Classification systems of the natural world are not necessarily based upon evolutionary thought. This is because most of the names given to the different ranks of life (e.g., Animalia, Plantae, Homo sapiens) stem from a time that precedes evolutionary biology. Without possessing modern genetics that enables one to abstract the core genes of a species, and the evolutionary common ancestry, how then, did these pre-evolutionary thinkers classify the world? By what means?
The most straightforward answer is: through language and observation. Through observation, scholars could examine life in its different forms, and through logic (reasoning by language), they could differentiate the organisms and their various traits, by giving them different names. And this is exactly what they did. As far as written human culture goes back, it has always been fascinated with how language enables us to refer to the world, to say both true and false things about it, and to classify its elements into different linguistic categories.
In other words, for the most part of western history, the most important instrument available to scholars was language. And because language was the only means by which knowledge could be obtained from the natural objects under investigation (most measurement techniques only evolved in the nineteenth century), language was either considered to be sacred or divine in and of itself, or to be the gift of a divine creator. In both cases, language was not, as now, understood to be a naturally evolved phenomenon that primarily enables communication. Language first and foremost enabled true and constant knowledge about the (divine) order in the world.
Whether one reads the Upanishads (Müller 1900), the Tao-teh-King (Hsüan and Crowley 1995), the teachings of Zoroastrism (Kapadia 1905), or the ancient Egyptian texts (Lichtheim 1976), all write that the world we live in is an orderly structured rather than a chaotic one. There appears to be a logic to the world that can be defined through language. As a consequence, for centuries scholars have been fascinated with finding the right language that enables us to call things by their right names.
In ancient Greek times (McKirahan 2003), the hierarchical order in the world would be called the logos (Coseriu 2003; Hillar 1998). That order and language were so intricately related to one another is clear by the following: the word logos does not only refer to the order in the world, it also translates as reasoning, logic, and language. Logos is furthermore the root word for knowledge and teaching and is remnant today in just about any science that ends with “logy,” like the science of biology.
The ancient Greeks (McKirahan 2003) endorsed the idea that we live in a world of plenty, where everything that can possibly exist, does indeed exist (the principle of plenitude). Everything is also continuously moving (the principle of continuity); all is coming and becoming (Barsanti 1992). This coming and becoming needs to be understood not from within an evolutionary perspective but from within a cyclic worldview. Animals grow, thrive, and die; they are never constant but continuously move or are being moved. The principle that caused this constant coming and becoming was called the logos, and the logos itself was assumed to be constant or unmovable. Because the world and everything in it is continuously becoming, the underlying order of things often remains hidden, until it is spoken. Individual human beings, for example, go through a series of life cycles, and it is difficult to grasp what remains constant. Yet, we can group all individuals, and give them the name “human.” Words therefore, according to Plato (Phaedus 245c–250d in Fowler 1921), allow us to grasp the essence of things: that which remains constant and is present in all individuals. Plato furthermore argued that these words or ideas (today we would call them concepts) are both constant and real; they are not prone to coming and becoming.
Elsewhere (Gontier 2008), I have already argued that the possession of language in a way enabled anybody who had it not only to find the order present in the world but also to create it. This creation of order implied classifying the world into linguistic categories that provide us with true and objective knowledge of the world. Naming is knowing, for the name of a thing was supposed to tell us something about its true essence. Perfect as the order in the world was understood to be, there could only be one language that called things by their proper names and that therefore gives us true knowledge of the world. All the other languages can merely provide false opinions (e.g., Plato’s Cratylus in Fowler 1921).
As a result, the field of etymology would arise (Socrates’ part in Plato’s Cratylus in Fowler 1921) that seeks to find the original formulations of words (in the hope that the original words might also provide insight into the essence of the things they connote), and also, the field of logic would originate, which examines the way language refers to the world.
It might come as a surprise for the biology reader, but it is in this context of classification of substances that concepts such as genera and species first appeared (Wilkins 2009). Originally, these terms had nothing to do with natural history, let alone evolutionary theory. Instead, they were core concepts of metaphysics, a field in philosophy also known as ontology, or that branch of philosophy that deals with finding out what is true and real and what is merely a fiction of our imagination.
