Eugenics is the term created by Sir Francis Galton to describe natural selection in application to humans. He suggested that the human race could be improved by selective breeding. Common tools for eugenics include things such as segregation, mass murder, and involuntary sterilization. There are many examples of this happening throughout history in all different parts of the world.
A good documentary to watch about this is The Eugenics Crusade.
The idea of survival of the fittest put into an economic context. During the Industrial Revolution in America, Herbert Spencer introduced the idea of survival of the fittest to a type of capitalism known as laissez faire. Laissez-Faire a French term that means to not interfere with someone else's affairs. When applied to the context of capitalism, this is a system of government that is as uninvolved in the economic side of things as possible with few regulations.
One of Darwin's concepts related to evolution. The concept of survival of the fittest was added into the 5th edition of On the Origin of Species, in chapter IV. Natural Selection, or the Survival of the Fittest. In the text it describes Natural Selection and Survival of the Fittest to be the same thing. The text also goes on to say that it is the "preservation of favourable variations, and the destruction of injurious variations." A more general idea behind survival of the fittest is that those who are weak die and those who are strong and can adapt will survive to reproduce. Survival of the fittest was later applied to other context like social and economic situations.
This is the deliberate killing of groups of people or entire nations. This is linked to the idea of eugenics which is usually the driving force behind genocides of groups of people. There are plenty of examples of this throughout history and throughout different parts of the world.
On the Origin of Species is Darwin's book where he presented the ideas of evolution and natural selection to the world. It was the first book to fully articulate the theory of evolution. Darwin-online.org has several editions of On the Origin of Species on their website. The first edition covered major topics such as variation (natural and domestic), natural selection, difficulties in the theory of descent, instinct, hybrids, and more.
Creationists look at the Christian Bible for the account of how the world was created. They don't believe in the evolution theory, but instead believe that God created everything. They take the chapter of Genesis in the Bible literally, and believe it happened exactly as written.
For more information: Creationism by Michael Ruse
Social Darwinism has led to some more extreme ideas that have hurt groups of people in the past. The practices that Social Darwinism bred such as involuntary sterilization and eugenics are the most to blame for the idea of unfit or inferior groups. Examples of groups that were regularly targeted as "unfit" by people who thought they were "fit" include homosexuals, individuals with mental illnesses or disabilities, the poor, minorities, immigrants, and many other groups.
Class stratification is a specific means of social stratification. This is the practice of society separating groups of people based on social class standing, and it effects who had resources and power. There are groups or classes who have power and those who do not. Typically the rich were in higher power than the poor. This was justified by the idea of survival of the fittest used by Social Darwinism and Laissez-Faire Capitalism. It was considered natural that groups of people or people in different social classes were not equal because those with the resources were simply considered more fit.
This idea ties back to the ideas of Laissez-Faire Capitalism, survival of the fittest, and class stratification. In these systems, those who had more wealth and power were more successful and considered more fit.
Social Darwinism was used a lot as a justification for ideas behind imperialism, colonialism, and generally racist policies. The main argument was that the groups doing these things were helping others to become "civilized" in their definition of the term. This means that they were imposing their own culture, values, and/or religion on other groups.
During the Gilded Age, 1870s-1900, there was a lot of change happening in America. There was an economic and industrial boom in America at the time.
People in positions of power at the time like Andrew Carnegie started looking at things like Social Darwinism to justify their success. It also allowed them to justify not helping those in need at the time because of the idea of survival of the fittest. It made those in power, like Carnegie, feel like they were more fit than those who were not, such as immigrants, poor, or mentally ill persons.
Racial and ethnic features, such as head shape, were used as "evidence" that some groups of people were "less evolved" than others. It was said that some groups were closer to the common ancestor than other groups on the timeline, and that made them inferior. This idea was used to encourage eugenic policies.
Forced and involuntary, these sterilizations were a type of eugenics. This happened to Americans, mostly done to immigrants, people who were mentally ill, and the poor. It was usually done without consent of the person being operated on, and they did not have knowledge of it happening until after the procedures. The idea behind the practice was that they were going to prevent traits that were undesirable from being passed down. A large number of states in America adopted laws to allow forced sterilization during the early parts of the 20th century.
Natural Selection is the "preservation of favourable variations and the rejection of injurious variations" according to Darwin. In simpler terms, 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. This is one part of the much larger process of evolution.