During a trip to the galapagos island, which observation led Charles darwin to suspect that organisms change over time

It was when he observed variations of the same species that led him to the theory of natural selection. The species he came across looked similar to those on the South American Mainland but were also subtly different as well. After he had returned back to England he started to develop the idea that the species from the mainland reached the Galapagos Islands and then changed, adapting to their new environments.