RANDOM VS DETERMINISTIC EVOLUTION. “At its core, evolution involves a profound tension between random and deterministic processes. Natural selection works systematically to adapt populations to their prevailing environments. However, selection requires heritable variation generated by random mutation, and even beneficial mutations may be lost by random drift. Moreover, random and deterministic processes become intertwined over time such that future alternatives may be contingent on the prior history of an evolving population.”
http://www.pnas.org/content/105/23/7899.full