Vorontsov, 1999. On the postulates of SET (according to the book 'Development of evolutionary ideas in biology')

In 1978–1980, Nikolay Nikolayevich Vorontsov (1934–2000) attempted to systematize the basic postulates of the Modern Evolutionary Synthesis (Synthetic Theory of Evolution, STE). In his last major work, published in 1999 (Vorontsov N. N. Razvitiye evolyutsionnykh idey v biologii. M.: Izd. otd. UNTs DO MGU, Progress-Traditsiya, ABF, 1999. 600 p.), he returned to this list of postulates and sought to show how interpretations of these issues had changed by the end of the 20th century. Below is a summary table of classical STE postulates and changes in their interpretations, compiled from the cited book. Vorontsov, 1999, pp. 457–463: In 1978–1980, I made attempts to formulate the basic postulates of the STE. These formulations certainly do not claim to be exhaustive; perhaps other researchers would divide some of the proposed postulates into several independent ones, while others might consider it necessary to merge some, but this is unlikely to alter their meaning significantly. It is easy to see that some of these postulates follow directly from Darwin’s own works, whereas others emerged during the development of evolutionism in the first half of the 20th century. It seems justified to distinguish the following 11 postulates of the STE.

Vorontsov, 1999, pp. 606–607: Let us compare the above [from the section of the cited monograph devoted to the discussion of current problems in evolutionary biology — Note by D.Sh.] with the basic postulates of the Synthetic Theory of Evolution. 1. The material for evolution consists, as a rule, of very small but discrete hereditary changes—mutations. In the STE, primary attention was given to so-called “point” gene mutations; chromosomal and, especially, genomic mutations were considered to a lesser extent by STE proponents during the period of “storm and assault.” Mutational variability—the supplier of material for natural selection—is random in character. Hence the name of this concept, proposed by its critic L. S. Berg (1922): “tikhogenez” (“quiet genesis”), or evolution based on chance.

1. The material for evolution consists, as a rule, of very small but discrete hereditary changes—mutations. In the STE, primary attention was given to so-called “point” gene mutations; chromosomal and, especially, genomic mutations were considered to a lesser extent by STE proponents during the period of “storm and assault.” Mutational variability—the supplier of material for natural selection—is random in character. Hence the name of this concept, proposed by its critic L. S. Berg (1922): “tikhogenez” (“quiet genesis”), or evolution based on chance.

2. The main or even the only driving factor of evolution is natural selection, based on the selection of random and small mutations. Hence the name of this theory – "selekogenesis" (development based on selection).

2. Natural selection undoubtedly remains the driving factor of evolution, but not the only one. Darwinian and "non-Darwinian" evolution are not mutually exclusive.

3. The smallest evolutionary unit is the population, not the individual, as was assumed based on the idea of "inheritance of acquired characteristics." Consequently, special attention to the study of populations as elementary structural units of species communities, to herds, to flocks, led to the emergence of a new direction in the 60s-70s of the 20th century – population biology. By the 60s-70s, it became clear that the term "population" without clarification often turns out to be vague. From a genetic standpoint, the definition of a population as a group of individuals among which interbreeding can actually occur within one generation seems fully justified, but it often draws criticism from ecologists. The latter speak of "geographic," "landscape," "ecological," and other types of populations. In the 1960s, the term "deme" term began to gain popularity as an elementary structure of a population within which gene exchange actually occurs within one generation. A special direction emerged – demecology. However, understanding the place of a deme in the hierarchical intraspecific structure requires not only the development of conceptual apparatus but also actual research conducted using uniform methods across the entire range. There are extremely few such works. It is not surprising, therefore, that the classic case of hierarchical spatial intraspecific structures in the agile lizard, studied by A. V. Yablokov, I. S. Darevsky, N. N. Shcherbak, and their colleagues, became one of the few examples of subordination of intraspecific structures of different ranks and entered textbooks. At the same time, according to I. A. Shilov, "it would be correct to speak not of spatial, but of spatio-ethological structure of populations." The same author emphasizes the groundlessness of disputes "about where in natural conditions a clear boundary can be drawn between two populations of the same rank"¹. The postulate of the population as the smallest evolutionary unit remains valid. Modern evolutionary biology, like the synthetic theory of evolution, leaves no room for Lamarckism with its idea of the possibility of individual evolution. However, a huge number of organisms without sexual reproduction remain outside this definition of a population, and in this, we see a significant incompleteness of the synthetic theory of evolution.

4. Evolution is divergent in nature, meaning one taxon can become the ancestor of several daughter taxa, but each species has a single ancestral type, and ultimately a single ancestral population. A certain conflict with point 3 can be traced in this postulate, because if a population evolves, not an individual, then the dichotomous tree of divergence still has a certain set of individuals at its base, not a single individual. F. G. Dobzhansky attempted to resolve this contradiction at the microevolutionary level by proposing a scheme of reticular, or network, evolution.

3. This postulate requires substantial revision. Symgenesis, synthegenesis, symbiogenesis, paraphyly, transduction of genetic material – all these indicate that evolution is far from always divergent.

5. Evolution is gradual (gradualistic) and prolonged. Speciation, recognized as a stage of the evolutionary process, is imagined as a step-by-step change of one temporary population by a series of subsequent temporary populations. The idea of the possibility of saltational origin of species, for example, due to genomic mutations such as polyploidy, was mainly developed by botanists, while the STS was formulated primarily by zoologists. At that time, there were practically no reliable examples of viable genomic mutations in animals.

