Systematics is the oldest discipline in biology. Systematics was indeed the starting point of biology, which began with naming and discriminating between organisms. The ancient civilizations already accumulated a fair amount of knowledge about plants and animals. However, traits of real science—not just knowledge preserved from generation to generation as an intellectual heritage, but rather a kind of knowledge actively enhanced through more and more appeals to the real-world phenomena—these traits were acquired by natural history only in Renaissance and post-Renaissance Europe. Yet well after the turning point of the 15-16th centuries, for nearly 200 more years in Europe it was mainly accumulation of raw descriptive material along with some early attempts of its organization. Systematics—the way we understand it today—was born in the early 18th century, its formation connected with the name of Carl Linnaeus (1707-1778) more than any other name. We are not saying that Linnaeus was the sole founder of systematics, but the undeniable fact is that his contribution was the most significant, even revolutionary; his ideas and works received prompt and overwhelming recognition. As A.-L. Jussieu has put it, the system of Linnaeus "prevaluit universo fere botanicorum consensu" [is prevailing due to nearly unanimous consensus of botanists] (Jussieu 1789: XXXIV). Linnaeus played a very significant part in the tremendous progress of the natural-world studies during the 18th century.

What we now perceive as the goal of specifically systematics, used to be the essence and basics of the entire botanical science for Linnaeus. "Fundamentum botanices duplex est: dispositio et denominatio" [The foundation of botany is dual: placement and nomination] (Linnaeus 1751, Sect. 151). Therefore, in Linnaeus' vocabulary the word "systematics" was absent, though he constantly employed such expressions as "system," "systematic," "systematist." The term "systematics" surfaced later on, most probably in German literature (Systemkunde in Willdenow 1792). Nearly at the same time and in the same sense, the term "taxonomy" was introduced in French literature (de Candolle 1813). All subsequent attempts to discriminate between both terms have proved to have little force; we should treat the two as synonyms, which is the way they are actually being used.

During the initial stages of its development, systematics was nearly entirely based on morphology. However, starting already from the mid-19th century, its connections with other biological disciplines quickly began to broaden. As a result of that, in the 20th century, systematics was enhanced by a number of particular divisions, which more or less separated themselves from the general Linnaean ("classical" or "traditional") trend. Here belong evolutionary systematics, microsystematics, biosystematics, differential systematics, experimental systematics; phylogenetic, phenetic, and numeric systematics; caryosystematics, immunosystematics, genosystematics, molecular systematics... (this list is by no means exhaustive).

New directions naturally initiated polemics and criticism aimed toward the previous stage of systematics; often times they have been striving to revise even the basic principles. At the same time, these new trends themselves have been subject to criticism. The general impression from the recent developments is that the more modestly a new division has claimed its space, the more serious its contribution to systematics is, and the more naturally it is integrated within the traditional Linnaean framework. The opposite is also true: the louder the criticism of Linnaeus has sounded, the more it was merely all about the erosion of the theoretical foundation of systematics. Accusations have often been totally unsubstantiated. For example, Heywood (1985) in fifteen pages made at least fifteen negative remarks concerning Linnaean ideas, yet he never cited Linnaeus himself.

Leaving aside such extreme appearances, we still find the wide-spread notion (usually borrowed second- or even third-hand) of Linnaeus' contribution to the natural science being rather inadequate and superficial. Basically, it can be summarized in three statements: 1. he elaborated a system for the plant kingdom that has proved to be rather handy though artificial; 2. he proposed a very useful binary (two-component) nomenclature for species; 3. however, he treated species as created by a Deity and unchanging.

In order to appreciate the true profoundness of the fundamental Linnaean heritage, one has to read Linnaeus in the original and then compare his words with those of subsequent significant contributors to the botanical systematics: Jussieu (1789) and de Candolle, the senior (1813, 1819).

When speaking about any prominent scientist, it is always possible to come up with a list of things he did not accomplish. However, much more important is the acknowledgment of his contributions to science. In this article I am trying to consider and evaluate the contribution of Linnaeus to the study of the diversity of living organisms from the positions formed at the brink of the 20th and 21st centuries. In order to distance myself from those critics of Linnaeus who leave their statements unsubstantiated, I am going to employ fairly large citations from Linnaeus' writings.

Systematics is a part of biology, a division that in a way occupies a central position among other divisions. The goal of systematics, its purpose is to help us navigate the diversity of living organisms. At the same time, systematics is the framework, the supporting structure that is essential for the organization of all biological knowledge. Any observed biological phenomenon (be it a structure, property, or process) is always referred to a certain taxonomic group. Observations concerning some undefined organisms are of little interest.

