These mutations occurred separately among millions of individuals over millions of generations.
Why? Until Prestin is produced, there is absolutely nothing for Natural Selection to select and conserve, so why would the required mutations accrue over generations?
Unless you're going to rely on that old stand-by Genetic Drift (aka Dumb Luck) which seems to be (in the evolutionists's mind, at least) capable of overcoming the most prohibitive odds.
"Often a cold shudder has run through me, and I have asked myself whether I may have not devoted myself to a fantasy." Charles Darwin