Modern man, in general, is familiar with the concept of evolution as a process of continuous development of life on the planet. It is usually believed that evolution is a process of adaptability and changeability of all forms of living organisms throughout their long existence. You can argue a lot about theories of the origin of life on the planet, about how it all began. But the generally accepted concept is that it is what everyone learns in school. At the same time, not everyone knows and understands what an elementary unit of evolution is – an individual, a group of organisms, a species.
Development of the theory
When we hear the word evolution, we immediately think of Charles Darwin (1809-1882). But long before him, the idea of the gradual development of life and such a concept as an elementary unit of evolution appeared in the philosophical thought of mankind. But it was Charles Darwin who introduced the scientific community … no, not the concept of evolution, butthose driving forces that will lead to significant, sometimes significant changes in organisms that end in the formation of new species. Species as a biological community of organisms, similar in a whole range of characteristics, capable of free interbreeding with the appearance of reproductive offspring. So, the subject of this article is the definition of the smallest unit in which a lasting and qualitative change can occur, leading to the appearance of something new and different from the parent forms.
Before Darwin
The point of view on the development of the organic world, which existed before the advent of Darwin's theory of the origin of species, is called pre-Darwinian. Without going into the wilds of evolutionary teaching, the dominant theory was theological (everything is from God) and theological-naturalistic (organisms strive for perfection, which again is from God). These theories consider the individual to be the elementary unit of evolution. For example, Jean-Baptiste Lamarck (1744-1829) explained the long neck of giraffes by their desire to reach the top branches and the transmission of this desire to descendants.
Darwin's Revolution
The merit of Charles Darwin is that in his work "The Origin of Species" he explained all the unthinkable variety of living forms on the planet as the result of the struggle for existence, natural selection. And the result of this process was the victory of the strongest and fittest individuals. Darwin emphasized that the elementary unit of evolution is a group of individuals, and not just single individuals. Natural selection works precisely when both single individuals and their natural groups fall under its action. It is in the group, according to Darwin, that signs that are unnecessary today, but tomorrow become decisive in the adaptability of organisms to constantly changing conditions of life, can be preserved. For Darwin, such a group is the species as an elementary unit of evolution.
Darwinism plus genetics
What Charles Darwin failed to explain in his "Origin" is how random changes are transmitted and fixed in offspring. After all, special signs should be blurred in the process of successive generational change. And it was at this time that the science of genetics appeared with its own laws of inheritance and recessive and dominant alleles accumulated in a group of organisms. Three laws of generality of the first generation of hybrids by G. Mendel, the double helix of hereditary information in DNA by J. Watson and F. Crick, molecular biology and gene structure, the development of embryology and cytology, ethology and paleontology, biochemistry and ecology - and a synthetic theory of evolution is born, dominant in today's scientific environment.
Symbiosis of Darwinism and modernity
The synthetic theory of evolution was formed in the middle of the twentieth century. To list the contribution of all evolutionary biologists to its formation is not enough for three pages. Let us note the biologists S. S. Chetverikov (1880-1959), F. G. Dobrozhansky (1900-1975) and I. I. Shmalgauzen (1884-1963). The main postulate of the theory - the elementary unit of evolution isa population as a distinct group of one species, living in the same territory and in a certain way isolated from other populations of a given species. It is the isolation of populations (ecological, geographical, reproductive) that leads to the formation of new species. The synthetic theory of evolution leads to the explanation of the mechanisms of this speciation by certain provisions, which also explain why the population is considered the elementary unit of evolution.
Basics of the synthetic theory of evolution
The data presented below do not claim to be complete and exhaustive information about the provisions of modern theory, but are considered in the context of the postulate that the population is an elementary unit of evolution.
Russian biologist and geneticist N. V. Timofeev-Resovsky (1900-1981) formulated the main provisions of STE on elementary units, phenomena and factors of biological evolution.
- The elementary unit of evolution is the population.
- The phenomenon of evolution in action is the change in the gene pool (the total set of genes of all individuals) of a population.
- The gene pool of a population is the hereditary material of evolution.
- Factors of evolution are mutation processes, isolation, population waves (population fluctuations) and selection.
Why population
Only a population as a group of individuals of the same species represents a single formation that can exist indefinitely as an integrity in space and time. Andonly within this community the probability of free interbreeding of individuals is always higher than the probability of interbreeding of individuals from different populations. Only the population meets the requirements of the evolutionary process, and therefore it is precisely this population that is the elementary unit of evolution. Only within this group with a different set of genotypes, individuals are selected according to phenotypic traits. Only in such a closed system can the phenotypically successful for the given conditions of existence of traits be consolidated in the genotype of the entire group, in the gene pool of the population. And, accumulating in the gene pool, change the individual genotypes of individuals, leading to phenotypic (external) differences.
Why isn't species the elementary unit of evolution?
View can also be considered an integral closed system that has existed for a long time. But each species, inhabiting a certain area, is distributed unevenly over the territory. And each part of it is a population, which theoretically can give rise to the process of speciation. Or maybe not. Some species, such as endemics, generally inhabit rather limited territories and are represented by one population (Arctic polar bear or Baikal seal). And there are species, such as common magpie, represented by hundreds of populations in various parts of the world.
Why is an individual not an elementary unit of evolution?
The evolutionary process implies the development and emergence of new features and propertiesorganism, leading to its greater adaptability. And here a chain of generations is needed - evolutionary history or evolutionary fate. One organism does not exist for any long time in order to develop and consolidate a trait throughout life. Therefore, a herd or flock cannot be an elementary unit - this group is not sufficiently isolated and, as a rule, does not exist for a very long time in the context of the number of generations. It is worth noting that this statement is not entirely suitable for prokaryotes (non-nuclear) as the simplest with a high reproduction rate.
