Encyclopedic YouTube
-
1 / 5
In fact, the "biogenetic law" was formulated long before the advent of Darwinism.
The German anatomist and embryologist Martin Rathke (1793-1860) in 1825 described gill slits and arches in mammalian and bird embryos - one of the most striking examples of recapitulation.
In 1824-1826, Etienne Serra formulated the "Meckel-Serra law of parallelism": each organism in its embryonic development repeats the adult forms of more primitive animals [ ] .
Facts contrary to the biogenetic law
Already in the 19th century, enough facts were known that contradicted the biogenetic law. Thus, numerous examples of neoteny were known, in which, in the course of evolution, ontogenesis shortens and its final stages fall out. In the case of neoteny, the adult stage of the descendant species resembles the larval stage of the ancestor species, and not vice versa, as would be expected with complete recapitulation.
It was also well known that, contrary to the "law of germinal similarity" and the "biogenetic law", the earliest stages of development of vertebrate embryos - blastula and gastrula - differ very sharply in structure, and only at later stages of development is a "knot of similarity" observed - the stage on which the structural plan characteristic of vertebrates is laid, and the embryos of all classes are really similar to each other. Differences in the early stages are associated with a different amount of yolk in the eggs: with its increase, fragmentation becomes first uneven, and then (in fish, birds and reptiles) incomplete superficial. As a result, the structure of the blastula also changes - the coeloblastula is present in species with a small amount of yolk, amphiblastula - with a medium amount, and discoblastula - with a large amount. In addition, the course of development in the early stages changes dramatically in terrestrial vertebrates due to the appearance of embryonic membranes.
Relationship of biogenetic law with Darwinism
The biogenetic law is often regarded as a confirmation of Darwin's theory of evolution, although it does not follow at all from classical evolutionary teaching.
For example, if the view A3 arose by evolution from an older species A1 through a series of transitional forms (A1 => A2 => A3), then, in accordance with the biogenetic law (in its modified version), the reverse process is also possible, in which the species A3 turns into A2 by shortening development and dropping out of its final stages (neoteny or pedogenesis).
R. Raff and T. Kofman speak just as sharply: “The secondary discovery and development of Mendelian genetics at the turn of two centuries will show that, in essence, the biogenetic law is just an illusion” (p. 30), “The last blow to the biogenetic law was dealt then when it became clear that ... morphological adaptations are important ... for all stages of ontogenesis" (p. 31).
”, proposed by Haeckel, Severtsov interpreted differently; for Haeckel, cenogenesis (any new traits that distorted recapitulation) was the opposite of palingenesis (preservation in development of unchanged traits that were also present in ancestors). Severtsov used the term "coenogenesis" to designate traits that serve as adaptations to the embryonic or larval lifestyle and are not found in adult forms, since they cannot have adaptive significance for them. Severtsov attributed to cenogenesis, for example, the embryonic membranes of amniotes (amnion, chorion, allantois), the placenta of mammals, the egg tooth of the embryos of birds and reptiles, etc.
Phylembryogenesis is such changes in ontogeny that in the course of evolution lead to a change in the characteristics of adults. Severtsov divided phylembryogenesis into anabolism, deviation and archallaxis. Anabolia is the lengthening of ontogenesis, accompanied by an extension of stages. Only with this method of evolution is recapitulation observed - signs of embryos or larvae of descendants resemble signs of adult ancestors. With deviation, changes occur at the middle stages of development, which lead to more dramatic changes in the structure of the adult organism than with anabolism. With this method of evolution of ontogeny, only the early stages of descendants can recapitulate the traits of ancestral forms. In archallaxis, changes occur at the earliest stages of ontogenesis, changes in the structure of an adult organism are most often significant, and recapitulations are impossible.
BIOGENETIC LAW(Greek bios life, genetikos referring to birth, origin) - a set of theoretical generalizations describing the relationship between the individual and historical development of living organisms.
B. h. was formulated in 1866 by him. zoologist E. Haeckel (E.N. Haeckel): “The series of forms through which the individual organism passes during its development, starting from the egg and ending with the fully developed state, is a brief, compressed repetition of the long series of forms passed by the animal ancestors of the same organism or generic forms of its species, starting from ancient times, the so-called. organic creation, up to the present time”, i.e. “ontogeny is a quick and short repetition of phylogeny”.
