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I.Yu.Popov

Periodical systems in biology

(a historical issue)

Popov I. Yu. “Periodical Systems” in Biology (a Historical Issue) // Die Entstehung biologischer Disciplinen. II / Hrsg. Hossfeld U., Junker Th. Berlin: VWB, 2002. S. 55-69.

“Periodical systems” in biology (a historical issue) <![if !supportFootnotes]> [1]<![endif]>

Igor Yu. Popov (St.-Petersburg)

Zusammenfassung

Versuche, Gruppen und Untergruppen sowie homologe Serien von Organismen nach dem Vorbild chemischer Gruppen zu beschreiben, sind seit der Mitte des 19. Jahrhunderts bekannt. Zur gleichen Zeit wurde eine andere Möglichkeit, Klassifizierungssysteme in Form von Tabellen zu entwickeln, in Betracht gezogen, nämlich die Entwicklung von Tabellen mit Eigenschaftskombinationen, welche die theoretisch möglichen Varianten von Organismen zeigen. Diese Tabellen bildeten “Koordinaten-Systeme” für die Merkmale realer Organismen. Später wurden diese Prinzipien sowohl in der Taxonomie einiger Organismusgruppen als auch in Studien der Variabilität genutzt. Die Daten aus Variabilitätsrehen, ähnlich den Reihen chemischer Substanzen, wurden von N.I.Vavilov (1920) verallgemeinert. Parallel dazu wurde ein Phänomen, das an die Eigenschaften der Systeme chemischer Elemente erinnert, von J. Willis (1920) entdeckt – “hollow curve”: wärend der Konstruktion des Systems jeder Gruppe bilden die Taxa eines Ranges Gruppen, deren Großen durch eine graduelle Serie von Zunahme und Abnahme characterisiert sind. Das System jeder Gruppe ist asymmetrisch, ebenso wie das System der Elemente, in dem die Größe der Untergruppen mit Zunahme des Atomgewichts ansteigt. Seit den 1920er Jehren wurden diesem Gebiet einige bedeutsame Fakten und Ideen hinzugefügt, doch wurde das Problem der “biologischen Periodizität” nur gelegentlich besonders in Studien der niederen Organismen (Bakterien, Pilze) behandelt, bei denen phylogenetische Rekonstruktionen weniger verbreitet sind. Fast alle Versuche der Analyse einer “chemischen Klassifizierung” in der Biologie waren nicht miteinander verbunden und hielten sich weit von den Hauptrichtungen der theoretischen Biologie entfernt. Die Schaffung von Systemen, die denen der Chemie gleichen, scheint in der Biologie unmöglich. Diese Situation erinnert an einen Zustand der Chemie zu Mendeleevs Zeiten. Es gibt etwas Ähnlichkeit in den Verallgemeinerungen von Chemie und Biologie. Trotzdem gibt es mindestens einen deutlichen Unterschied: in der Biologie hängen alle großen Verallgemeinerungen mit der Idee der Evolution zusammen. Die Idee der Evolution, insbesondere im Darwinschen Sinne, hatte negativen Einfluß auf die Analyse der “biologischen Periodizät”.

Summary

Attempts to describe groups and subgroups, as well as homologous series of organisms by analogy with chemical ones are known from the middle of the XIX century. At the same time another opportunity to construct systems of classification in the form of tables was considered, namely - construction of the tables of combinations of features displaying theoretically possible variants of organisms. These tables formed «systems of co-ordinates » for the characteristic of real organisms.

                 Subsequently these principles were used in taxonomy of some groups of organisms, as well as in studies of variability. The data on rows of variability similar to rows of chemical substances were generalized by N. I. Vavilov (1920). Simultaneously a phenomenon reminding one of the features of systems of chemical elements was discovered by J. Willis (1920) – «hollow curve»: during the construction of system of any group taxa of one rank form groups, which sizes are characterised by a gradual series of increase-decrease. The system of any group is asymmetric, as well as the system of elements, in which the size of subgroups increases in the process of increase of atomic weight.

