Final answer:
Darwin's observations of finches with various beak shapes and tortoises with different shell shapes on the Galapagos Islands contributed to his theory of evolution through natural selection.
Step-by-step explanation:
Charles Darwin's observations on the Galapagos Islands were fundamental in forming his Theory of Evolution by natural selection. Notably, Darwin observed that the Galapagos finches had a wide variety of beak shapes which correlated with their feeding habits and specific island habitats. Furthermore, he noticed that the Galapagos tortoises varied in shell shape from island to island, which suggested adaptation to different environments. These observations led Darwin to propose that species originate through a process of adaptation to their surroundings, and that over time these adaptations can lead to the formation of new species.