The diversity of living beings is the result of long evolution, so one can say that systematics is aimed at presenting the results of evolution of living organisms in an organized, thoughtful manner. It is a well-known fact that the major mechanism of evolution, natural selection, works at the level of whole organisms and higher (populations, colonial and symbiotic structures). Accordingly, systematics is oriented towards these levels of organization. Of course, it is possible to separately consider the evolution of certain structures or functions as such, apart from whole organisms; however, one should keep in mind that parts of organisms cannot evolve on their own. If they were able, they might have existed as independent components of ecosystems. However, we don't find skeletons, carpels, nor DNA strands living free. Hence systematics presents the system of whole organisms rather than their parts or traits.

Upon evaluating affinity of organisms, systematics groups them in units (taxa). Assessments are made through consideration and critical interpretation of all facts known about certain organisms: their macro- and micromorphology, physiology, biochemistry, genetics, ecology, ethology, and so on; these data are provided by appropriate biologic disciplines. Systematics itself does not contain any such facts—it only produces judgments. The system as a whole is composed of a multitude of specific judgments embracing groups of living beings at different taxonomic levels (Skvortsov 1981: 25).

Hence systematics is a purely theoretical domain of biology, while its product, the system, is a theoretical construction, a specific biological theory, one of the most important in science.

A transition from a particular discipline to systematics involves interpretation, evaluation of particular characters' importance, and making a taxonomic judgment based on that assessment. From the logical perspective, this is a transition from particular factual data of analytical nature to inductive judgment of synthetic character.

Essentially all taxonomic judgments, from those most particular to most general, are of tentative character. They are nothing but working hypotheses, whose validity and effectiveness is tested, as it normally happens elsewhere in science, by their ability to explain observed facts, especially those that surfaced after the hypotheses were formulated. With the progress of systematics, hypotheses are being strengthened, corrected, or else substituted with new, more valid, better working ones. The non-stop revision of the system constitutes the very essence, the major content of systematic research. It is very important for a scientist to furnish formulated judgments and speculations with exact nomenclature as well as means helping placement of every organism within the system, i. e., diagnoses for taxa and identification keys. This is as far as systematics essentially can go. The system is just a supporting structure for organizing our knowledge about living things, while the knowledge itself belongs to specific biological domains outside systematics.

Linnaeus (Philos. bot., Sect. 186-191) was the first to clearly recognize "character essentialis," a critical attribute of the system, a concise and clear characteristic of a taxon that makes it different from closely related taxa (or "character factitius," which can include any expressive characters suitable for identification of a certain taxon). He treated these two categories differently from "character naturalis," a description that may contain all kinds of characters, and as many of them as the author wishes. De Candolle, the senior (1813, 1819) perfected the same idea by dividing his course of botanical theory into three major parts: taxonomy, descriptive botany (botanique descriptive or phytographie), and terminology, the latter essentially supplemental to the second part. Though de Candolle made his divisions not exactly the way we would do it now (in particular, he moved an important part of morphology right to taxonomy), this did not really affect the principal approach. Later on, along with the epithet "descriptive," there emerged other terms, such as "systematic," "comparative," "evolutionary" (as regards botany, morphology, physiology, biochemistry, etc.)

Linnaeus was the first to introduce to the natural science the system principle as well as the notion of the system itself.

"System" is a word of Greek origin. In the ancient world it was in use in about the same capacity as it is now; however, the word did not make it into the classic Latin, nor to Medieval scientific Latin. A research (Stein 1968) provides that the designation "system" was recovered from oblivion at the very start of the 17th century. However, before Linnaeus, it had only been used in abstract science: logics, metaphysics, theology.

Linnaeus' fundamental work "Systema naturae" was published in 1735, when the author, who was then very young (only 28), lived in Holland. This remarkable piece of writing is only as long as a few pages, which are not even numbered, though printed in folio. "Systema naturae" is a peculiar kind of manifesto, an outline for subsequent activities of the author. It contains nearly all of Linnaean principal statements formulated as compact aphoristic theses—in the same style that later became so characteristic for the rest of Linnaeus' writing. There is no concrete descriptive data from either of the three "kingdoms" of Nature (i. e., mineralogy, botany, and zoology). This material was gradually filled in during the subsequent editions. The twelfth edition was the last one prepared by Linnaeus himself. Published in 1766-68, it consisted of four volumes, whose total size was more than 2,500 pages.

Meanwhile, Linnaeus transferred the elaboration of general problems, those specifically related to the field of botany, to a series of separate works: "Fundamenta botanica" (1736), "Critica botanica" (1737a), "Classes plantarum" (1738), and finally, as a concluding summary, "Philosophia botanica," which was published much later, in 1751.