                 Since 1920s few significant facts and ideas were added to this field, but the problem of «biological periodicity» was being stated from time to time, especially in studies of lower organisms (bacteria, fungi), in which phylogenetic reconstructions are less popular.

                 Almost all attempts of the analysis of «chemical classification» in biology were not connected with each other, and are far away from the main trends of theoretical biology.

                 The creation of systems similar with chemical ones seems impossible in biology. This situation reminds a condition of chemistry in Mendeleev' s time. There is some similarity of generalisations of chemistry and biology. However, there is at least one very sharp distinction: in biology all large generalisations are related with the idea of evolution. The idea of evolution, in particular in Darwinian sense, made a negative influence on the analysis of «biological periodicity».

The taxonomists note quite often, that there isn’t any group of living organisms, which would not require a complete revision. Since Linnaeus time the systems of classification are being reconsidered, and it is difficult to imagine that this process will stop. Some biologists tried to finish with it resolutely, that is they tried to create a system which describes a variety of organisms in such a way that new data can be put in it like new elements were put into Mendeleev’s system or organic substances into homologous rows. This paper is devoted to a historical analysis of the works in the direction given.

Series of forms and the tables of combinations of features

Periodical law says: «The properties of elements, as well as the properties of simple and complex bodies formed by them, are in periodic dependence in their atomic weight»<![if !supportFootnotes]>[2]<![endif]>. In other words, the elements differing greatly in atomic weights can demonstrate the greater similarity in properties, than elements similar on weight. In the same way the living organisms, which are not in close relationship, can have the profound features of similarity. When grouping them in lines, they could remind the periods of the Mendeleev’s table or the homologous series of molecules.

One of the first biologists, who paid attention to this circumstance, was an American palaeontologist Edward Cope (1840-1897). When he did it (1868) the periodic system of chemical elements was not discovered yet, but it is obvious, that there was something similar in the imagination of Cope. He wrote about groups and subgroups of elements differing in respect to oxidising properties stressing their analogy to genera and species of organisms. Cope described the objects of his researches – mainly extinct vertebrates - by analogy to groups of elements. Moreover he noted the similarity of the variety of organisms with the homologous rows of organic substances<![if !supportFootnotes]>[3]<![endif]>.

Cope also considered another opportunity to find an order in the variety - drawing up the tables of combinations of features. He put the species or other taxa in such tables, like points into two-dimensioned system of co-ordinates. Different variants of variability were used as units of measurements. Such system differed radically from the construction of the systems of elements and molecules, but could carry out to some extent similar functions.

Further, the similar principles were used at taxonomy of some groups of organisms - fungi, algae and some other lower plants, molluscs, etc. On of the papers had a remarkable title “Ueber die Periodizaet in dem System der Pantopoden”<![if !supportFootnotes]>[4]<![endif]>. Its author – Russian zoologist Wladimir Schimkewich (1858-1923) - used the same principle, as was used in Cope’s papers, that is drawing up tables of combinations of features (He did it independently from Cope). Pantopodes are animals with different number of pairs of legs and different number of segments in each pair. It turned out very useful to build systems of their combinations, and thus to present their precise system. However, Schimkevich has emphasised, that the system is not something comparable in its importance with the system of elements in chemistry. Such tables of descriptions of rows remained within the framework of special researches in taxonomy or morphology.

Approximately at the same time, at the end of 19 - beginning 20, the graceful and beautiful theories of evolution were developed, in which the existence in biology something similar to chemical elements was postulated. The ancient philosophical idea, that all living creatures are constructed by a combination of some primary units, has got a rather concrete biological outline in the concepts of symbiogenesis<![if !supportFootnotes]>[5]<![endif]> and hybridisation<![if !supportFootnotes]>[6]<![endif]>.

According to these concepts, an existing biological variety is like a variety of molecules made of rather small number of elementary units. These units were genes or the essences similar to bacteria, which entered the every possible form of cohabitation with each other. This idea was beautiful and is tempting. For some authors it was very difficult to refuse from it. For example, one of them, Russian botanist A. Famintsyn, tried to prove symbiogenesis experimentally during 50 years, despite the fact that he did not receive any data, which would be desirable for him<![if !supportFootnotes]>[7]<![endif]>. Other enthusiasts on symbiogenesis or hybridisation were also not very successful in revealing “elementary units”. «The elements» of a biological variety always appeared different in different taxa.

