The theory of evolution is one of the most significant scientific theories that has revolutionized our understanding of life on earth. It explains how species change over time, adapting to their environment, and how new species arise.

There are three essential conditions that form the basis of the theory of evolution. Let’s take a closer look at each one.

The First Condition: Variation

One of the most fundamental aspects of evolution is variation. Variation refers to the differences between individuals within a population. These differences can be physical characteristics such as height, weight, or coloration, or they can be genetic variations that affect an organism’s ability to survive and reproduce.

Example: A population of birds might have variations in beak size and shape, which could affect their ability to feed on different types of food.

Without variation, there would be no genetic diversity within a population, and hence no opportunity for natural selection to occur.

The Second Condition: Heritability

The second essential condition for evolution is heritability. Heritability means that traits are passed down from parents to offspring through genes.

Example: If a bird with a particular beak shape has better access to food and thus higher survival rates and reproductive success than other birds with different beak shapes in its population, it will pass on its genes for that particular beak shape more frequently to its offspring.

If a trait isn’t heritable, then natural selection cannot act upon it because it won’t persist in future generations.

The Third Condition: Selection

The final condition necessary for evolution is selection. Selection occurs when certain traits provide an advantage in survival or reproduction over other traits within a population.

Example: In our bird population example, if a drought occurs and food becomes scarce, birds with larger or differently shaped beaks may have an advantage over birds with smaller or differently shaped beaks. This is because they can more easily access the available food, which increases their chances of survival and reproductive success.

Natural selection can lead to changes in a population over time, as individuals with certain advantageous traits are more likely to survive and reproduce, passing on their favorable traits to future generations.


In conclusion, the theory of evolution requires three essential conditions: variation, heritability, and selection. These conditions provide the basis for natural selection to occur and lead to changes in populations over time. By understanding these critical components of evolution, we can better understand how species change and adapt in response to their environment.