Here's why:

* Definition: Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more successfully than those less adapted.

* Mechanism: It's a continuous and ongoing process, driven by the following factors:

* Variation: Individuals within a population have slight differences in their traits.

* Inheritance: These traits are passed down from parents to offspring.

* Differential Survival and Reproduction: Individuals with traits better suited to the environment are more likely to survive, reproduce, and pass on those traits.

* Outcome: The result of this process is evolution: the gradual change in the genetic makeup of a population over time.

In summary: Natural selection is the process that drives the result of evolution.