D
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. If the statements above are true, each of the following could be true EXCEPT:
A: A species possesses a trait whose effects are all neutral for the survival of that species.
B: A species possesses a trait that reduces the species' survival potential.
C: All the effects of some genetic mutations contribute substantially to the survival of a species.
D: A genetic mutation whose effects are all neutral to a species is favored in natural selection.