Evolutionary doctrine(from Latin evolutio - deployment) - a system of ideas and concepts in biology that affirm the historical progressive development of the Earth's biosphere, its constituent biogeocenoses, as well as individual taxa and species, which can be included in the global process of evolution of the universe.
Although a single and generally accepted theory biological evolution has not yet been created, the very fact of evolution is not questioned by scientists, since it has a huge number of direct confirmations. According to the theory of evolution, all currently existing species of organisms evolved from previously existing ones through long-term changes. Evolutionary theory deals with analysis individual development individual organisms (ontogenesis), evolution and development paths of groups of organisms (phylogeny) and their adaptations.
The idea that the forms of life observed in the modern world are not unchanged is found among ancient philosophers - Empedocles, Democritus, Lucretius Cara. But we do not know about the facts that led them to such a conclusion, although there is not enough data to state that this is a brilliant speculative guess.
In the Christian world, the creationist point of view dominated for many centuries, although suggestions were made about the existence of “antediluvian” monsters, caused by rare finds of fossil remains at that time.
As facts accumulated in natural science in the 18th century. Transformism emerged - the doctrine of the variability of species. But supporters of transformism (the most prominent - J. Buffon and E. Geoffroy Saint-Hilaire in France, E. Darwin in England) used mainly two facts to prove their views: the presence of transitional forms between species and the similarity of the general structure of large groups of animals and plants . None of the transformists raised the question of the reasons for changes in species. The largest naturalist of the turn of the XVII-XIX centuries. J. Cuvier explained the change in faunas with the theory of catastrophes.
In 1809, the work of J.B. was published. Lamarck’s “Philosophy of Zoology,” in which the question of the reasons for changes in species and evolution was first raised. Lamarck believed that changes in the environment lead to changes in species.
Lamarck introduced the concept of gradations - the transition from lower to higher forms. Gradations, according to Lamarck, occur as a result of the inherent desire for perfection in all living things; the inner feeling of animals gives rise to the desire for change. Observations of natural phenomena led Lamarck to two main assumptions: the “law of non-exercise and exercise” - the development of organs as they are used and the “inheritance of acquired properties” - traits were inherited and subsequently either developed further or disappeared. Lamarck's work did not make much of an impression on the scientific world and was forgotten for exactly fifty years.
New stage in development evolutionary theory came in 1859 with the publication of Charles Darwin's seminal work, On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life. Basic driving force evolution according to Darwin is natural selection. Selection, acting on individuals, allows those organisms that are better adapted for life in a given environment to survive and leave offspring. The action of selection leads to the disintegration of species into parts - daughter species, which, in turn, diverge over time into genera, families and all larger taxa.
Darwin's arguments in favor of the idea of evolution ensured widespread acceptance of the theory. But Darwin was also convinced of the heritability of acquired traits. Failure to understand the discrete nature of heredity led to an insoluble paradox: changes should have died out, but in fact this did not happen. The contradictions were so serious that Darwin himself, at the end of his life, doubted the correctness of his theory, although at that time Mendel’s experiments had already been carried out that could confirm it. The apparent weakness of Darwinism became the reason for the revival of Lamarckism as neo-Lamarckism.
Only the work of many subsequent generations of biologists led to the emergence synthetic theory of evolution(STE). Unlike Darwin's theory, STE does not have one author and one date of origin, but is the fruit of the collective efforts of scientists of different specialties from many countries. After the rediscovery of Mendel's laws, proof of the discrete nature of heredity, and especially after the creation of theoretical population genetics, Darwin's teachings acquired a solid genetic foundation. A broad synthesis between genetics and Darwinism occurred rapidly in the 1930s and 40s. Genetic ideas penetrated taxonomy, paleontology, embryology, and biogeography. The authors of the synthetic theory disagreed on a number of fundamental problems and worked in different areas of biology, but they were almost unanimous in their interpretation of the following basic principles: the local population is considered the elementary unit of evolution; the material for evolution is mutation and recombination variability; natural selection is seen as main reason development of adaptations, speciation and origin of supraspecific taxa; genetic drift and the founder principle are the reasons for the formation of neutral traits; a species is a system of populations reproductively isolated from populations of other species, and each species is ecologically isolated (one species - one niche); speciation consists of the emergence of genetic isolating mechanisms and occurs primarily under conditions of geographic isolation; conclusions about the causes of macroevolution (the origin of supraspecific taxa) can be obtained through the study of microevolution, built on the basis of accurate experimental data, field observations and theoretical deductions. There is also a group of evolutionary ideas according to which speciation (the key moment of biological evolution) occurs quickly - over several generations. In this case, the influence of any long-term evolutionary factors is excluded (except for cutting selection). Such evolutionary views are called saltationism (Latin “saltatotius”, from “salto” - I gallop, jump), ideas about evolution as a discontinuous process with stages of rapid progressive evolutionary changes, alternating with periods of slow, insignificant changes. Saltationism is a poorly developed direction in the theory of evolution. According to the latest concepts of SET, gradual (proceeding at a constant low speed) changes can alternate with saltation ones.
| ]The idea of organisms changing over time is first found among the Greek pre-Socratic philosophers. Anaximander, a representative of the Milesian school, believed that all animals originated from water, after which they came to land. Man, according to his ideas, was born in the body of a fish. The ideas of homology and survival of the fittest can be found in Empedocles. Democritus believed that land animals descended from amphibians, and they, in turn, spontaneously generated in the mud. In contrast to these materialistic views, Aristotle considered all natural things to be imperfect manifestations of various permanent natural possibilities, known as "forms", "ideas" or (in Latin transcription) "species" (lat. species). However, Aristotle did not postulate that real types of animals are exact copies of metaphysical forms, and gave examples of how new forms of living beings could be formed.
In the 17th century, a new method emerged that rejected the Aristotelian approach and sought explanations of natural phenomena in the laws of nature, uniform for all visible things and not requiring unchangeable natural types or a divine cosmic order. But this new approach had difficulty penetrating the biological sciences, which became the last stronghold of the concept of an unchanging natural type. John Ray used a more general term for animals and plants to define unchanging natural types - “species” (Latin species), but, unlike Aristotle, he strictly defined each type of living being as a species and believed that each species could be defined by traits that are reproduced from generation to generation. According to Ray, these species are created by God, but can be variable depending on local conditions. Linnaeus's biological classification also viewed species as unchanging and created according to a divine plan.
However, at that time there were also naturalists who thought about the evolutionary change of organisms that occurs over a long time. Maupertuis wrote in 1751 about the natural modifications that occur during reproduction, accumulating over many generations and leading to the formation of new species. Buffon proposed that species could degenerate and change into other organisms. Erasmus Darwin believed that all warm-blooded organisms probably descend from a single microorganism (or "filament"). The first full-fledged evolutionary concept was proposed by Jean Baptiste Lamarck in 1809 in his work “Philosophy of Zoology”. Lamarck believed that simple organisms (ciliates and worms) constantly generate spontaneously. Then these forms change and complicate their structure, adapting to the environment. These adaptations occur due to the direct influence of the environment through the exercise or non-exercise of organs and the subsequent transmission of these acquired characteristics to descendants (later this theory was called Lamarckism). These ideas were rejected by naturalists because they had no experimental evidence. In addition, the position of scientists was still strong, believing that species are unchanging, and their similarities indicate divine design. One of the most famous among them was Georges Cuvier.
The end of the dominance in biology of ideas about the immutability of species was the theory of evolution by natural selection, formulated by Charles Darwin. Influenced in part by Thomas Malthus's Essay on Population, Darwin observed that population growth leads to a "struggle for existence" in which organisms with favorable characteristics begin to predominate, as those without them die. This process begins when each generation produces more offspring than can survive, resulting in competition for limited resources. This could explain the origin of living beings from a common ancestor due to the laws of nature. Darwin developed his theory starting in 1838 until Alfred Wallace sent him his paper with the same ideas in 1858. Wallace's paper was published that same year in one volume of the proceedings of the Linnean Society, along with a brief excerpt from the works of Darwin. The publication in late 1859 of Darwin's On the Origin of Species, which explained the concept of natural selection in detail, led to the wider acceptance of Darwin's concept of evolution.
