Over successive generations, moths develop spots that resemble eyes on their wings that scare off predators. this characteristic would be a

In this example of evolutionary development, we can see a selective advantage.
Developing of new characteristics, in this case, the spots on moth's wings is a part of the process of adaptation of organisms to their environment.
The new characteristics are acquired through mutations and natural selection filters the ones that are the most beneficial for the holder.
For example, a  mutation which results in moths having shorter wings is disadvantageous, because it makes the individual who possesses it less likely to survive and reproduce.
On the other hand, developing of spots that resemble eyes can be advantageous, since it enables the holder of the trait to be more successful and more likely to leave offspring.