Final answer:
The heritability of variation in traits among Darwin's finches is sometimes observed (Option C).
Step-by-step explanation:
The finches likely dispersed from one parent species and natural selection based on different food sources in differing habitats led to adaptive changes, notably in the different beak shapes of the finch species, each suited to a different food type.
It is essential to recognize that there is inherited variation in traits within a species, as this variation is a cornerstone of natural selection. Without such variation, evolution through natural selection would not be possible. Darwin saw that the beak shape of the finches varied and speculated that it had adapted over time to help the finches acquire different types of food. The work of Peter and Rosemary Grant with the Galápagos finches illustrates this concept, as they found that changes in beak shape were heritable and could lead to evolutionary changes in the population.
Therefore, the finches exhibited different traits that were passed down through generations, sometimes resulting in adaptations to their environment. The heritability of certain traits, such as beak size, is highlighted by the Grants' observation that during certain environmental pressures like El Niño events, finches with certain beak shapes were more likely to survive and reproduce, passing on those traits to the next generation.
Thus, the correct option is C.