"Evolution is a biological process, civilization is a conceptual one."
But I repeat that one drives the other. If populations with preponderate genetic traits like intellegence, creativity, even temperament etc. are more likely to develop a civilized culture - then having that population replace by a more barbaric population will negatively impact that societies civilization AND their gene pool.
My point was that the repetition of this process throughout history has resulted in a sort of de-evolution of the species. Replacing more cooperative and civilized societies with increasingly competitve, aggressive, amoral and greedy ones. Granted that sociological factors may be an even stronger influence such as mass emotion and thought manipulation by the mass media - but that doesn't deny the genetic component.