Final answer:
The finches with beak adaptations allowing them to eat large seeds are an example of genetic variation, which is crucial for natural selection to occur and drive evolutionary changes within the population.
Step-by-step explanation:
The subset of finches capable of eating large seeds exemplifies genetic variation, which is a requirement of natural selection. The variation in beak sizes among Darwin's finches that allows different individuals to eat seeds of various sizes is essential to the process of natural selection. In a given environmental context, some of these traits provide advantages that lead to greater reproductive success compared to others, gradually shifting the population's traits over time.
When finches with larger beaks have better access to large seeds, they are more likely to survive and reproduce, passing on the genes associated with larger beak size. Conversely, when smaller seeds are more abundant, finches with smaller beaks have a reproductive advantage. This ongoing process demonstrates how selective pressures can lead to a change in the distribution of traits within a population, a fundamental aspect of adaptive evolution.