The theory of evolution by natural selection is one of the most fundamental ideas in biology. It was first proposed by Charles Darwin in his book “On the Origin of Species” in 1859. The basic premise of the theory is that species evolve over time through a process of natural selection, where individuals with advantageous traits are more likely to survive and reproduce.

The Key Ideas

There are several key ideas that form the basis of the theory of evolution by natural selection:

1. Variation within a population

All individuals within a population exhibit variation in their traits or characteristics. This variation can be due to differences in genetics, environmental factors, or a combination of both.

2. Competition for resources

As populations grow, individuals must compete for limited resources such as food, water, and shelter. This competition results in differential survival and reproduction rates among individuals with different traits.

3. Differential survival and reproduction

Individuals with traits that make them better adapted to their environment are more likely to survive and reproduce than those with less advantageous traits. Over time, this leads to a gradual change in the frequency of these traits within the population.

4. Natural selection

Natural selection is the process by which advantageous traits become more common within a population over time. This occurs because individuals with these traits are more likely to survive and reproduce, passing on their genes to future generations.


One classic example of natural selection is the peppered moth during the industrial revolution. Prior to this period, peppered moths had light-colored wings that blended in well with tree bark.

However, as pollution from factories increased, so did the amount of soot on trees, making them darker in color. As a result, moths with darker wings became more common because they were better camouflaged and less likely to be eaten by predators.

Another example is the evolution of antibiotic resistance in bacteria. When antibiotics are used to treat bacterial infections, some bacteria may have mutations that make them resistant to the drug. These resistant bacteria are then more likely to survive and reproduce, passing on their resistance genes to future generations.


The theory of evolution by natural selection is a powerful idea that has had a profound impact on our understanding of the natural world. By recognizing the importance of variation, competition, and natural selection, we can better understand how species evolve over time and how they are able to adapt to changing environments.