Darwin thought that the plants and animals of the Galapagos Islands were similar to those of the nearby coast of South America because
A) their ancestors had migrated from South America to the Galapagos Islands.
B) other scientists in South America had written about similar species
C) the island organisms had the same nucleotide sequences in their DNA as the mainland organisms.
D) he found fossils, proving that the animals and plants had common ancestors
The correct response is A. The popular idea during the time of Darwin's research was that all of the living things were exactly the way they were throughout history and that Earth was only a few thousand years old. When Darwin traveled to South America, he encountered many fossils that resembled animals of his time, and yet, were different in terms of size and modifications. He reasoned that they must be an earlier version of the animals that existed in his time. He reasoned that living things had ancestors that they descended from. When he explored the Galapagos, this idea as well as the fact that the animals he encountered were different from those on the mainland in Equador, and yet had similarities, helped formulate his ideas about Natural Selection. An example is the Darwin finches. He reasoned that ancestral finches from the South America migrated to the Galapagos and over time, and due to different environmental pressures on the different islands, many species arose due to Natural Selection.