Darwin decided it was possible for a species to change from one form and develop into another over time. This led him to the notion that all life forms were not fixed, but continuously changing or evolving. The other part of the theory was that living things weren't the result of many separate creations, but of long, intertwining biological histories. His general idea was that amongst a family of plants or animals, individual members carried hereditary traits. These traits would be general to the individual's family, but not the species. It was these traits that could give the members a better chance of survival and means by which to reproduce. This was what Darwin called "natural selection" or "survival of the fittest." According to the theory, those individuals with slightly better adaptations would get more food, be healthier, live longer and, most importantly, have more mates. As time progressed, traits would become more obvious; therefore later generations would be more defined and, possibly after thousands of generations, form new species.
Although Darwin did not address human evolution in his book, some of his followers began to incorporate his ideas on natural selection into the inequality of society. Basically, they took Darwin's theory of natural selection, which was intended to apply only to selection through genetic variability, and applied it to selection between human groups differentiated by culture alone. The concept, referred to as social Darwinism, embraced all efforts to apply Darwinian biology and evolution to human society. Through the years, social Darwinism became widely popular and was used to justify predatory capitalism, social classes, racial prejudices, and imperialism.
One of the many social Darwinists was a man named William Graham Sumner. In his lectures and writings, Sumner became one of the leading proponents of laissez-faire economics and social Darwinism, opposing all government efforts to regulate business or to combat social inequality.
In his book, That it is Not Wicked to Be Rich, Sumner spoke of social classes in the United States. He argued that social existence was a competitive struggle among individuals possessing different natural capacities and traits. Overall, those with better traits succeeded, becoming wealthy and powerful, while those lacking in inner discipline or intelligence sank into poverty. He felt that people who were poor we born to be that way, and they could do nothing about. Because of this, Sumner was against government assistance of any kind.
As you can see, Charles Darwin's theory of natural selection was a risky thing to reveal in a time when society was looking for answers to the many hardships it faced. The social Darwinists, including William Graham Sumner, twisted Darwin's theory into explaining the inequality of society, along with many other societal problems. Although Darwin never encouraged this interpretation of his ideas, it is interesting to see how so many people devoted their lives to such an unworthy cause.