In rare circumstances, though, the mutation can be beneficial. Mutations are a mechanism for how species evolve. For example, suppose a mutation in an animal’s DNA causes the loss of an enzyme that makes a dark pigment in the animal’s skin. If the population of animals has moved to a light colored environment, the animals with the mutant gene would have a lighter skin color and be better camouflaged. So in this case, the mutation is beneficial.
Peppered Moths are normally white with black speckles across the wings. This patterning makes it well camouflaged against the light colored trees found in their environment. Some  Peppered Moths however have almost completely black wings and are normally not as well camouflaged. During the Industrial Revolution trees in urban areas were made so black from soot that the darker moths were better camouflaged.
Prior to the Industrial Revolution which moth was least likely to reproduce?