Three of Darwin's observations on galapago islands?

Answer 1

Darwin in the Galapagos Islands

Three of Darwin's observations on the plants and animals of the Galapagos Islands contributed to his realization that species are not immutable, specially created forms. First, he saw that closely related populations on nearby islands vary in appearance, as he explained in The Voyage of the Beagle1: "My attention was first thoroughly aroused, by comparing together ... the mocking-thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifasciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham Islands ... belonged to M. melanotis."

Second, Darwin noted that the inhabitants of an island usually have close affinities with forms on the adjacent continent, rather than with species occupying similar environments elsewhere in the world. This seemed to suggest that they were not created independently1: "It is probable that the islands of the Cape de Verd group resemble, in all their physical conditions, far more closely the Galapagos Islands, than these latter physically resemble the coast of America, yet the aboriginal inhabitants of the two groups are totally unlike; those of the Cape de Verd Islands bearing the impress of Africa, as the inhabitants of the Galapagos Archipelago are stamped with that of America."

Third, after returning to England, Darwin was informed by the ornithologist John Gould that many of the bird species in the Galapagos Islands that seemed to belong to different families were, in fact, all related members of a single family, previously unknown to science - and now known as Darwin's finches. Darwin quickly realized the implications of such phenotypic and ecological diversity1: "Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken and modified for different ends."

Answer 2

1. Variation in species: Darwin noticed that each island had unique species that were similar to those on the mainland yet had adapted to their specific island environments.
2. Adaptive radiation: He observed various species had evolved to fill different ecological niches on the islands, leading to the development of diverse forms.
3. Geographical isolation: The isolated nature of the islands allowed for species to evolve separately from their mainland counterparts, leading to the development of distinct adaptations.