But evolution does not start from scratch every time. A closer analogy might be playing the slot machines, but every time BAR comes up, it stays in the window and only the non-BAR drums roll. Eventually, you can be assured of making all BARS.
Better check your analogy Junior, casinos rely on some probabilities to stay in business. When you roll a pair of dice, one of them stops before the other.
I did not say every time.However, it does start from scratch when it comes to creating an entirely new gene. New genes are always necessary for macro-evolution. In fact whole sets of new genes are required to give an organism new faculties. These new genes start from nothing, and until they provide a new faculty that can be tested by "survival of the fittest" are just useless DNA. Therefore the many different random mutations required to achieve the proper sequencing of the new gene cannot be helped by selection.