Darwinism "is the doctrine that all living things are biological descendants of common ancestors that have been modified by unguided variations and natural selection." 
It is named for the nineteenth century English naturalist Charles Darwin, who held that natural selection in combination with random mutation is the directive or creative force of evolution.
The theory of natural selection is one of two major evolutionary theories advanced by Darwin, the other being the theory of descent with modification.
A popular documentary, Expelled: No Intelligence Allowed, aptly described how Adolf Hitler followed Darwin's ideas to their logical conclusion: the wholesale slaughter of millions of people.
The modern version of the theory of evolution, based on Darwin's original theory, is sometimes called "Neo-Darwinism".