The Origin of Species is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology. Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. It presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. Darwin included evidence that he had gathered on the Beagle expedition in the and his subsequent findings from research, correspondence, and experimentation. Darwin's aims were twofold: to show that species had not been separately created, and to show that natural selection had been the chief agent of change.