Watch the dancing done by Darwinians in explaining the role of natural selection in the preservation of gene sequences and explaining the changes allowed in those preserved areas(the "same" areas as those in mice and men)in fish.
Suppose it doesn't require selection? If selection were the cause of stability, we would see wobble around a central island of stability.
More likely, conservation is a central tendency, and conserved fragments will be found in a normal distribution of sizes.
That is just my hunch, not the theory of a biologist.