Short Answer 
The process of natural selection requires three essential steps: establishing variation within a population, ensuring that traits are heritable, and differentiating reproductive success based on those traits. Variation provides the foundation for selection, heritability allows advantageous traits to be passed down, and differential reproductive success leads to a higher prevalence of favorable traits over generations.
Step 1: Establish Variation
For natural selection to take effect, there must be a clear variation within a population. This means that not all individuals are identical; they differ in some traits. This variation is crucial because it provides the raw material for selection. Important aspects of this step include:
- Different traits among individuals, such as color or size.
- Variation should exist across the population, enabling potential selective pressures.
Step 2: Ensure Heritability
The next requirement is that these traits must be heritable, meaning they can be passed down from one generation to the next. This ensures that the advantageous traits can be inherited over time, impacting future generations. Key points to consider include:
- Traits are genetic and can be transferred through reproduction.
- Heredity allows for the continued evolution and adjustment of species over time.
Step 3: Differentiate Reproductive Success
Finally, there must be differential reproductive success based on the variations. This means that individuals with certain traits will produce more offspring than those without those traits. Aspects of this condition include:
- Individuals with favorable traits are more likely to survive and reproduce.
- Over time, this leads to an increase in the frequency of advantageous traits within the population.