A question was floated on JU not too long ago about why left wing atheists who believe in evolution don't believe in social Darwinism. First, the question is filled with assumptions and generalizations about the people in question (possibly a symptom of a well baited lefty trap). Here I will try to answer the question as best as I can.
Simply put, they are two vastly different concepts. Evolution is the theory (as in scientific theory, not the hunch of evolution, but I digress) where random genetic mutations occur, and in a state of nature, those with positive effects allow the creature to have a better chance of survival, and therefore a better chance of passing these mutations onto its offspring. In the long run, these mutations will become commonplace, and presto, we have evolution.
Social Darwinism, on the other hand, is little more than an attempt to apply Darwin's theories where they don't apply. The basic theory is that those who die in society are the stupid/inferior ones (say, Sudanese, Ethiopians, or simply poor black people), and those who don't die are the ones who are superior and need to live and keep the inferior genes out.
Here's the main problem, though. Social Darwinism ignores socioeconomic factors, and doesn't realize that we are not living in a state of nature. Simply put, you are probably more likely to be disadvantaged because of socioeconomic factors (say, growing up as a poor minority in an area with a lot of crime). Also, by using Social Darwinism to attempt to justify cuts to aid to disaster-stricken areas (such as Sudan or Ethiopia), you are saying that the reason why people are starving in Ethiopia is because they are inferior, ignoring the fact that Ethiopia ain't exactly the most arable land in the world, and the reason people are getting killed in Sudan is because they are genetically inferior, not that the people doing the killing have a hell of a lot more guns. Can someone please explain to me why having a lot of AK-47s makes the militias in Sudan genetically superior to the people they kill?
Sadly, this kind of thought is becoming commonplace (perhaps I should say again. We all remember what happened when this kind of thinking took hold in Germany), and usually leads down the dark path of racism. If you look around, you see a disproportionate number of minorities in the lower class. Then the train of thought follows: black people are slightly genetically different from white people, a lot of black people are poor, therefore white people are genetically superior to black people. Of course, this train of thought ignores the years of oppression, which we are only now beginning to end. Is it not possible that it will take a few generations for things to even out?
Social Darwinism is little more than the not quite fully thought out theory that racists, imperialists and far-righters use to convince morons that they are right and have "science" backing them up. It's time to put this idiocy to rest.