Final answer:
Charles Darwin observed different-shaped beaks among Galapagos finch species, attributing the variation to adaptations for specialized feeding strategies. This differentiation is an example of adaptive radiation.
Step-by-step explanation:
The species of finches that Charles Darwin found on the Galapagos Islands exhibited different structural adaptations, one of which was the different-shaped beaks. Darwin noted that the particular shape of each bird's beak was well-suited to their niche and food source. For instance, some finches developed large, strong beaks to break open hard seeds, while others had long, narrow beaks adapted for eating small seeds or reaching into flowers for nectar. Darwin's observations led him to suggest that the beaks of the finches had evolved through natural selection, based on the food resources available in their specific habitats on the islands. This is a classic example of adaptive radiation, where a single ancestral species diversifies into several species, each with adaptations suited to different environmental niches.