Though Linnaeus discussed the principle questions of systematics in botanical compositions, his works proved to be very influential in zoology, as well. The one to be named is the zoological part of "Systema naturae," whose tenth edition (1758) is now considered a starting point for the priority count in the zoological nomenclature. In some zoological works (Artedi 1738, Fabricius 1788), not only the ideas, but even the writing style appears to be remarkably similar to that of Linnaeus. ^[1] Linnaeus considered Artedi to be his older friend and confederate. The two of them shared their principle approaches and worked them out together. After Artedi's death, it was Linnaeus who rescued, edited, and facilitated publication of his friend's writings. No wonder that their contents and style are similar to that in Linnaeus' works. See more about Linnaeus' scientific alliance with Artedi at: http://artedi.fish.washington.edu/Geninfo/artedi.html. (Translator's note)

Linnaeus develops the idea of the hierarchical system of taxa. He is contrasting his system to all other ways of depicting the diversity of living organisms, such as lists, catalogs, dichotomous arrangements—be it according to general habit, useful properties, or any other chosen characters. Linnaeus designates all other methods as synoptic. Therefore, [grouping of plants (or animals) can be either synoptic or systematic] "Dispositio vegetabilium vel synoptice vel systematice absolvitur" (Philos. bot., Sect. 154). [Synoptic divisions are arbitrary] "Synopsis tradit divisiones arbitrarias" (Philos. bot., Sect. 154). And [the system is the Ariadne's thread of botany; without it botany is inevitably going to be in disarray] "Filum ariadneum botanices est systema, sine quo chaos est Res herbaria" (Philos. bot. Sect. 156). Linnaeus believed that [of all things ever proposed or employed in botany, there is nothing more beautiful, useful, and necessary than the method of arranging plants in the system] "Nil pulchrius, nil magis utile et necessarium in botanices desideratum et inventum est quam systematica plantarum methodus" (Classes pl., praefatio).

Linnaeus proposed five levels of hierarchy: varieties, species, genera, orders, and classes. Of course, he realized that any such hierarchy, taken by itself, might be considered as a kind of purely logistical classifying structure. In order to distance himself from this kind of treatment and emphasize the material, tangible nature of the proposed groupings, Linnaeus compared his taxa hierarchy with that of military subdivisions—from legion to a single warrior; he also compared his system with a territorial division of a country—from the entire state to a single estate. He repeatedly used these comparisons with some variations in editions of "Systema naturae" as well as in "Philosophia botanica" (Sect. 155). The comparison with the geographic map is repeated a few times elsewhere in his writings.

The hierarchic system resulted in placement of every single plant in a certain species, every species in a certain genus, every genus in an order, every order in a class. There is a certain place for every plant, so that any particular plant is characterized not only by its specific characters, but also (and more than anything else) by its position within the system. And the entire system presents the plant kingdom as a certain organized entity.

According to Linnaeus, [a teacher, when presenting to pupils a complete system elaborated by someone else, proceeds from the general overview to particular details; an inventor, while in the process of building his system, goes the opposite way—from the particular to the general], i. e., from species to genera, from genera to orders and classes: "Docenti procedendum a generalibus ad singularia quaeqae, dum inventa explicat; ut inventori, contra, a singularibus ad generalia eundum fuit" (Genera pl. 1737b, Sect. 8). This tells us that Linnaeus made a clear distinction between a synthetic, inductive process of the system construction and an analytic, deductive process of plant identification with a help of a key. Misunderstanding of this distinction lead some critics of Linnaeus to accusations stating that he saw the species as nothing but a product of the logical division of the genus.

Linnaeus believed that species and genera are real, natural entities, though their limits, as presented by certain authors, might need corrections. Natural limits of any certain species are provided by its continuous reproduction in progeny. The naturality of genera is based on the naturality of species. "Genera tot dicimus, quot similes constructae fructificationes proferunt diversae species naturales" [There are as many genera as there are variations of reproductive organs in natural species] (Philos. bot., Sect. 159).

[Delimitation of particular genera is not always a straightforward process; it requires attentive and consistent observation] "Generum limites attenta et sedula observatione inquirere debemus" (Genera pl. 1754, praef., p. II). It is important that [characters critical in diagnostics of one genus do not necessarily play the same role with other genera] "Quae in uno genere ad genus stabiliendum valent, minimo idem in altero necessario praestant" (Philos. bot., Sect. 169).

This sounds so up-to-date and so irreconcilable with common accusations of apriorism in Linnaeus' works! Linnaeus elaborates this thought even further. "Scias: characterem non constituere genus, sed genus characterem. Characterem fluere e genere, non genus e charactere. Characterem non esse, ut genus fiat, sed ut genus noscatur" [Mind: no characters constitute the species, but rather the species defines its characters. Characters are derivatives of the genus rather than the genus is derived from its characters. Characters are essential not for declaration of a certain genus, but rather for learning about it.] (Philos. bot., Sect. 169). Here the genus, the same way as the species, is considered to be a certain biological entity, which even sounds like a hint towards evolution. No wonder these words of Linnaeus were later noted by Charles Darwin, though Linnaeus was not an evolutionist (see more here below).

As opposed to species and genera, the higher taxa (orders and classes), even those of his own system, let alone those of other authors, were considered by Linnaeus as conventional [creations of nature and art] : "Naturae opus semper est species et genus, ... naturae et artis classis et ordo" (Philos. bot., Sect. 169). Nevertheless, Linnaeus was confident that natural limits could be outlined for the higher taxa, as well. As a first step in that direction, he proposed 67 orders as "fragments" of the natural system, which he intended for a future discussion and development (Classes pl.: 485-514; Philos. bot., Sect. 77). Each order had a name as well as a list of pertaining genera, but no diagnostic characters. Those orders, however, did not embrace all of the plants known already at that time.

