The Development of Biological Classification Systems


Ancient times

Natural history begins with Aristotle and other ancient philosophers who sought to analyze the diversity of the natural world. Natural history was understood by Pliny the Elder to cover anything that could be found in the world, including living things, geology, astronomy, technology, art and man.

De Materia Medica was written between 50 and 70 AD by Pedanius Dioscorides, a Roman physician of Greek origin. It was widely read for more than 1,500 years until supplanted in the Renaissance, making it one of the longest-lasting of all natural history books.

From the ancient Greeks until the work of Carl Linnaeus and other 18th century naturalists, the predominant view of natural history was the 'scala naturae' or 'Great Chain of Being' – an arrangement of minerals, vegetables, more primitive forms of animals, and more complex life forms on a linear scale of supposedly increasing perfection, culminating in our species


From the thirteenth century, the work of Aristotle was rigidly incorporated into Christian philosophy.

During the Renaissance, scholars (herbalists and humanists, particularly) returned to direct observation of plants and animals to understand natural history, and many began to accumulate large collections of exotic specimens and unusual monsters.

Leonhart Fuchs was one of three founding fathers of botany, along with Otto Brunfels and Hieronymus Bock. Other important contributors to the field were Valerius Cordus, Konrad Gesner (Historiae animalium), Frederik Ruysch, or Gaspard Bauhin. The rapid increase in the number of known organisms prompted many attempts at classifying and organizing species into taxonomic groups, culminating  in the system of the Swedish naturalist Carl Linnaeus.

Extract from:-

The birth and development of taxonomy

The Linnaean era

The Swedish botanist Carolus Linnaeus is regarded as the father of taxonomy, as he developed a system known as Linnaean classification for categorization of organisms and binomial nomenclature for naming organisms.

His works implemented a standardized binomial naming system for animal and plant species, which proved to be an elegant solution to a chaotic and disorganized taxonomic literature. As a result, the Linnaean system was born, and is still used in essentially the same way today as it was in the eighteenth century. Currently, plant and animal taxonomists regard Linnaeus' work as the “starting point” for valid names (at 1753 and 1758 respectively). Names published before these dates are referred to as “pre-Linnaean”, and not considered valid (with the exception of spiders published in Svenska Spindlar). Even taxonomic names published by Linnaeus himself before these dates are considered pre-Linnaean.

Development of the modern classification system

Combining Fossil Records with living organisms

Whereas Linnaeus classified for ease of identification, the idea of the Linnaean taxonomy as translating into a sort of dendrogram of the Animal- and Plant Kingdoms was formulated toward the end of the 18th century, This resulted in the speculative, but widely read Vestiges of the Natural History of Creation, published anonymously by Robert Chambers in 1844.

In 1859, Charles Darwin published the Theory of Evolution which effectively swept aside the rigid Christian view and opened the way to study evolution.

Tree of Life representations became popular in scientific works, with known fossil groups being incorporated. One of the first modern groups tied to fossil ancestors were birds. Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842. The resulting description, that of dinosaurs “giving rise to” or being “the ancestors of” birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th century, palaeontologists worked to understand the history of animals through the ages by linking together known groups. With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of evolution of the major groups was in place. With the evolutionary taxonomy being based on Linnaean taxonomic ranks, both living and fossil records were compatible.

Including Bacteria into the structure

The introduction of the microscope allowed the study of cells which were classified as Protista and first introduced into the structure as a third Kingdom by Haeckel in 1866 (He also renamed the Kingdom of Vegetabilia to Plantae – a term still in use today).

Fungus (Plural; Fungi)

A fungus is any member of the group of eukaryotic organisms that includes unicellular microorganisms such as yeasts and molds, as well as multicellular fungi that produce familiar fruiting forms known as mushrooms.

These organisms are classified as a kingdom, Fungi, which is separate from the other life kingdoms of plants, animals, protists, and bacteria. One difference that places fungi in a different kingdom is that its cell walls contain chitin, unlike the cell walls of plants, bacteria and some protists. Similar to animals, fungi are heterotrophs, that is, they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Growth is their means of mobility, except for spores, which may travel through the air or water (a few of which are flagellated). Fungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (is a monophyletic group). This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek μύκης, mukēs, meaning “fungus”).

In the past, mycology was regarded as a branch of botany; today it is a separate kingdom in biological taxonomy. Genetic studies have shown that fungi are more closely related to animals than to plants.

A summary of the different kinds of proposed classification schemes.

A timeline of the proposed classification schemes.

 Taxonomy structure and Ranks

Wikipedia Biological classification

Basic Structure

Taxonomic ranks


A species is often defined as the largest group of organisms where two hybrids are capable of reproducing fertile offspring, typically using sexual reproduction.

Naming of species is in a internationally recognised binomial form. Genus name followed by species. The carrion crow species becomes Corvus corone.

Presence of specific locally adapted traits may further subdivide species into “infraspecific taxa” such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae).

In the case of Corvus corone, two distinct populations exist, Western and central Europe and eastern Asia. It was thought that these became separated in the last ice age and have independently developed to have distinct differences. The species name having a suffix to identify them. They are Corvus corone corone and Corvus corone orientalis respectively.


The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera.

There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:

  • monophyly – all descendants of an ancestral taxon are grouped together;
  • reasonable compactness – a genus should not be expanded needlessly; and
  • distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; note that DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).


What does and does not belong to each family is determined by a taxonomist — as is whether a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family. Some taxa are accepted almost universally, while others are recognised only rarely.

The naming of families is codified by various international codes.

  • In fungal, algal, and botanical nomenclature, the family names of plants, fungi, and algae end with the suffix “-aceae”, with the exception of a small number of historic but widely used names including Compositae and Gramineae.
  • In zoological nomenclature, the family names of animals end with the suffix “-idae”


Taking an example from our website, the Carrion Crow (Species – Corvus corone) is in the Genus Corvus which is shared with some 46 species world-wide, including our Raven and Jackdaw.

These all belong to the family Corvidae (called the Crow Family) which has about 23 different Genera listed world wide. The number of species is now 132 which now include Magpie and Jay.