* Variation: Individuals within a population have variations in their traits, often due to genetic differences.

* Competition: Organisms compete for limited resources such as food, water, shelter, and mates.

* Survival & Reproduction: Individuals with traits that make them better suited to their environment are more likely to survive and reproduce, passing on those advantageous traits.

* Differential Reproduction: Individuals with less advantageous traits are less likely to survive and reproduce, leading to a decrease in those traits within the population.

* Gradual Change: Over many generations, this process of survival of the fittest leads to a gradual shift in the overall population's traits, making them better adapted to their environment. This is evolution.

In simpler terms:

Imagine a population of rabbits. Some have brown fur, some have white fur. In a forest environment, brown fur helps rabbits blend in and avoid predators. Brown rabbits are more likely to survive, reproduce, and pass on their brown fur genes. Over time, more rabbits in the population will have brown fur. This is natural selection leading to evolution.

Key Points:

* Natural selection acts on individuals, but evolution happens at the population level.

* Evolution is not a goal-oriented process. It's a response to changing environmental pressures.

* Natural selection is not the only factor contributing to evolution. Other mechanisms like genetic drift and gene flow also play a role.

In essence, natural selection is the mechanism that drives evolution. It's the process of "survival of the fittest" that leads to changes in the genetic makeup of populations over time, resulting in the diverse life forms we see today.