In honour of Linnaeus’ 300th birthday, and to rescue him from the canard that he merely applied Aristotelian logic to biology, I offer up this essay on his view of classification and species. I do not think Linnaeus was an essentialist in the Mayrian sense – he nowhere specifies that species have essences, only that there are diagnostic descriptions or definitions that allow naturalists to identify species in the field or in museum collections. But I’m no Linnaean scholar, so if anyone has information to the contrary, let me know.
Not much is known about the early education of poor Swedish student named Carl Linnaeus.1 Born in 1707, Linnaeus died in 1770, the most celebrated Swede of his day. In 1761, he was knighted with the vernacular name Carl von Linné, and took the Latinized name Carolus Linnaeus. Linnaeus
was a medical student turned botanist, and trained in Holland where he published his first botanical works. Before Linnaeus, species were given all kinds of descriptive names, usually in Latin, up to ten
words or so long. Each author made up their own terms, and there was no real convention for referring to species. On Linnaeus’ account, both species and genera were fixed, real and known by definitions. He
apparently believed that the genus was more real that species, and he allowed late in life that species may occasionally arise, but only within genera, through hybridization. Some (e.g., Stafleu 1971; Mayr 1969, 1982) consider Linnaeus to be an essentialist regarding species. This was due to the fact that, unlike the medieval logical conception, for Linnaeus all species (at least in botany, zoology and mineralogy)
were infimae species. He attempted to provide a diagnostic definition for each species,
although his practice and adopted motto “In scientia naturali principia veritatis observationibus confirmari debent” (in natural science, the principles of truth ought to be confirmed by observation, Stafleu 1971) suggests that he was not firmly wedded to a priori essentialism.
In the Systema Naturae
(10th edn, 1759, p7, Linne 1956) Linnaeus proposed a system of five ranks under the summum genus of the Empire of Nature (Imperium Naturae):
the last three of which corresponded to the logical ranks of genus intermedium, genus proximam, and (infimae) species. He also added a subspecific category of Varietas, which was the logical individuum. Later taxonomic conventions added the ranks of Phylum between Kingdom and Class, and Family between Order and Genus, giving seven ranks.2 The philosophical notion of species was not entirely helpful in botany, so Linnaeus changed it a little. Instead of there being any number of subaltern genera, he made the scale of classes absolute, and instead of working downwards, he started in the middle (at the genus). Linnaeus’ ranks began at species, and these existed in genera. Hence, to name a species you needed to give the generic name and the species name. Humans are members of the genus Homo (or Man; according to Linnaeus, one of several3) and our species is called sapiens (the wise one)4. So in Latin our “name” is “the wise man”. Humans, under his initial system, are:
Animals (Regnum Animale),
Mammals (Classis Mammalia),
Primates (Ordo Primates),
Man (Genus Homo),
Wise or rational (Species sapiens).
What Linneaus did was to make species and genera fixed ranks. He established this universal system for the naming and classification of all organisms. There were, for example, various kingdoms – plants
(Plantae) and animals (Animalia). Each species had a street address (its generic name, or genus) and a street number (its species name, or epithet).5
Now, taxonomists (those who classify taxa, or groups of organisms6) could use a single and relatively simple system for their organisms, and all could agree on how to name them, and what to name.
Linnaeus was definitely a special creationist – that is, he believed that each species was created specially by God, and Haller famously said of him that he thought himself a “second Adam” (Ramsbottom 1938: 195n), and he personally said the “God creates, Linnaeus disposes”. He wrote:
“There are as many species as the Infinite Being produced diverse forms in the beginning.” (Species tot sunt diversae quot diversas formas ab initio creavit infinitum Ens, Fundamenta botanica No. 157, 1736).
However, in 1744 he was forced to allow that some species are the result of hybridization, at least in plants, because he thought he observed it happening. A species of plant he placed in a genus Peloria (from the Greek pelor, meaning monstrosity) was in stem and leaf
structure part of the Linaria genus, but the flower was clearly different (Hagberg 1952: 196f; Glass 1959a). This admission was widely known by subsequent writers (e.g., Lee 1810; Gray 1821).
Still, he thought that genera were real and the possibilities for change limited. According to Larson (1967), Linnaeus imagined in the Fundamenta fructifications “that God created one species for each natural order of plants differing in habit and fructification from all others. These species, mutually fertile, gave birth to as many genera as there were different parents, their fructification somewhat changed” (p317).
