Final answer:
Darwin observed that finch species have different beak shapes that reflect their adaptation to different food sources in their habitats, which is an example of natural selection and adaptive radiation.
Step-by-step explanation:
Charles Darwin observed that finches' beak shapes were specialized according to their unique environments. The variations in beak shape amongst finch species can be attributed to natural selection based on different food sources available in their differing habitats. This adaptation is evidenced in the different beak shapes of the finch species, each of which is suited to a different food type.
For example, the seed-eating birds have thicker, stronger beaks which are well-suited to break hard nuts, while the nectar-eating birds have long beaks tailored for reaching into flowers to extract nectar, and the insect-eating birds have beak shapes that are efficient for stabbing and impaling insects. Darwin's finches are a classic example of adaptive radiation in an archipelago, showcasing how change in the genetic variation for beaks in response to the availability of diverse food sources can lead to the evolution of different beaks suited to specific food sources.