4. Evolution, as we have shown, does not necessarily proceed gradually. Speciation by polyploidy, due to chromosomal rearrangements, essentially occurs suddenly. It is not excluded that in individual cases, individual macroevolutionary events may also have a sudden character.

6. A species consists of many subordinate units – subspecies, populations – that are morphologically, physiologically, and genetically different but not reproductively isolated. This concept is called the concept of a broad polytypic biological species. Of course, the creators of the STS clearly imagined that there are many species with limited ranges, within which it is impossible to divide the species into independent subspecies, and that relict species may consist of a single population. The fate of such species is usually short-lived.

7. The idea of a polytypic species is generally maintained, however, in the practice of modern systematics using genetic research methods, it often happens that the broad species concept proves to be insignificant and is replaced by a more fragmented understanding of the species' scope.

7. Allele exchange, "gene flow," is possible only within a species. If a mutation has a positive selective value throughout the entire range of the species, it can spread through "gene flow" to all its populations and subspecies. This leads to a concise and quite exhaustive definition of a biological species: a species is a genetically cohesive and closed system. If a selectively valuable mutation arises, for example, in common squirrels in France, it can eventually spread eastward to Kolyma and Kamchatka. Due to migration and selection pressure, a certain gene flow occurs even across such significant territorial barriers as large rivers, mountain ranges, etc. "Clinal break" zones, i.e., disruptions in the gradual change of allele frequencies, are associated either with areas of secondary contact restoration between formerly isolated populations or with zones of changing selection coefficients or even selection direction. Species integrity is ensured by the possibility of interbreeding and gene flow between different populations within the species. Species closure (as we now know well, far from always absolute) is ensured by a complex system of barriers, isolating mechanisms of evolution, which prevent gene exchange between the gene pools of different species. The functions of "isolating mechanisms of evolution" are ambiguous. On the one hand, they ensure the separation of gene pools of different species; on the other hand, many etiological isolation mechanisms help individuals of the opposite sex of the same species find each other. Thus, the second function of many isolation mechanisms is to ensure panmixia within the species.

5. The postulate that a species is a genetically closed and cohesive system is generally maintained. However, we know cases of gene flow leakage through non-absolute barriers of evolutionary isolation mechanisms; the evolutionary role of transduction is subject to study.

8. Since the criterion of the so-called biological species is its reproductive isolation, these species criteria are not applicable to forms without sexual reproduction, agamic, amphimictic, parthenogenetic forms (consequence of point 7).

8. Recognizing the inadequacy of the reproductive criterion of species, we still cannot offer a universal definition of a species for both sexually reproducing and agamic forms.

9. Thus, outside the concept of the biological species of the STS, a huge number of species of prokaryotes, lower eukaryotes without sexual reproduction, as well as some specialized forms of higher eukaryotes – both animals and plants that have secondarily lost sexual reproduction – have been found. Strictly speaking, this same species criterion is also unacceptable for species over time, because assessing the degree of reproductive isolation between populations of different generations is difficult for the few cases where it is theoretically possible, and meaningless for the vast majority of others. As a result, the formal application of this criterion forces followers of the biological species concept to abandon the concept of species in paleontology. All fossil forms remain outside the biological species concept. For them, it is proposed to use terms such as "chronospecies" or "fratry" as equivalents of species. But replacing terms does not solve the problem.

It should be recalled that the entire vast species diversity of the modern Earth's population is less (I find it difficult to say how many times) than the number of extinct species. Since modern higher eukaryotes with sexual reproduction constitute a smaller proportion compared to the number of species of modern forms without sexual reproduction and extinct species of all taxa, it is clear that the scope of application of reproductive criteria of the biological species concept is quite limited.

Understanding the imperfection of the biological species concept, Russian researchers, the Polyansky brothers, actively discussed the problem of species in plants and animals without sexual reproduction in the 1950s. V. I. Polyansky dedicated a special book to the problem of species in algae; Yu. I. Polyansky discussed the problem of species in protozoa. Yu. I. Polyansky mentioned the concept of "evolution of evolution," outlined by I. I. Shmalhausen in his unfinished works. This topic was later developed by historians of science K. M. Zavatsky and E. I. Kolchinsky. According to Yu. I. Polyansky (1904-1993), the problem of species should be approached from the position of "evolution of evolution," understanding that different criteria of biological species may exist for different taxonomic levels.

Outside this system – the species – evolution effectively stops, i.e., macroevolution, or evolution at the level above species, proceeds only through microevolution. According to the STS, there are no macroevolutionary laws different from microevolutionary ones, although there are phenomena (parallelism, convergence; analogy and homology) that are easier to study at the macroevolutionary level.

6. Macroevolution can proceed both through microevolution and through its own pathways.

10. Any real, not a collective, taxon has a monophyletic origin (consequence of point 4). Monophyletic origin is a mandatory condition for the very existence of a taxon. Many followers of the STS after Haeckel believe that the principle of monophyly should be extended to the origin of the entire living world. More cautious followers of the STS avoid this issue due to the lack of sufficient evidence for the initial stages of the origin and development of life.

10. In evolution, along with monophyly, paraphyly is widespread.

11. Based on all the postulates mentioned, it is clear that evolution is unpredictable, has an undirected character towards some ultimate goal, i.e., is non-teleological.

11. Despite the colossal number of factors influencing the evolutionary process, evolution can be to some extent predictable. Although evolution is not teleological, due to existing limitations, by assessing past history, the genotypic environment, and the possible influence of the environment, we can predict general evolutionary trends.