The important event in this story took place in 1920, when Nikolay Vavilov (1887-1943) – an outstanding Russian geneticist and organiser of scientific researches - formulated the law of homologous series in variation. Vavilov collected enormous material on variation of cultivated plants. He collected the plant samples from all over world and organised its researches in the network of stations created by him in different parts of USSR. His researches seemed to be only applied ones, but their value was much greater than the needs of agriculture. Vavilov made significant generalisations about laws of variability, about a species problem and about the centres of an origin of groups of plants. This part of his activity was not quite realised for different reasons, and first of all because of orgy of Lysenkoism. In 1930s he courageously struggled with it and died in unequal struggle.

Vavilov described numerous series of parallel variability of cultivated plants. Such facts were known since Darwin’s time<![if !supportFootnotes]>[8]<![endif]>, but Vavilov investigated them especially profoundly. He presented a lot of tables and formulas describing variability of dozens of plant species (fig. 1, 2), noted their similarity to the series of homologous series of hydrocarbons and expressed some ideas on extrapolation of the data received on more high levels of classification and on other objects. Moreover, in some cases Vavilov predicted a discovery of forms unknown before. Therefore his generalisation has the reason to be called as «law».

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Fig. 1. The formula of “Vavilov’s law”: L, L, L. – “radicals”, i. e. the features determining the differences between species, a, b, c,… - the parallel variations (Vavilov, 1968, p. 36).

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Fig. 2. The “homologous rows” of N. I. Vavilov - system of plant variations in form of table (fragment) (Vavilov, 1968. P. 25).

When N. I. Vavilov presented his report on homological series in 1920 in Saratov a rather remarkable case took place. During a thunder of applause finishing the report professor V. P. Zalensky (chairman of the meeting) said: «Biologists welcome their own Mendeleev». Since that time at least in Russia Vavilov acquired a glory of “Mendeleev of biology”<![if !supportFootnotes]>[9]<![endif]>.

Despite the greatest respect, which each biologist feels to N. I. Vavilov and to his scientific papers, there very few attempts to use the “law” as the basis of taxonomy or to develop it in some way. Only one paper was found, in which the possibility of employing of Vavilov’s law as “Mandeleev’s table” was considered – this is a monograph on the genus Cicer (Leguminosae) by famous Russian botanist, explorer of Central Asia Mikhail Popov. He stated a problem of theoretical system, that is of such system, that would not require a radical revision in future, but would just be added by new data according to some theoretical principles. The law of Vavilov seemed a method to fulfil this task. In this connection M. G. Popov considered two questions: 1) whether within the limits of racial variability of one species ever appear the forms absent at other related species; 2) whether “law” is applicable to the taxa of a higher than species level. There was not a final answer to the first question. The assumption was stated that such forms exist, but "it is not clear, what is their character like and how often they appear" because of lack of a material. The more certain data are given to the second question. In family Leguminosae the genus Vicia is nearest to genus Cicer. The genus Vicia is much more various, and it is completely incredible, that in a genus Cicer the plenty of species similar to those of the sort Viciа could be discovered. On the other hand, in a small genus Cicer there are forms absent at Vicia. The conclusion was made of these facts that is impossible to use  “the law of homologous series” for construction of system of genera or higher taxa.

As well as his predecessors M. G. Popov expressed an idea on construction of systems on the basis of the analysis of combinations of features. He noted that such methods are used in some empirical botanical studies. Unfortunately, this tempting idea seemed to him unrealisable. In the tables of combinations the empty crates, «interdictions» or «restrictions» came to light, in which it was difficult to reveal any regularities. M. G. Popov concluded pessimistically, that he would present to a scientific public a new empirical system of genera of Leguminosae, which though seems to him acceptable, would be radically reconsidered by somebody after him<![if !supportFootnotes]>[10]<![endif]>.

