How has Darwinism affected American ideologies? How does it relate to government, education, and literature today?

There are really two broad kinds of "Darwinism" we must consider here.

The first is the scientific theory of evolution by Darwinian natural selection. This theory is absolutely unassailable. It is one of the most brilliant, predictive, and well-supported scientific theories ever devised. This kind of "Darwinism" forms the foundation of biology, neuroscience, and psychology as we know it, and a growing movement among economists seeks to apply it to economics as well. In this sense, it is Darwinism that tells us the nature of what it is to be human and our place in the web of life and the cosmos itself.

The second is the social ideology of Social Darwinism. This is an ideology that emerged in the early 20th century which sought to use the theory of Darwinian evolution to justify various social policies, nearly all of them slanted toward rich White males just as social policies had been slanted toward rich White males for centuries prior. Pseudoscientific theories were devised to justify starving the poor, oppressing women, and discriminating against racial minorities. Some of these theories even contributed to the ideology of "racial superiority" that the Nazis used to rationalize the Holocaust.

It is my personal opinion that Darwinism in the scientific sense actually contributed very little to Social Darwinism. Most of the oppressive and discriminatory policies were similar to those already in place, and simply sought new "scientific" (pseudoscientific) justifications. It is unfortunate that a shallow reading of concepts like "survival of the fittest" can be used in this way, but it isn't really the fault of Darwin or evolutionary biology that a deep and powerful scientific truth can be abused by those in power to oppress others.