The basis for the creation of B. h. the work of F. Muller "For Darwin" (1864) served, in which it was shown that phylogenetically new signs of adult organisms arise as a result of a change in ontogenesis in descendants - lengthening or deviation from the ontogenesis of ancestors. In both cases, the structure of the adult organism changes.
According to Haeckel, phylogeny occurs by summing up the changes in an adult organism and shifting them to earlier stages of ontogenesis, i.e. phylogeny is the basis for ontogenesis, Krom plays the role of an abbreviated and distorted record of the evolutionary transformations of adult organisms (see Ontogeny, Phylogeny) . From these positions, Haeckel divided all the signs of a developing organism into two categories: palingenesis (see) - signs or stages of individual development that repeat or recapitulate in the ontogenesis of descendants the stages of phylogenesis of adult ancestors, and cenogenesis - any signs that violate recapitulation. Haeckel considered the cause of cenogenesis to be the secondary adaptations of organisms to the conditions in which their ontogenesis proceeds. Therefore, temporary (provisional) devices that ensure the survival of an individual at certain stages of individual development and are absent in an adult organism, for example, the embryonic membranes of the fetus (coenogenesis proper), as well as changes in the laying of organs in time (heterochrony) or place (heterotopias) and secondary changes in the path of ontogenesis of this organ. All these transformations disrupt palingenesis and thus make it difficult to use embryological data for the reconstruction of phylogenesis, for which, as A. N. Severtsov (1939) showed, Haeckel formulated the B. z.
At the beginning of the 20th century A number of authors have proved that Muller (F. Muller), who postulated the occurrence of phylogenetic changes as a result of transformations in the processes of ontogenesis, more correctly than Haeckel explained the relationship between individual and historical development, justified at the present time from the standpoint of genetics. Since evolution occurs in a number of generations, only generative mutations that change the hereditary apparatus of gametes or zygotes matter in it. Only these mutations are transmitted to the next generation, in which they change the course of ontogeny, due to which they appear in the phenotype of descendants. If in the next generation ontogenesis proceeds in the same way as in the previous one, then the adult organisms of both generations will be the same.
On the basis of the idea of the primacy of ontogenetic changes, A. N. Severtsov developed the theory of phylembryogenesis - a description of the methods (modes) of evolutionary changes in the course of ontogenesis, which lead to the transformation of the organs of descendants. The most common way of progressive evolution of organs is anabolism, or the superimposition of the final stages of development. In this case, to the stage at which the development of the organ in the ancestors ended, a new one is added (lengthening of ontogenesis), and the final stage of the ontogenesis of the ancestors appears to be shifted to the beginning of development:
Anabolisms E, F, G, H lead to further development of the organ and cause recapitulation of ancestral states (e, f, g). Consequently, it is during evolution through anabolism that the palingenetic path of ontogenesis arises, however, in this case, there is not a shift in the stages of ontogenesis, but a further phylogenetic development of the organ that already existed in the ancestors.
The second mode of phylembryogenesis is deviation, or deviation at intermediate stages of development. In this case, the development of the descendant organ begins in the same way as in the ancestors, but then it changes direction, although additional stages do not arise:
Deviations rebuild ontogeny, starting from intermediate stages (c1, d2, d3), which leads to a change in the definitive structure of the organ (E1, E2, E3). Recapitulation in abc1d1E1 ontogenesis is traced at ab stages, and in abc1d3E3 ontogeny, at abc1 stages. The third, rarest, mode of progressive evolution is archallaxis, or a change in the primary rudiments of organs:
Archallaxis is characterized by the transformation of the earliest stages of ontogenesis, starting from its initiation (a1, a2, a3), which can lead to the emergence of new organs that were absent in the ancestors (E1, E2, E3) - primary archallaxis, or to a radical restructuring of the ontogeny of an organ without significant changes in its definitive structure - secondary archallaxis. With this mode of evolution, there is no recapitulation.
