Charles Darwin is the author of On the Origin of Species and the namesake of Darwinism. Darwinism is the name given to the theory of evolution that involves natural selection to determine how animals and plants adapt and change overtime to survive in their environment. Evolution also covers more complex ideas like genetic drift, gene flow, and more. However, natural selection is the main idea taken by Social Darwinist and used for their purposes.

As Darwin put it, natural selection is the "preservation of favourable variations and the rejection of injurious variations." This means that natural selection is the process where living organisms that adapt to their environment tend to survive longer and reproduce more in order to pass on their genetic material to their offspring.

A bit of background on Darwin, he worked as a naturalist on the HMS Beagle which spent time in the Galapagos Islands, South America, and other islands in the Pacific Ocean. He had detailed notebooks about the plants and animals that he observed. The findings from this voyage helped him to come up with the theory of evolution that we know today.

If you are interested in reading more about this topic, then click on the hyperlinks imbedded in the text. They will take you to open source versions of Darwin's book On the Origin of Species. You can find other publications by Darwin and more on him as a person at Darwin Online.