1. Variation: Individuals within a population exhibit variation in their traits, meaning they are not all identical. This variation can be in physical characteristics, behavior, or any other aspect that affects their survival or reproduction.

2. Inheritance: Traits are passed down from parents to offspring. This means that offspring inherit the characteristics that helped their parents survive and reproduce.

3. Overproduction: Organisms produce more offspring than can survive. This creates competition for resources like food, water, and shelter.

4. Differential survival and reproduction: Individuals with traits that make them better suited to their environment are more likely to survive and reproduce. This means they are more likely to pass on their advantageous traits to their offspring.

In summary: Natural selection is the process where organisms with traits better suited to their environment survive and reproduce more successfully, leading to the gradual evolution of populations over time.