Definition of natural selection in biology, 3 Types & Example

Definition of natural selection in biology

Natural selection is the process by which organisms that are better adapted to their environment survive, pass on genes, and produce more offspring.

It is an evolutionary mechanism that causes species to change and diverge over time.

More than a century earlier, in 1958, Charles Darwin (1809–1882) and Alfred Russell Wallace (1823–1913) jointly accepted the theory of evolution by natural selection and published the book Origin of Species.

In 1859 Darwin published a separate book on the origin of species by natural selection.

Definition of natural selection in biology

After Darwin’s death, the neo-Darwinism theory based on the genetic character was developed when genes were discovered in 1901 by American scientists Morgan, Shatton, etc.

Facts that influenced the development of Darwin’s thinking or the theory of natural selection

In 1831, Darwin was a naturalist on the voyage when he was just 22 years old. As a naturalist, he observed, collected, and analyzed samples of plants, animals, rocks, and fossils. He spent more than three years exploring nature on islands and distant continents.

During his long journey, Darwin made many observations that helped him to develop the theory of evolution.

Darwin follows Lamarck’s view and believes that species can change over time. The fossils he found helped to follow Lamarck’s theory more easily.

From Charles Lyell’s book Principles of Geology, Darwin concluded that evolution had had enough time to produce the great diversity of life because he observed that the Earth and its life were much older.

In the late 1830s, Darwin attended a meeting of animal breeders and read their publications carefully. He was aware that humans could breed animals and plants to acquire valuable traits by choosing plants or animals to allow for reproduction over time. They can change the properties of an organism. He called this type of variation in an organism; artificial selection.

Darwin wondered how artificial selection could be done in nature, found a solution in the book by Thomas Robert Malthus, and knew that populations could grow faster than their resources could, eventually leading to a struggle for existence. can.

The term fitness was coined by Darwin and refers to the relative ability of an organism to survive and produce offspring. Diversity occurs naturally, so he called this type of selection natural selection.

Darwin spent many years reflecting on the work of Lamarck, Lyell, and Malthus, what he knew about artificial selection and observation, and the results of their travels. Gathering all the ideas and all together helped to formulate his theory.

Wallace also traveled to various places to study nature and developed a theory of evolution similar to that of Darwin. Wallace sent Darwin a letter he had written explaining his theory of evolution. Wallace’s idea helped validate Darwin’s theory.

At the time of the controversy over the theory of natural selection, Wallace was in Indonesia and could not defend Darwin’s defense by adding his point of view. Therefore, the theory is known as Darwinian rather than Darwin-Wallace’s theory of evolution.

Darwin’s natural selection theory

The Darwin–Wallace theory states that “a change in species through the existence of a type of organism that exhibits natural variation that provides it with an adaptive advantage in the environment, and thus a new environmental equilibrium, evolution by natural selection.” It happens”.

The process of natural selection is an ongoing process of massive trial and error for all living matter.

Natural selection includes the following five elements (factors or causes of natural selection).

Universal Phenomenon of Variation:

Each group of organisms (animals and plants) can differ in a number of ways, known as variation. Darwin and Wallace did not know the source of the age variation and believed it to be one of the innate characteristics of the organism. However, we now know that inherited variations are caused by mutations.

Extremely Natural Rate of Multiplication:

Without environmental checks, each species has great fertility (the reproduction rate increases geometrically). If all species continued to survive and reproduce, it would soon be challenging to survive, obtain food, and collect all other species from the earth.

Struggle for existence:

There is an intraspecific, interspecific, or environmental struggle for existence (competition for food, mate, location, as well as survival in drought or cold).

The consequent elimination of the unsuitable and the existence of only those that are satisfactory adaptations:

Some of the changes shown by living things make them better adapted to survive; There are other obstacles that bring about the elimination of bosses. The core of natural selection theory is the idea of survival of the fittest.

Inheritance of mutation or recombination for success in the struggle for existence:

The individual that survives will give rise to the next generation and with this method, successful variations are passed on to the next generation.

A less fit individual is removed before being reintroduced.

Successive generations become better adapted to their environment. If environmental conditions change, further adaptation occurs.

Descendants (different from their ancestors) can arise from the operation of natural selection over time over many generations. In this way, two or several more species may arise or arising from the same ancestral stock.

What are the criticisms of natural selection theory?

Darwin did not mention vestigial organs found in animals.

The role of mutation in the origin of new species is not involved. Without mutation, new species would never have evolved by natural selection.

Variation, whether genetic or somatic, because the only genetic variations are heredity.

For these reasons Darwin’s theory failed in humans; The human population never stagnates, not only struggling for survival but also continuing the life cycle like beggars, and instead of surviving, humans become fittest only in arrival.

Different types of natural selection

Population geneticists have classified three types of natural selection that can occur in nature. These are as follows:

Directional selection

When a population shows a particular trend through time, the variation that can occur is called directional selection. This happens when the environment is constantly changing. The directional selection process favors individuals who are better adapted to the new environment or situation or to the new ecological situation.

The directional selection also shifts a species’ gene pool toward the highest level of adaptation that can be accessed in the new environment.

A very simple example of directional selection is the neck of a giraffe. Each giraffe has a different neck length. This variation in trait gives different advantages to each giraffe as the longer neck giraffe is easier to access a food source, therefore better able to survive and reproduce. Over time, long-necked giraffes will reproduce more offspring and pass their genes on to the next generation. Thus, future generations of giraffes have longer necks. If directional selection persists, this new population may eventually become a new species.

Stabilizing selection

  • In this type of selection, the mean values ​​of a given trait are used to eliminate the extreme values ​​in a population. It is the most common type of selection occurring in a population and is homeostatic that maintains the status quo. This selection reduces the variability in the population.
  • For example: in a plant, plants that are higher in height are exposed to more wind and are prone to blowing over, while plants with a smaller height can be enriched with abundant sunlight. fails. Thus, the average height of the plants provides both adequate sunlight and wind protection.

Disruptive selection

In this selection, two adaptive traits are selected when the population is present in a heterogeneous environment. It favors the extreme if they have better traits or fitness and the intermediates are disadvantageous. This selection results in diversification related to traits.

   For example, an area that has black, brown, and white rabbits has both white and black hares. Natural selection would favor both white and black traits as they both prove useful for camouflage. Gray’s intermediate property does not prove useful, so selective pressure works against the property.

Evolutionary biologists also recognized sexual selection and group and kin selection.

Sexual selection

Most species of animals are dimorphic (male and female). Males and females differ in terms of color, particular song patterns, behavior, sex organs, abilities, etc.

Sexual selection is directly related to differential reproduction, which includes finding and obtaining a mate, copulation, fertilization, and parental care.

Organisms whose mates are more able to secure and are more suited to the environment. The purpose of sexual selection is reproduction which requires an individual to be able to find and protect a mate and produce viable offspring.

In 1938, Huxley recognized two types of sexual selection; Epigamic selection (based on the choice between males and females) and intrasexual selection (this selection is based on interactions between animals of the same sex, usually males).

Group and kin selection

Group selection is the selection of a group of individuals to prefer one group over another, leading to the development of a trait that is beneficial to the group.

The altruistic behavior of an individual involved in kin selection occurs when natural selection favors a trait that benefits the members of the group concerned.

What is most important for natural selection?

  • Natural selection drives the evolution and diversity of life on Earth.
  • Favorable traits are transmitted through generations.
  • Natural selection can lead to speciation, where an ancestral species gives rise to a new and distinctly different species.

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Definition of natural selection in biology, 3 Types & Example

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