The randomness of mutation has confused many people, since it implies that evolution also is random. (If evolution is random, how can exquisite adaptations be explained?) The trick lies in recognizing the difference between the source of variation—where the raw material necessary for evolution comes from—and what happens to this variation once it is there. Natural selection is anything but random. It’s no accident that weapons performing poorly are culled, while those performing well are retained and expanded. Given sufficient time and enough variation to work with, natural selection will push the evolution of weapons in directions that are anything but random. Consequently, new mutations infusing genetic variations into biological systems is random, but the evolution that subsequently unfolds in those populations very often is not.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 889