One of the main mechanisms of evolution along with mutations, migration processes and gene transformations is natural selection. Types of natural selection imply changes in the genotype that increase the body's chances of survival and procreation. Evolution is often seen as a consequence of this process, which may result from differences in species survival, fertility, pace of development, mating success, or in any other aspect of life.
Natural balance
Gene frequencies remain constant from generation to generation, provided that there are no disturbing factors that upset the natural balance. These include mutations, migrations (or gene flow), random gene drift, and natural selection. Mutation is a spontaneous change in the frequency of genes in a population, which is characterized by a low rate of development. In this case, the individual passes from one population to another and then mutates. Random gene drift is a change that is transmitted from one generation to another in a completely random way.
All these factors change the frequency of genes without taking into account the increase or decrease in the probability of the organism surviving and reproducing in its natural environment. All of them are random processes. And natural selection, types of natural selection are moderate disruptive consequences of these processes, since they multiply the frequency of beneficial mutations over many generations and eliminate harmful components.
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 environment. is he
can act on any inherited phenotypic traits and, using 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 directed and effective in adaptive evolution. Natural selection, 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 is evolving.
The concept of natural selection
Natural selection is one of the cornerstones of modern biology. It acts on the phenotype, the genetic basis of which gives a reproductive advantage for 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 a population.
The concept itself was formulated and published in 1858 by Charles Darwin and Alfredo Russell Wallace in a joint submission of documents regarding the origin of the species.
The term has been described as an analogue of artificial selection, that is , it is a process by which animals and plants with certain traits are considered desirable for breeding and reproduction. The concept of "natural selection" was originally developed in the absence of a theory of heredity. At the time Darwin wrote his writings, 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 by which the animal organism adapts and evolves. At its core, individual organisms that are best adapted to the environment survive and reproduce most successfully, producing fertile 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 causes members of a particular population to change over time. In fact, it can be divided into five main stages: variability, inheritance, selection, time and adaptation.
Darwin on natural selection
According to Darwin’s teachings, natural selection consists of four components:
- 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 offspring produced. On the other hand, some character traits are not related to differences between individuals, for example, the number of eyes in vertebrates.
- Inheritance. Some traits are successively transmitted from parents to offspring. Such traits are inherited, while others are strongly influenced by environmental conditions, and they are inherited poorly.
- High population growth rates . The bulk of the animals annually produce offspring in much larger quantities than are necessary for an equal distribution of resources between them. This leads to interspecific competition and premature mortality.
- Differential survival and reproduction. All types 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 takes place over successive generations and is defined as the differential reproduction of genotypes. Any change in the environment (for example, a change in the color of a tree trunk) can lead to local adaptation. The following types of natural selection (table No. 1):
| Types of Natural Selection | Examples |
| Stabilizing | Birth weight of human babies, number of hatched eggs in birds and amphibians |
| Directed | The evolutionary changes in teeth, the length of the legs in horses, the bright color of plants to attract pollinators, the large and small beak in birds, depending on the size of the food |
| Diversification (subversive) | Coloring of animal hair depending on habitat and season, change in body size over time |
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 individuals most adapted to the environment in the population. Due to this, diversity within one species decreases. However, this does not mean that all individuals are absolutely identical.
Stabilizing natural selection and its species can be briefly described as averaging or stabilization, in which the population becomes more uniform. 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 human characteristics are the result of such selection. A person’s birth weight is not only a polygenic trait, it is also controlled by environmental factors. Mid-birth babies are more likely to survive than too small or too large.
Directional Natural Selection
This phenomenon is usually observed in conditions that have changed over time, for example, weather, climate or the amount of food can lead to directional selection. Human participation can also accelerate this process. Hunters most often kill large individuals due to meat or other large decorative or useful parts. Consequently, the population will tend to skew towards smaller individuals.
The more predators kill and eat slow individuals in the population, the more skew will be towards the more successful and faster representatives of the population. Types of natural selection (table with examples No. 1) can be more clearly demonstrated using examples from wildlife.
Charles Darwin studied directional selection when he was in the Galapagos Islands. The beak length of local finches has changed over time due to available power sources. In the absence of insects, finches with large and long beaks survived, which helped them eat the seeds. Over time, there were more insects, and with the help of directional selection, bird beaks gradually became smaller.
Features of diversification (subversive) selection
Subversive selection is a type of natural selection that opposes the averaging of species characteristics in a population. This process is the rarest if you describe the types of natural selection briefly. Diversification selection can lead to speciation of two or more different forms in places of sharp changes in the environment. Like directional selection, this process can also be slowed down due to the destructive influence of the human factor and environmental pollution.
One of the best-studied examples of disruptive selection is the butterfly case in London. In rural areas, almost all individuals were light colored. However, these same butterflies were very dark in industrial areas. There were also specimens with medium color intensity. This is due to the fact that dark butterflies learned to survive and escape from predators in industrial areas in urban areas. Bright moths in industrial areas were easily detected and eaten by predators. The opposite picture was observed in rural areas. Butterflies of medium color intensity were easily visible in both places, and therefore very few of them remained.
Thus, the meaning of disruptive 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 evolved from simple life forms 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 have 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 path to genetic diversity must not be lost, as well as the ability at the cellular level to respond to changing environmental conditions.