Great English scientist C. Darwin(1809-1882) developed scientific theory of evolution of living nature. Darwin's main work 1859 - “The origin of species by means of natural selection, or the preservation of favored breeds in the struggle for life.” An evolutionary factor is a driving force that causes and consolidates changes in populations as elementary units of evolution.
Darwin's historical merit not that he pointed out the presence of biological evolution (many thinkers spoke about this long before him), but that he revealed the material factors of evolution (heredity and variability) and one of the driving factors (natural selection) and thereby revealed reasons for biological evolution. Factors of evolution- Darwin's triad - variability and mutations, heredity, natural selection.
Variability- the ability of living organisms to change, acquire new characteristics under the influence of external (non-hereditary variability) and internal (hereditary variability) environmental conditions. Hereditary variability may be combinative and mutational. Combinative variability is associated with the occurrence of different combinations of allelic genes (recombinations). Mutations are stable changes in genetic material and, as a consequence, an inherited trait. The result of mutations is the appearance of new characteristics in the daughter organism that were absent in its parents. Darwin distinguished certain, uncertain and relative variability. A certain variability is the acquisition of new characteristics in a significant number of organisms belonging to a given species, under the influence of various factors of the external and internal environment. Uncertain variability is the acquisition of new characteristics by individual organisms belonging to a given species under the influence of external and internal environmental factors. Relative variability is the relationship between the acquisition of new characteristics by different organs and organ systems.
Heredity- the property of living organisms to ensure the transmission to offspring of genetically encoded information about any characteristics. Communication between generations occurs through reproduction. Hereditary properties are transmitted from generation to generation through germ cells (during sexual reproduction).
Natural selection- the main evolutionary factor promoting the survival of “favorable” structural features and the elimination of unfavorable ones. The process of survival of individuals with hereditary changes useful in given environmental conditions and their subsequent reproduction. The selecting factor is environmental conditions: high or low air temperature; excess or lack of moisture, light, food. Highlight three forms of natural selection, most often occurring in nature: leading, or driving (expands the boundaries of hereditary variability of a population), stabilizing (divides populations into parts), disruptive (divides populations into parts). Natural selection is not a random, but a strictly natural process that gives direction to evolution and ultimately creates complex adaptations similar to the result of “intelligent design.”
Calling the modern theory of evolution "Darwinism" or "Darwin's theory" - not correct, because biological science has come very far in understanding evolution since Darwin's original theory. New factors of evolution:
Population waves– periodic fluctuations in population size. For example: the number of hares is not constant, every 4 years there are a lot of them, then a decline in number follows. Meaning: During decline, genetic drift occurs.
Genetic drift- if the population is very small (due to a disaster, disease, decline in the population wave), then the characteristics are preserved or disappear regardless of their usefulness, by chance.
Insulation- a factor in the evolutionary process that influences the processes of crossing individuals with each other. Isolation promotes the divergence of characteristics and reinforces the differences between individuals of isolated groups. The duration of isolation is of some importance.
Migrations individuals from population to population are also an important source of genetic diversity in a population. Thanks to free crossing during migration, genes are exchanged between individuals of a population of the same species (gene flow). In this case, the genes of migrating individuals are included in the gene pool of populations during crossing. As a result, the gene pool of populations is updated.
Interrelation of the driving forces of evolution . Although of all the elementary evolutionary factors the leading role in the evolutionary process belongs to natural selection, it can occur only in the presence of mutational variability that creates material for selection, and represents the main (but not the only) factor of evolution. Thus, mutations, recombinations, migrations, population waves, genetic drift and isolation are also important non-directional evolutionary factors. In nature, they act together, but the role of each can be enhanced in a specific environment. All these factors provide genetic heterogeneity of populations.
Between artificial and natural selection there is no impassable abyss: cereals with non-shedding seeds were bred by us unconsciously, and vice versa, termites and ants have an agriculture with a million-year selection of fungal species that can no longer exist independently.
Anti-evolutionists are wrong when they say that artificial selection has not created a single new species. Many species of wild animals belonging to the same genus, and sometimes to different genera, are in principle capable of interbreeding and producing fertile offspring, but under natural conditions they almost never do this. Corn is one of the clearest living evidence of the power of artificial selection. The wild ancestor of corn, the teosinte plant, had a tiny ear with a small number of small ones. Several thousand years of artificial selection turned teosinte into corn.
Charles Darwin comes down to a line of logical propositions confirmed by experiments and other research. Thus, he proved that all types of living organisms are characterized by individual hereditary variability for any characteristics; they all multiply exponentially; within species there is a struggle for existence due to limited vital resources; In this struggle, only adapted individuals survive and further reproduce.