Since then, the modern synthesis has been expanded to explain biological phenomena at all levels of organization of living things and stages of individual development. The latter became the prerequisite for the emergence of the Evo-Devo concept.
Criticism of evolutionism[ | ]
Criticisms of evolutionism appeared immediately after evolutionary ideas emerged in the early nineteenth century. These ideas were that the development of society and nature is governed by natural laws, which became known to the educated public through the book of George Combe (English)Russian“The Constitution of Man” () and the anonymous “Vestiges of the Natural History of Creation” (). After Charles Darwin published On the Origin of Species, much of the scientific community agreed that evolution is a fact, since Darwin's theory is based on experimental evidence. In the 30s and 40s of the 20th century, scientists developed the synthetic theory of evolution (STE), which combined the idea of Darwinian natural selection with the laws of heredity and data from population genetics. Since that time, the existence of evolutionary processes and the ability of modern evolutionary theories to explain why and how these processes occur has been supported by the vast majority of biologists. Since the advent of STE, almost all criticism of evolutionism has been carried out by religious figures (mainly Protestants), rather than scientists.
Evolutionism and religion[ | ]
It should be noted that the accusations of atheism and denial of religion, brought by some opponents of the teaching of evolution, are based to a certain extent on a misunderstanding of the nature of scientific knowledge: in science, no theory, including the theory of biological evolution, can either confirm or deny the existence of such subjects from the other world, like God (if only because God could use evolution in the creation of living nature, as stated by the theological doctrine “theistic evolutionism”).
Attempts to contrast evolutionary biology with religious anthropology are also mistaken. From the point of view of scientific methodology, a popular thesis “man came from apes” is only an oversimplification (see reductionism) of one of the conclusions of evolutionary biology (about the place of man as a biological species on the phylogenetic tree of living nature), if only because the concept “man” is polysemantic: man as a subject of physical anthropology is by no means identical to man as a subject of philosophical anthropology, and it is incorrect to reduce philosophical anthropology to physical anthropology.
Some believers different religions do not find evolutionary teaching contrary to their faith. The theory of biological evolution (along with many other sciences - from astrophysics to geology and radiochemistry) contradicts only the literal reading of sacred texts telling about the creation of the world, and for some believers this is the reason for rejecting almost all the conclusions of natural sciences that study the past of the material world (literalist creationism ).
Among believers who profess the doctrine of literalist creationism, there are a number of people who are trying to find scientific evidence for their doctrine (so-called “scientific creationism”). The scientific community recognizes such evidence as untrue, and the directions themselves as pseudoscientific.
Recognition of evolution by the Catholic Church[ | ]
See also [ | ]
Notes [ | ]
- Kutschera U., Niklas K. J. The modern theory of biological evolution: an expanded synthesis // Naturwissenschaften. - 2004. - Vol. 91, no. 6. - P. 255-276.
- , With. 118-119.
- , With. 124-125.
- , With. 127.
- Torrey H. B., Felin F. Was Aristotle an evolutionist? // The Quarterly Review of Biology. - 1937. - Vol. 12, no. 1. - P. 1-18.
- Hull D. L. The metaphysics of evolution // The British Journal for the History of Science. - 1967. - Vol. 3, no. 4. - P. 309-337.
- Stephen F. Mason. . A history of the sciences. - Collier Books, 1968. - 638 p.- P. 44-45.
- , With. 171-172.
- Ernst Mayr. . The growth of biological thought: diversity, evolution, and inheritance. - Harvard University Press, 1982. - ISBN 0674364465.- P. 256-257.
- Carl Linnaeus (1707-1778) (undefined) (unavailable link) Archived April 30, 2011.
- , With. 181-183.
- , p. 71-72.
- Erasmus Darwin (1731-1802) (undefined) (unavailable link). // University of California Museum of Paleontology. Retrieved February 29, 2012. Archived January 19, 2012.
- , With. 201-209.
- , p. 170-189.
- , With. 210-217.
- , p. 145-146.
- , p. 165.
- , With. 278-279.
- , With. 282-283.
- , With. 283.
- Stamhuis I. H., Meijer O. G., Zevenhuizen E. J.//Isis. - 1999. - Vol. 90, no. 2. - P. 238-267.
- , With. 405-407.
- Dobzhansky T. Nothing in biology makes sense except in the light of evolution // The American Biology Teacher. - 1973. - Vol. 35, no. 3. - P. 125-129.
- Avise J.C., Ayala F.J. In the Light of Evolution IV. The Human Condition (introduction) // Proceedings of the National Academy of Sciences USA. - 2010. - Vol. 107. - P. 8897-8901.
- Johnston, Ian C. …And Still We Evolve. Section Three: The Origins of Evolutionary Theory (undefined) . // Liberal Studies Department, Malaspina University College (1999). Retrieved April 30, 2010. Archived September 27, 2006.
- IAP Statement on the Teaching of Evolution Archived copy September 27, 2007 on the Wayback Machine, Interacademy Panel.
- In a detailed work on creationism, The Creationists (English)Russian Historian Ronald Numbers traces the religious motivations and attempts at scientific analysis of famous creationists, beginning with George Frederick Wright (English)
Biological evolution - irreversible, directed, historical development of living nature, accompanied by changes in the genetic composition of populations, the formation of adaptations, the formation of new and extinction of old species, changes in biogeocenoses and the biosphere as a whole.
Evolutionary teaching studies the general patterns and driving forces of the development of life on Earth. When studying the evolutionary process, it is advisable to distinguish two levels: the population-species level and the levels of supraspecific order (families, genera, orders, etc.). Populations and species are structures that actually exist in time and space; supraspecific orders are the unification of actually existing species into larger systematic taxa based on certain characteristics, primarily related to their common origin. Therefore, in evolutionary teaching there are two sections: microevolution and macroevolution.
Microevolution - this is the initial stage of evolutionary changes that occurs within a species and leads to the formation of new intraspecific groups, and ultimately to the formation of new species. Macroevolution- studies the evolution of supraspecific orders. The basic processes leading to micro- and macroevolution are similar. The fundamental difference lies in the time during which these processes occur: microevolution - tens and hundreds of thousands of years, macroevolution - millions of years.
Methods for studying evolution:
For microevolution analysis
1. Population genetic method (studies the genetic structure of populations, analyzes changes in the gene pool of populations over time, as well as the intensity of the mutation process in populations)
2. Hybridological method (allows us to analyze the role of combinative variability in the phenotypic diversity of individuals within a species)
3. Ecological methods (allow us to clarify the role of biotic and abiotic factors affecting the structure and dynamics of species). Diverse in their forms: observation, experiment, modeling.
To analyze macroevolution
- Paleontological
a) study of fossil transitional forms (Devonian Ichthyostega, Jurassic proto-bird Archaeopteryx, animal-like reptile Lycaenops)
b) restoration of phylogenetic series - a sequence of fossil forms related to each other in the process of evolution (series of mollusks, horses)
2. Morphological methods - based on the principle: the internal similarity of organisms can show the evolutionary relationship of the compared forms. The structure of homologous organs, rudimentary organs, atavisms, and histological features of tissues are studied.
3. Embryological methods are aimed at identifying embryonic similarities and studying recapitulation. The law of germinal similarity was formulated by K. Baer: “The earlier stages of ontogenesis are studied, the more similarities are found between organisms.” The essence of recapitulation lies in the fact that at the beginning of embryonic development, many structural features of ancestral forms seem to be repeated (recapitulated): early stages development, the characteristics of more distant ancestors are repeated, and at later stages - of close ancestors.
- Methods of biochemistry and molecular genetics study the structure of proteins and nucleic acids of organisms belonging to different families, orders, classes. Based on the degree of differences in the structure of proteins and nucleotides, the degree of phylogenetic relationship of various taxa can be determined.
The doctrine of microevolution
The main processes leading to microevolution occur within a species, in intraspecific groups. Individuals of any species are distributed unevenly within the species range. The centers of the largest concentration of individuals are separate populations of this species. It is in populations that events occur that lead to the formation of new species. Therefore, populations are elementary evolutionary units.
