* The Galapagos Finches: These birds, with their diverse beak shapes adapted to different food sources, were a key inspiration for Darwin's theory of evolution by natural selection. He noted how the finches on different islands had different beaks, leading him to hypothesize that these variations were driven by the need to adapt to different environments and food sources.
* Barnacles: While less glamorous than the finches, Darwin's meticulous study of barnacles for eight years was instrumental in developing his understanding of evolution and adaptation. He meticulously documented the complex anatomy and life cycles of these marine creatures, demonstrating how they adapted to different environments. This work strengthened his belief in the gradual nature of evolution and the importance of studying seemingly insignificant organisms.