In his Republic, Plato (in Fowler 1921: 514a–520a) wrote a famous passage that today is known as the “Allegory of the Cave,” wherein he argued that reality was layered into more and less real things. The thought of an image of a thing for example, is less real than the image of the thing or the thing in itself. In his philosophy, everything we see in this world is but a mere instantiation of real, true and perfect ideas that reside in a transcendental reality. To come to the essence of things, Plato, and especially Aristotle (in his Organon, Barnes 1984; Deverreux and Pellegrin 1990), would argue that we need to order the world by dividing the wholes into their parts and distinguishing the particular from the universal. Especially in the latter regard, genera and species came in handy. Living organisms could be grouped into species and genera, but so could anything else in the world be divided into genera (e.g., furniture), species (e.g., chair), and individuals (e.g., the chair you are now sitting on).
Controversy would arise over whether these genera and species actually exist (as realists would claim) or whether they are mere concepts that help in theory formation (as nominalists would argue). Plato, a realist, would argue that there exists a transcendental world that contains all ideas, i.e., all essences of things. Aristotle, on the contrary, would argue that essences are part of the things themselves. That a chair is a piece of furniture is part of its essence, and this essence is somehow argued to be “carried” by the chair. Besides defining species based upon the genera they are part of, Aristotle (Deverreux and Pellegrin 1990) would also define species based upon their differentia. Differentia are qualities or properties possessed by one species in the genus but not by another. Humans for example, were animals that differed from all others through their reason and intellect. In other words, species got differentiated from one another based upon particular qualities they possessed or did not posses. Such dichotomous logical relationships would underlie all future classification systems.
As Lovejoy (1936) rightly points out, it is the Greeks’ obsession with classification that would found ideas of a great chain of being or scala naturae (Barsanti 1995). The idea of a scala naturae first originated with Aristotle. In two of his works, The History of Animals and The Generation of Animals (Barnes 1984), he made the first attempt to classify all beings in the world from inanimate (non-living and soulless) to animate (living and in possession of a soul).
Nature proceeds little by little from things lifeless to animal life in such a way that it is impossible to determine the exact line of demarcation, nor on which side thereof an intermediate form should lay. Thus, next after lifeless things comes the plant, and of plants one will differ from another as to its amount of apparent vitality; and, in a word, the whole genus of plants, whilst it is devoid of life as compared with an animal, is endowed with life as compared with other corporeal entities. Indeed, as we just remarked, there is observed in plants a continuous scale of ascent towards the animal. So, in the sea, there are certain objects concerning which one would be at a loss to determine whether they be animal or vegetable. For instance, certain of these objects are fairly rooted, and in several cases perish if detached. (Aristotle 588b: 4–14 in Barnes 1984; emphasis mine)
This “continuous scale of ascent” was based upon the kind of soul (Aristotle I, 1, 402-III, 13, 435 in Barnes 1984) the beings possessed (none for inanimate or lifeless beings, a vegetative, animal or intellectual soul for living beings); the potential they had to actualize; and the cause by which they actualized their potential (the moving principle or efficient cause, best compared with the mode of mobility the beings possessed). The scale was therefore also hierarchical, moving from the simple to the complex, the less perfect to the more perfect. The like was assumed to bring forth the like: in Aristotle’s account, no evolution from one species to another or within species existed. Nonetheless, he argued that it was difficult to demarcate the elements on the scale, probably because in his view, everything was constantly coming and becoming. Biologists today still use some of the taxa first introduced by Aristotle.
The classification systems that could be built by making use of logic could be based upon true knowledge, or mere opinion, and so these systems themselves could also be classified hierarchically. The more accurate a system, or the language of the system, the more it truly represented reality, and the closer it literally became a reflection of reality. Finding the right logical system that enabled the true classification of the world would be the primary concern of Western philosophy up until the nineteenth century (Rieppel 2010).