Population- a minimal self-reproducing group of individuals that inhabit a certain space for a long time, forming an independent genetically open system. A species, unlike a population, is a genetically closed system: there are various barriers that prevent individuals of different species from interbreeding. These barriers are called "isolation". There are different types of populations: island and ribbon.
Basic characteristics of the population.
- 1. Environmental characteristics.
1. Population range(natural barriers, radius of individual activity, availability of food, mating partner, number of individuals). There are:
a) trophic area
b) reproductive range
2. Number of individuals in the population(fertility, duration life cycle, time to reach reproductive period). Of particular importance is the minimum number of individuals, upon reaching which the population may disappear for various reasons (anthropogenic impacts, natural disasters, diseases within the population).
3. Population dynamics. The size of any population is subject to constant fluctuations as a result of the influence of various biotic and abiotic factors. These fluctuations in numbers are called “population waves.” Population waves can be seasonal, or periodic (insects, annual plants) and non-periodic (changes in the prey-predator system, favorable conditions in the food chain - the presence of a large amount of food).
4. Age composition of the population determined by the presence of individuals of different age groups in the population. Disruption of population reproduction and, as a result, population aging is the first step towards its extinction.
5. Sex composition of the population determined by primary, secondary and tertiary sex ratio. The sex structure of a population is the numerical ratio of males and females in different age groups. We can talk about sex ratio only if there are individuals of different sexes in the population. The main genetic mechanism determining the sex ratio is heterogamety of either sex.
- 2. Genetic characteristics of the population
1. Population gene pool- the totality of all genes of individuals in a population. This set includes genes that were passed on from previous generations and genes that arose at a given historical moment in the existence of the population. Newly emerged genes do not manifest themselves phenotypically (since most of them are recessive), but their presence in the future can significantly affect the fate of the population.
2. Genetic heterogeneity of the population characterized by the diversity of genotypes of individuals in a population. Any individual has its own individual genotype, which determines the individuality of phenotypic characteristics. The main mechanisms of this individuality are combinative variability and the mutation process.
Genetic processes in a population. The main genetic characteristics of the population are the frequency of occurrence:
Genes (quantitative ratio of alleles)
Genotypes (quantitative ratio of genotypes)
Phenotypes (quantitative ratio of phenotypes)
The ratios of these indicators are based on the mechanisms of combinative variability: the distribution of chromosomes and genes during meiosis and the random fusion of gametes during fertilization.
A mathematical justification for these ratios was proposed by J. Hardy and G. Weinberg; their law allows one to calculate the relative frequency of genotypes and phenotypes in a population. But it should be remembered that this law applies to an ideal population, and one of the main criteria of a given population is its large size. In other words, the relationships between genes and genotypes in populations can only be maintained when there are a large number of individuals. In small populations, the ratios of genotypes may be disrupted. Domestic scientists N.P. Dubinin and D.D. Romashev found that in small populations, due to random reasons, heterozygous individuals disappear, and the population becomes genetically homogeneous. Individuals with genotypes AA and aa begin to predominate in it. This phenomenon is called “genetic drift” or genetic-automatic processes.
Maintaining certain ratios of genotypes in a population leads to the presence in it intrapopulation polymorphism - the existence in a population of two or more different genetic, and, consequently, phenotypic, groups in a state of long-term equilibrium. Examples: people with different blood types, blondes and brunettes, blue eyes and brown eyes etc.
The genetic heterogeneity of a population determines not only the phenotypic diversity of individuals, but also affects the historical perspective of the existence of the population and the species as a whole. But no matter how diverse the gene pool of a population is, it cannot by itself ensure the evolutionary process: it must be influenced by some factors. And these factors are called elementary evolutionary factors.
Elementary evolutionary factors.
1. Mutation process. When assessing the role of mutations in evolutionary processes, the following should be noted:
The mutation occurs in one individual and is passed on to one daughter. Subsequently, with the change of generations, the process of accumulation of mutations in the population occurs;
During sexual reproduction, only generative mutations can be transmitted to descendants;
The mutation must not adversely affect the viability or reproductive functions of the organism, i.e. in terms of biological significance it should be neutral. And the harmfulness or usefulness of a mutation will manifest itself in the course of natural selection. But it should also be remembered that harmfulness and usefulness are relative. Examples, flightless forms of insects on the islands (C. Darwin), upright walking - human diseases, sickle cell anemia - malaria;
Mutations can change any hereditary characteristics and properties of the organism;
The manifestation of mutations depends on the genetic environment into which the mutant gene enters. This is reflected in the phenotypic characteristics of gene expression - expressivity and penetrance.
When considering the role of mutations, it should also be taken into account that the resulting mutation leads to the disappearance of a previously existing characteristic (property). The gene pool of a population is the result of long-term selection of the best combinations of genes. Therefore, evolutionary mechanisms have emerged that limit genetic variability:
At the organismal level: mitosis and meiosis
At the cellular level: chromosome pairing - conversion of mutations to heterozygous
state
At the DNA level: repair mechanisms
The significance of the mutation process. Maintains a high degree of heterogeneity of natural populations, thereby creating the basis for the action of other evolutionary factors. The mutation process is the supplier of elementary evolutionary material.
2. Population waves. Changes in the number of individuals are characteristic of any population. This occurs as a result of the action of various abiotic and biotic factors, which can lead to an increase or, conversely, a decrease in population size. And fluctuations in numbers can be different: thousands, hundreds of thousands, and even millions of times. In a population that has experienced a decline, allele frequencies may differ significantly from the original population. The remaining gene pool will determine the new genetic structure of the entire population during the next increase in numbers. In this case, previously existing mutations in small concentrations may disappear, and the concentration of other mutations may randomly increase. In this case population waves act as a supplier of evolutionary material.
As the population size increases, individuals migrate, which leads to an expansion of the population range. There may be different habitat conditions at the boundaries of the range. And under different conditions, preferential reproduction of certain groups of organisms may be observed. An example is melanism in butterflies. In this case population waves contribute testing new genotypes to identify the usefulness or harmfulness of traits.
3.Insulation - the emergence of any barriers preventing free crossing. The obstacle to crossing leads to the consolidation and increase of differences between populations.
In nature, there is spatial isolation and biological isolation. Spatial isolation can exist in two forms: isolation by any barriers (water, land, mountains) and isolation by distance, which is determined by the possibility of interbreeding of closely living individuals.
Biological isolation can be divided into pre-copulatory (eliminating crossing) and post-copulatory.
Precopulatory isolation is represented by the following forms: ecological-ethological (organisms occupy different ecological niches: swamp and forest birds; different timing of gamete formation, different mating and nesting instincts) and morphophysiological isolation (size of organisms, differences in the structure of reproductive organs).
Post-copulatory or intrinsic genetic isolation is caused by mechanisms that disrupt the fusion of gametes, normal development embryo, the emergence of sterile hybrids, reduced viability of hybrids.
Insulation value: consolidates and strengthens the initial stages of genetic differentiation of the population.
The driving and guiding elementary evolutionary factor is certainly natural selection.
Natural selection is carried out in nature through the struggle for existence, both in direct form (intraspecific and interspecific) and in indirect form (struggle against unfavorable environmental conditions). C. Darwin substantiated the premises of natural selection:
Uncertain variability (genotypic - modern term)
“Any sign that is insignificant at first glance, when environmental conditions change, can play a decisive role in the struggle for life”
The desire of organisms to reproduce exponentially.
Charles Darwin wrote: “ The preservation of favorable individual differences and variations, and the destruction of those which are unfavorable, I call NATURAL SELECTION, OR SURVIVAL OF THE FITTEST.”
However, in the course of natural selection, what matters is not survival or death, but the differential reproduction of individuals. The very fact of survival without leaving offspring will have no consequences for evolution. Only those individuals that can leave numerous offspring are promising for evolution. Therefore, in the modern interpretation, natural selection is the selective preservation and reproduction of genotypes. But the selection of genotypes occurs exclusively through the selection of phenotypes, since the phenotype reflects the characteristics of the genotype. And at the same time, natural selection affects all vital signs and properties.
Currently, there are more than 30 forms of natural selection, but the main forms can be called: stabilizing, driving, disruptive, sexual selection.
