Darwin’s theory of evolution

a) his experiences on the voyage of the Beagle

During his trip, Darwin remarks in regard to the similarity of Galápagos wildlife to that on the South American continent, "The circumstance would be explained, according to the views of some authors, by saying that the creative power had acted according to the same law over a wide area".

Darwin notes the gradations in size of the beaks of species of finches, suspects that species "are confined to different islands", "But there is not space in this work, to enter into this curious subject."

b) Lyell’s Principles of Geology

Lyell’s Principles of Geology attempts to explain the former changes of the Earth's surface, by reference to causes now in operation. The main point was that the present is the key to the past; in other words, that geological remains from the distant past can, and should, be explained by reference to geological processes now in operation and thus directly observable.

c) Malthus’s essay about populations

The therory presented in this essay suggested that growing population rates would contribute to a rising supply of labour that would inevitably lower wages. In essence, Malthus feared that continued population growth would lend itself to poverty. OVERALL, this theory lead to the development of the theory of natural selection by Darwin.