One of the Neo-Platonists, Porphyry, would write both an introduction to, and a commentary on Aristotle’s logical categories (Emilsson 2005). The commentary, entitled Isagoge, included an overview of different ancient writings on the hierarchical nature of genera and species (Pombo 2006: 221–3). Interpreters and translators of Porphyry’s work would come to illustrate this hierarchy in diagrams of the following kind (Fig. 1): binary oppositions are the extreme ends of one, higher substance. The directionality of the legs of the diagram could be structured from top to bottom or vice versa, or from left to right, but in all cases, this diagram is always a timeless, evolutionless, and even unnatural structure. Ever since, brackets like these have been the major means to depict dichotomous logical relations between different elements.
Porphyry’s Isagoge would become translated and commented upon by one of the most influential early Christian philosophers, Boethius, who in turn highly influenced the scholastics of the Middle Ages. Scholastics (de Libera 1995) are those philosophers that engaged in the “universalia debate”: a continuation of the ancient Greek debate on how we can form logical systems to adequately categorize and refer to the world; and what the ontological status of language in these categorization systems is.
Tree metaphors are highly characteristic of Judaic and Christian religion. The book of Exodus talks about the appearance of God as a burning bush. Genesis tells the story of how Eve ate an apple from the tree of knowledge of good and evil, thereby causing her and Adam to be expelled from paradise. Knowledge for Christians was therefore iconographically associated with trees, and Porphyry’s way of categorizing things easily allowed for a synthesis between his classification system and tree iconographies. These trees would become known as Arbor Porphyriana, Porphyrian trees, and they would become one of the most influential tools to depict logical relations amongst natural and supernatural things.
One of the scholars who made use of these trees was the Majorcan medieval philosopher Ramón Llull, who lived from 1232 to 1315. He too engaged in the search for apt categories to gain knowledge of the world. And this knowledge, as a Christian scholar, took on the form of a tree. He even wrote a work in 1295 entitled Arbor Scientiae (Tree of Science). Figure 2 depicts the natural and logical Porphyrian tree as it was introduced in 1512 by Alonzo de Proaza to illustrate Lull’s book On New Logic (De Logica Nova), written in 1303 (Llull 1303).
In another book of his that was entitled Liber de Ascensu et Descensu Intellectus (The book of the ascent and descent of the intellect), written in 1304, Llull combined Aristotle’s ideas of a scale of nature with Christian theology (Llull 1304). The book described how the intellect could ascend and descend the chain of being from the elementary level up until the divine. Lull was a Christian scholar, but he spent most of his time in Muslim North Africa and would preach for the unification of Judaism, Christianity, and Islam. He was highly influenced by Plato, Plotinus and the Neo-Platonists (which in turn is more an Arab tradition), and Jewish cabbalism (Scholem 1995).
Inspired by Plato’s Allegory of the Cave, Neo-Platonists such as Plotinus (de Libera 1995) would describe reality as a hierarchically layered structure that is closer or further away from “The One.” The One was the name given to the single ordering principle that was assumed to lie at the creation of the plenty (i.e., the world and all its non-living and living elements). Christian scholars like Llull would associate The One with God. As in ancient Egypt, The One was compared to the Sun that shines its rays over the world. The further away from the sun, the less the rays shine upon it, and therefore the less perfect it is. The closer to the sun, the more it receives its heat, and by analogy, the closer a being is to the One or God, the more perfect that being is. The world could therefore be ordered in accordance to what was closer or further away from the Sun, or The One (ordering principle), or God.
At the base of Llull’s chain of being lie natural elements such as stones and fire. These are followed by plants and animals, humans and angels. The latter stand closest to God, who stands at the top of the chain. Llull argued that the intellect can ascend and descend the “ladder” of divine creation through intellectual exercise, from the elements via the natural beings, over the angels, through God. Because the intellect was able to make such a journey on the stairway to heaven, it was also able to gain knowledge of these elements. In the Valéncia edition of this work, published several centuries later in 1512, Alonso de Proaza would also illustrate this idea of the ascent and descent of the intellect (Fig. 3).