1.Stabilizing selection- this is the preferential survival of organisms that have characteristics that do not have noticeable deviations from the norm characteristic of a given population. This selection takes place under stable conditions of the population. Classic example: G. Bumpas - 1911 - Manhattan - 327 sparrows numb from frost and snowstorm: deviations according to average size by any trait (wing length, tarsus length, beak height, weight and body length) contributed to the elimination of individuals from the population. The action of stabilizing selection explains all cases of preservation of characteristics at any level of organization: 2 eyes, a five-fingered limb, body weight, a certain level of hormones (45, XO), etc. But stabilizing selection does not prevent the accumulation of mutations, which at this stage of the population’s existence do not manifest themselves phenotypically. This leads to the creation of a reserve of hereditary variability. When environmental conditions change, this variability serves as material for the transformation of the population under the influence of driving selection.
2. Driving selection leads to a shift in the reaction norm of a trait towards an increase or decrease. With directed changes in the environment, individuals with individual characteristics that correspond to these changes survive. A classic example: the neck and limbs of a giraffe. Traits that promote survival at low temperatures: increased fertility, increased size of the liver and heart (increased energy metabolism), increased body size (decreased heat transfer) are the result of driving selection. This form of selection leads to the emergence of new adaptations through a directed restructuring of the gene pool of the population.
In nature, driving and stabilizing selection constantly coexist together, and we can only talk about the predominance of one or another form in a given period of time for a given trait.
3. Disruptive selection aims to divide the original population into two or more different morphological groups.
The three forms of selection listed above characterize three possible states of the population: its immutability, unidirectional change and multidirectional change leading to fragmentation.
4. Sexual selection- occurs between individuals of the same sex for the opportunity to participate in the sexual process. In this case, bright colors, features of singing and shouting, weapons for tournament battle, development muscular system play an important role in determining a partner.
Paths and methods of speciation
The interaction of elementary evolutionary factors leads to the final result of microevolution - speciation. Speciation is the division (in time and space) of a previously single species into two or more. And from the position of genetics, speciation is genetic division open system populations into genetically closed systems of new species.
The following pathways of speciation are distinguished:
1. True - one population gives rise to two new species. In this case, the number of species increases.
2. Philitic - a new species arises through a gradual change over time of the same species without any divergence (divergence) of the original group. Prove this form Speciation is possible only with the involvement of paleontological material. One possible example is the evolution of horses.
3. Hybridogenic - a new species arises as a result of the hybridization of two existing species. Most examples are associated with plants: cultivated plum (a hybrid of cherry plum and sloe), mountain ash, hybrid forms of raspberries, tobacco, and rutabaga. In animals - khanorik (a hybrid of a ferret and a mink).
In true speciation, two main modes can be distinguished: allopatric and sympatric speciation.
Allopatric speciation. In this case, the separating populations are spatially (geographically) isolated from each other.
Main stages:
1. Change in the genetic composition of the population, accumulation
reserve of hereditary variability.
2. Population waves: with increasing numbers
individuals in the population migrate, as a result
The population area is expanding significantly.
There may be different conditions at the boundaries of the range,
in which certain types of
divided groups of organisms.
With a decrease in the number of individuals, the original range
population may change: decrease or disintegrate
be two (or more). In the latter case, the original
the population splits into two, and between them arose
geographical insulation. But the early stages of the section
population, it is relative: individuals are more likely to cross-breed
differ within their own population than with the neighboring one.
3. Geographically isolated populations are defined
For some time, they exist in isolation. In each of them
additional mutations occur that lead to
lead to the formation of different gene pools. And this
leads to the emergence various forms biologists
ical isolation, including genetic isolation. From the moment
the emergence of two genetically closed systems, we
has the right to talk about the emergence of two new species from
single population.
At all stages, natural selection plays the main role.
Sympatric speciation- speciation occurring within the original range of a species on the basis of non-spatial isolation. Researchers identify several isolation options that can separate a primarily single population: chronological (according to the timing of reproduction), ecological and genetic.
Examples of speciation in lakes are given as chronological (seasonal) isolation. So, for example, in the lake. Sevan is home to an endemic species of trout, represented by several forms that differ morphologically, as well as in terms of spawning time.
Genetic isolation occurs as a result of a significant change in the karyotype of a group of individuals within the original population. More often mutations are represented by polyploidies. Polyploid forms are known in chrysanthemums, potatoes, and tobacco.
Evolution of phylogenetic groups
Among the forms we can distinguish primary ones - phyletic evolution and divergence, and secondary ones - parallelism and convergence.
Directions of evolution:
Arogenesis- development of a group with a significant expansion of the adaptive zone (a set of ecological conditions representing a possible living environment for a given group of organisms) and with access to other natural zones under the influence of the group acquiring some large, previously absent adaptations (aromorphoses). The result of arogenesis is the emergence of new types and classes of animal and plant life.
Allogenesis- development of a group within one adaptive zone with the emergence of similar forms, differing in adaptations of the same scale (idioadaptation). The result is the emergence of orders, families, and genera within the class.
Accent placement: evolutionary teaching
Evolutionary doctrine- a system of ideas and concepts in biology that affirm the historical progressive development of the Earth’s biosphere, its constituent biogeocenoses, as well as individual taxa and species, which can be included in the global process of evolution of the universe. Evolutionary teaching deals with the analysis of the formation of adaptation (adaptations), the evolution of individual development of organisms (ontogenesis), factors directing evolution, and specific paths of historical development (phylogeny) of individual groups of organisms and the organic world as a whole. The basis of evolutionary teaching is evolutionary theory. Evolutionary teaching also includes the concepts of the origin of life and the origin of man.
History of evolutionary teaching
The first ideas about the development of life, contained in the works of Empedocles, Democritus, Lucretius Cara and other ancient philosophers, were in the nature of brilliant guesses and were not substantiated by biological facts. In the 18th century In biology, transformism was formed - the doctrine of the variability of species of animals and plants, opposed to creationism, based on the concept of divine creation and the immutability of species. The most prominent transformists of the 2nd half of the 18th and 1st half of the 19th centuries - J. Buffon and E. J. Saint-Hilaire in France, E. Darwin in England, J. V. Goethe in Germany, C. F. Roulier in Russia - they substantiated the variability of species mainly by two facts: the presence of transitional forms between closely related species and the unity of the structural plan of organisms of large groups of animals and plants. However, they did not consider the causes and factors of species change.
The first attempt to create a holistic evolutionary theory belongs to the French naturalist J. B. Lamarck, who outlined his ideas about the driving forces of evolution in his “Philosophy of Zoology” (1809). According to Lamarck, the transition from lower to higher forms of life - gradation - occurs as a result of the immanent and universal desire of organisms for perfection. Lamarck explained the diversity of species at each level of organization by the gradation-modifying influence of environmental conditions. According to Lamarck’s first “law”, exercise of organs leads to their progressive development, and lack of exercise leads to reduction; according to the second “law”, the results of exercise and non-exercise of organs, with a sufficient duration of exposure, are fixed in the heredity of organisms and are further transmitted from generation to generation, regardless of the environmental influences that caused them (see Lamarckism, Acquired characteristics). Lamarck’s “laws” are based on the erroneous idea that nature is characterized by a desire for improvement and the inheritance of acquired properties by organisms.
The true factors of evolution were revealed by Charles Darwin, thereby creating a scientifically based evolutionary theory (set out in the book “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life,” 1859). The driving forces of evolution, according to Darwin, are: indefinite variability - the hereditarily determined diversity of organisms in each population of any species, the struggle for existence, during which less adapted organisms die or are eliminated from reproduction, and natural selection - the survival of more adapted individuals, as a result of which they accumulate and beneficial hereditary changes are summed up and new adaptations arise. Lamarckism and Darwinism in the interpretation of evolution are diametrically opposed: Lamarckism explains evolution by adaptation, and Darwinism explains adaptation by evolution. In addition to Lamarckism, there are a number of concepts that deny the importance of selection as the driving force of evolution (Autogenesis, Mutationism, Nomogenesis, etc.). The development of biology confirmed the correctness of Darwin's theory. Therefore, in modern biology, the terms “Darwinism” and “Evolutionary doctrine” are often used as synonyms. The term “synthetic theory of evolution” is also close in meaning, which emphasizes the combination (synthesis) of the main provisions of Darwin’s theory, genetics and a number of evolutionary generalizations of other areas of biology.
