Here's why:

* Natural selection is the process where organisms with traits better suited to their environment survive and reproduce more successfully, passing those advantageous traits to their offspring.

* Random mutations are changes in an organism's DNA that occur by chance. While they are the source of new genetic variations, they are not directly responsible for the selection of those variations.

Here are the factors that do contribute to natural selection:

* Variation: Organisms within a population have different traits.

* Inheritance: Traits are passed down from parents to offspring.

* Overproduction: Organisms produce more offspring than the environment can support.

* Differential survival and reproduction: Organisms with traits better suited to their environment are more likely to survive and reproduce.

In short, mutations provide the raw material for natural selection, but it's the environment that determines which mutations are favored.