In addition to that, it's certainly not a 'glitch'. A genetic glitch would be a (possibly short-lived) mutation which is still in the 'beta' phase, so to speak,

In addition to that, it's certainly not a 'glitch'. A genetic glitch would be a (possibly short-lived) mutation which is still in the 'beta' phase, so to speak, or else a harmful side effect of an otherwise beneficial mutation (e.g. albinism). This is a paradigmatic example of an ordinary useful mutation which persisted because it increased fitness.