To answer the question, we need to consider how the population of mice may be influenced over time. Given that a hawk is hunting the mice, the most relevant factors include the benefits and consequences of predation.
The overall changes in the population of mice can be best explained by natural selection, as the hawk's hunting behavior is a form of predation that can impact the survival and reproduction of the mice, selecting against certain traits and influencing the overall population dynamics.
Thus, the correct response is:
natural selection.