Asymmetry of the systems of classification

In parallel to all this another phenomenon reminding the important feature of periodic system was described. As it is known, the periodicity among chemical elements becomes distorted as the atomic weight is increased (that is in the lower part of Mendeleev’s table) because such groups of elements appear which are similar both in atomic weight and properties. These groups become larger as the atomic weight becomes larger, that is why in some parts of the table the periodicity is noted not among elements but among the groups of elements.

The systems of biology are asymmetric too. The regularity called by its discoverer – John Christopher Willis (1868-1858) – “hollow curve” is observed among them. During the elaboration of the systems of classification of some taxa or during the description of flora and fauna the objects form groups differing in size. Thus, the greatest part of genera has only one species while the quantity of genera with great number of species is minimal<![if !supportFootnotes]>[11]<![endif]>.

It seemed more probable to expect the opposite situation. The category of a genus was proposed to unite several species in it. Describing numerous genera which has only one species seems senseless. It is much more convenient to describe genera so that the quantity of species in them differed a little. However, systems of every taxa become more and more asymmetric as the research of them is progressing, that is some genera become greater, they separate into “sections”, “superspecies”, “subgenera” while other ones remain small. The same situation take place among species: some species become greater having a lot of subspecies, morphs, ecotypes, etc. while other ones remain homogenous tending to be genera.

The studies of Willis were criticised extremely roughly. Approximately such estimations were given to it: «nonsense», «rubbish», «the laws, which could be found in stock exchange news or in the telephone lists», etc.<![if !supportFootnotes]>[12]<![endif]> It is clear that using the law of Willis in taxonomy is extremely inconvenient. The system of any group looks as attempt to hide the revealed regularity. The concept of Willis is almost forgotten. His papers are cited rarely and mainly in relation with biogeography. However the hollow curve still reveals in modern taxonomic researches, despite the efforts of taxonomists to squeeze organisms in Procrustean bed of convenient system of traditionally taxa.

A good modern illustration of "hollow curve" could be seen, for example, in the system of Coregonide fishes (white fishes) existing now. About 27 species are described among them, which are incorporated in 3 genera. 1 genus – Stenodus (inconnu) - includes only one species differing greatly from all other white fishes. The genus Prosopium unites 6 species, other white fishes belong to a genus Coregonus. The last genus has very complex structure. The groups of species of unequal size, called «subgenera» or «superspecies» are revealed in it. Besides rather «good species», there are some Coregonus species extremely inconvenient for taxonomists. So, within the limits of a species Сoregonus lavaretus (white fish) it is possible to describe dozens of well-distinguished forms, both ecological, and geographical ones. In northern part of Western Europe several forms were described as “species”. Some of them have a number of parallel features with other white fish species, that is why they were called by the same Latin names (C. peled, C. muksun)<![if !supportFootnotes]>[13]<![endif]>. If to raise a rank of intraspecific forms of Coregonus lavaretus up to specific ones, it would be necessary to raise rank of other species related with it up to genera, then to raise the rank of genera Prosopium and Stenodus up to a family, then to reconsider all system of Salmonides, and so on. It would be extremely inconvenient, that is why the specialists on Coregonidae would hardly recognise the “hollow curve”.

John Willis explained the existence of a “curve” simply by the age: the large and various groups appeared earlier, and had time to spread and differentiate. The small ones appeared relatively recently. In view of the fact of parallel evolutionary trends and homological series it is possible to add that groups differing in age tend to develop in similar directions. In the case of Coregonidae it means that Coregonus appeared before other ones and had time to spread and to differentiate, while Stenodus appeared relatively recently, and consequently had no time to be divided even into two species. (Note, that the traditional reconstruction of phylogenies on the basis of the analysis of similarity and distinction will result in completely opposite viewpoint: as Stenodus differs most significantly from the group of species of Coregonus, it was separated from the basic trunk of their evolutionary development earlier.) If it so, and if to take into account the existence of parallelism between taxa of a different level, the cargo of the years lived causes «periodicity» of properties of organisms just as the increase of atomic weight results in periodicity among chemical elements. Thus, the generalization of Willis and the data about parallelisms specifies a certain vague image of periodic system.