Inspired by the idea of creating a natural system, Linnaeus promotes it in various ways in many of his writings. Here are just a few quotations:

"Emendant, augeant, perficeant hanc methodum qui possunt; ...qui valent, botanici sunt eximii" [Those who have the ability should improve, broaden, elaborate this method; ... he who is capable of doing so is an outstanding botanist] (Classes pl.: 487).

"Methodi naturalis fragmenta studiose inquirenda sunt. Primum et ultimum hoc in botanicis desideratum est" [The fragments of the natural method are to be thoroughly studied. This is the first and last thing we are expecting from botanists] (Philos. bot., Sect. 77).

"Methodus naturalis hinc ultimus finis Botanices est et erit" [The natural method is, and is going to be the ultimate goal of Botany] (Philos. bot., Sect. 163, 206).

At the same time, Linnaeus realizes that this goal is not going to be reached anytime soon: "Methodus naturalis et nostrae et omnium inventarum methodis longe preferri deberet, sed rideo omnes methodos naturales hactenus exclamatas" [The natural method is much more preferential than our method as well as any other proposed methods; at the same time, all methods that have so far been declared to be natural, deserve only ridicule] (Genera pl. 1754, p. V). Here Linnaeus is talking about the artificial system of his own.

"Nec sperare fas est, quod nostra aetas systema quoddem naturale videre quaet et vix seri nepotes. Attamen plantes nosse studemus; ideoque interim artificiales assumendae sunt classes et succedaneae" [We don't have hopes for our contemporaries to see the truly natural system, hardly even for remote descendants. However, we are aspiring to learn more about plants; therefore, for the time being we have to accept imperfect, artificial classes] (Genera pl. 1754, p. V).

Apparently, the idea of the "natural method" or "natural system" was of a slogan-like nature. And this slogan has proved to be rewarding. Was it ever possible for any naturalist studying the diversity of living beings to remain indifferent to this call? Indeed it still sounds to us like "we shall overcome"! At the same time, in the context of the eighteenth-century science, which was seeking absolute, indestructible truth, the very acknowledgment of the tentative nature of knowledge and a future gradual movement toward the truth was a great methodological innovation, which has never been adequately appraised.

There is one more important consideration. In the 18th century, the widespread notion was that all of the natural diversity and, at the same time, organization in Nature was nothing but a depiction of the Creator's plan. So it would seem quite natural for Linnaeus to declare his natural method to be capturing this plan. However, Linnaeus never refers to a Divine creation outline. His system remains the system of Nature. Meanwhile, the plan of the Creator remained living in the minds of naturalists long afterwards. The major American zoologist L. Agassiz wrote during the second half of the 19th century that the system was "instituted by Divine intelligence as the categories of his mode of thinking" (Agassiz 1859: 8-10; see also Agassiz 1880: 42).

But what exactly is the "naturality" of a system? What are its criteria? What is the difference between the natural and artificial system? Linnaeus sees the major difference in the purpose: "Ordines naturales valent de natura plantarum, artificiales in diagnosi plantarum" [The natural system should depict the nature of plants, while an artificial one serves only their identification] (Genera pl. 1764, praefatio). "Nulla hic valet regula a priori, nec una vel altera pars fructificationis, sed solum symmetria omnium partium" [It is impossible to provide any a priori rules for attaining the naturality of the system, impossible to consider one or another part of reproductive organs to be critical; it's only the combination of all parts in their entirety that can be helpful] (Classes pl.: 487).

De Candolle (1819: 50-51) presents this difference in a similar manner: "Artificial methods have... the only purpose and the only result of providing an opportunity to find out... the names of living beings." The natural ones are oriented at "the study of plants—in themselves as well as in their actual relationships to each other" (de Candolle 1819: 29). According to de Candolle, neither Adanson nor Buffon recognized the difference between the natural and artificial method (de Candolle1819: 61). Therefore, de Candolle says, these authors remained on the roadside of systematics advancement.

As I said before, Linnaeus liked to explain the relationship of natural groups in the system by using a comparison with a geographic map, in which the territories of different sizes and variable nature were in subordination to each other. In his book (1792), one of Linnaeus' students, Giseke, recorded two lectures by Linnaeus on natural orders, which even contain a sketch as an illustration of this comparison. The title is remarkable: "mappa geographico-genealogica affinitatum ordinum" [geographic-genealogical map] ! This is a prototype of many a diagram of later authors who depicted systematic relationships in two-dimensional images. For example, recently a similar diagram has been proposed by Thorne (1976).

