1. Overproduction: Organisms produce more offspring than the environment can support. This leads to competition for resources.

2. Variation: Individuals within a population exhibit variation in their traits. These variations can be inherited.

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

4. Adaptation: Over time, the frequency of advantageous traits increases in a population, leading to adaptation to the environment.

In essence, natural selection is a process where nature "selects" the individuals best suited to their environment, allowing those individuals to reproduce and pass on their advantageous traits. This process gradually shapes species over time.