In the Pralectiones (1744), Linnaeus went further:
The principle being accepted that all species of one genus have arisen from one mother through different fathers, it must be assumed:
That in the beginning the Creator created each natural order only with one plant with reproductive power.
That by their various mixings different plants have arisen which belong to the mother’s natural order as they are similar to the mother with regard to their fructifications, and are, as it were, species of the order, i.e., genera.
We may assume that plants have arisen within the orders, i.e. by genera of one order, may mix with each other. In this way there will arise species that should be referred to the mother’s genus as her daughters. [quoted in Larson, loc. cit.]
Linnaeus thus employed the Great Chain of Being in a rather unusual way. Most “chainists” accepted what was later called the Principle of Plenitude (the lex completio), which stated that God would create everything that could be created, since he would not make an incomplete creation (Lovejoy 1936; Glass 1959a). This usually meant that species graded into each other is a series of varieties.
Linnaeus instead represented species using the metaphor of countries adjoining each other (in the Philosophia botanica §77). In his early writing, all the territory is pretty much filled – as he said, nature does not make jumps – but the countries are discrete and distinct from one another. In the later work, this strict fixism of the first edition of the Systema Naturae has been modified. All hybrids did was fill in a rare empty bit of territory in God’s time and plan. The borders were set by the genera, and all genera arose from a single species created by God. At the end of the 1750s, says Hagberg (1952: 199), Linnaeus was in a state of perplexity with respect to species. In 1755, he published Metamorphosis plantarum, dealing primarily with the development of plants, but also with monstrosities and varieties. Such later hybrids he called the “children of time” in an anonymous entry in a competition at St Petersburg in 1759 (Hagberg 1952: 201f), and also in the Species plantarum (1753, 2nd edition 1762-63), where he speculated that a species of Achillea (yarrow, or staunchweed), alpina, might have formed from another, ptarmica, “[an] locus potuerat ex praecedenti formasse hanc?” (“Could this have been formed from the preceeding one by the environment?”, in volume II, 1266 of the second edition, quoted in Greene 1959: 134). Hagberg says, “Linnaeus never succeeded in pin-pointing his new
conception of species. But the old one, that formed the basis of Systema Naturae, was utterly and irrevocably abandoned.”
Moreover, Linnaeus also noted that species grew differently according to the conditions of their locale. Of the genera Salix, Rosa, Rubus, and Hieracium, (willows, roses, brambles, and hawkweeds), Linnaeus said that their description was problematic
because of variability (“metamorphosis”) of form in different soils and climates (Ramsbottom 1938: 200f). Habitat-induced variability will become an issue under Göte Turesson’s
investigation in the early 20th century (see below). Linnaeus also experimented on propagating a hybrid geranium, with success, in 1759 (Ramsbottom 1938: 210f); he believed that maternal influences of
hybrids affected the “medullary substance” and fructification of plants, but the leaf structure was due to the paternal species As time went on, he removed the statement that there were no new species
from his 1766 edition of the Systema Naturae, and crossed out the statement natura non facit saltum from his own copy of his Philosophia Botanica. A full account of Linnaeus’ various pronouncements on species can be found in Ramsbottom (1938).
When Linnaeus was working, European trade and exploration was limited. Linnaeus himself classified around 6,000 species of mainly Mediterranean and northern European plants, and later animals (Stafleu 1971). This was more than had been done before, but still it was a fraction of what we know today. His students and adherents sent him specimens from around the world, and there was a steady “trade” in
specimens between him and other taxonomists and collectors (Müller-Wille 2003). Linnaeus hoped that his system would enable taxonomists to list all actual species, but he also knew that his system was artificial – that is, not the pure result of studying the actual characters of organisms, but also imposing an a priori scheme on them for convenience. He hoped there would be a “natural” scheme developed on the basis of an aggregation of characters, but he was never able to do more than a partial sketch of one. In his later work, he set up a “rational” system that allowed for there to be
3,600 genera in plants, each of which could generate species through hybridization. Although this was supposed to be a “natural” system (one based on the closeness of resemblance of all traits of the organisms and not just a single character), in fact he chose just three features of plants and restricted the varieties to 60 types of each (hence 603 = 216,000 maximum of plant species). However, this was fragmentary and in an appendix, and not developed further.
