Here's a breakdown:

* Evolution: The gradual change in the inherited traits of a population over many generations.

* Natural Selection: The process by which organisms better adapted to their environment tend to survive and reproduce more successfully than others. This leads to the gradual accumulation of favorable traits in a population over time.

While "natural selection" is the core mechanism, the broader theory of evolution encompasses other processes like:

* Genetic Drift: Random changes in the frequency of alleles (gene variants) in a population.

* Gene Flow: The transfer of genetic material between populations.

* Mutation: Changes in the DNA sequence that can introduce new traits.

These mechanisms, along with natural selection, contribute to the diversity and complexity of life on Earth.