The concept of a neutral network is particularly illuminating. Neutral networks loosen the requirements on the mutation rate for selection to remain effective. What needs to be preserved in a population is not a particular sequence, but rather a shape. Yet it is deeply enabling, because it permits evolutionary change to occur by allowing the sequence context to vary silently until a single point mutation can become phenotypically consequential.
Neutrality also influences predictability of adaptive trajectories in seemingly contradictory ways.
On the one hand it increases the uncertainty of their genotypic trace. At the same time neutrality structures the access from one shape to another, thereby inducing a topology among RNA shapes which permits a distinction between continuous and discontinuous shape transformations. To the extent that adaptive trajectories must undergo such transformations, their phenotypic trace becomes more predictable.