English naturalist and geologist Charles Darwin first published On the Origin of Species in 1859. The idea of evolution and that all earth's species have descended from a common ancestor had already been around for some time. What was new about Darwin's work was that it found a way to explain evolution using a theory called natural selection. This claimed that species change in small ways, gradually, over long periods of time; the individuals who happen to be best suited to their environment survive, and live to produce lots of offspring. Darwin's theory explained why everything in our world is a perfect fit - without God necessarily pulling the strings. The ideas contained in the Origin of Species changed the thinking of much of the world.
Victorian society was outraged at the idea that God had not created life in a perfect form. The Church thought it would lead to people's faith in God crumbling - and even today, there are some religious groups who do not accept Darwin's idea that all life evolves.