Evolution is the change in traits inherited across successive generations. One of the ways this occurs is through natural selection, which helps to accentuate and spread those traits that favor survival and reproduction. Although Charles Darwin didn’t realize it at the time, this is what he saw in the islands’ differing flora and fauna, and in the finches that—although similar in size—exhibited important distinctions in the shape and size of their beaks.
The famous voyage of the Beagle took Charles Darwin around the world as an unpaid companion to captain Robert Fitzroy, allowing him to explore some of the Galapagos’ most isolated locations. Darwin knew almost intuitively that there was something special about the Galapagos Islands as evidenced by an observation he wrote about evolution prior to arriving: “if there is the slightest foundation for it, the zoology of the Galapagos will be well worth examining.”
On September 15, 1835, the Beagle docked on San Cristobal Island and spent the following five weeks travelling to different islands in the archipelago. While on Santiago Island, it was brought to his attention the great differences among giant tortoises that existed from island to island, and on Floreana, he found the mockingbirds differed to those he had observed on San Cristobal.
These were the observations that became the foundation for his theory of evolution, and that led to the publication in 1859 of On the Origin of Species, the book that eventually paved the way for the acceptance of evolution.