An extremely interesting part of "Philosophia botanica" is one devoted to "plant forces" (Philos. bot., Sect. 336-365). Here Linnaeus aims to demonstrate that the presence of a certain substance in a plant is congruent with the attribution of the plant to a certain natural taxon—first and foremost to a genus, and then even to a particular order and class. Hence the presence of certain active substances provides a criterion for the naturality of a taxon. The opposite is also true: it makes sense to further search for similar active substances within a natural taxon. Indeed this looks like the beginnings of chemosystematics!

De Candolle (1819: 64-73) made an attempt to analyze and clarify the mode of action of a researcher aspiring to the construction of a natural system. He identified three different approaches: tâtonnement (a kind of intuitive trial), comparaison générale (general comparison), and subordination des caractères (subordination of characters). Linnaeus, apparently, formed his "natural" orders using the first method—by intuition. He notes that [attribution of a plant to a certain order often times is apparent right from the appearance of the plant] "Habitus... in plantis saepe harum ordines naturales primu intuitu manifestat" (Philos. bot., Sect. 163). The second of the three methods, general comparison, apparently was used by Adanson (1763), who compared plants by a number of characters and then compiled his natural families by uniting those plants having the highest number of matching characters. This method was revived in the mid-20th century by neo-Adansonians, protagonists of quantitative systematics. The method of character subordination was employed by Jussieu (1789). There is no doubt that none of the three approaches was fully satisfactory; none of the authors had a feeling that he reached his goal and the fully natural system was constructed.

In Linnaeus' time (and even somewhat earlier), there existed a term "affinitas" that signified "a relationship between plants." Being ambiguous, it proved to be convenient. It could mean anything from proximity, vicinity, contiguity, closeness to similarity, connection, attribution, finally even relation.

It was only in the late 19th century, with the triumph of the evolutionary approach, that the slogan of the natural system received a solid foundation. The term "affinitas," so vague before, now acquired a quite definite meaning—"relation." Both parties—systematics and evolutionary theory— benefited from this alliance. Here is what Darwin said in this respect in "The Origin of Species," (Chapter 13; in accordance with the British tradition, he was using the term "classification" instead of "system" or "systematics"): "Such expressions as that famous one of Linnaeus, and which we often meet within a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent, the only known cause of the similarity of organic beings, is the bond..., which is partially revealed to us by our classifications."

Linnaean systematics proved to be more ready for the adoption of the evolutionary theory than other biological disciplines; specifically, it was not at all affected by the genetic anti-Darwinism of the early 20th century. Systematics switched to the tracks of evolutionary biology amazingly seamlessly and naturally. The Linnaean (and even pre-Linnaean) term "affinitas" (affinity, affinité, Verwandschaft) has remained fully in use. Also, the difference between the natural and artificial system has remained the same, the former retaining its heuristic meaning, the latter remaining useful as a means of cataloging. We can define the natural system as a depiction, by means of taxa hierarchy, of our notions about the affinity between groups of living beings (Skvortsov 1981).

K.A. Timiryazev (1939: 78) made the following expressive statement: "An artificial system is as much a means as any catalog, while the natural system is in itself the goal of the scientific research." Employing the notion of "living matter," one may define the natural system as the depiction of genetic program differentiation within the living matter for a certain epoch. Finally, resorting to even more abstract notions, we may call it a topologic-genetic model of the biota.

Thus the natural system is still further highlighted as a certain absolute goal, which we approach as an asymptote, so that any particular version of the system proposed today is only tentative, presumptive, and temporary.

Before Linnaeus, the major systematic unit had been the genus. The notion of the genus fits most with the everyday-life plant and animal identification: a birch, an aster, a sedge, a cat, etc. In the botanical literature, the category of the genus had been rather consistently elaborated and introduced already by the start of Linnaeus' scientific activity—mostly through the works of J.P. de Tournefort. Of course, it was fully understood that genera weren't uniform, but more or less variable within—sedges and cats can be different! For the description of this variability, there existed such terms as "species," "varietas," "proles," "lusus," though they did not carry any certain meaning and were treated merely as variations of the genetic type. There were no fixed names associated with them.

John Ray (Raius) was consistently using the term "species." However, his "species" were recognized by inherited characters distinguishable to the highest possible extent of detail. Hence in Ray's works at the start of the 18th century there were 2-3 times as many plant species as in Linnaeus' works in the mid-18th century.

Here is how Linnaeus himself depicted the situation. "Partem aggredior botanices in hunc usque diem intactam, nostraeque relictam industriae... Praesertim ab anno 1660, in hunc usque diem per Morisonum, Rajum... tandem quaedam in generibus nitent certitudo. Hi viri laboriosissimi, videntur nobis, omnes suas vires generibus impedisse, specierum vero characteres posteris reliquisse elaborandos" [We are entering here the part of botany so far intact, left for our diligence... Starting mostly from 1660 and up until now, thanks to works by Morison, Ray, (and others—a total of 27 authors is listed by Linnaeus—A. S.), there has finally been achieved fair confidence as regards genera. These most zealous gentlemen, as we understand, dedicated all their efforts to genera, while characters of species have been left for the future generations to elaborate] (Critica bot.: 146).

