Final answer:
The beetle population will adapt over time through natural selection by shifting towards individuals with darker coloration, which allows them to blend in better and avoid predators.
Step-by-step explanation:
Natural selection is a process by which organisms in a population develop traits that allow them to survive and reproduce. In the case of beetles, if the tree trunks they hide on become darker due to pollution, the beetles with darker coloration will be more likely to survive because they can blend in better and avoid predators. Over time, the population of beetles will shift towards individuals with darker coloration, as they have a higher chance of survival. This is an example of adaptation through natural selection.