The analysis “of periodic systems”, homologous rows and co-ordinate systems at the recent time

The works by John Willis, Nikolay Vavilov and their not numerous adherents were being made in the difficult period in the history of biology, which was determined as “the eclipse of Darwinism”, “crisis of the evolutionary theory”, “confusion in taxonomy”, etc.<![if !supportFootnotes]>[14]<![endif]> At that time the abundance of various theories appeared and intensive search of ways of development of biology took place. Further the ideas in spirit of the synthetic theory were gradually formed and then they occupied a leading position in biology.

In the books, which have served as a basis of the synthetic theory, the analysis of problems discussed above is absent. “New” or “evolutionary”, “phylogenetic”, “numeric” and the other systematics developing in the recent period are also not connected with the searches of “periodic systems”. These searches have remained far away from the main ways of development of theoretical biology. Nevertheless works about “homologous series”, “periodic systems” and systems of co-ordinates occurred from time to time. More often they remain within the framework of special empirical studies.

The systems in the form of tables were especially actively used in the study of various lowest organisms - bacteria, algae and fungi. This is due to the fact that the reconstruction of the evolutionary destinies of these organisms is difficult, while facts or speculations on evolution are traditionally used in taxonomy. This contradiction with tradition forces scientists to search for other ways. One of them is the construction of systems of the tables of combinations of features similar to Punnet’s lattice. In such a way the “phenotypic systematic” of bacteria of G. Zavarsin, the “typological systematic” of fungi of Lar. Vasilieva were created<![if !supportFootnotes]>[15]<![endif]>.

Similar methods were also elaborated independently from microbiologists and mycologists. The tables of combinations of features were used by Е. Е. Kovalenko during the study of morphology of amphibians, however, with other purposes. They were applied to the study of “behaviour of variability” - definition of a degree of variability, distinctions of variability of different groups, definition of evolutionary constraints, estimation of frequencies of variants, etc.<![if !supportFootnotes]>[16]<![endif]>

The systems in the form of tables can be productive in some cases, but they turn out very bulky. Something like Mendeleev’s system exists only in imagination of the researcher like a multidimensional space. Nevertheless we have tried to display essence of these methods in the simple scheme – scheme of a variation of hypothetical group of small mammals “Х”, characterised by three groups of features (types of colouring, structure of a tail and ears)<![if !supportFootnotes]>[17]<![endif]>. System in the form of the table illustrates all possible combinations of features, on which it is possible to mark the known forms, to fix «interdictions» and, probably, to predict a discovery of the new forms (Fig. 3).

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Figure 3. The scheme of variation of hypothetical group of mammals “X” characterized by combinations of 4 features – the length of tail (A), type of fur-trim of tail (B), type of coloration (C), size of ears (D) (Kovalenko, Popov, 1997. P. 78).

Besides such tables outgoing from empirical works some theoretical studies were also undertaken. Russian biologist and philosopher A. A. Liubishev (1890-1972) and his followers were especially active in this field. They stressed the importance of the analysis of laws of evolution, of parallelisms in particular, have introduced some new terms for their characteristics, and criticised traditional notions<![if !supportFootnotes]>[18]<![endif]>. One of the central ideas of Liubishev’s works consisted in precise separation of problems of the “forms”, “systematics” and “evolution”. This differentiation stated a question of systems similar to chemical ones, but it was hardly developed. The studies of Liubishev and his adherents leave impression of some incompleteness. The most of results of their works has remained in so-called «epistolary heritage» - diaries, records of discussions, letters, etc. There are few articles and books on «laws» of biology, and they are written rather in philosophical than in scientific language. One of the authors of this tradition - Yu.V.Chaykovsky – worked intensively on the analysis of “dyatropics” – the science on variety. Studying dyatropics he proposed an “anti-phylogenetic” scheme of the highest taxa in form of concentric circles divided into sectors. The main criteria of this system were «ecological-physiological», that is the type of a feeding - osmotrophic, phagotrophic and autotrophic<![if !supportFootnotes]>[19]<![endif]> (Fig. 4).

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Figure 4. The “eco-physiological macrosystem” by Yu. V. Chaykovsky. (Chaykovsky, 1986, p. 23).

