Final answer:
Darwin's observations of finch beak variation and tortoise shell shapes on the Galápagos Islands directly contributed to his theory of natural selection, where adaptive traits become more prominent in a population over time. Subsequent research by the Grants supported this theory by documenting changes in finch beak sizes due to environmental conditions, illustrating the heritable aspect of beneficial adaptations.
Step-by-step explanation:
The birds that Charles Darwin observed on the Galápagos Islands played a crucial role in the development of his theory of evolution by natural selection. The finches on each island had beak shapes uniquely adapted to the type of food available in their specific environment. For instance, finches that fed on large seeds developed large, strong beaks to crack them open, while those that fed on small seeds had smaller beaks suited for extracting these seeds. The observation that finch beaks and the giant tortoises' shell shapes were well-matched with their respective environments led Darwin to hypothesize the mechanism of natural selection, where traits beneficial for survival in an environment become more common in successive generations.
Darwin's insight was that species could change over time because individuals with traits better suited to their environment would survive and reproduce more effectively. This process would lead to the accumulation of advantageous traits within the population over generations. The later research by Peter and Rosemary Grant, which documented the change in beak sizes of Galápagos finches in response to environmental conditions further supported Darwin's theory. This foundational concept introduced the idea that such adaptations are inherited and that this process leads to the evolution of species.