Modern evolutionary teaching
The development of genetics has made it possible to understand the mechanism of the emergence of uncertain hereditary variability, which provides material for evolution. This phenomenon is based on persistent changes in hereditary structures - mutations. Mutational variability is not directed: newly emerging mutations are not adequate to environmental conditions and, as a rule, disrupt already existing adaptations. For organisms that do not have a formed nucleus (Prokaryotes), mutational variability serves as the main material for evolution. For organisms whose cells have a formed nucleus (Eukaryotes), combinative variability - the combination of genes during sexual reproduction - is of great importance. The elementary unit of evolution is the population. The relative isolation of populations leads to their reproductive isolation—limiting the freedom of interbreeding of individuals from different populations. Reproductive isolation ensures the uniqueness of the gene pool - the genetic composition of each population - and thereby the possibility of its independent evolution. In the process of struggle for existence, the biological diversity of the individuals composing a population is manifested, determined by combinative and mutational variability. In this case, some individuals die, while others survive and reproduce. As a result of natural selection, newly emerging mutations are combined with the genes of individuals that have already been selected, their phenotypic expression changes, and new adaptations arise on their basis. Thus, it is selection that is the main driving factor in evolution, causing the emergence of new adaptations, the transformation of organisms and speciation. Selection can manifest itself in different forms: stabilizing, ensuring the preservation of already formed adaptations in unchanged environmental conditions, driving, or leading, leading to the development of new adaptations, and disruptive, or breaking, causing the emergence of polymorphism with multidirectional changes in the population’s habitat.
In modern evolutionary teaching, the idea of the factors of evolution has been enriched by the identification of the population as an elementary unit of evolution, the theory of isolation and the deepening of the theory of natural selection. Analysis of isolation as a factor providing an increase in the diversity of life forms underlies modern ideas about speciation and species structure. Allopatric speciation, associated with the dispersal of the species and the geographic isolation of marginal populations, has been most fully studied. Less studied is sympatric speciation caused by ecological, chronological or ethological (behavioral) isolation. Evolutionary processes occurring within a species and culminating in speciation are often combined under the general name of microevolution. Macroevolution is the historical development of groups of organisms (taxa) of supraspecific rank. The evolution of supraspecific taxa is the result of speciation occurring under the influence of natural selection. However, the use of different time scales (the evolution of large taxa consists of many stages of speciation) and study methods (using data from paleontology, comparative morphology, embryology, etc.) makes it possible to identify patterns that escape the study of microevolution. The most important tasks of the concept of macroevolution are the analysis of the relationship between the individual and historical development of organisms, the analysis of the patterns of phylogenesis and the main directions of the evolutionary process. In 1866, the German naturalist E. Haeckel formulated the biogenetic law, according to which the stages of the phylogeny of a given systematic group are briefly repeated in ontogenesis. Mutations appear in the phenotype of an adult organism as a result of the fact that they change the processes of its ontogenesis. Therefore, natural selection of adult individuals leads to the evolution of ontogenetic processes - the interdependencies of developing organs, called ontogenetic correlations by I. I. Shmalgauzen. The restructuring of the system of ontogenetic correlations under the influence of driving selection leads to the occurrence of changes - phylembryogenesis, through which new characteristics of organisms are formed in the course of phylogenesis. In the event that a change occurs at the final stage of organ development, further evolution of the ancestral organs occurs (Anabolia); There are also deviations of ontogenesis at intermediate stages, which leads to the restructuring of organs (deviation); changes in the formation and development of early rudiments can lead to the emergence of organs that were absent in the ancestors (Arhallaxis). However, the evolution of ontogenetic correlations under the influence of stabilizing selection leads to the preservation of only those correlations that most reliably support the processes of ontogeny. These correlations are recapitulations - repetitions in the ontogenesis of descendants of the phylogenetic states of their ancestors; thanks to them, the biogenetic law is ensured. The direction of phylogeny of each systematic group is determined by the specific relationship between the environment in which the evolution of a given taxon takes place and its organization. Divergence (divergence of characters) of two or more taxa arising from a common ancestor is due to differences in environmental conditions; it begins at the population level, causes an increase in the number of species and continues at the level of supraspecific taxa. It is divergent evolution (which determines the taxonomic diversity of living beings. Parallel evolution is less common. It occurs in cases where the initially divergent taxa remain in similar environmental conditions and develop similar adaptations on the basis of a similar organization inherited from a common ancestor. Convergence (convergence of characters) occurs in cases where unrelated taxa adapt to the same conditions. Biological progress can be achieved through a general increase in the level of organization, which determines the adaptation of organisms to environmental conditions that are broader and more diverse than those in which their ancestors lived. Such changes - aromorphoses - occur. rarely and necessarily give way to allomorphoses - divergence and adaptation to more particular conditions in the process of mastering a new environment. The development of narrow adaptations in the phylogeny of a group leads to specialization.
The 4 main types of specialization identified by Schmalhausen - telomorphosis, hypomorphosis, hypermorphosis and catamorphosis - differ in the nature of adaptations, but all lead to a slowdown in the rate of evolution and, due to the loss of multifunctionality by the organs of specialized animals, to a decrease in evolutionary plasticity. If stable environmental conditions are maintained, specialized species can exist indefinitely. This is how “living fossils” arise, for example, many genera of mollusks and brachiopods that have existed from the Cambrian to the present day. With sudden changes in living conditions, specialized species die out, while more flexible ones manage to adapt to these changes.
The doctrine of evolution and mainly its theoretical core - evolutionary theory - serve as both an important natural science justification for dialectical materialism and one of the methodological foundations of modern biology.
Zlygostev A. S.
Sources:
- Great Soviet Encyclopedia
Evolutionary teaching is the science of the causes, driving forces, mechanisms and general patterns of the historical development of the living world. Evolution in biology is the continuous directed development of the living world, accompanied by changes in the structure and levels of organization of different groups of organisms, allowing them to more effectively adapt and exist in a wide variety of living conditions.
The doctrine of evolution is the theoretical basis of biology, since it explains the main features, patterns and development paths of the organic world, allows us to understand the reason for the unity and enormous diversity of the organic world, and to clarify the historical connections between in different forms life and foresee their development in the future. The doctrine of evolution summarizes the data of many biological sciences, allows us to understand the mechanisms and directions of variability in living matter and use this knowledge in the practice of breeding work.
The doctrine of evolution did not arise immediately. It arose as a result of a long struggle between two fundamentally opposing systems of views on life and its origin - the ideas of the Divine creation of the world and ideas about the spontaneous generation and self-development of life. Based on these views, two directions have emerged in science - creationism, which develops the ideas of the creation of the world by God or a Higher Mind, and the second - evolutionism, which allows for the possibility of spontaneous generation and self-development of the organic world. There were also ideas about the eternity of life in nature.
Already in ancient times, these ideas were actively discussed, and such outstanding thinkers of their own made a great contribution to their development.
The pre-Darwinian period of development of evolutionary ideas in the biology of time, such as Thales of Miletus, Anaximander, Anaximenes, Heraclitus, Empedocles, Democritus, Plato, Aristotle and many others.
In the Middle Ages, the ideas of creationism and the immutability of the world dominated mainly.
The most prominent scientists of the pre-Darwinian period in the development of biology were C. Linnaeus and J. B. Lamarck.