Probably, the most modern author, who is keen on “periodicity” in biology, is Swedish cytogeneticist А. Lima de Faria. Rather recently ignoring absolutely the century experience he has declared his “discovery” – the discovery of the phenomenon of “biological periodicity”. It is difficult to find a precise formulation of the characteristics of this phenomenon in his papers. It is explained by huge quantity of examples, which are usually called in biological literature convergences or parallelisms, as well as the examples of similarity of some organic and inorganic objects (snow-flake - Radiolaria, layers in minerals and solutions – layers in plant tissues, etc.). He noted that “the periodicity” was discovered recently, that is why its mechanisms are not clear yet<![if !supportFootnotes]>[20]<![endif]>.

Thus, looking for the order in a nature some ways of researches, which show something similar to classification of chemistry are revealed: the description of homologous series of variability, the study of asymmetry of systems of classification, construction of systems of co-ordinates - tables of combinations of features. However in systems of biology there are no elementary units similar to chemical ones. Their existence was postulated in some works, but they were not connected with attempts of creation of systems of classification.

Almost all works discussed above were not connected with each other. This story consists of fragments and hints. The questions related with chemical classification appear regularly and independently in biology during the last 150 years. The efficiency and clearness of chemical systems charmed biologists so that they tried to find the same in their science. However it is difficult to note a progress in these studies. Since 1920s few significant facts and ideas could be added.

Considering the reasons of this situation a majority of biologists or theorists dealing with biology could decide that the studies in this field are absolutely hopeless. The objects of biology seem so complex and diverse, that any general laws, notions, concepts, systems, elementary units, etc. could exist. From the authors of the vitalism and up to Ernst Mayr the largest theorists of biology expressed pathetic statements about uniqueness of biology. This situation can look differently for the historian of science, if we put attention to a history of discovery of Mendeleev’s periodical system.

A discovery of “periodic law” and theoretical biology:

Similarities and differences

 An opinion about hopelessness of searches of the laws describing a variety of all chemical elements and connections was also expressed by many chemists of XIX century. A known Russian historian of chemistry Bonifatiy Kedrov wrote about them: “the vast majority of the chemists of West was convinced that the ordering of elements can not go further than grouping some part of them in accordance to chemical similarity”<![if !supportFootnotes]>[21]<![endif]>. It concerns not only to the chemists of West. Some eminent Russian chemists also were of the same opinion. N. N. Zinin, for example, was anxious about the fact, that Mendeleev stopped the experimental work and took a great interest in useless researches.

According to the legend the periodic system dreamed to Mendeleev. However the specialists say, that such things do not occur casually. Despite almost hostile conditions there were some predecessors of Mendeleev. On the one hand, there were some “practicians”, which created systems of classification, but did not consider them valuable, i.e. did not see or did not show existence of the periodic law. Their tables were used in the textbooks and in practical researches. (In the same way in biological systematics the “periodic systems” are sometimes used, but they do not exceed the limits of empirical studies.). On the other hand, there were also theorists. B. de Chancourtois offered a rather graceful system. It represented a line twining a cylinder as a spiral (“vis tellurique”). Each element occupied the certain place on a line passing numerous gaps. According to the experts, the system contained “a lot of incongruities”<![if !supportFootnotes]>[22]<![endif]>. R. Newlands like Mendeleev subsequently used an atomic weight as the main principle of the construction of system. He has revealed a prototype of the periodic law named “as the law of octaves”. Newlands was confused strongly with criticism. One of the critics asked him with poisonous irony: “Didn’t the author tried to arrange elements in the order of the alphabet, instead of according to atomic weight?”<![if !supportFootnotes]>[23]<![endif]> Such comments coincide with the comments about the data of J. Willis.

Mendeleev was much more persistent then his predecessors. He was interested by practical needs - statement of bases of chemistry in the educational programs, as well as theoretical ones. Finally he achieved a success showing once again that on such high level of researches the opposition of «theory» and «practice», the applied and fundamental importance loses any sense.

