Major Non-Scholastic Motives
The problematic character of the new cognitive situation, taking shape as a result of the antischolastic revolution, is primarily determined by the multiplicity of the natural-philosophical world pictures interpreting the orderliness of the System of Nature in different ways. One of the deepest of them includes different natural-philosophical comprehension of fundamental properties of Nature, viz. its continuity (“nature does not make leaps”) and its “unity in the plural.” For systematics proper, the core of this difference constitutes a contradiction between the acceptance or denial of the natural (real) status of discrete groups of organisms (taxa) and their ranks. Within scholastic systematics, this problem was not seriously considered: a generic-species scheme implementing discrete Aristotelian logic inevitably generated discrete taxa;
in a similar, mostly logical, way, discrete ranks were fixed. Both these discretenesses were taken by scholastic systematics as “metaphysical given,” as an evident and therefore undisputable manifestation of the universal System of Nature. However, a transition to post-scholastic systematics makes this a central problem; it is considered in the context of several basic concepts, viz. the hierarchical Natural System, the linear Natural Order, the two-dimensional “map of Nature,” and the branching “Tree of life.” Some natural philosophers oppose these concepts as suggesting fundamentally incompatible properties of Nature (Buffon, Lamarck), whereas others consolidate them in different ways within specific natural methods (Jussieu, Cuvier).
With regard to ranked hierarchy, its growing fragmentation becomes an important novelty, making it “less discrete” to a degree. Expanding knowledge of taxonomic diversity reveals a more complex structure of mutual affinity of organisms and makes the canonical ranks of Tournefort-Linnaeus insufficient for its description. Accordingly, the system of ranks is developed first by the invention of more categories (i.e., cohort, series, tribe, etc.) and then by the introduction of auxiliary ones, subordinate and superordinate (i.e., subfamily and superfamily). At the same time, a skeptical attitude toward the meaningfulness of ranked hierarchy is expressed regarding the non-equivalence of similarly denoted categories in different sections of the Empire of Live Nature [Brown 1810]. As a consequence of all these disagreements, the ranked system established by the beginning of the 19th century loses its certainty and stability and becomes really chaotic. In the second half of the 19th century, a new very fractional ranked hierarchy is stabilized [Gray 1858], making it, contrary to recognized opinion, non-Linnaean to a certain extent [Needham 1911; de Queiroz 2005; Pavlinov 2015, 2018]. In the 20th century, skepticism about the system of fixed ranks will revive and lead to a proposal to abandon it (see Section 6.3).
An idea of the continuous Natural Order, as an alternative to that of the discretely fragmented Natural System, is an embodiment of the natural-philosophical understanding of Nature as the unbroken Great Chain of Being. It goes back to Aristotle’s idea of the Ladder of Perfection, which at the time under consideration is better known as the Ladder of Nature (Scala Naturae) [Lovejoy 1936; Rieppel 2010a; Archibald 2014]. This “Ladder” (or “Chain”) implies three interrelated fundamental properties of the Universe: continuity, linear ordering, and polarity. This means that the diversity of essences is ordered into a single gapless sequence according to a certain gradient interpreted as either a regression or progression. Regression corresponds to the ideas of the emanation of the One (Platonism) or embodiment of the Divine plan of creation (bibleism): the further a certain essence “falls away” from its source, with which gradation begins, the less perfect it is. Progression is more consistent with the understanding of Aristotle’s Ladder of Perfection as a sequential transformation of beings from less to more developed: so it leads from inert matter through living entities (plants and then animals) to mankind and further to supernatural creatures (angels, etc.).
An important part of the “Ladder” natural philosophy is the conception of Nature as a whole interconnected by a single chain of affinities due to the unity of its integrative creative principle, viz. a prototype or archetype [Kanaev 1963; Hammen 1981;
Pozdnyakov 2015]. One of the most peculiar and important features of this natural philosophy is that it implicitly contains a general idea of the development of Nature, which is not only the world of being but also the world of becoming [Rieppel 1985; Hopwood et al. 2010]. According to this idea, diversity of organisms appears due to the sequential “unfolding” (evolutio) of the prototype, just as a simply organized embryo “evolves” into a much more complex and perfect adult organism. This “Ladder” worldview gains very great influence among natural philosophers of this time; it contains important prerequisites for the formation of both early typological and evolutionary conceptions usually placed in opposition [Hammen 1981; Richards 1992; Pavlinov 2018].
