Modern man, in general, is familiar with the concept of evolution as a process of continuous development of life on the planet. It is generally believed that evolution is a process of adaptability and variability of all forms of living organisms throughout their long existence. You can argue a lot about the theories of the origin of life on the planet, about how it all began. But the generally accepted concept is this, that is what everyone is teaching at school. Moreover, what is an elementary unit of evolution - an individual, a group of organisms, a species - far from everyone knows and understands.
Theory development
At the word "evolution" we immediately recall 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 is Charles Darwin who belongs to the introduction to the scientific community ... no, not the concept of evolution, but those driving forces that will lead to significant, sometimes significant changes in organisms that result in the formation of new species. Species as a biological community of organisms, similar in a whole complex of characters, capable of free crossing with the appearance of reproductive offspring. So, the subject of this article is the definition of the smallest unit in which a long and qualitative change can occur, leading to the emergence of something new and different from the parental forms.
To Darwin
The point of view on the development of the organic world that existed before the theory of the origin of species of Darwin appeared is called the Darwinian. Without going into the jungle of evolutionary doctrine, the dominant theory was theological (all from God) and theological and naturalistic (organisms strive for perfection, which is again from God). These theories consider the individual to be an elementary unit of evolution. For example, Jean Baptiste Lamarck (1744-1829) explained the emergence of a long neck in giraffes by their desire to reach the upper branches and the transmission of this desire to descendants.
Darwin Revolution
The merit of Charles Darwin is that in his work “The Origin of Species” he explained the whole unthinkable variety of living forms on the planet as a result of the struggle for existence, natural selection. And the result of this process was the victory of the most powerful and fit individuals. Darwin emphasized that the elementary unit of evolution is a group of individuals, and not just single individuals. Natural selection works just then, when both individual individuals and their natural groups fall under its action. It is in the group, according to Darwin, signs that are unnecessary today can be preserved, but tomorrow they have become decisive in the adaptability of organisms to constantly changing living conditions. In Darwin, such a group is a species as an elementary unit of evolution.
Darwinism plus Genetics
What Charles Darwin could not explain in his Origin ... is that random changes are transmitted and fixed in the offspring. Indeed, special features should be blurred in the process of successive generations. And it was precisely 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. The three laws of commonality of the first generation of G. Mendel’s hybrids, the double helix of hereditary DNA information of 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.
The symbiosis of Darwinism and modernity
A synthetic theory of evolution formed in the mid-twentieth century. Three pages are not enough to list the contribution of all evolutionary biologists to its formation. We 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 is a population as a separate group of one species, living in one territory and in a certain way isolated from other populations of this 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 an explanation of the mechanisms of this speciation by certain provisions that also explain why the population is considered to be an elementary unit of evolution.
The basic principles of the synthetic theory of evolution
The data given below do not pretend to be complete and comprehensive information on the provisions of modern theory, but are considered in the context of the postulate that a 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 a population.
- The phenomenon of evolution in action is changes in the gene pool (the general set of genes of all individuals) in a population.
- The gene pool of a population is the hereditary material of evolution.
- Evolution factors are mutation processes, isolation, population waves (fluctuations in numbers) and selection.
Why is the population
Only a population as a group of individuals of one species represents a single entity, which can exist indefinitely as an integrity in space and time. And only within this community is the probability of free mating of individuals always higher than the probability of mating individuals from different populations. Only a population meets the requirements of the evolutionary process, and therefore it is precisely it that is the elementary unit of evolution. Only within this group with a different set of genotypes do individuals undergo phenotypic selection. Only in such a closed system can the phenotypically successful conditions for the existence of traits in the genotype of the entire group, in the gene pool of the population, be consolidated. And, accumulating, in the gene pool, change the individual genotypes of individuals, leading to phenotypic (external) differences.
Why isn’t a species an elementary unit of evolution?
The view can also be considered a holistic closed system that exists for a long time. But each species, inhabiting a specific area, is unevenly distributed over the territory. And each part of it is a population that theoretically can give rise to the process of speciation. Or maybe not. Some species, such as endemic species, generally inhabit rather limited territories and are represented by a single population (Arctic polar bear or Baikal seal). And there are species, such as the common forty, represented by hundreds of populations in various parts of the world.
Why is an individual not an elementary unit of evolution?
The evolutionary process involves the development and emergence of new signs and properties of the organism, leading to its greater fitness. 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 sign 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 does not quite fit prokaryotes (non-nuclear) as the simplest with a high reproduction rate.