The circles in the illustration of Llull’s works are also important. Circles represented another “scale” by which knowledge could be depicted (Barsanti 1992; Pombo 2006). Trees and circles were the most common way to represent any type of knowledge system in the Middle Ages. Spheres were used because they were assumed to be perfect and more harmonious than trees. The circle in the illustration represents the different types of intellect. Llull made a series of such circle scales, including one that listed the 16 properties of God (Fig. 4).
Listing the properties of God was another activity that was the result of categorizing the knowledge one had about God and his act of creation, and this knowledge too would not infrequently be illustrated in tree diagrams. The tradition of listing God’s attributes can also be found, and might even have originated, in Judaism, especially in cabalism, a European school of thought that reigned from the eleventh to the thirteenth century. In the twelfth century, the notion of a tree of life first appeared in association with theorizing on the attributes of God in the cabbalistic book called Bahir (the content of this book is assumed to go back to the first century; Kaplan 1989).
This concept of a tree of life served as a visualization of the ten sephiroth or attributes of God (JHWH). It is called the tree of life because the attributes of God are also assumed to lend an insight into creation: the sephiroth are “emanations” and “enumerations” of God (Kaplan 1989). As was the case with Llull’s work, the first illustration of the tree of life only appears in the sixteenth century, where it served as the cover of a book by Paul Riccius (1516) on cabbalism called De Portae Lucis (Fig. 5, left). In the image, the attributes of God are depicted as circles, and these circles are connected by “branches” that together depict the “tree of life.” The cabalistic tree of life also presents a scale of nature; it isn’t a stairway or ladder, but it does provide a representation of cosmology, as can be seen in a later drawing of the tree by Kircher that also includes celestial bodies (Fig. 5, right).
Scala naturae are often translated in English as chains of being. The concept of “chain of being” implies that all beings, natural, and, because of the religious undertones, also often supernatural beings, are connected to each other as elements on a chain. Each element has its necessary and fixed place within the chain. The order is hierarchical: elements that are placed higher on the scale have superiority over elements that are placed lower on the scale. The elements that form the chain are thus classified from less to more real, perfect, good, etc. And in Christian theology, they are also less or more perfect creations of God.
The concept of “scala naturae” however implies more than just a “chain of being”: they are more than just a visualization of the creation of natural and supernatural beings and their placement in an ontological system. The scala naturae are meant to be true and actual scales, maps and measurements of the whole of nature. They are mappings of the true and whole structure of the world (Barsanti 1995).
The more advanced the knowledge of the natural world and the universe became, the more elements these scales of nature would include. The scala naturae are therefore best understood as part of a genuine enterprise to map all elements that exist in the universe, and also to demonstrate the place that all these elements have in creation. The sixteenth century alchemists (Silver 2000), chemists avant-la-lettre, would be responsible for the ever-increasing number of elements and disciplines that needed to fit these scales in order to provide a true representation of both reality and the arts that study it. These scales would be depicted in trees and circles, or in a combination thereof.
In his book entitled Utriusque Cosmic Maioris Scilicet et Minris Metaphysica, Physica atque Technical Historia (Metaphysical, Physical and Technical Description of Both Worlds, Namely the Microcosmos and Macrocosmos) published from 1617 to 1621, Robert Fludd provides a more advanced scale (Fig. 6) that combined a representation of the universe with a representation of the human arts by which “the ape of nature” (the human being) can study the universe (Fludd 1617–1621), as well as a chain of being from the supernatural to the natural beings and elements (see also Griffioen 1996).
In the same book, he also provides a key (Fig. 7) of the macrocosmos. A strong case can be made for viewing such keys as more abstract representations of Porphyrian trees where brackets serve as “branches” of the “tree” and the binary oppositions are supplanted by a multitude of opposing elements in the system.
Scales and keys such as those found in the work of Fludd (1617–1621) would be drawn well into the nineteenth century, and together with ladders and chains they would be the major diagrams by which religious and more scientific works were illustrated (Barsanti 1995; Bowler 1973; Rieppel 2010). These diagrams would become filled with an ever-increasing number of elements and species, in parallel with an increasing knowledge of the natural world. But the principle idea underlying these scales would remain the same: everything in nature is assumed to be ordered by a divine plan (Fig. 8).