As Darwin completed his five year voyage as naturalist aboard the __________, he made numerous observations that influenced his ideas on natural selection. Along the east coast of South America, he noticed that their __________ appeared very similar to the __________ of Africa. However, they could not be related as they belonged to different continents, therefore their similarities must be due to their __________ environments. On the Galapagos Islands, he noticed that marine iguanas were uniquely adapted to their environments with their large __________ to cling to rocks and their __________ snouts to gather algae. Also on the Galapagos Islands, he noticed that while the island __________ were similar in appearance, the size of their __________ differed. Darwin speculated that these species arose from a mainland population. Because of their __________, they developed their own adaptations to their environments.