Things don't evolve by chance alone! Natural selection, the key to evolution, is not a random chance process. The environment applies very specific pressures. In that way, Mother Nature selects for certain characteristics. In a desert, for example, certain strategies for plant survival are favored while others are selected against. Since major environments often last a long time, their effect on evolving life is not random. In the desert, the edge goes to plants with better and better adaptations for reproducing despite the heat and lack of water.

Mutations may be thought of as random, but mutations are not the same thing as evolution. They merely enrich the gene pool whose diversity natural selection acts upon one major consequence of the constraint of gradualis.