Among “ladderists” of the second half of the 18th century involved in the conceptual history of systematics, the most notable is Georges-Louis Leclair de Buffon. At the beginning of his career, he is unconditionally committed to the idea of the continuity of Nature: in his early treatise “Preliminary Reasoning...” he argues that “only individuals really exist in nature, while genera, orders, classes exist only in our imagination” (cited after [Buffon 1835: 44]). However, later Buffon abandons such an absolute nominalism and acknowledges the reality of species: he begins a small opus “On Nature...” with the statement that “an individual [...] is nothing in Nature; a hundred and a thousand individuals are still nothing in Nature. Species are the only creatures of Nature, eternal and unchanging like itself’ (cited after [Buffon 1843:52]). His argument in favor of species reality originates from the ancient generative species concept and repeats the viewpoints of Ray and Linnaeus: each species at its beginning had a prototype molded by the Creator, based on which all other organisms of this species are reproduced as its copies [Farber 1972; Bowler 1973; Sloan 1979, 1987; Wilkins 2009; Richards 2010; Pavlinov 2013a]. This marks a radical break with a pure classification interpretation of species and very soon becomes a dominant concept, leading directly to its historical interpretation.
To understand the route of the conceptual history of systematics, it is important to keep in mind a deep natural-philosophical background of the species-generative concept, which attracts the attention of not only naturalists but also philosophers. Thus, G. Leibniz, despite his adherence to an idea of the continuity of Nature, believes (before Buffon) that the existence of generative chains of ancestors and descendants witnesses the real division of Nature into species [Look 2009]. This idea is taken up by I. Kant (with reference to Buffon) and included in the general natural-philosophical principle of the historical development of Nature [Mensch 2013].
The Ladder of Nature is most often represented graphically as a linear scheme of the arrangement of organisms in (usually) ascending series. Obviously, such a representation (as a kind of cognitive model) is more than schematic by showing only principal stages of the prototype’s “evolution,” so it is far from being an adequate reproduction of the idea of gapless Nature. Thereby, elements of discreteness are introduced indirectly into the representation of the Ladder, while its true continuity is only implied. Another serious problem is that the real diversity of living beings does not fit into such a one-dimensional ordering; therefore, linear diagrams are usually supplemented with short lateral branches showing variants of the realizations of particular stages of a progressive perfection. This indicates a smooth transition from the linear Natural Order to the branching “Tree of Life”; it is worth noticing that the latter is mentioned by the most devoted “ladderist” Charles Bonnet [Archibald 2014].
In systematics, an idea of the fundamental continuity of the Ladder of Nature leads to an unconditional nominalism: living nature is a continuous series of organisms without any noticeable gaps in it, so there is no discretely ranked hierarchy of discrete groups (species, genera, etc.). Thus, if “gaps in Nature do not exist, it obviously follows that our classifications do not describe it. The classifications we create are completely nominal” [Bonnet 1769: 28]. The first true evolutionist and convinced “ladderist” Jean-Baptiste de Lamarck fully agrees with this conclusion and claims in his “Zoological Philosophy...” [Lamarck 1809] that all taxonomic categories “commonly used in natural sciences, are purely artificial aids [...] Nature has made nothing of this kind [so it] has not really formed either classes, orders, families, genera or constant species but only individuals” (cited after [Lamarck 1963: 20-21]). In other words, though hierarchical classifications are permissible and even useful, they are arbitrary: as the continuous Chain of Being has no joints, it can be cut at any of its “links” by constructing any arbitrary taxa and categories which are of practical value only.
