1. Variation: Individuals within a population exhibit variation in their traits. This variation can be in physical characteristics, behaviors, or even the ability to resist diseases.

2. Inheritance: These variations are, at least partially, heritable, meaning they can be passed down from parents to offspring.

3. Overproduction: Organisms produce more offspring than the environment can support. This leads to competition for resources like food, shelter, and mates.

4. Differential Survival and Reproduction: Individuals with traits that make them better adapted to their environment are more likely to survive and reproduce, passing on those advantageous traits to their offspring. This process is called natural selection.

In summary:

* Variation provides the raw material for evolution.

* Inheritance ensures that these variations can be passed on.

* Overproduction leads to competition and a struggle for survival.

* Differential Survival and Reproduction favors individuals with advantageous traits, leading to gradual changes in the population over generations.

This process of natural selection, acting on variation over many generations, leads to the gradual adaptation of species to their environments, resulting in the diversity of life we see today.