* Individuals don't evolve: Natural selection acts on existing variations within a population. An individual organism's genes remain the same throughout its life.

* Selection acts on traits: Natural selection favors individuals with traits that make them better suited to their environment. These traits are encoded in genes.

* Changes in gene frequency: Over time, the frequency of advantageous genes increases in the population, while the frequency of less advantageous genes decreases. This change in gene frequency across generations is what constitutes evolution.

* Differential reproduction: Individuals with advantageous traits are more likely to survive, reproduce, and pass on their genes. This differential reproduction is the driving force behind natural selection.

In essence, natural selection doesn't change an individual; it changes the makeup of a population by favoring the survival and reproduction of individuals with advantageous traits.