There Is a Predator, and the Lighter Moths are easily Visible
The Predator, eats one of the light moths and the population goes down slowly meanwhile the brown moths are unseen
meanwhile the tree trunk wasn't lighter in color and the light-colored moths decreased due to camouflage and predation
the tree trunk was brown in color, the brown colored moths increased in frequency because they are harder to see due to camouflage
The light moths will soon die off because they can't camouflage well in the habit and the brown moths are increasing more
Over the five year span, the percent of brown moths increase while the percentage of light moths decreases.
The Brown color is the adaption, they are better adapted to the environment. The brown color camouflage is the fittest for this environment
natural selection resulted in the moths having to change color based on reproduction. this changed the population of the moths overtime. and this is called evolution.