If one of the effects of a genetic mutation makes a substantial contribution to the survival of the species, then, and only then, will that mutation be favored in natural selection
This process is subject to one proviso, namely that the traits that were not favored, yet were carried along by a trait that was favored, must not be so negative as to annul the benefits of having the new, favored trait
A genetic mutation whose effects are all neutral to a species is favored in natural selection.