Through phylembryogenesis, the evolutionary reduction of organs also occurs. There are two types of reduction: rudimentation (underdevelopment) and aphasia (without a trace). During rudimentation, an organ that was normally developed and functioned in the ancestors loses its functional significance in the descendants. In this case, according to A. N. Severtsov, the reduction is carried out by means of negative archallaxis: the priming of the descendants is smaller and weaker than that of the ancestors, develops more slowly and does not reach the ancestral definitive stage. As a result, the organ of the descendants is underdeveloped. With aphasia, the reducing organ not only loses its functional significance, but also becomes harmful to the body. The ontogenesis of such an organ, as a rule, begins and for some time proceeds in the same way as in the ancestors, but then negative anabolism occurs - the organ resolves, and the process proceeds in the reverse order of development, up to the disappearance of the bookmark itself.
The theory of phylembryogenesis is close to Muller's ideas. However, A. N. Severtsov singled out the modus of archallaxis, which can be observed only during evolutionary transformations of parts, and not the whole organism, studied by Muller. Soviet biologists proved that not only organs, but also tissues and cells of multicellular organisms evolve through phylembryogenesis. There is evidence of evolution through phylembryogenesis not only of developed organs, but also of provisional adaptations (coenogenesis). It has also been found that in a number of cases heterochronies play the role of phylembryogenesis.
Thus, phylembryogenesis is a universal mechanism of phylogenetic transformations in the structure of organisms at all levels (from cell to organism) and stages of ontogenesis. At the same time, phylembryogenesis cannot be considered primary and elementary evolutionary changes. As is known, evolution is based on mutational variability. Both phylembryogenesis and generative mutations are inherited and manifest during ontogenesis. However, mutational variability, unlike phylembryogenesis, is individual (each new mutation is characteristic only of the individual in which it arose), and the mutational changes that appear for the first time are not of an adaptive nature. Phylembryogenesis, in all likelihood, is a complex of mutations that have passed natural selection and become the genotypic norm. In this case, phylembryogenesis is a secondary transformation that occurs as a result of the preservation and accumulation of mutations that change morphogenesis (see), and thus the development of adult organisms in accordance with environmental changes. Natural selection more often preserves changes that only build ontogenesis, less often - changing intermediate stages, and even more rarely - transforming morphogenesis from its very first stages. This explains the different frequency of occurrence of anabolism, deviations and archallaxis. Consequently, phylembryogenesis, being a mechanism for the formation of phylogenetically new characters, is at the same time the result of a mutational rearrangement of individual development.
Haeckel's ideas about the predominance of phylogenetic changes over ontogenetic ones and Muller's ideas about the primacy of the restructuring of the course of ontogenesis, leading to phylogenetic transformations in the structure of organisms, are one-sided and do not reflect the complexity of the evolutionary relationship between ontogenesis and phylogenesis. From modern positions, the relationship between the individual and historical development of an organism is expressed as follows: “phylogenesis is a historical series of known ontogenesis” (I. I. Shmalgauzen, 1969), where each subsequent ontogenesis differs from the previous one.
Bibliography: Lebedin S. N. Correlation of onto- and phylogenesis, bibliography of the question, Izv. Scientific in-ta im. Lesgaft, vol. 20, no. 1, p. 103, 1936; Müller F. and Haeckel E. Basic biogenetic law, trans. from German, M.-L., 1940; Severtsov A.N. Morphological patterns of evolution, p. 453, M.-L., 1939; Severtsov A. S. To the question of the evolution of ontogenesis, Zhurn. total biol., t. 31, no. 2, p. 222, 1970; Shmalga u-zen I. I. Problems of Darwinism, p. 318, L., 1969.
A. S. Severtsov.
Haeckel-Muller's biogenetic law or the main biogenetic law says: every living being in its individual development (ontogeny) repeats to a certain extent the forms passed by its ancestors or its species (phylogenesis).
This law played an important role in the history of the development of science, but at present, in its original form, it is not recognized by modern biological science.
According to the modern interpretation of the biogenetic law, proposed by the Russian biologist A.N. Severtsov at the beginning of the 20th century, in ontogeny there is a repetition of the signs of not adults, but their ancestors.