With amazing insight and extraordinary intuition of a naturalist, Linnaeus discerned another level of closeness (affinitas) and integration, that could be objectively and reasonably found in the majority of animals and plants—a level lower than the genus in its established meaning. He secured the name "species" for this level and accepted it as the primary "building brick" of systematics.

In order to emphasize the objectivity of the species category, Linnaeus states that all species were created as such at the "beginning of things," during the creation of the world. "Species tot sunt, quot diversas formas ab initio produxit Infinitum Ens; quae formae, secundum generationis inditas leges, produxere plures, at sibi semper similes. Ergo species tot sunt, quot diversae formae s. structurae hodienum occurrunt" [There are as many species as there were different forms initially created by the Infinite Creature; these forms, in accordance with laws of reproduction built into them, have produced many others, though always similar to themselves. Hence the number of species is the same as the number of different forms or structures occurring today] (Classes pl.: 5; Philos. bot., Sect. 157; Genera pl. 1754: 1)

"Novas species dari in vegetabilibus negat generatio continuata, propagatio, observationes quotidianae" [Continuity of generations, propagation experience, as well as our everyday observations are contradictory to a possibility of new species emergence] (Philos. bot., Sect. 157). "Naturae opus semper est species... Species constantissimae sunt, cum earum generatio est vera continuatio" [Species are always products of Nature (and not of a human brain!—A. S.). Species are most constant, since the progeny generated by them is their true continuation] (Philos. bot., Sect. 162).

While introducing taxonomic units to the reader, Linnaeus (Philos. bot., Sect. 157-162; Genera pl., 1754, # 5-6) starts with the species, which he describes completely independently from the genus. When he proceeds to the genus, in his definition there is a dependence upon the species: according to Linnaeus, there are as many genera, as there are different types of reproductive organs in natural species. Only the characters common to all species within the genus should be mentioned in the genus' diagnosis (Philos. bot., Sect. 193).

At the same time, Linnaeus resolutely delineates the species from the lower-level categories, i. e., varieties. "Varietates tot sunt, quot differentes plantae ex ejusdem speciei semine sunt productae. Varietas est planta mutata a caussa accidentali" [There are as many varieties as many plants can be produced from seed of one particular species. A variety is a plant accidentally changed due to some random cause] (Philos. bot., Sect. 158). Varieties are of interest to practical workers, particularly horticulturists. Cultivation produces varieties, but at the same time it tests them for stability. Therefore, varieties could be completely eliminated from systematics. The insignificant ones should be excluded without doubt, and only those most pronounced and constant, useful for their qualities ("ob usum publicum"), might be listed after the species description (Philos. bot., Sect. 158, 306, 316). In other words, according to Linnaeus, it's not that the species is derived from varieties, but rather varieties are random and mostly short-lived derivatives within the species.

Linnaean thesis about the equal "naturality" of the species and genus did not reign long. According to Jussieu (1789), only species existed in nature as such, whereas genera were just groups ("fasciculi") formed by the researcher from species upon evaluation of their affinity ("conglomerentur ratione affinitatis"); orders are formed in a similar manner from genera. Jussieu's understanding of "naturality" was not consistent: for species, in case they were recognized and delimited correctly, it meant the objective, unconditional reality of existence; yet for higher taxa "naturality" meant that characters on which delimitation was based were significant in nature. De Candolle, as well as the majority of other authors of the late 18th-early 19th century, was of the same opinion. Using contemporary language, we should say that they considered only the species to be real, its objective existence established; the rest of taxonomic ranks remained provisional.

The chronicle of further developments in understanding of species is complicated and contradictory, and the literature on this subject is vast and hard to summarize. I have made an attempt to write a concise historic essay elsewhere (Skvortsov 1967). At this point I'd just like to highlight the fact that early evolutionists of the 19th century reduced the species, as well, to a tentative, conventional category. Consequently, the interest toward varieties then grew. In contrast to the Linnaean approach, varieties were reinstalled in their position of proper taxonomic units. The notorious aphorism "a variety is a starting species" became popular. In many minds this aphorism is valid today.

However, the ecologic-genetic-populational model of the species based on the 20th-century works, particularly those by Komarov (1901, 1940), Jordan (1905), Turesson (1922, 1925), Chetverikov (1926), Dobzhansky (1937), Mayr (1942, 1969)—this model is c loser to the Linnaean than Lamarckian or early Darwinian model, at least in three important ways: 1. acceptance of the species as objective reality, i. e., a principal possibility to provide evidence for the species rank (certainly this does not mean that all real situations can be fully described within the species concept—natural situations are diverse, and in systematics judgments are always tentative); 2. acceptance of the species as the major unit of systematics; 3. rejection of the role of varieties as species' predecessors. From the perspective of the new model, only an isolated population can be a "species-starter."