It should be noted that the general idea of the Ladder of Perfection is quite organic not only to the Natural Order but also to the Natural System. In the latter, it is embodied in its simplest form by the rule of progression, which determines the arrangement of taxa of the same rank according to the levels of advancement (progressiveness) of the respective organisms. It occurs in the classifications in two main versions: some implement it as a regression series with the most advanced organisms being listed first (i.e., Linnaeus, Cuvier, etc.), whereas others do that as a progression series beginning with the most primitive organisms (i.e., Adanson, Lamarck, almost all classifications of the 19th and 20th centuries).
The metaphor of taxonomic map represents the structure of taxonomic diversity in a two-dimensional planar scheme similar to a geographical map [Stevens 1984a, 1994; Lesch 1990; Pavlinov 2018]. This metaphor is most consistent with the “network” picture of the world, which focuses on the totality of multilateral connections “all with all” without any preferential axis [Barsanti 1992]. In it, natural groups of organisms are likened to the territorial units of different levels of generality (islands, archipelagos, mainlands, etc.) to reflect a close mutual affinity between “neighbors”; so, both taxonomic hierarchy and discreteness are clearly presumed by this metaphor. Within the realm of systematics, such a metaphor was mentioned by Linnaeus in his “Philosophy of Botany...,” and the respective scheme appears (probably for the first time) in the work of his disciple Paul Giseke as a “map of geographic genealogical affinity” [Giseke 1792]. A half of a century later, the geologist and zoologist Hugh Strickland directly indicates that “the true order of affinity can only be exhibited (if at all) by a pictorial representation on a surface [...] illustrated by a series of maps” [Strickland 1841: 192; italics in the original], Bertrand de Jussieu in Paris and A.-P. de Candolle in Geneva bring this metaphor to reality by planning botanical gardens under their curation so that the distribution of plants over the territory would reflect their systematic affinity [Stevens 1994]. It is noteworthy that, for one of the founding fathers of botanical natural systematics, A.L. de Jussieu, chain and map are not alternatives: the natural method
connects all forms of plants into an indissoluble whole and follows step by step from simple to complex [...] in an unbroken series, like a chain whose links represent countless species [...] or like a geographical map, in w'hich the species are distributed over territories, provinces and kingdoms.
Jussieu 1789: xxxiv
This metaphor loses its popularity from the middle of the 19th century due to growing interest in tree-like genealogical schemes, and yet its indirect influence on taxonomic ideas of post-scholastic systematics is noticeable. It explicitly introduces into systematics the concept of hiatuses, which separates taxa just like physical space separates islands and archipelagos on a map [Stevens 1994]. In this way, this metaphor indirectly anticipates the modern concept of quantitative taxonomic distance: Strickland believes that, on such a map, “the distance from each species to every other is in exact proportion to the degree in which the essential characters of the respective species agree” [Strickland 1841: 185].
Considered epistemically, the metaphor of a taxonomic map is remarkable in two respects. Firstly, it represents not the actual, but an “imaginary” reality, showing what is important to a cartographer, affecting (by feedback) the latter’s perception of the reality it displays [Winther 2020]. Secondly, it implies a substantially different logical procedure as compared to the generic-species classification. The latter is based on a logical division of notions and thus divides a set into its subsets. In contrast, mapping implies territorial zoning, which is a kind of partonomic division of the whole into parts; this important distinction will receive special attention in the 20th century [Meyen 1977; Rodoman 1999; Chebanov and Martynenko 2008; Lyubarsky 2018].
The tree-like representation of relations between objects (organisms, ideas, etc.) goes back to neo-Platonism and Medieval scholasticism, where it is realized in the form of the classification “tree of Porphyry.” The latter is more than popular in scholastic systematics and is partially preserved until the middle of the 19th century. With an assimilation of the evolutionary idea by post-scholastic systematics, this classification tree is replaced by another, genealogical one. It is important to keep in mind that there is no direct logical link between these two categories of trees; a fundamental difference between them is as follows [O'Hara 1991, 1992; Pavlinov 2007a, 2015,
2018; Podani 2013]. The classification tree is a dividing tree: it shows sequential logical partitions of general notions into particular ones; in systematics these are taxa divided into subtaxa. In contrast, the genealogical tree is a connecting tree: it shows connections between objects according to the degree of their affinity determined by their origins (say, species from species). However, operationally, the latter tree is converted into a classification in the same manner as the “tree of Porphyry,” i.e., by dissecting it “branches” in a descending (deductive) manner.
