Final answer:
Biologists Peter and Rosemary Grant discovered the rapid evolution of finches on Daphne Major, providing observable evidence for Darwin's theory of natural selection.
Step-by-step explanation:
The Grants discovered rapid evolution by natural selection among the finches on Daphne Major, a small island in the Galápagos archipelago. Over the course of more than 30 years, they meticulously documented changes in finch populations, noting how beak sizes and shapes evolved as environmental conditions on the island fluctuated. This research related directly to Darwin's work on evolution and natural selection. Charles Darwin had observed variations among Galápagos finches during the Voyage of the Beagle, which led him to formulate his theory of evolution by natural selection. The Grants' findings provided contemporary, observable evidence for this process, reinforcing and expanding upon Darwin's foundational ideas.