Due to these circumstances, the Linnaean understanding of the species has seamlessly docked the modern concepts. Moreover, there is good reason to believe that particularly the Linnaean naturalistic tradition prevented systematics from sinking into genetic anti-Darwinism, which was in full swing in the first third of the 20th century.

As for varieties, of course they should not be counted as a taxonomic category. This approach was implemented already in Komarov's school and the "Flora of the USSR" (1934-1960). However, this school understood species in a very narrow sense and rejected subspecies; therefore, it was not accepted and could not be further developed. Meanwhile, it is the acceptance of subspecies that helps to exclude varieties (Skvortsov 1971), referring the latter to the realm of morphology. As for cultivated varieties or cultivars, these are essentially not biological entities, but rather agri- or horticultural.

The fact that the contemporary Code of Botanical Nomenclature still places varieties (along with forms) among other taxa should be attributed, of course, to a number of intricately interlacing considerations (mostly of historic nature, connected to the problems of priority); this does not depict the biological situation.

Finally, let's look at the position of Linnaeus as regards the possibility of changes in species and appearance of new species. For authors of historic discourses, this has been all but the favorite topic. Linnaeus has been reproached for considering species constant; on the other hand, in order to offset these accusations, his words have been scrutinized for evidence of his doubts in the constancy of species. It seems as though the only person who approached this theme with a really deep understanding was Yuzepchuk (1957: 49-50), who wrote: "Linnaeus played a great positive role in the study of the species... particularly by developing the theory of species constancy, which made him a target for accusations coming from those who lost the historic perspective." Indeed why would Linnaeus refer to the species creation at the beginning of the world? In order to claim his own religious correctness? This does not sound serious, particularly in the situation where the official church did not require any such statements from biologists, as I mentioned before (Skvortsov 1967: 14). It is quite obvious that this reference was used as a strong argument—strong for the audience of the time—as evidence in favor of the Linnaean notions about the real existence and prolonged stability of species.

By promoting the idea of species stability Linnaeus opposed the belief in a possibility of spontaneous generation of organisms or regeneration of one species into another, which used to be widespread at the time, even among scientists. Even though the bright mind of the naturalist Linnaeus rejected the idea of spontaneous generation as early as the 18th century, Louis Pasteur still had to fight the same notion in the 19th century. In the early 20th century, my own grandmother still believed that lice "appeared" in large numbers on people prone to anxiety during troublesome years of the civil war. Let alone my grandmother, as late as the mid-20th century some professors and academicians insisted that wheat could regenerate into rye and even further into knapweed and that a small perching bird might become a cuckoo.

During the first half of the 18th century, science still accepted the creation of the world and counted four to seven thousand years since the creation day. According to Linnaeus, all species remained unchanged during that time span. However, from the modern perspective, the age of seven million years (and sometimes even 70 million!) for a species does not seem unreasonable. Hence, if the absolute time scale is taken into account, then we now consider species a thousand times more constant than Linnaeus did. So it becomes awkward to accuse Linnaeus of "fixism."

The logical sense of taxa themselves as well as their names has significantly changed in the course of the systematics development. This development had started before Linnaeus and continued after him, up until the present time. We owe two important advancements to Linnaeus: first of all, he introduced the system approach and the "nested" hierarchy of taxa (meaning taxa of a lower level nested within an upper-level taxon); along with that, he proposed binary nomenclature, "nomina trivialia".

Pre-Linnaean groupings had been based on all kinds of different characters. They were rather groupings of characters and qualities than those of organisms. Besides, they were not subordinate to each other; the same species could belong to different groups. In Linnaeus' system there were five levels of hierarchy. Contemporary systems may contain up to twenty and even more levels; however, this difference is purely quantitative, with all the principles fully retained. We build the system starting from the study of characters (qualification), then proceed to placement of the taxon in relation to other taxa (recall Linnaeus' comparison with the geographic map!), and finally to detecting genetic relations and connections, "affinitas" among taxa. In other words, we move from qualification to another procedure that might be called nexification (from Latin nexus—connection). Nexification depicts the essence of the system. When describing an unknown plant to colleagues, we name it first and then situate it within the system, mentioning the rest of the facts about the plant only afterwards.

In pre-Linnaean time, the species was not considered an independent category, but only a variant of the genus different in certain characters. Linnaeus himself considered a concise description of specific characters (i. e., qualification) to be a truly scientific species epithet. The eighth part of "Philosophia botanica" is dedicated to "differentia"—differences. "Differentia specifica continet notas, quibus species a congeneribus differt. Nomen specificum autem continet differentia notas essentiales" [Differentia of a species contain characters that make this species different from other species of the same genus. And the species' name contains essential characters of the differentia] (Philos. bot., Sect. 256). Linnaeus made an enormous effort in order to provide names of this kind for all species of animals and plants known to him—and he was very proud of this achievement. "Primum incepi nomina specifica essentialia condere, ante me nulla differentia digna existit" [I was the first to start creating essential species names, before me no decent differentia existed] (Philos. bot., Sect. 258)

Within the contemporary species model based on facts of ecology and populational genetics, there is no possibility left for understanding the species as a certain group of characters used for the purpose of sorting certain specimens. A species is a population or else a complex system of populations, consisting not only of adult specimens but of those at all stages of ontogenesis, including all types of diaspores. In other words, it is a certain living mass possessing a gene bank (Skvortsov 1971, 1982). So the most important part here is the discovery of ecological and genetic connections between specimens, rather than the assessment of character manifestation in particular members of the population, i. e., nexification rather than qualification.