Mendeleev used cards, on which the name of one element and its properties were written and then “played patience” with them. Now it seems that it was very easy to discover the law through such method. It was enough to put these cards in line according to the increase of atomic weight and then to divide it in “periods”. However it turned out that a certain system came to light only if some results of empirical researches would be reconsidered, that is it was necessary to make something inconceivable: to address to “practicians” with the instruction to correct their results. Surprisingly, such “instruction” from Mendeleev produced a desirable effect in some cases. Such story occurred with “ecaaluminium”(gallium) predicted by Mendeleev<![if !supportFootnotes]>[24]<![endif]>.

Playing patience with cards-elements was only one of technical methods while the whole way to discover a periodic system was very difficult and painful search. Mendeleev tried to reveal “natural groups” of elements and their compositions using different principles. He looked for typological similarities or relationships like idealistic morphologists. Moreover, in terms of biology Mendeleev could be named gradualist. He considered a variety of chemical substances the series of gradual changes of properties. Working on the system of elements he analysed more general principles of classification and evolution. The analysis of homologous series of organic molecules was also used in these studies<![if !supportFootnotes]>[25]<![endif]>. Mendeleev did not know anything about mechanisms determining periodicity - protons, neutrons, electrons, etc. However the lack of this information has not prevented him to make the system, because he found a good “diagnostic feature” of them - atomic weight.

In Mendeleev’s time the existence of the periodic law was not always considered evident. The reaction of a scientific community was not always enthusiastic. In some cases the comments on it, again, almost coincide with the evaluation of the Willis’s law. For example, a famous German chemist R. Bunsen claimed: “I can do a lot of such generalisations on the basis of lists, which are printed in exchange news”<![if !supportFootnotes]>[26]<![endif]>. Despite this pretentious statements similar generalisations were not made any more.

The similarity of a scientific climate around the discovery of the periodical systems and the similar attempts in biology is very great. There is also some similarity in generalisations - revealing a typological order, parallelisms, homologous series and asymmetry.

However there is at least one sharp distinction between attempts of ordering of objects of chemistry and biology. In biology all the most known generalisations are closely related with an idea of development or evolution. The great majority of studies to find an order among organisms include evolutionary speculations. No chemist will tell, for example, that copper originated from calcium through selection of small variations during the adaptation to the best temperature of melting, but in biology such statements are normal. Moreover, the drawing up of the every possible genealogical scheme is extremely popular. Concerning problems discussed above, this way leads to impasse. “The periodic systems” became popular mainly among those studies of those organisms, which hardly caused the enthusiasm on reconstruction of phylogenies.

Not only the evolutionary approach but also the most popular concept – the idea of natural selection - hardly influenced the studies of “periodicity”. It pays the main attention to the selection of variants of variability, and the question what chooses selection from, appears not so important. («it is true that it is less important for the understanding of evolution to know how genetic variation is manufactured than to know how natural selection deals with it» - E. Mayr<![if !supportFootnotes]>[27]<![endif]>). The construction of all systems mentioned above was connected with non-Darwinian evolutionary concepts, criticised for idealism, essentialism, vitalism and other heresies.

E. Cope was known as the leader of American neolamarckians. The adherents of orthogenesis or nomogenesis approved the Vavilov’s studies and cited them as a confirmation of their ideas<![if !supportFootnotes]>[28]<![endif]>. Vavilov himself also sympathised nomogenesis. John Willis came to the conclusions opposite to Darwinism practically on each question of the theory of evolution. The theory of hybridisation, symbiogenesis were also opposed to Darwinism. The most modern author A. Lima de Faria called one of his books “evolution without selection”<![if !supportFootnotes]>[29]<![endif]>, etc.

Some papers on evolution are known in chemistry too, but, certainly, they are not comparable to that volume, which occupies the idea of evolution in biology, and they are rather of philosophical character. In this respect chemistry is sharply opposed to biology, which has a slogan formulated by Dobzhansky: “Nothing in biology makes sense except in the light of evolution”<![if !supportFootnotes]>[30]<![endif]>. However, something at least has it. The searching for an order, similar to an order among objects of chemistry could be productive without the analysis of evolutionary factors or evolutionary relationships among organisms.

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