Final answer:
Darwin's finches exemplify adaptive radiation where they evolved different beak shapes to utilize diverse food sources across the Galápagos Islands, confirmed by the Grants' long-term research showing natural selection affecting beak size.
Step-by-step explanation:
Darwin's finches are a classic example of adaptive radiation, a process where organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches. Initially descended from a common ancestor, these finches dispersed across the Galápagos Islands, facing different environmental conditions on each island. Natural selection, driven by the availability of different types of food sources, like seeds and insects, led to variations in finch beak shapes, sizes, and strengths. This diverse beak morphology is perfectly adapted to their specific dietary needs, exemplified in the finches' ability to use their beaks to consume a variety of food types - from cracking hard seeds to extracting insects.
One of the most compelling pieces of evidence for this adaptative process comes from the work of Peter and Rosemary Grant. They documented how certain weather conditions, like those brought by El Niño, favored finches with beaks better suited to the available food source. These conditions led to measurable changes in beak size within finch populations over time, showcasing natural selection in action.