Carl Linnaeus (1707-1778) - an outstanding Swedish scientist. It was he who made an attempt to summarize the data available at that time about the diversity of the organic world and create its scientific classification, setting out his views on these issues in the “System of Nature” (1735). He is the creator of taxonomy and nomenclature - the sciences about the principles of classification and the rules for their naming. K. Linnaeus considered species to be the main taxonomic category of plants and animals, defining it as a set of similar individuals reproducing their own kind. He grouped species into genera. In his system, he identified five taxonomic categories of different levels: class, order, genus, species, variety. To name species, K. Linnaeus used binary nomenclature, that is, a double name - indicating the names of the genus and species (for example, red fly agaric, red deer, etc., where the first word is the name of the genus, and the second is the name of the species). He made descriptions of species and their names in Latin, the language then accepted in science. This greatly facilitated mutual understanding between scientists from different countries, since in different languages the same species can be called completely differently. Therefore, it is still customary to write the scientific names of plants, mushrooms or any other organisms in Latin, which is understandable to specialists from different countries. In total, K. Linnaeus compiled descriptions of about ten thousand species of plants and animals, combining them into 30 classes (24 classes of plants and 6 classes of animals). However, K. Linnaeus' system was artificial, based on the similarity of only external characteristics. Thus, he included coelenterates, sponges, echinoderms, and even cyclostomes in the class of worms, which now belong to completely different types of animals. He divided plants into classes according to the presence or absence of a flower, the shape of the flower and the number of stamens and pistils in it. But at the same time, he absolutely correctly classified man as a primate. This was a revolutionary step for that time. It is no coincidence that the work of C. Linnaeus was banned by the Vatican for a long time. K. Linnaeus considered species to be unchangeable, existing in the state as God created them. But he noted that varieties can change over time. The great merit of K. Linnaeus is that his taxonomy actually reflected the results of evolution - the diversity of organisms from simple forms to more complex ones, and taxonomic categories for the first time determined the hierarchy and subordination of different groups of organisms - from species to classes.
A very important figure in biology is Jean-Baptiste Lamarck (1744-1829), a French scientist who created the first holistic evolutionary doctrine, the foundations of which he outlined in his work “Philosophy of Zoology” (1809). In it he proved for the first time that variability is inherent in all species. J.B. Lamarck considered the main reasons for variability to be the influence of the external environment and the desire of living organisms for perfection, implanted in them by God. Thus, according to Lamarck, the process of evolution is, as it were, planned by the Creator himself. Lamarck considered exercise or non-exercise of organs to be the main mechanism of species variability. Under the influence of changing environmental conditions, animals have to change their habits and methods of obtaining food. For example, a giraffe, which has to reach up for tree leaves, eventually stretched its neck (organ exercise), and a mole that lives underground experienced loss of vision (organ failure). Lamarck gave a more detailed classification of animals compared to Linnaeus, dividing them into 14 classes. He separated vertebrates from invertebrates. The 14 classes of animals he identified were divided according to the degree of complexity of the structure into 6 gradations (steps of complexity). Thus, he included polyps in the 1st gradation, radiated animals and worms in the 2nd, insects and arachnids in the 3rd, crustaceans, annelids, barnacles and mollusks in the 4th, and fish and reptiles and to the 6th - birds, mammals and humans. He quite rightly noted the origin of higher forms of animals from lower ones and believed that man descended from monkeys. Lamarck’s merit is also the introduction into science of the terms “biology” and “biosphere”, which subsequently became widespread.
By the middle of the 19th century, science was ripe for the creation of an evolutionary doctrine in biology. There were many reasons for this. Let's name just a few of them.
1. The end of the era of great geographical discoveries (XV-XVIII centuries) showed humanity all the diversity of the world.
Previously, during the ancient world, antiquity, and the early and middle Middle Ages, people lived in their own cities and villages, and their travel range was limited to only a small set of adjacent regions. This created the illusion of monotony and stability of the surrounding world (see article:). The era of travel around the world revealed the complete inconsistency of these ideas. Numerous descriptions of new lands, their nature and the tribes, plants and animals inhabiting them appeared, which destroyed the usual views about the homogeneity and immutability of the world.
2. Active colonization of newly discovered lands by Europeans required the compilation detailed descriptions nature, climate and resources of these areas, which significantly expanded people's knowledge about nature. It was no longer single travelers who took part in this work, but large masses of people, which contributed to the rapid dissemination of new knowledge among the general population of European countries.
3. Development of capitalism in countries Western Europe accelerated progress in technology and scientific research necessary for the development of industry.
4. The intensive development of science, in turn, accelerated the process of creating evolutionary teaching. At this time, many sciences about nature were actively developing, testifying to its integrity and certain development: geology, which showed the unity of the structure of minerals and rocks in different regions of the Earth; paleontology, which has accumulated large number fossils, long-extinct plants and animals, which testified to the antiquity of life and the replacement of some of its forms by others. In addition, fossil organisms were discovered that clearly constitute transitional links between currently existing and extinct forms. These facts required their explanation. Advances in comparative anatomy revealed the common structure of many groups of plants and animals and showed the existence of transitional forms between individual groups of organisms. Cytology revealed the general nature of the cellular structure of plants and animals. Embryology has found similarities in the development of embryos in different groups of animals. Significant advances have been made in the field of plant and animal breeding, indicating the possibility of artificially changing their forms and productivity.
All this taken together prepared the basis and conditions for the development of evolutionary teaching.
Creation of the evolutionary theory of Charles Darwin and A. Wallace
The foundations of the modern theory of evolution were created by the outstanding English scientist-encyclopedist Charles Darwin (1809-1882). Charles Darwin's compatriot, zoologist Alfred Wallace (1823-1913), worked independently of him at the same time and came to very similar conclusions.
Charles Darwin's scientific interests as a naturalist were extremely diverse: he was engaged in botany, zoology, geology, paleontology, theology, and was interested in issues of selection, etc. A major role in the life of Charles Darwin and the formation of his scientific ideas was played by trip around the world as part of the expedition on the Beagle ship in 1831-1836. There he was able to thoroughly study the specifics of the fauna of the Galapagos Islands, South America and several other areas of the world. Already during this period, Charles Darwin began to form basic evolutionary ideas and he was approaching the discovery of the principle of divergence - the divergence of characters in the descendants of a common ancestor as a mechanism of form and speciation. A major role in the formation of Charles Darwin’s evolutionary ideas was played by his participation in paleontological excavations in Uruguay, where he became acquainted with some extinct forms of giant sloths, armadillos and a number of invertebrates. Returning from the expedition, Charles Darwin wrote a number of monographs and gave presentations that brought him recognition from the scientific community and wide fame.
Analyzing the rate of reproduction and the actual size of populations in nature, Charles Darwin wondered about the reasons for the extinction of some forms and the survival of others. To solve this problem, he draws on the ideas of Thomas Malthus (1766-1834) about the struggle for existence in human society, outlined by the latter in his work “An Essay on the Law of Population.”
This is how Charles Darwin came up with his own ideas about the role of the struggle for existence in the processes of survival of species in nature and the significance of natural selection as the most important factor, which determines the direction of evolution. Charles Darwin considered intra- and interspecific competition to be the main mechanisms of the struggle for existence, and he considered selective death as the basis of natural selection. These processes can be accelerated when populations are spatially isolated. Charles Darwin quite correctly noted that it is not individual individuals that evolve, but species and intraspecific populations, that is, the evolutionary process occurs at the supraorganismal level.
Charles Darwin assigned a special role in evolution to the hereditary variability of organisms in populations and the sexual reproduction of organisms as one of the main factors of natural selection.
Charles Darwin considered the process of speciation to be gradual; he drew certain parallels with natural and artificial selection, leading to the formation of subspecies, species and breeds or varieties of animals and plants. He also emphasized the importance of other sciences (paleontology, biogeography, embryology) in proving evolution. These works were awarded the highest award of the Royal Scientific Society. The quintessence of these works was the work “The Origin of Species by Means of Natural Selection or the Preservation of Favored Races (Forms, Breeds) in the Struggle for Life,” published by Charles Darwin in 1859 and which has not lost its significance in our time.
A. Wallace also presented very similar views on the evolution of the living world and its mechanisms. Even many terms in the works of both scientists coincided.
A. Wallace turned to Charles Darwin, as a famous evolutionist, with a request to review and comment on his work. The reports of both scientists on this topic were published in one volume of the Proceedings of the Linnean Society, and A. Wallace himself and the scientific community unanimously recognized the priority of Charles Darwin in these matters. The evolutionary doctrine itself for a long time bore the name of its founder - Darwinism.
The most important merit of Charles Darwin and A. Wallace was that they identified the main factor of evolution - natural selection - and thereby discovered the reasons for the evolution of the living world.