Often, the law of germinal similarity, formulated by K. M. Baer in 1828, is compared with the biogenetic law, from which it follows that embryos successively pass in their development from general features of the type to more and more special features; last of all, signs develop that indicate that the embryo belongs to a certain genus, species, and, finally, development ends with the appearance of the characteristic features of this individual.
A number of researchers (Severtsev, 1939; Shmalgauzen, 1969; Ivanova-Kazas, 1939) have shown that the law of germline similarity and the biogenetic law are determined by different mechanisms, and, accordingly, these are two different laws.
Severtsev (1939) argued that there is no ontogeny in unicellular organisms, and only for Volvox recognized its presence in the most primitive form.
Following Severtsov, most embryologists deny the existence of individual development at the cellular level of organization, however, with this approach, it is not clear on the basis of what the morphogenetic mechanisms of the first multicellular animals were formed?
The phrase "cell ontogeny" was probably the first to use Bauer (1935). A student of Baer - Tokin (1939) noted that an individual (tomite), formed as a result of the division of the ciliary ciliates, receives a different set of cirrs (ciliary tufts) and, accordingly, must restore the missing tufts. Tokin interpreted such a process as ontogenesis, and he considered the last stage of the formation of a new ciliary apparatus to be recapitulations.
Ciliates, unlike other protists, have a cell body with clearly visible, even at the light-optical level, external structures. First of all, it is a cell mouth, the ciliates are characterized by transverse division, as a result of which one of the daughter cells, one of the daughter cells receives a cystome (and the corresponding ciliary apparatus), and the other must complete its construction. As it turned out, the construction of a new oral apparatus (stomatogenesis) proceeds in different groups of ciliates in different ways. The sequence of processes that occur in the stomatogenesis of ciliates is interpreted as ontogenesis.
The stages of stomatogenesis are considered as recapitulations.
Corliss (1968) suggests that examples of recapitulations of ancestral characters can be found in many protozoan taxa. This is especially true for groups with complexly formed external structures: pellicle or various kinds of skeletal formations. In his opinion, such examples can be found in myxosporidium (sculpture of the walls of spores), gregarine (membrane of gametocysts), etc.
I. V. Dovgal, unlike other protistologists, believes that stomatogenesis of ciliates and the early stages of metamorphosis of the dispersal stages of sessile ciliates (and similar processes in other groups of unicellular organisms) are a manifestation not of a biogenetic law, but of Baer's law of germline similarity (Dovgal, 2000; Dovgal , 2002). He takes as a basis the formulation of the law of germline similarity from the monograph by I. I. Shmalgauzen (1969).
The biogenetic law is not valid for unicellular organisms. Baer's law of germline similarity holds for protists.
Question 1.
All multicellular organisms develop from a fertilized egg. The processes of development of embryos in animals belonging to the same type are largely similar. In all chordates, an axial skeleton - a chord - is laid in the embryonic period, a neural tube appears, and gill slits form in the anterior part of the pharynx. During the embryonic development of vertebrates, gill slits and their corresponding septa are laid in the pharynx, but in reptiles, birds, and mammals they do not develop into gills. The fact of laying the gill apparatus in the embryos of terrestrial vertebrates is explained by their origin from fish-like ancestors that breathed through gills.
The structure of the heart of the human embryo in the early period of formation resembles the structure of this organ in fish, namely, it has one atrium and one ventricle. Toothless whales develop teeth during the embryonic period. Subsequently, they collapse and dissolve.
The plan of the structure of chordates is also the same.
These facts confirm the validity of the law of germinal similarity formulated by K. Baer: "Embryos already from the earliest stages show a certain general similarity within the limits of the type."Question 2.
In the early stages of development, vertebrate embryos are extremely similar. Later, in the structure of the embryos, signs of a class, genus, species, and, finally, signs characteristic of a given individual appear. The similarity of the embryos serves as evidence of their common origin.
The divergence of signs of embryos in the process of development is called embryonic divergence and is explained by the history of this species, reflecting the evolution of one or another systematic group of animals.Question 3.
This phenomenon is explained biogenetic law Müller-Haeckel:
ontogenesis (individual development) of each individual is a brief and quick repetition of the phylogeny (historical development) of the species to which this individual belongs.
