from the nearly infinite arrangement of possibilities?

Mathematical Simplicity May Drive Evolution’s Speed

Take the octopus, how did it evolve? The answer lies in a change in their  niche in the environment.  Snails got blown into the ocean and eventually become octopus, but it is the ocean that prunes the decision tree, the ocean is not the snail's natural habitat.  So major portions of the decision tree get pruned, especially the fact that the ocean rapidly depreciated the value of the shell, greatly simplifying matter.  But in the process, evolution left the arms to evolve quite naturally into whatever fit the environment. After cutting off a major branch of the gene set, the residual is unrestricted in the new niche and the first workable mutation takes over, yielding a random, but workable organism.