If we are taking Social Darwinism to be the idea of "survival of the fittest" and that there is a weeding out to society, I would say that the incident involving Candy's dog is one such moment. The discussion that precedes the decision is reflective of Social Darwinism. Carlson's fundamental argument is that the dog is "no good" or of no purpose to anyone. Carlson brings up the points that the dog is no good to anyone. Few argue back, and even Candy fails to launch a real adequate defense. Candy cannot avert what is a Social Darwinist argument in that the dog's condition necessitates him being "weeded out." I think that another moment could actually be when George shoots Lennie. The idea of an organism being "unable to support itself" is something that is evident at the end of the novella. Lennie is not going to be able to escape the clutches of the mob led by Curley and Carlson. There will be an inevitable reckoning whereby Lennie is going to be weeded out and in this, George does the only humane thing possible. In a moment where survival is nearly impossible, George does what must be done. It is here where I think that some level of Social Darwinism is most evident.