Therefore, in all vertebrates, including their higher representatives, a notochord is laid, which is later replaced by the spine. During the embryonic development of vertebrates, gill slits and their corresponding septa are laid in the pharynx, but in reptiles, birds, and mammals they do not develop into gills. The fact of laying the gill apparatus in the embryos of terrestrial vertebrates is explained by their origin from fish-like ancestors that breathed through gills.Question 4.
biogenetic law played an outstanding role in the development of evolutionary ideas. Many scientists in their writings subjected it to further development. Particularly great is the contribution to the deepening of ideas about the evolutionary role of embryonic transformations of our domestic scientist A. N. Severtsov. He established that in individual development the signs are repeated not of adult ancestors, but of their embryos. For example, gill slits are formed in the embryos of birds and mammals. Their structure is similar to the structure of the gill slits of fish embryos, and not the gills of adult fish.
In a number of cases, changes that distinguish the structure of adult organisms from the structure of ancestors appear in the embryonic period. Sometimes these changes are superimposed on the process of organ formation that has already been completed in general, lengthening its development. This is how the wing of a bird develops - by transforming the almost formed rudiment of the horny scales of reptiles.
In some cases, changes occur in the middle stages of organ development. Finally, changes can affect the very rudiment of the organ, and development will follow a path different from the path of development of the given rudiment in the ancestor. So, in the process of hair formation in mammals, the stage of scale formation completely falls out, as was the case with their ancestors - fish and reptiles. The stages inherent in the ancestors also fall out during the laying of vertebrae in snakes, teeth in mammals, etc. In case of deviation from the stages of development of the ancestors or changes in the rudiments themselves, the biogenetic law is not respected and the signs of the ancestors are not repeated.
If new traits are hereditary, that is, they are the result of mutations in the corresponding genes and have an adaptive value for adult organisms, then they are preserved by selection.
Thus, phylogenesis is based on changes occurring in the ontogeny of individual individuals.
The repetition of structures characteristic of ancestors in the embryogenesis of descendants is called recapitulations. Recapitulate not only morphological characters - notochord, anlage of gill slits and gill arches - in all chordates, but also features of biochemical organization and physiology. Thus, in the evolution of vertebrates, there is a gradual loss of enzymes necessary for the breakdown of uric acid, a product of purine metabolism. In most invertebrates, the end product of the breakdown of uric acid is ammonia, in amphibians and fish it is urea, in many reptiles it is allantoin, and in some mammals uric acid is not broken down at all and is excreted in the urine. In the embryogenesis of mammals and humans, biochemical and physiological recapitulations were noted: the release of ammonia by early embryos, later urea, then allantoin, and, at the last stages of development, uric acid.
However, in the ontogeny of highly organized organisms, a strict repetition of the stages of historical development is not always observed, as follows from the biogenetic law. Thus, the human embryo never repeats the adult stages of fish, amphibians, reptiles and mammals, but is similar in a number of features only to their embryos. The early stages of development retain the greatest conservatism, due to which they recapitulate more completely than the later ones. This is due to the fact that one of the most important mechanisms of integration of the early stages of embryogenesis is embryonic induction, and the structures of the embryo that form in the first place, such as the notochord, neural tube, pharynx, intestine and somites, are the organizational centers of the embryo, from which the whole course of development depends.
The genetic basis of recapitulation lies in the unity of the mechanisms of genetic control of development, which is preserved on the basis of common genes for the regulation of ontogenesis, which are inherited by related groups of organisms from common ancestors.The German scientists F. Müller (1828) and E. Haeckel (1866) established the law of the correlation between ontogenesis and phylogenesis, which was called the biogenetic law. According to this law, the ontogenesis of any organism is a brief repetition (recapitulation) of the main stages of the phylogenesis of the species to which the given organism belongs. E. Haeckel and F. Müller believed that successive changes in the shape of an individual during individual development are due to phylogenesis, that is, the development of the genus to which the given species of animal belongs. According to the biogenetic law, the embryos of systematically superior animals are similar to adult inferior ancestors. Evolution is carried out by adding new stages at the end of development.
The biogenetic law finds many confirmations in the data of comparative anatomy, embryology and paleontology. For example, in the embryos of birds and mammals, at a certain stage of embryonic development, the rudiments of the gill apparatus appear. This is because terrestrial vertebrates evolved from gill-breathing fish-like ancestors.