The element of nexification is distinct in the modern method of nomenclatural types. In the 19th century, systematics was oriented on the morphological understanding of the type, so that characters for a certain taxon were obtained from "typical" specimens. As opposed to that, the modern nomenclatural type might be not at all typical in any respect. It should just belong to the taxon.

"Differentia" in "Philosophia botanica" consists of 50 sections; yet only a half of a single Sect. 257 is devoted to "nomina trivialia" (binary names). Linnaeus himself treated them as just another convenient instrument. As it is stated in Sect. 257, they might even consist of a single word, indeed any word borrowed from anywhere; there were no particular rules proposed as regards these names. However, already during Linnaeus' life span, "nomina trivialia" became extremely popular and promptly ousted "differentia." This is a well-known fact, which is readily explained from the convenience viewpoint.

This change from "awkward" to "convenient" names had yet another, semantic-logical aspect, which is worthy of attention. Polinomial names had contained descriptions of species characters, hence had been connotative; whereas "nomina trivialia," while not supposed to contain any such descriptions, were essentially denotative. The binary nomenclature was innovative not only because it changed the number of words in the species epithet. It also changed the very semantic-logical essence of the epithet by approximating it to a proper name. Denotation had already existed in names of genera; however, names of higher taxa before Linnaeus as well as in Linnaeus' works were mostly connotative (examples in Linnaeus: Monandria, Diandria, ...Ensatae, Spathaceae...). A few of connotative names have survived until now: Monocotyledonae, Dicotyledonae, Cruciferae, Umbelliferae... However, the modern Botanical Code has been steering toward denotation: Liliidae, Rosidae, Brassicaceae, Apiaceae... Connotation is excluded to such a complete extent that, for example, Paeonia daurica is considered a legitimate name for a peony from the Crimea Peninsula, and Lilium pensylvanicum— for a daurian lily. ^[2] Dauria—South Siberia east of Lake Baikal.(Translator's note)

It is quite obvious that denotations are nothing but a special application of the nexification principle. Therefore, it turns out that for taxonomic ideology (and, accordingly, the procedures), the major direction of development has been from qualification and classification of individual living beings to their nexification, and in the nomenclature, accordingly, from connotation to denotation.

Finally, we should add a few more considerations about names. If Linnaeus regarded species to be the foundation of the system, then why is the genus name an obligatory part of the species name? Isn't it evidence in favor of some critical opinions (e. g., Cain 1958) claiming the genus to be at the foundation of Linnaean system and seeing the species as just a product of logical division of the genus? The explanation has been given by Linnaeus himself: "Quaecunque plantae genere conveniunt, eodem nomine generico designandae sunt" [Plants that are being united in a single genus should be designated by the name of this genus] (Critica bot. et Philos. bot., Sect. 213.) Plants are united in a genus—and not separated from the genus! Here is more: "Quod magis conveniens est quam quod fratres eadem gaudent cognomine? Si haec regula non locum haberet, necessaria essent tot nomina primaria, quot species. Nomina haec memoria teneri necessario debent specifica non item: quae enim ad haec rite tenenda sufficeret memoria?" [What's more appropriate than a common name that brothers bear? If we don't accept this rule, then we will need as many primary names as there are species. It will be necessary to memorize all these names. But whose memory is going to be sufficient for their retention?] (Critica bot., Sect. 213, p. 8).

De Candolle (1819: 255) provides a similar (incidentally, quite obvious) explanation: binary nomenclature eases the memory; on the other hand, it pinpoints the position of a species in the system, which is even more important. And nowadays we often go even further by providing the higher-rank coordinates for the species: family, order, class. For example: Circaea alpina L. (Onagraceae—Myrtales—Rosidae) or Echeveria DC. (Crassulaceae, Rosidae). Apparently, these coordinate relations have nothing to do with any "logical divisions."

The idea of uninomials—single-word names independent from the genus name has been proposed multiple times, starting from the 18th century up until the 20th, but has always turned out to be stillborn. As early as in 1819, de Candolle, the senior (1819: 255) already referred to this idea with undisguised irony.

I'd like to thank the Russian Fund for Fundamental Studies (RFFI) for support of my work in systematics. I am also grateful to my colleague R.V. Trokhinskaya for her help with the manuscript preparation.

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Translation I.Kadis
9 May - 31 December 2007 [broken links repaired]