I'll get you started here, gorski. (Here, I extend the definition so that it does not just include humans. There is no reason to limit the discussion to human society when so many other animals live in societies.)
Social Darwinism is the idea that the mechanism of natural selection outlined in Darwinism can be used to explain the way that societies of social animals develop, who thrives within those societies and who does not.
In its very narrowest sense, it can be taken to be a truism - those maladapted to survive in a given society are unlikely to reproduce, and so to pass on any traits that have their basis in genetics. This isn't really 'social Darwinism' as such, it's just simple Darwinism. One's evolutionary fitness includes one's ability to exist alongside one's conspecifics. Extended wider, its historical usage has been either as a justification for pre-existing power relations within human societies or as a guide to how to manipulate societies in order to improve them.
Scientifically, this wider usage is nonsense - in most instances where it is applied, insufficient generations have passed for such relations to be explained in any way at all by genetics; this is a simple case of looking in the wrong place for an answer. Politically, it is invariably hateful, bashing the poor. And nobody, absolutely nobody, on this thread or the last (with the possible exception of gorski himself!) has even hinted at thinking along these lines.