However, in a short period of individual development, an individual cannot repeat all the stages of evolution, which took place thousands or millions of years. Therefore, the repetition of the stages of the historical development of the species in the individual development of the individual occurs in a compressed form, with the loss of a number of stages. In addition, embryos do not resemble adult forms of ancestors, but with their embryos. Thus, in the ontogeny of mammals there is a stage at which gill arches are formed in the embryos. In the embryo of a fish, on the basis of these arcs, a respiratory organ is formed - the gill apparatus. In the ontogenesis of mammals, it is not the structure of the gill apparatus of adult fish that is repeated, but the structure of the anlages of the gill apparatus of the embryo, on the basis of which completely different organs develop in mammals.
Based on the biogenetic law and using embryological data, it is possible to recreate the course of the historical development of certain groups of organisms. This is especially important in cases where fossil remains of ancestral forms are unknown for any group, i.e., when the paleontological record is incomplete. Let's take just one classic example. Systematic position and origin of ascidians ( Ascidiae), leading a sedentary lifestyle, were completely unclear for a long time, and only the famous study by A. O. Kovalevsky (1866) on the development of these animals finally resolved the issue. A free-swimming tailed larva emerges from the ascidian egg, similar in structure to chordates ( Chordata). During the metamorphosis of the larva that has settled to the bottom, the tail with the chord and muscles and the sense organs disappear, the neural tube is reduced to the degree of a small nerve bundle, there is an increased growth of the abdominal surface of the body, siphons are formed, etc., i.e. there are features of the organization associated with a sedentary lifestyle. The formed young ascidian has almost nothing in common with other chordates. In this example, the larva, by its organization, recapitulates (repeats) the main structural features of the free-floating ancestor. Thus, the natural place of the ascidians in the system of the animal kingdom was found.
Of particular interest to evolutionary zoology are recapitulations, i.e. repetition in the course of individual development of the characteristic features of the structure of more or less distant ancestors. A typical example of recapitulation is given by Academician A.N. Severtsov in his book "Morphological patterns of evolution", published in 1913 in Germany. In modern tailless amphibians in the adult state, the tibia and fibula are fused together, while in tadpoles they are separated. Stegocephalians, from which modern amphibians evolved, also had two separate tibias. Consequently, the presence of separate tibias in tadpoles can be considered as a recapitulation of one of the features of the hind limbs characteristic of the ancestral skeleton.
Recapitulation is not limited to morphological features. They can also be identified during the ontogenetic formation of the functions of various organs and tissues. It is known that during the evolution of vertebrates, the enzymes necessary for the breakdown of uric acid were gradually lost. So, in some reptiles and birds, the end product of nitrogen metabolism is uric acid, in amphibians and most fish, urea, and in primary invertebrates, ammonia. It turned out that the embryo of birds in the early stages of development releases ammonia, in the later stages - urea, and only in the last stages - uric acid. Similarly, in tadpoles, the end product of metabolism is ammonia, and in frogs, urea.
The manifestation in an unchanged form of primitive, ancient, palingenetic features (from the Greek palaios - ancient; palingeneses - signs that have passed into the ontogeny of an animal from its phylogenesis) are interfered with by coenogenesis - various signs that arose in ontogenesis as an adaptation to the living conditions of the embryos of larvae and adult animals. Amnion, chorion, allantois Amniota, huge spinning glands of insect larvae, etc. can serve as an example of coenogenesis.
Further embryological studies (A.N. Severtsov, I.I. Shmalgauzen) showed that there were many omissions in the Müller-Haeckel theory, and the main one was that the history of the adult organism was considered in isolation from the history of the embryo. Despite this, one should not underestimate the great importance of the biogenetic law in the development of evolutionary doctrine.
Modern embryological research has shown that the law is true only in general terms.
There is not a single stage in development at which the embryo would completely repeat the structure of any phylogenetic ancestor;
In ontogenesis, the structure is repeated not of the adult stages of the ancestors, but of their embryos. For example, a mammalian embryo never completely repeats the structure of a fish, but at a certain stage of development, gill slits and gill arteries are laid in it.
