What are several observations which led Charles Darwin to first suggest the theory of evolution by natural selection?

Answer 1

Darwin, however, noticed similarities among species all over the globe, along with variations based on specific locations, leading him to believe that they had gradually evolved from common ancestors.

He came to believe that species survived through a process called "natural selection," where species that successfully adapted to meet the changing requirements of their natural habitat thrived, while those that failed to evolve and reproduce died off.

He wrote about the finches he found on other islands away from the main island, although nearly identical in all other ways to mainland finches, had different beaks. Their beaks had adapted to the type of food they ate in order to fill different niches on the Galapagos Islands. Their isolation on the islands over long periods of time made them undergo speciation.

Answer 2

Some of the observations that led Charles Darwin to suggest the theory of evolution by natural selection were the diversity of traits within species, the variation in populations, the struggle for existence due to limited resources, and the adaptations of organisms to their environment. These observations pointed to the idea that organisms are adapted to their environment through a process of natural selection.