3. Natural selection - identifies the mechanism of survival of units with the necessary hereditary changes and their further reproduction. Selection is the result of the struggle for existence. The following mechanisms are distinguished:
a) formation of hereditary changes;
b) survival and preservation of individuals with these changes in the corresponding habitat;
c) the reproduction of these units, the growth of their numbers and the spread of useful hereditary changes.
The driving forces of evolution, interacting with each other, make it possible to explain the formation of other species in nature. Materials accumulated in different branches of biology have a logical conclusion only when they correspond to the principle of evolution.
The great merit of Charles Darwin lies in explaining the process of development and formation of species. It was this fact that made Darwin's evolutionary theory a generally accepted theory.
In nature, a lot of events constantly occur that affect the gene pool of any population of organisms. And they all belong to the driving forces of evolution. In their capacity, Charles Darwin singled out natural selection and the struggle for existence.
Modern biologists consider genetic drift and mutation frequency to be the driving forces of evolution. Refinements and additions to the theory of evolution became possible after the development of molecular biology and decoding of genomes. What factors are considered to be the driving forces of evolution, according to modern synthetic theory, we will consider in this article.
Heredity: nuclear and cytoplasmic
The property of all living organisms to transmit characteristics from generation to generation (heredity) is not in vain considered to be the driving forces of evolution. It is heredity that ensures the continuity and consolidation of valuable adaptations for the survival, reproduction and discreteness (individuality and diversity) of species. The material for evolution is the entire set of chromosomes (genotype) in the nucleus of an organism’s cell. In addition, some cell organelles have their own circular DNA, which is inherited independently from mother to offspring (plastids in plants and mitochondria in all living organisms).
Variability is the key to species diversity
The driving forces of evolution also include the ability of descendants to acquire characteristics that the parent forms did not have. But not all variability leads to the consolidation of new features in the genotype. Phenotypic variability, as a factor of adaptability to the environment, does not affect the gene apparatus, but is a form of manifestation of the genotype in the phenotype and is within the limits of the reaction norms of the trait. It is not considered one of the driving forces of evolution. In the context of our article, genotypic variability (mutational and combinational), with changes in the genotype, is of interest.
Combinative variability
This type of variability is directly related to the sexual process and is expressed in the independent divergence of chromosomes and the processes of crossing over (exchange of sections between homologous chromosomes) as a result of meiosis during the formation of sex cells (gametes). It was the different combinations of genes and their alleles in the genome of gametes and the emergence of sexual reproduction that accelerated evolutionary processes on the planet and became a significant acquisition in facilitating adaptability to environmental conditions for panmictic (sexually reproducing) organisms.
Genomic level mutations
The largest species that changes the entire genome (set of genes) without affecting the structure of the chromosomes.
- Polyploidy is an increase in multiples of the haploid (n) set (3n, 4n, 5n, 6n, 7n, and so on) of the number of chromosomes of an organism. This type of mutation is inherent in many plants and simple animals.
- Aneuploidy is the appearance of extra or loss of chromosomes as a result of disturbances in the passage of meiosis. As a result, an organism with a full set of chromosomes (2n) develops monosomy (2n-1), trisomy (2n+1) or nullisomy (2n-2). Most often, such individuals are not viable or are carriers of severe genetic diseases (Down syndrome in humans is associated with the presence of a third chromosome in pair 21).
Chromosomes and their mutations
In this case, as a result of disturbances in the passage of gametogenesis (the formation of gametes), rearrangements occur in the structure of the chromosomes themselves. Such mutations change the functioning of combinations of genes, less often individual genes, but do not affect the change in the number of chromosomes. There are many types of mutations at this level. We will only name duplications (doublings) and deletions (losses) of a chromosome region.
Gene level mutations
These are mutations of the smallest scale - a point change in one gene. It is this type of mutation that is most often referred to as the driving forces of evolution, since they contribute to an increase in the number of new alleles in the genotype and diversity within the species. Changes in one gene lead to changes in one or more (with multiple effects) traits, increasing the variability of phenotypes. As such mutations accumulate in a population, they become a factor in evolution.
Waves of numbers
A sharp increase in the number of individuals or its catastrophic reduction is called waves of life or population waves. Changes in numbers can occur as a result of many factors (fires, volcanoes, epidemics, disappearance of natural enemies). But all of them are random in nature and lead to changes in the gene pool of the entire population, when outsiders can be in the forefront and vice versa.
Isolation as a factor and driving force of biological evolution
Isolation as free crossing between populations of the same species of panmictic organisms is a clear sign of the action of this factor of evolution. Most species on the planet appeared due to the emergence of populations. The following types are distinguished:
- Spatial (geographical, anthropogenic).
- Biological (ecological, morphological, ethological, genetic).
In any case, when a barrier of free interbreeding arises between populations, we can talk about the beginning of the process of speciation.
