Well, you done read up on Social Darwinism. Very good. Wish more folks around here would do some research.
Social Darwinism isn't really "evolution", though. Evolution requires that an entity (as we shall generalize) be manifested through some kind of property of inheritance. Where the offspring of two entities share the genetic information from both parents.
In SD, there are no "entities" that correspond to animals, no genetic code that determines the expressing of social behavior, and no shaping of future social behavior according to inheritance in the strict sense.
On the other side of the coin, we have social behavior that differs from culture to culture. But rarely does social behavior come about because of the "merger" of two parent cultures with anything resembling inheritance. Social behavior changes because of war, poverty, invasion, massive catastrophes, sudden wealth, military expansion, changes of climate, technological inventions, and the like.
SD went the way of the Dodo largely because it just wasn't possible to build a plausible model of SD based on "evolution". Sure, culture "changes" but not in the well-defined, constrained, genetic way that life changes. That, and because SD was used to justify some seriously badass cultures in the not-too-distant past.
There is an element of "natural selection" in SD, however, and I suppose that's what keeps SD from reappearing every so often. But then we see cultures that appear to have negative social (and individual) value actually thriving and amassing huge throngs of believers.

Go figger.
My vote is that Social Darwinism doesn't rate as a "science". Not yet. Maybe not ever.