Here's a breakdown:

* Natural selection is a key mechanism of evolution. It states that organisms with traits better suited to their environment are more likely to survive, reproduce, and pass those advantageous traits on to their offspring.

* This leads to a gradual increase in the frequency of those beneficial traits in the population over time, while less advantageous traits become less common.

* Survival of the fittest is a common but sometimes misleading phrase used to describe natural selection. It's important to note that "fittest" doesn't necessarily mean strongest or biggest, but rather best adapted to the specific environment.

Let me know if you'd like more details on natural selection or any other evolutionary concepts!