There are some candidates for the most powerful idea in the history of science and humanities. Nicolaus Copernicus’ heliocentric view of Earth’s place in the universe is certainly one, as is Einstein’s theory of relativity. However, for the breadth of its application and the impact it has had on modern civilization, it would be hard to beat the theory of evolution by natural selection of Charles Darwin (1809-1882).
Up to Darwin On the origin of the species was published in 1859, it was difficult to see how the natural world could have been anything other than designed. The important point here is its complexity. As William Paley argued, it seems almost unimaginable that something as complex and highly worked as the human eye could have emerged purely by natural mechanisms. The eye just seems too precisely specified to be anything other than the creation of an intelligent entity (by which just about everyone means God). The importance of Darwin is that he showed exactly how this kind of “design” could have happened without a designer.
Darwin was influenced by Thomas Malthus’ famous population essay, in which Malthus argued that a population’s ability to sustain itself tends not to keep pace with its rate of growth. The lesson Darwin drew from this is that the living world is necessarily deeply competitive (“red beak and claw”, as one of his disciples would say later). Life is characterized by a struggle for existence – or, more accurately, for reproduction – since any species will tend to produce more individuals than it can support. It was this intuition that led Darwin to his theory of evolution by natural selection.