In summary, Linnaeus proposed a five rank taxonomic system, and there were only a set number of species possible, although later he was forced by various observations, including his own, to accept that new species could be created through hybridization. All that remains of his taxonomy are the names and general ranks of his system, but even this has been dramatically modified, with such groups as tribes,
sub-families, and so on being added to deal with the massive increase in species discovered since.
Linnaeus distinguished between the diagnostic characters (characters) and actual traits (notae) of organisms, but it seems not much came of this distinction. He appears to have despaired of a natural system in his foreseeable future, and so promoted a purely diagnostic and hence conventional taxonomy, even though he believed that species were themselves natural, along with genera. This tension underlies much of later taxonomy.
1 I am informed by Staffan Müller-Wille (pers. comm.) that Linnaeus, being from a relatively poor district of Sweden, Småland, known (presumably by an Englishman) as the “Scotland of Sweden”, was taught from old standard textbooks, and not out of the neo-Platonists early or late, as far as is recorded (see also Frängsmyr 1983; Koerner 1999; Goerke 1973). According to Hagberg (1952: 44ff), he was greatly influenced by Aristotle’s Historia Animalium as a young student.
2 According to the Oxford English Dictionary, phylum is a term first coined by Cuvier, in Regne Animal (1817), to cover his four embranchements, later adopted and made popular by Ernst Haeckel. Family is most probably Adanson’s term (Judd et al. 1999: 40). The Strickland Code of 1842 (Strickland et al. 1843: 119) mentions “families”, noting they ought to be ended in -idea, and this implies families were in common use by that time. It also allows subfamilies. Mayr, Linsley and Usinger (1953: 272) give the introduction of “family” to Latrielle in 1796, but do not give any information regarding phylum. In botany, phylum is not used, and instead the rank is division, probably introduced in Alphonse de Candolle’s 1867 Rules submitted to the Paris meeting that year of the International Botanical Congress. The present International Code of Zoological Nomenclature does not regulate higher taxon ranks above superfamily (Winston 1999: 32), and so phylum is in effect an informal rank. Recent attempts to revise the rank of kingdom and add empire, or domain (Woese 1998; Syvanen and Kado 1998; Margulis and Schwartz 1998; Williams and Embley 1996; Baldauf, Palmer, and Doolittle 1996) are thus legitimated by tradition even if not widely accepted.
Late note: I just found a copy of De Candolle’s “lois”, or laws of botanical nomenclature via Gallica ((bless the Biblioteque Nationale!) and yes, it was there these terms were introduced, but it was accepted in 1868, not ’67. “Phylum” was, I recall, instroduced to zoology in the 1870s.
3 Huxley describes the initial history of hominoid classification, and notes that while there had been some excellent descriptions of orangutans and chimpanzees in the 18th century, Linnaeus relied on second-hand sources, and classified four species under the genus Homo: Under the specific epithet of troglodytes, he combined the prior “species” of Homo sylvestris (probably a juvenile chimp), and Homo nocturnus (a badly-represented orangutan) (cf. Huxley 1906: 10-13) in the 1758 (tenth edition) Systema naturae (p25), apart from Homo sapiens. Huxley also lists Homo caudatus (a cat tailed ape, either mythical or a misunderstanding of a description of a baboon), but by the tenth edition at least, this was no longer in evidence. It is occasionally noted that by the established rules of nomenclatural priority, chimpanzees should therefore be included in Homo on Linnaean grounds as well as on cladistic grounds (which is argued in, for instance, Diamond 1991). However, troglodytes explicitly mentions the Orangutan in the Systema Naturae, while the chimp is more likely to be Simia satyrus, in another genus altogether (p25).
4 It is sometimes thought that sapiens means “the knowing one”, but a check of various Latin dictionaries of the Latin of the time and earlier indicates that it means “wise” or “sage”.
5 In modern practice, the genus name is always capitalized and the species epithet is always lower case, and both are always italicized. Other taxonomic ranks are capitalized but not italicized.
6 According to Mayr (1982: 870n), the term taxon was proposed in 1926 by Meyer-Abich (see also Lam 1957, who discusses the term in more detail, noting that it is a nomenclatural term for a phylogenetic group). Hence in this context it is an anachronism. Stafleu notes that Linnaeus’ own general term for taxa was phalanx, but that it did not catch on.
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