Color enhanced portrait of Charles Robert Darwin (1809-1882), English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection. His seminal works: On the Origin of Species (1859) his theory with compelling evidence for evolution. The Descent of Man (1871) he examined human evolution and sexual selection and The Expression of the Emotions in Man and Animals (1872) one of the most enduring contributions from 19th century psychology.