Species as a stage of the evolutionary process
The basic evolutionary unit is the species. It is the species, according to Charles Darwin, that is the central link in the evolutionary process. The very idea of a species was formulated back in ancient times by Aristotle, who considered a species as a collection of similar individuals. K. Linnaeus also adhered to approximately the same ideas about the species, considering it as an independent, discrete and unchanging biological and systematic structure. Currently, the species is considered as a group of individuals that actually exists in nature. The remaining systematic categories are to a certain extent derivatives of the species, distinguished by scientists on the basis of certain characteristics (genera, families, etc.).
In modern biology, a species is a collection of populations of individuals that have hereditary similarities in morphological, physiological and biochemical characteristics, interbreed freely and produce fertile offspring, are adapted to certain living conditions and occupy a certain territory - habitat. A species is the main structural and taxonomic unit in the system of living nature and a qualitative stage in the evolution of organisms.
Type criteria
Each species is characterized by many characteristics, which are called species criteria.
1. Morphological criteria include the similarity of the external and internal (anatomical) structure of organisms. Morphological characters are very variable. For example, trees growing in dense forests and in open spaces look different. Sometimes within the same species there may be individuals that differ greatly in morphology. This phenomenon is called polymorphism. This may be due to the presence of different stages of development of plants and animals, alternation of sexual and asexual generations, etc. Thus, the larval and adult stages of many insects are completely different from each other. The morphological stages of jellyfish and polyps in coelenterates, gametophyte and sporophyte in pteridophytes, etc. differ.
If individuals differ in two morphological types, then they are called dimorphic (for example, sexual dimorphism).
At the same time, there are cases of high morphological similarity between different species. Such species are called sibling species.
Without knowing all this, each specific morphological type can be mistaken for independent species or, conversely, different but morphologically similar species may be incorrectly assigned to the same species. Thus, the morphological criterion cannot be the only one when determining the species.
2. The genetic criterion of a species implies the existence of a species as an integral genetic system that makes up the gene pool of the species (the totality of genotypes of all individuals belonging to this species).
Each species is characterized by a certain set of chromosome numbers (in humans, for example, the diploid set of chromosomes 2n is 46), a certain shape, structure, size and coloring of the chromosomes. Different species have different numbers of chromosomes, and by this criterion one can easily distinguish species that are very similar in morphology (twin species). This is how species of common voles, very similar to each other, having 46 and 54 chromosomes, and black rats (with diploid sets of chromosomes 38 and 42) were separated. Different number chromosomes in different species allows individuals to freely interbreed with members of their own species, forming viable and fertile offspring, but, as a rule, it provides partial or complete genetic isolation when crossing with individuals of other species - causing the death of gametes, zygotes, embryos, or leading to the formation non-viable or infertile offspring (remember, for example, a mule - an infertile hybrid of a donkey and a horse, a hinny - an infertile hybrid of a horse and a donkey).
Currently, the genetic criteria of the species are supplemented by molecular analyzes of DNA and RNA (gene mapping, determination of the sequence of nucleotides in nucleic acid molecules, etc.). This allows not only to separate closely related species, but also to determine the degree of relatedness or distance between different species, and facilitates phylogenetic analysis of certain groups of species, allowing one to identify related relationships between different species and groups of organisms and the sequence of their formation.
However, despite the great potential of genetic analyses, they also cannot be absolute criteria for determining species. For example, representatives of completely different groups of plants, fungi or animals can have identical sets of chromosomes. In nature, there are also known cases of interspecific crossings with the production of viable and fertile offspring (for example, in some species of canaries, finches, willows, poplars, etc.).
3. The physiological criterion includes the unity of all life processes in all individuals of the same species. These are the same methods of nutrition, metabolism, reproduction, etc. This is the similarity of biological rhythms of individuals of the same species (periods of activity and rest, winter or summer hibernation). These characters are also an important characteristic of the species, but not the only one.
4. The biochemical criteria of a species include, for example, the similarity of the structure of proteins, the chemical composition of cells and tissues, the totality of all chemical processes, occurring in all representatives of the species, etc. This category of characteristics also includes the ability of some types of organisms to form biologically active compounds (such as antibiotics, toxins, alkaloids, etc.) and any other organic matter(organic acids, amino acids, alcohols, pigments, carbohydrates, hydrocarbons, etc.), which is widely used by humans in various biological technologies. These are also very important characteristics of the species, complementing its other characteristics.
5. The ecological criterion of a species includes the characteristics of its ecological niche. This is a very important characteristic of the species, reflecting its place and role in biocenoses and in biogeochemical cycles of substances in nature. It includes characteristics of the species’ habitats, the diversity of its biotic connections (place and role in food chains, the presence of symbionts or enemies, etc.), dependence on natural factors (temperature, humidity, lighting, acidity and salt composition of the environment, etc.) , periods and rhythms of activity, participation in the transformations of certain substances (oxidation or reduction of sulfur, nitrogen, decomposition of proteins, cellulose, lignin or other organic compounds etc.). That is, this is a complete description of where the species is found in nature, when it is active, in what and how its vital activity is manifested. But this criterion is not always sufficient to determine the species.
6. The geographical criterion includes the characteristics and size of the area occupied by the species on the planet. In this territory the species occurs and goes through a full development cycle. The habitat is called primary if the formation of the species occurred precisely in this territory, and secondary if the territories were occupied by the species due to random migrations, natural disasters, human movement, etc. The habitat can be continuous if the species is found throughout its entire space in suitable habitats . If a habitat breaks up into a number of isolated and remote territories, between which migrations or the exchange of spores and seeds are no longer possible, then it is called discontinuous. There are also relict habitats occupied by ancient, accidentally surviving species.
Species that occupy vast areas of the earth and are found in different ecological and geographical zones are called cosmopolitans, and those that occupy only small (local) territories and are not found in other places are called endemics.
Species with extensive ranges are characterized by a certain geographical variability, called clinal variability. The latter species may also have geographic forms and races and certain ecotypes adapted to specific habitats within their range.
As noted above, none of the above criteria is sufficient to characterize the species and the latter can only be characterized by a set of characteristics.
Populations
A species consists of populations. A population is a collection of individuals of the same species that have a common gene pool, inhabit a certain territory (part of the species’ range) and reproduce by free crossing. Populations, in turn, consist of smaller groups of individuals - families, demes, parcels, etc., connected to each other by the unity of the occupied territory and the possibility of free crossing.
The connection between parents and offspring ensures the continuity of the population over time (the presence of several generations of individuals in the population), and free sexual reproduction maintains the genetic unity of the population in space.
Populations are the structural unit of a species and the elementary unit of evolution.
Populations are dynamic groups; they can unite with each other, break up into daughter populations, migrate, change their numbers depending on living conditions, adapt to certain living conditions, die in favorable conditions.
Within the species' range, populations are distributed very unevenly. There will be more of them and they will be more numerous in favorable conditions of existence. On the contrary, in unfavorable conditions and at the boundaries of their range they will be rare and few in number. Sometimes populations have an island or local distribution, for example, birch groves in the Urals and Siberia or floodplain groves and forests in the steppe zone.
The number of individuals per certain unit of area or volume of the environment is called population density. Population densities vary greatly between seasons and years. It changes most dramatically in small organisms (for example, mosquitoes, algae that cause blooms in water bodies, etc.). Large organisms have more stable population numbers and densities (for example, woody plants).
Each population is characterized by a certain structure, which depends on the ratio of individuals of different sexes (sexual structure), age (age structure), sizes, different genotypes (genetic structure), etc. The age structure of populations can be very complex. This can be most clearly observed in woody plants, where individual individuals can exist for many tens and even hundreds of years, taking active participation in cross-pollination processes. Thus, populations are formed consisting of many generations related to each other. In other populations, the age structure may be very simple, such as in annual plants, which are evenly aged groups.
Populations are constantly changing in time and space, and it is these changes that represent elementary evolutionary processes. This is why populations are called elementary evolving structures.
The mechanisms and patterns of population variability in nature and their genetic basis were studied in detail by the largest Russian geneticists and evolutionists A. S. Serebrovsky (1892-1948) and S. S. Chetverikov (1880-1959). Their works and the works of their followers created the foundations of population genetics.
