What is natural selection? Types of natural selection (table)

One of the main mechanisms of evolution along with mutations, migration processes and gene transformations is natural selection. Types of natural selection mean such changes in the genotype, which increase the chances of the body to survive and continue the genus. Evolution is often seen as a consequence of this process, which can result from differences in species survival, fertility, development rates, mating success, or in any other aspect of life.

Natural balance

The gene frequencies remain constant from generation to generation, provided that there are no disturbing factors that disturb the natural balance. These include mutations, migration (or gene flow), random gene drift, and natural selection. Mutation is a spontaneous change in the frequency of genes in a population characterized by a low rate of development. Thus the individual passes from one population to another and then is modified. The random drift of genes is a change that is transmitted from one generation to another in a completely random way.

All these factors change the gene frequencies without taking into account the increase or decrease in the probability of survival of the organism and reproduction in its natural environment. All of them are random processes. And natural selection, the types of natural selection, are the mild disorganizing consequences of these processes, as they multiply the frequency of useful mutations over many generations and eliminate harmful constituents.

What is natural selection?

Natural selection contributes to the preservation of those groups of organisms that are better adapted to the physical and biological conditions of their habitat. is he
Can act on any inherited phenotypic traits and, through selective pressure, can affect any aspect of the environment, including sexual selection and competition with members of the same or other species.

However, this does not mean that this process is always directional and productive in adaptive evolution. Natural selection, the types of natural selection in general, often lead to the elimination of less adapted options.

Variations exist within the entire population of organisms. This is partly because random mutations occur in the genome of one organism, and its offspring can inherit such mutations. Throughout life, genomes interact with the environment. Consequently, the population evolves.

The notion of natural selection

Natural selection is one of the cornerstones of modern biology. It acts on a phenotype, the genetic basis of which gives a reproductive advantage for a greater prevalence in the population. Over time, this process can lead to the emergence of new species. In other words, this important (though not the only) evolutionary process within the population.
The very concept was formulated and published in 1858 by Charles Darwin and Alfredo Russell Wallace in a joint presentation of documents concerning the origin of species.

The term was described as an analog of artificial selection, that is, a process by which animals and plants with certain characteristics are considered desirable for breeding and reproduction. The concept of "natural selection" was originally developed in the absence of the theory of heredity. At the time of Darwin's writing of his works, science still had to develop modern theories of genetics. The combination of traditional Darwinian evolution with subsequent discoveries in the field of classical and molecular genetics is called modern evolutionary synthesis. 3 types of natural selection remain the main explanation for adaptive evolution.

How does natural selection work?

Natural selection is the mechanism through which the animal organism adapts and evolves. At its core, individual organisms that are best suited to the environment survive and most successfully multiply, producing a prolific offspring. After numerous breeding cycles, such species are dominant. Thus, nature filters out poorly adapted individuals for the benefit of the entire population.

This is a relatively simple mechanism that forces representatives of a certain population to change over time. In fact, it can be divided into five main stages: variability, inheritance, selection, time and adaptation.

Darwin about natural selection

According to Darwin's teaching, natural selection consists of four components:

1. Variations. Organisms within the population exhibit individual differences in appearance and behavior. These changes may include body size, hair color, spots on the face, voice properties or the number of produced offspring. On the other hand, some character traits are not related to differences between individuals, for example, the number of eyes in vertebrates.
2. Inheritance. Some features are consistently transmitted from parents to offspring. Such traits pass by inheritance, while others are strongly influenced by environmental conditions, and they are inherited weakly.
3. High growth rates of the population. The majority of animals annually produce offspring in a much larger quantity than is necessary for an equal distribution of resources between them. This leads to interspecific competition and premature mortality.
4. Differential survival and reproduction. All kinds of natural selection in populations leave behind those animals that can fight for local resources.

Natural selection: types of natural selection

Darwin's theory of evolution radically changed the direction of future scientific thought. At its center is natural selection, a process that occurs over successive generations and is defined as differential reproduction of genotypes. Any change in the environment (for example, a change in the color of the tree trunk) can lead to adaptation at the local level. There are following types of natural selection (Table No. 1):

Stabilizing selection

Often the frequency of mutations in DNA in some species is statistically higher than in others. This type of natural selection helps to eliminate any extremes in the phenotypes of the individuals most adapted to the environment in the population. Due to this, the diversity within one species decreases. However, this does not mean that all individuals are obtained exactly the same.

Stabilizing natural selection and its species can be briefly described as averaging or stabilization, in which the population becomes more homogeneous. First of all, polygenic traits are affected. This means that the phenotype is controlled by several genes, and there is a wide range of possible outcomes. Over time, some of the genes are turned off or masked by others, depending on the favorable adaptation.

Many features of a person are the result of this selection. The weight of a person at birth is not only a polygenic sign, it is also controlled by environmental factors. Newborns with an average weight at birth are more likely to survive than with too little or too much.

Directional natural selection

This phenomenon is usually observed in conditions that have changed over time, for example, the weather, climate or quantity of food can lead to targeted breeding. Human participation can also accelerate this process. Hunters most often kill large individuals because of meat or other large decorative or useful parts. Consequently, the population will tend to skew toward smaller individuals.

The more predators kill and eat slow individuals in the population, the more skewed toward more successful and fast representatives of the population. Types of natural selection (table with examples No. 1) can be more clearly demonstrated with the help of examples from wildlife.

Charles Darwin studied directional selection when he was in the Galapagos Islands. The length of the beak of local finches changed over time due to available power supplies. In the absence of insects, finches with large and long beaks survived, which they helped to eat seeds. With the passage of time, the insects became larger, and with the help of directed selection the bird's beaks gradually acquired smaller sizes.

Features of diversification (subversive) selection

Subversive selection is a kind of natural selection that opposes the averaging of species characteristics in a population. This process is the rarest, if we describe briefly the types of natural selection. Diversification selection can lead to speciation of two or more different forms in places of abrupt changes in the environment. Like directed selection, this process can also be slowed down due to the destructive influence of the human factor and environmental pollution.

One of the most studied examples of subversive selection is the case of butterflies in London. In rural areas, almost all individuals had a light color. However, these same butterflies were very dark in industrial areas. There were also specimens with an average color intensity. This is due to the fact that dark butterflies have learned to survive and escape from predators in industrial areas in urban conditions. Light moths in industrial areas are easily detected and eaten by predators. The reverse picture was observed in rural areas. Butterflies of medium color intensity were easily visible in both places, and therefore they were very few.

Thus, the meaning of subversive selection is the movement of the phenotype to the extreme, which is necessary for the survival of the species.

Natural selection and evolution

The main idea of the theory of evolution is that all species diversity gradually developed from simple forms of life that appeared more than three billion years ago (for comparison, the age of the Earth is about 4.5 billion years). Types of natural selection with examples from the first bacteria to the first modern humans played a significant role in this evolutionary development.

Organisms that were poorly adapted to their environment, are less likely to survive and leave offspring. This means that their genes are less likely to be passed on to the next generation. The way to genetic diversity should not be lost, as well as the ability at the cellular level to respond to changing environmental conditions.