Meaning of Natural Selection

What is Natural Selection:

Natural selection is one of the fundamental mechanisms of evolution. Through natural selection, individuals best adapted to a certain condition or situation survive and transmit this characteristic to their offspring.

Biological evolution is the process that explains the transformations of living beings through time. Besides natural selection, the other mechanisms of evolution are mutations and genetic drift.

What is natural selection?

The central evolutionary mechanism proposed by Charles Darwin is summarized in the following ideas:

  • The individuals that make up a species present differences or variations among themselves.
  • Between individuals there is a struggle for existence, imposed by environmental restrictions.
  • Those individuals whose variations make them more "advantageous" compared to the rest are more likely to transmit these traits to their offspring.

Necessary conditions for natural selection to operate

The theory of evolution by natural selection is based on three principles: phenotypic variability, heritable and differential biological fitness.

Phenotypic variability

There must be phenotypic variation in a population as a fundamental requirement for evolutionary change. These variations can be found at the physical, physiological or behavioral level and are ubiquitous within populations. If all the individuals in a population were exactly the same, there would be no natural selection.


A key aspect of natural selection is that traits can be inherited, that is, that they can be passed on to subsequent generations. An individual can adapt to a specific environmental condition, but if it does not leave descendants, its survival characteristics will disappear and will not contribute to the evolution of the species.

Differential biological suitability

Overgrowth and limited resources provoke a struggle for existence in which some organisms survive and others do not. Success in survival is not a random process but partially driven by some differences that exist between organisms.

In this sense, some individuals may have traits that make them better adapted to a certain environment, which means that they are more likely to reproduce and have more offspring than individuals with less favored traits. This variation favors the reproductive success of the individual.

Examples of natural selection

A simple example of how natural selection works.

An example of how natural selection works is outlined in the figure above. In this example, generation 1 has two characteristics, the greenest being the one that prevails in a given environment. It is important to note that individuals as such do not change. This generation gives rise to generation 2, which will not only have the parental trait but also by random mutations other traits appear: darker greens and yellows.

From generation 2 the yellows die and the greener colors prevail. These reproduce and give rise to generation 3 with three different shades of green. After many generations, mutations and natural selection, the N generation is predominantly made up of the darkest greens, which is the most favored trait in that environment.

Antibiotic resistance

Disease-causing bacteria are found in very large populations, and they are not all created equal. If some of them have a genetic characteristic that makes them resistant to antibiotics, they will survive the antibiotic treatment while the others die. As a result, the surviving bacteria will multiply and transmit antibiotic resistance to their offspring.

Charles Darwin and natural selection

Charles Darwin (1809-1882) was a 19th century English naturalist and biologist. Between 1831 and 1836, Darwin participated in a scientific expedition aboard the H.M.S. Beagle, which took him to South America and various Pacific islands. During his journey, he collected and observed a wide variety of animal and plant species, as well as fossils and geological formations.

In his masterpiece The origin of species through natural selection , Darwin captured his ideas about evolution. It was in successive editions of the book that the title was shortened to The origin of species.

Synthetic theory of evolution or neo-Darwinism

Darwin established the theory of natural selection without knowing the bases of genetic inheritance. In the 20th century the theory was reformulated, combining Mendelian and population genetics with natural selection in what is now known as the synthetic theory of evolution or neo-Darwinism.

Misconceptions about natural selection

The concept of natural selection can lead to confusion and misunderstanding among the general public. Here are some common mistakes regarding natural selection:

  • "Survive the Strongest": Natural selection does not mean that the strongest of individuals can survive. It is useless to be the strongest if in the end this individual leaves no offspring.
  • "Natural selection favors those who live better or longer": again we are in a common error which is to believe that individuals who live in better conditions for a long period of time are more adapted. Phenotypic traits that promote an easier or longer life are evolutionarily irrelevant, unless they can be inherited.
  • "Natural selection chooses the best adapted individuals": in this case it is the traits that allow individuals to adapt to their environment and that can be inherited that explain the evolutionary process in that species. That is, natural selection is not an entity or force that chooses which are the fittest individuals.
  • "Natural selection fixes favorable characteristics": a characteristic that is favorable at one time may be detrimental under other conditions. Again, natural selection does not imply that a characteristic will remain constant in subsequent generations.
  • "Evolution and natural selection are synonymous": The concepts of evolution and natural selection are not interchangeable; not all evolution can be explained by natural selection, nor do all the results of natural selection lead to evolutionary change.
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