Charles Darwin, English naturalist, 1874.

Charles Darwin (1809-82) English naturalist. Cartoon, depicting Darwin's head superimposed on an ape's body, showing another ape its reflection in a mirror, a reaction to views put forward in The Descent of Man, his work on human evolution first published in 1871. Darwin (1809-1882) was employed as naturalist on HMS Beagle from 1831-1836. He first made his name as a geologist, but is remembered for his momentous contributions to biology - primarily his demonstration that evolution has occurred and his discovery of the principle of natural selection of heritable variation as the cause of evolution. His famous book Origin of Species was published in 1859. (Photo by Ann Ronan Pictures/Print Collector/Getty Images)