Answer:
Darwin observed that finches in the Galápagos Islands had different beak shapes which slightly varied among nearby islands
Darwin observed that tortoises in the Galápagos Islands belonged to the same species, although they were slightly different on each island
Step-by-step explanation:
Darwin's observations as described above enable him to develop his theory of natural selection. Darwin thought that species could change over time to adapt to their environments and suggested that new species could originate from similar species. Darwin observed that individuals in a given population exhibited variations and they proposed that these variations could be accumulated gradually over long time periods. Then, Darwin proposed his theory of natural selection to attempt to explain these observations: individuals whose variations gives them an adaptive advantage to survive in their environments have more chances to reproduce, thereby these individuals will have more representatives in the next generations. Subsequently, the accumulation of gradual changes (variations) will lead to new species being formed.