Social Darwinism is the application of Darwin's "survival of the fittest" theory, which, when applied to the social landscape, discourages the reproduction of those deemed to be undesirable to the future of human development. Undesirables included those that were too weak, ill, poor or in some other way perceived as having traits that would hurt society as a whole, in terms of survival, if passed on to offspring. Social Darwinism is also closely linked to eugenics.
Social Darwinism posits that biology is destiny, and came about as a direct result of Darwin's Theory of Evolution, which seemed to show that species did change due to natural selection. The study and greater understanding of genetics has essentially undermined social Darwinism over the years, but during the 19th century, the concept gained increasing popularity. At that time, it was thought that by removing biological elements that were seen as weak, humanity continue to evolve in the right way.
Although there have been many arguments to the contrary, it is believed that Darwin himself believed in social Darwinism. This is certainly an unfortunate and difficult view to accept given his huge contribution to science. However, many lessons were learned as a result of social Darwinism, in particular, how dangerous such views can be. As such, rigorous moral and ethical guidelines were put in place with regard to the application and research of genetics in modern science.