Genealogically interpreted tree diagrams have been known since at least the Middle Ages; their branching order could be either ascending or descending depending on the position of the respective “starting points.” In the earliest versions, they illustrate genealogical relations between biblical characters, then between representatives of the noble families; starting from the 16th century, such diagrams illustrate genetic links between human tribes and languages [Gontier 2011; Archibald 2014]. The possibility of representing the Natural System in a form similar to the family tree is noticed by the naturalist Peter Simon Pallas in the middle of the 18th century [Barsanti 1992; Kolchinsky et al. 2004; Archibald 2014]: in his “Index...” he writes that “the system of organic bodies is best represented in the form of a tree that comes directly from the root from the most simple plants and animals and takes shape of closely adjoining double animal and plant trunk” [Pallas 1766: 23-24].
In scholastic and early post-scholastic systematics, connecting trees of affinity are most often represented as undirected networks [Stevens 1994; Rieppel 2010a]. The first such schemes were published by R. Morison in the second half of the 17th century (see Section 2.3.2). The natural systematician John Lindley likens complex networks of affinity of plants “to rays drawn from the center of a sphere, which spread in all directions, and impinge upon the affinities of other spheres in their neighborhood” and concludes from this that “all attempts at discovering a lineal arrangement are chimerical” [Lindley 1835: 42]. Such network diagrams are sometimes combined with the above taxonomic maps, as in one of the books by A.-P. de Candolle [Stevens 1994]. The earliest rooted (vertical) genealogical schemes appear in the early 19th century; the first of them are occasionally descending (for example, in Lamarck’s “Zoological Philosophy”) but ascending trees soon become most popular, and nowadays they are usually called phylogenetic trees.
Another “hot point” of early post-scholastic systematics is shaped by the discussion of choice of classifying characters; two general approaches are considered and substantiated. In one of them, dominating throughout the 19th century, it is asserted
From this viewpoint, linking "tree thinking” exclusively to genealogy [O’Hara 1997; Baum and Smith 2013] is incorrect: actually, “tree thinking” is no less characteristic of scholastics than of phylogenetics. Moreover, considered from a taxonomic perspective, the genealogical tree does not differ greatly from the classification tree. To emphasize the fundamental difference between these two metaphors, it is better to speak of “genealogical” or “evolutionär}'” thinking rather than “tree thinking” [Pavlinov 2005, 2007a],
that these characters should reflect certain most significant vital functions of organisms and/or some of their fundamental structural features (body plans). This approach, whose foundations are laid by botanists A.L. de Jussieu and A.-P. de Candolle and zoologist G. Cuvier, continues to a certain extent an essentialist tradition in the Ray-Magnol version; it is characteristic of natural systematics of botanists, early typology, and some “esoteric” theories. In another approach, characters are mainly assigned a diagnostic function: they serve as indicators (“marks”) of natural groups. This position may be considered a continuation of the development of the method of scholastic systematics by Tournefort and Linnaeus, and is characteristic of the natural method of M. Adanson and, subsequently, of evolutionary interpreted systematics.
An important part of the anti-scholastic motivation of the emerging “new systematics” becomes the shift from essentialist to nominalist interpretation of taxonomic names [Pavlinov 2015,2018]. M. Adanson appears the first here too: he affirms the key principle of a new understanding of taxonomic nomenclature, according to which “names denote objects [...] and do not express their nature or at least their most essential features” [Adanson 1763: cxxii-cxxiv]. At the beginning of the 19th century, his main thesis “a name is just a name” becomes a symbol of the all contemporary nomenclature.