Main types of evolutionary process
Divergence
C. Darwin called divergence the divergence of characters in the process of evolution, leading to the emergence of new forms or taxa of organisms descending from a common ancestor. Divergence also leads to the transformation of some organs of the body into others in connection with the performance of new functions. For example, after vertebrates reached land, their forelimbs underwent significant changes depending on the development of certain types of habitats and lifestyles (running in lizards, wolves, cats, deer or others, burrowing in moles, wings in birds, winged in bats). mice, grasping in monkeys, a hand in humans, flippers during the secondary development of the aquatic environment by ichthyosaurs, walruses or cetaceans, etc.). Such organs, which have a common origin but perform different functions, are called homologous. Homologous organs are plant leaves, pea tendrils, cactus spines, barberry thorns, etc.
Convergence
Convergence is the independent occurrence of similar characteristics in organisms that have different origins (not related to each other), or in organs that have different origins but perform similar functions. Most often, convergence occurs when similar types of habitats are populated. For example, convergent similarity is observed in the wings of butterflies and chiropterans, the burrowing limbs of moles and mole crickets, the gills of fish and crustaceans, the kicking legs of lagomorphs and locusts, etc. But sometimes convergent similarity arises under the influence of the similarity of functions performed, for example, the amazing similarity of the structure of the eyes of mammals and cephalopods. But in any case, these organs are formed from different parts embryos of these animals.
Parallelism
Parallelism is a type of evolution in which convergent similarities arise from homologous organs. Homologous organs or morphological forms that once had a common origin, but then changed and ceased to be similar to each other, under new conditions again acquire features of great similarity. This is a secondary similarity of former related forms. For example, a fish-like streamlined shape arises secondarily during the transition of animals from a terrestrial lifestyle to an aquatic one. Remember the similarity in structure of sharks (primary aquatic animals) and ichthyosaurs and cetaceans (secondary aquatic animals). In cats, saber-toothing arose at different times in different species. The reason for parallelism is the same direction of natural selection and a certain genetic proximity between such groups of organisms.
Phyletic evolution
Phyletic evolution, or phylogeny, is a type of evolutionary process in which there is a gradual transformation of some taxa into others without the formation of lateral branches. In this case, a continuous series of populations (taxa) is formed, in which each taxon is a descendant of the previous one and the ancestor of the subsequent one, without having sister taxa. This type was described by the American researcher J. Simpson in 1944.
While studying the patterns of plant evolution, the outstanding Russian (Soviet) geneticist N.I. Vavilov discovered interesting phenomena, which he called the law of homological series. This law directly follows from the analysis of the relationships and relationships between different types of evolutionary process and shows the great similarity of evolutionary changes in related groups of organisms. The reason for this is the similarity of mutations of homologous genes in the gene pools of related species. Therefore, knowing the spectrum of variability of one species (or genus), it is possible with high probability to predict the diversity of forms of another species (or genus). Moreover, entire families of plants can be characterized by a certain cycle of variability, found in all its genera and species. Thus, knowing the forms of variability in barley, N.I. Vavilov very accurately predicted and subsequently discovered similar forms in wheat.
Rules of evolution
To summarize the presentation of the processes of micro- and macroevolution, we can cite several general rules, to which these processes are subject.
1. Continuity and unlimited evolution - evolution arose from the moment of the formation of life and will continue continuously as long as life exists.
3. The rule of origin of specialized groups from non-specialized ones. Only unspecialized, broadly adapted groups can give rise to evolution and cause the formation of specialized groups.
4. The rule of progressive specialization of groups. If a group of organisms has taken the path of specialization, then the latter only deepens and there is no return (Depere's rule).
5. The rule of irreversibility of evolution. All evolutionary processes are irreversible, and all new evolutionary processes occur on a new genetic basis (Dollo's rule). For example, after reaching land, a number of animals returned to an aquatic lifestyle, retaining their evolutionary acquisitions. In particular, both ichthyosaurs and cetaceans are secondary aquatic animals, but they did not turn into fish, but remained reptiles or mammals, retaining all the features of their classes.
6. Rule of adaptive radiation. Evolutionary development occurs in different directions, promoting the settlement of different habitats.
Phylogeny and systematics as a reflection of evolutionary processes
The study of micro- and macroevolutionary processes makes it possible to establish phylogenetic (that is, related) connections between different groups of living organisms and determine the time of appearance of these forms.
Phylogenesis is the process of historical development of a group or specific type. Phylogeny can also be called a long continuous series of multiple ontogenies, reflecting the main evolutionary rearrangements. The study of phylogeny makes it possible to establish family relationships between different taxa and to clarify the mechanisms and time of evolutionary restructuring of certain groups of living organisms.
The following main forms of phylogeny are distinguished:
1) monophyly - the origin of different species from one common ancestor;
2) paraphyly - the simultaneous formation of species through the synchronous divergence of an ancestral form into two or more new species;
3) polyphyly - the origin of a group of species of organisms from different ancestors through hybridization and/or convergence.
Mechanisms and methods of phylogenetic changes
1. Strengthening (intensification) of the functions of the body or its organ, for example, an increase in the volume of the brain or lungs, leading to an intensification of their activity.
2. Reducing the number of functions. An example would be the transformation of a five-fingered limb in artiodactyl and equid animals.
3. Expanding the number of functions. For example, in cacti, the stem, in addition to its main functions, performs a storage function.
4. Change of functions. For example, the transformation of walking limbs into flippers in secondary aquatic mammals (walruses, etc.).
5. Replacement of one organ with another (substitution). For example, in vertebrates the notochord is replaced by a bony spine.
6. Polymerization of organs and structures (that is, an increase in the number of homogeneous structures). For example, the evolution of unicellular organisms into colonial and then into multicellular forms.
7. Oligomerization of organs and structures. This is the opposite process of polymerization. For example, the formation of a strong pelvis by fusion of several bones.
Systematics as a reflection of evolutionary processes
Systematics is the science of the position of organisms in the general system of the living world. There are many systems in the organic world. Among them, there are artificial systems that take into account only purely external similarities between organisms (an example is the system of K. Linnaeus), and natural or phylogenetic systems.
Knowledge of taxonomy is necessary not only from the point of view of determining the type of organism (although this is already very important), but also to understand its place (and often its role) in the living world, to understand its origin and family relationships with other organisms.
Modern taxonomy is based on a thorough study of phylogenetic relationships between different groups of organisms and, in fact, largely reflects the main stages in the development of the organic world from simple to complex forms. This is exactly how the material on the taxonomy of plants and animals is presented in school textbooks.
An integral part of taxonomy is taxonomy - the science of the principles of classification of living beings.
The basic taxonomic unit is the species formed in the process of microevolution. Related species are grouped into genera, and closely related genera into families. Families that have some common characteristics are grouped into orders (in botany) or into orders (in zoology). Orders and orders are combined into classes based on the similarity of a number of large characters - one or two cotyledons in flowering plants, structural and developmental features in animals (reptiles, birds, mammals, etc.).
The similarity of some fundamental characteristics allows us to combine classes into types (in animals) or divisions (in plants). Example - flowering plants (have a flower and seeds protected by a fruit), chordates (presence of a chord), arthropods (jointed limbs), etc. Moreover, types, classes, and often orders can unite not only related, but also convergently similar forms.
Types or divisions are united into kingdoms based on the similarity of structure and functions performed by large groups of organisms. For example, photosynthetic organisms that release oxygen during photosynthesis are classified as plants. Kingdoms tend to be of polyphyletic origin.
Kingdoms can be united into superkingdoms and empires. Currently, the following life forms are distinguished.
Non-cellular life forms - viruses.
Cellular life forms:
1) the superkingdom (or empire) of Prokaryotes (includes the kingdoms of Archaebacteria and True Bacteria); 2) the superkingdom (or empire) of Eukaryotes (kingdoms of Animals, Plants and Fungi). Protozoa are often grouped with animals.
Thus, large systematic categories (kingdoms, types (divisions), classes, orders (orders) are essentially a reflection of the main directions of the evolutionary process.
