Final answer:
Charles Darwin returned with 32 finch specimens collected from the Galápagos Islands; these finches had diversified through adaptive radiation, with each species evolving unique beak structures and other features to adapt to specific island habitats.
Step-by-step explanation:
The correct answer to the question is B. 32 specimens of finches that Darwin returned with from his journey aboard the HMS Beagle. These specimens were crucial in his development of the theory of natural selection. During Darwin's exploration of the Galápagos Islands, he observed 13 different types of finches, with variations in beak structure, body form, and plumage, that had diversified from a common ancestor through a process known as adaptive radiation. This concept refers to the evolution of various species from a single ancestor, due to adaptation to different environmental pressures, such as available food sources or habitats.
Adaptive radiation is exemplified by the finches Darwin studied. As they dispersed across different islands with varying conditions, they evolved distinct characteristics suited to their specific niches. For instance, one bird had a large beak to crack open large seeds, while another could extract small seeds from confined spaces, illustrating how the finches diversified based on the food resources available on each island.