natural selection

Biologist

2022

We explain what natural selection is, its principles, function and types. Also, why it is so slow and its relationship with evolution.

Natural selection is a key mechanism in the evolutionary process.

What is natural selection?

In biology, natural selection is the process of adaptation to the environment through which only living beings with certain characteristics they reproduce and thus transmit to the next generation their genotype or genome.

It is a key mechanism in the evolutionary process, which guarantees that parents inherit physical, physiological, behavioral characteristics from their descendants. reproductive or of any other nature, as long as they are in favor of the survival of the species.

Natural selection is a slow process that takes place over generations. It is inserted in the logic of survival of the fittest, as the British naturalist Charles Darwin (1809-1882) intuited it in his studies. This concept was part of the first theories about the evolution and it was a very important contribution to the field.

An easy way to understand natural selection as Darwin formulated it is that the world is constantly change, and the forms of life, to perpetuate themselves, they are forced to design strategies and mechanisms to adapt to these changes.

Thus, natural selection is the process that "chooses" or "favors" the individuals better adapted to deal with their environment, allowing them to reproduce and pass on their characteristics to future generations.

Those that are not favored by natural selection, either because they did not adapt quickly enough or did not adapt poorly, are destined to perish and become extinct.

Natural selection is the main engine of evolution, within the currently accepted modern synthetic theory, and its continuous effects are studied both in laboratories and in the field.

Purpose of natural selection

Individuals better adapted to the environment have more offspring.

The "purpose" of natural selection (the quotes are because it does not have a form of intelligence behind it, that is, it is a blind, biological process) is none other than the survival of life, which means the constant adaptation of life to its surroundings.

Another way of looking at it is that natural selection has the purpose of protecting the genes more suitable for the survival of life, spreading them to future generations, and instead extinguishing useless or unhelpful genes.

For example, in an environment of competence between species a genetic change (say, a mutation) occurred in a given individual allows it to avoid predators and reproduce faster than others of its species.

This maximizes the number of descendants that survive the predators. It is very probable, by natural selection, that after a few generations the species is constituted mainly by individuals endowed with this beneficial mutation, and those devoid of it are extinct.

On the other hand, if the mutation was harmful, for example, if instead of reproducing faster it would mean that the individual has a color more striking for predators, it is very likely that, by natural selection, said individual and its descendants become extinct, eaten by predators, while the others continue to reproduce.

As will be seen in both examples, natural selection has the "purpose" that individuals best adapted to the environment reproduce and add characteristics to the species (by inheriting them from their descendants). Finally, when these changes are radically different, they can eventually lead to the production of a new species.

Types of natural selection

Directional selection benefits individuals with certain characteristics.

There are four types of natural selection, depending on the proportion of individuals who survive generationally:

  • Stabilizing or normalizing selection. Also known as "negative" selection, it is the most common type of natural selection, in which "common" or "average" individuals are genetically privileged over those with abnormal characteristics. It is a way of keeping the traits of a species intact. A good example of this is fetuses humans: those who are very underweight will be more vulnerable to disease and dying early, but those who are too heavy will be more prone to possible problems during childbirth, so natural selection chooses those of average weight to proliferate.
  • Directional or positive selection. Opposed to the previous case, this selection model favors some specific trait within the population of the species, so it "leads" it in some address determined. An example of this is the color change of a certain species of European moths, recorded at the beginning of the industrialization. The natural color of the moths, which previously allowed them to blend into the environment as a camouflage, began to make them stand out rather, because smog from industrial chimneys sooty walls and tree bark. Then a change occurred and a new form of brown moths began to proliferate, multiplying as predators ate the others, until eventually only brown moths remained.
  • Disruptive selection. Unlike the previous two forms of natural selection, in this case individuals of the species that are far from the average are favored, that is, that show outstanding characteristics, even if they are opposed to each other. This type of selection usually leads to specialization, that is, the emergence of new species. An example of this was what Darwin observed in certain birds in the Galapagos Islands: they were similar enough to be of the same species, but they differed in their beaks: some had it large (adapted to eat large seeds) and others small ( adapted to eating small seeds). Medium-billed birds became extinct, as they could not eat well seeds, large or small.
  • Sexual selection. Not always considered a form of natural selection, sexual selection consists of the competition between the members of a species to reproduce, so that those males that attract the most females, or that can ensure intercourse, are the ones that reproduce more and better. , imposing its genome over those who cannot do it or lose in said competition.

Principles of natural selection

Eventually, natural selection creates new species.

The principles of natural selection can be summarized in the following statements:

  • Life is in constant competition to adapt to the environment.
  • Only the best adapted life forms survive and reproduce.
  • Traits that allow for better adaptation are thus passed on to future generations.
  • Life forms that do not adapt well perish and, unable to reproduce, become extinct.
  • Eventually, adaptive changes lead to the creation of a new species.

Why is natural selection so slow?

Natural selection is a matter of generations, it is not immediate at all. That is why the evolutionary process is so slow: it requires a change introduced in the generations, which is imposed on the others as several times of life elapse.

In the case of long-lived animals, such as itself human being, that process is tremendously slow, but this process in the microorganisms simpler, such as virus, it is tremendously fast.

Proof of the latter is that the flu virus continues to afflict us year after year, in slightly different new ways, despite the fact that we have a immune system designed to combat and remember it. The virus mutates, adapts, and can spread again, in a process that responds perfectly to natural selection.

Artificial selection

Domestic animals are modified by artificial selection.

When we speak of artificial selection, we refer to natural selection, when it is not due to the conditions of adaptation to life in its environment, but is caused by the intervention of human beings.

It is also known as selective breeding, and it is the reason behind the particular evolution of the domestic speciessuch as dogs, cats, types of beef or poultry.

!-- GDPR -->