I once asked a libertarian his thoughts on what we should do with those that are unable to be productive in our economic system, and he uttered, without hesitation, natural selection. This response no doubt aroused anger in me, but I too have shared similar sentiments. When we are thriving and committed to self-interest, then empathy is an empty word until we need it from others.
The libertarian’s comment, however, was a curious one since this system has not worked in his favor, and I would not say that he was thriving but rather surviving. I would like to explore the topic of how anyone, including myself, could be attracted to the ugly in libertarianism by looking at our personality differences and the logic that we use. Here though I want to talk about social Darwinism.
My understanding of evolutionary theory is that it is about change over time that results in life adapting to its environment. The idea of “survival of the fittest” is a term coined not by Darwin but by a political theorist named Herbert Spencer. When seeing how it has been metaphorized, however, I think there is little room to doubt that libertarians are using this because it fits their personality.
Darwinianism was misleadingly metaphorized in terms of “competition,” a competitive struggle for scarce resources in which only the strong and cunning emerge victorious, garnering the goods necessary for life and happiness. 
Libertarians, however, are conflating natural with artificial selection. The mechanism that explains our adaptations is natural selection, which means that some individuals possessed traits that others didn’t that allowed them to reproduce and survive more successfully. It is artificial selection when we construct our system based on self-interest at the exclusion of other adaptations.
For example, our moral emotions that involve sympathy and empathy evolved to assist with cooperation. These have a tendency of being looked at as weaknesses within our system since this leads to dependency or even solidarity. But if we disparage adaptations involved in cooperating, then it is no longer “natural” since we are being influenced by the social norms that we have created.
I took a random sample from a search on “capitalism and evolution” and had no difficulty in finding so-called experts on the idea that capitalism is a form of natural selection, but no serious evolutionary biologist believes this. Below this individual claims that it is moral to weed out the weak and that laziness is a choice, where the former idea is callous and the latter one borders on absurd.
Having gov’t provided safety nets means that even the most destructive, racist, lazy people will receive help automatically. They should face the consequences of their life choices…It may seem harsh to want only the “fit” to survive. I think ignorance, laziness and various other irresponsible attributes/behaviours should die a painful death.
I don’t think that he is irrational because his logic works for his worldview, nor do I think that he is not smart but rather has personality characteristics and past experiences that make him attracted to the idea of “survival of the fittest”. He seems uninformed on human nature and biology though and should probably stick with teaching Math at his highschool.
Just because we construct an economic system in which we have to compete to make a living, one in which self-interest triumphs and sympathy is akin to weakness, this does not mean that life is a competitive struggle for survival. Evolution has no direction, and we have every right to use our moral emotions just as much as our self-interest. That is, the following is not a law of nature.
The normative implication is that the social order, in every domain, is naturally and optimally governed by principles of competitive self-interest and that anything that interferes with that is unnatural and immoral. 
On the other hand, if our guiding principle in our lives is based on maximizing self-efficacy and self-interest, then life will be a competitive struggle for survival. If we put productivity and innovation on the higher moral ground at the cost of the well-being of those that can’t keep up, then we are seriously fooling ourselves into believing that we are building a better society.
That said, there are parallels between natural selection and our competitive behavior within free-markets; in fact, natural selection may track economic behavior better than the “invisible hand” . But this explains it at the behavioral level, and we can’t assume that all behaviors are adaptive. If we want to go further, then we must appeal to evolutionary psychology, in which I am on the fence.
 Coyne, Jerry A.. Why Evolution Is True. Penguin Publishing Group.
 Frank, Robert H. The Darwin Economy. Princeton University Press.
 Frank, Robert H. The Darwin Economy – Why Smith’s Invisible Hand Breaks Down. fs.com
 Frank, Robert H. The Invisible Hand, Trumped by Darwin? newyorktimes.com
 Gittins, Ross. Darwinian model of economics flawed for firms. SMH.com
 Lakoff, George. Philosophy In The Flesh.
 Meyer, Christopher, and Kirby, Julia. Runaway Capitalism. Harvard Business Review.
 Ridley, Matt. What Charles Darwin Owes Adam Smith. Learn Liberty.
 Vugt, Van Mark. Why the Invisible Hand from Biology is Better Than the Invisible Hand from Economics. evonomics.com.
 Wilson, David Sloan. This View of Life. Knopf Doubleday Publishing Group.