The struggle for existence as a tool of natural selection
The instrument of natural selection is the struggle for existence, when only an organism more adapted to given conditions will survive and leave fertile offspring. Their struggle for existence happens:
- Inside - the most cruel and irreconcilable. Competition between representatives of the same species for food resources, territory, better living conditions and the opportunity to leave offspring leaves no chance for weak and unadapted individuals.
- Between representatives of different species, but occupying the same ecological niche. As an example, the competition for plant food between the giraffe and the zebra led in the process of evolution to physiological characteristics, reducing competition to a minimum.
The struggle of organisms with unfavorable conditions. Example: the fat humps of a camel and the fleshy leaves of succulents as adaptive mechanisms of life in the desert. Or the glowing organs of deep-sea fish.
Darwin's evolutionary doctrine, which appeared in the middle of the 19th century, was not without problems, but still won the sympathy of the world scientific community, becoming the most popular theory explaining the origin of humans and other species on the planet. However, it would be fair to note that this theory, over the course of a century and a half of its existence, under the pressure of criticism and problems with missing elements, itself experienced evolution, no matter what tautology this may be.
The leading direction in modern science is called the synthetic theory of evolution. It arose as a result of a rethinking of a number of statements of classical Darwinism, as well as the inclusion of some auxiliary sciences in the study of the origin of species: molecular biology, ecology, genetics, cytology, paleontology and others. But what does she tell us? What are the driving forces of evolution? What conditions made the world the way we see it today?
Driving forces of evolution
As a result of a number of specific reasons, living organisms undergo changes. They can be both negative and positive. In the latter case, organisms adapt better than others to external conditions, displacing hapless competitors from the ecological niche.
Based on the results, we can state that evolutionary changes have taken place. Modern scientists identify the following main driving forces of evolution: the struggle for existence, as its consequence - natural selection, and the last - the variability of organisms with a change of generations, which can be caused by various mutations. Let's look at all these reasons in more detail: 
Conclusion
Thus, the driving forces of evolution predetermine the change in living organisms on the planet and the transformation of nature itself.
Driving factors of evolution- factors that direct various elementary changes resulting from mutations towards the formation of adaptations of organisms to changes in environmental conditions. The driving force of evolution is called natural selection, which is a consequence of the struggle for existence in its various forms. The discrepancy between the number of individuals appearing in a population and the means for their life inevitably leads to a struggle for existence. Struggle for existence- complex and diverse relationships of individuals within species, between species and with inorganic nature. Charles Darwin distinguished three forms of struggle for existence: 1) intraspecific - relationships between individuals belonging to the same species; 2) interspecific - relationships between individuals belonging to different species; 3) the fight against unfavorable conditions of inorganic nature - the relationship of organisms with inanimate nature. The consequence of the struggle for existence is natural selection.
Natural selection - a process as a result of which predominantly individuals with hereditary changes that are useful under given conditions survive and leave behind offspring. This factor of evolution is always directional in nature, it improves adaptations to the conditions of existence, affects all organisms at any age, follows the phenotype and comes down to the selection of genotypes with a reaction norm corresponding to the conditions of a given environment. Natural selection is especially effective against dominant mutations. Quite often in nature it is carried out in favor of heterozygotes (selection for sickle cell anemia). Depending on the direction of adaptive changes, natural selection can be driving, stabilizing, or disruptive.
Driving selection- this is selection, causes a gradual change in the phenotype, leads to a change in the reaction rate in one specific direction. It is carried out in new conditions in favor of changes that are favorable in these conditions. Driving selection is associated with the emergence of new adaptations. Examples of the action of driving selection are the formation of resistance against pesticides in insects and industrial melanism in birch moth butterflies.
Stabilizing selection - This is the selection of individuals, which, with a constant phenotype, is accompanied by a narrowing of the reaction norm and eliminates deviations from it. This form of selection manifests itself when environmental conditions become stable. Stabilizing selection ensures that a particular phenotype that best suits the environment is maintained and rejects any less adaptive changes. An example of the action of stabilizing selection is the preservation of the streamlined body shape of fish and the size of flower parts.
Tearing (disruptive) selection- this is selection that leads to the appearance of several phenotypes and is directed against average intermediate forms. It appears when environmental conditions have changed so much that the bulk of the species loses its adaptability, and individuals with extreme deviations from the average norm gain advantages. This form of selection leads to polymorphism - the existence within a population of two or more forms with sharply different characteristics. An example of the action of discontinuous selection is the emergence of populations of insects with long wings and without wings on islands where strong winds constantly blow.
According to the synthetic theory of evolution, natural selection directs various elementary changes in phenotypes resulting from mutations towards the formation of adaptations of organisms to changes in environmental conditions. This is what it's all about creative role natural selection, which is why it is called driving force of evolution.
