Final answer:
The finches observed by Darwin on the Galapagos shared a common ancestor; their diverse beak shapes were examples of adaptations to different food sources on the islands.
Step-by-step explanation:
Among the finches that Charles Darwin observed on the Galapagos Islands, the correct answer to the question is B) Shared a common ancestor. The finches are a prime example of adaptive radiation, where a single species gives rise to multiple species that exploit different ecological niches. Darwin noted that the finches had beaks of varying shapes and sizes, which were well-suited to the specific food sources available on each island. This observation led him to the idea of natural selection, where organisms with traits better suited to their environment are more likely to survive and reproduce. For example, finches that ate seeds had thicker, stronger beaks for cracking them open, whereas finches that ate insects had thinner, more pointed beaks for capturing them. These birds did not all behave the same way, have the same beak shapes, or sing the same kind of song, but they were all descended from a common ancestor that had likely dispersed from the mainland.