Taxonomy, in a broad sense the science of classification, but more strictly the classification of living and extinct organisms i.e., biological classification. The term is derived from the Greek taxis (arrangement) and nomos (law). Taxonomy is, therefore, the methodology and principles of systematic botany and zoology and sets up arrangements of the kinds of plants and animals in hierarchies of superior and subordinate groups. Among biologists the Linnaean system of binomial nomenclature, created by Swedish naturalist Carolus Linnaeus in the 1750s, is internationally accepted.
Popularly, classifications of living organisms arise according to need and are often superficial. Anglo-Saxon terms such as worm and fish have been used to refer, respectively, to any creeping thing snake, earthworm, intestinal parasite, or dragon and to any swimming or aquatic thing. Although the term fish is common to the names shellfish, crayfish, and starfish, there are more anatomical differences between a shellfish and a starfish than there are between a bony fish and a man.
Historical background
People who live close to nature usually have an excellent working knowledge of the elements of the local fauna and flora important to them and also often recognize many of the larger groups of living things (e.g., fishes, birds, and mammals). Their knowledge, however, is according to need, and such people generalize only rarely.
However, some of the earliest forays into formal, but limited, classification were undertaken by the ancient Chinese and ancient Egyptians. In China a catalog of 365 species of medicinal plants became the basis of later hydrological studies. Although the catalog is attributed to the mythical Chinese emperor Shennong who lived about 2700 bce, the catalog was likely written about the beginning of the first millennium ce. Similarly, ancient Egyptian medical papyri dating from 1700 to 1600 bce provided descriptions of various medicinal plants, along with directions on how they could be used to treat illnesses and injuries.
From the Greeks to the Renaissance
The first great generalizer in Western classification was Aristotle, who virtually invented the science of logic, of which for 2,000 years classification was a part. Greeks had constant contact with the sea and marine life, and Aristotle seems to have studied it intensively during his stay on the island of Lesbos. In his writings, he described a large number of natural groups, and, although he ranked them from simple to complex, his order was not an evolutionary one. He was far ahead of his time, however, in separating invertebrate animals into different groups and was aware that whales, dolphins, and porpoises had mammalian characters (that is, observable features, or traits, of an organism) and were not fish. Lacking the microscope, he could not, of course, deal with the minute forms of life.Although it provided for centuries a procedure for attempting to define living things by careful analysis, it neglected the variation of living things. It is of interest that the few people who understood Charles Darwin’s Origin of Species in the mid-19th century were empiricists who did not believe in an essence of each form.
Aristotle and his pupil in botany, Theophrastus, had no notable successors for 1,400 years. In about the 12th century ce, botanical works necessary to medicine began to contain accurate illustrations of plants, and a few began to arrange similar plants together. The first flowering of the Renaissance in biology produced, in 1543, Andreas Vesalius’s treatise on human anatomy and, in 1545, the first university botanic garden, founded in Padua, Italy. After this time, work in botany and zoology flourished. John Ray summarized in the late 17th century the available systematic knowledge, with useful classifications. He distinguished the monocotyledonous plants from the dicotyledonous ones in 1703, recognized the true affinities of the whales, and gave a workable definition of the species concept, which had already become the basic unit of biological classification. He tempered the Aristotelian logic of classification with empirical observation.
The Linnaean system
Carolus LinnaeusCarolus Linnaeus, portrait by Alexander Roslin, 1775; in the Nationalmuseum, Stockholm, Sweden.
Carolus Linnaeus, who is usually regarded as the founder of modern taxonomy and whose books are considered the beginning of modern botanical and zoological nomenclature, drew up rules for assigning names to plants and animals and was the first to use binomial nomenclature consistently (1758). Although he introduced the standard hierarchy of class, order, genus, and species, his main success in his own day was providing workable keys, making it possible to identify plants and animals from his books. For plants he made use of the hitherto neglected smaller parts of the flower.
Linnaeus attempted a natural classification but did not get far. His concept of a natural classification was Aristotelian; i.e., it was based on Aristotle’s idea of the essential features of living things and on his logic. He was less accurate than Aristotle in his classification of animals, breaking them up into mammals, birds, reptiles, fishes, insects, and worms. The first four, as he defined them, are obvious groups and generally recognized; the last two incorporate about seven of Aristotle’s groups.
The standard Aristotelian definition of a form was by genus and differentia. The genus defined the general kind of thing being described, and the differentia gave its special character. A genus, for example, might be “Bird” and the species “Feeding in water,” or the genus might be “Animal” and the species “Bird.” The two together made up the definition, which could be used as a name. Unfortunately, when many species of a genus became known, the differentia became longer and longer. In some of his books Linnaeus printed in the margin a catch name, the name of the genus and one word from the differentia or from some former name. In this way he created the binomial, or binary, nomenclature. Thus, modern humans are Homo sapiens,
Classification since Linnaeus
Classification since Linnaeus has incorporated newly discovered information and more closely approaches a natural system. When the life history of barnacles was discovered, for example, they could no longer be associated with mollusks because it became clear that they were arthropods (jointed-legged animals such as crabs and insects). Jean-Baptiste Lamarck, an excellent taxonomist despite his misconceptions about evolution, first separated spiders and crustaceans from insects as separate classes. He also introduced the distinction, no longer accepted by all workers as wholly valid, between vertebrates—i.e., those with backbones, such as fishes, amphibians, reptiles, birds, and mammals—and invertebrates, which have no backbones. The invertebrates, defined by a feature they lack rather than by the features they have, constitute in fact about 90 percent of the diversity of all animals.
Classification is used in biology for two totally different purposes, often in combination, namely, identifying and making natural groups. The specimen or a group of similar specimens must be compared with descriptions of what is already known. This type of classification, called a key, provides as briefly and as reliably as possible the most obvious characteristics useful in identification. Very often they are set out as a dichotomous key with opposing pairs of characters. The butterflies of a region, for example, might first be separated into those with a lot of white on the wings and those with very little; then each group could be subdivided on the basis of other characters. One disadvantage of such classifications, which are useful for well-known groups, is that a mistake may produce a ridiculous answer, since the groups under each division need have nothing in common but the chosen character (e.g., white on the butterfly wings). In addition, if the group being keyed is large or given to great variation, the key may be extremely complex and may rely on characters difficult to evaluate. Moreover, if the form in question is a new one or one that is not in the key (being, perhaps, unrecorded from the region to which the key applies), it may be identified incorrectly. Many unrelated butterflies have a lot of white on the wings a few swallowtails, the well-known cabbage whites, some of the South American dismorphiines, and a few satyrids. Should identification of an undescribed form of fritillary butterfly containing much white on the wings be desired, the use of a key could result in an incorrect identification of the butterfly. In order to avoid such mistakes, it is necessary to consider many characters of the organism—not merely one aspect of the wings but their anatomy and the features of the various stages in the life cycle.
Systems of Classification
A. Traditional Classification (Linnaean System)
Developed by Carl Linnaeus in the 18th century.
Based on physical characteristics.
B. Modern Classification (Phylogenetics & Cladistics)
Uses evolutionary relationships and genetic data.
Constructed using DNA analysis and fossil records.
Includes cladistics, which groups organisms based on common ancestry.
C. Three-Domain System (Woese’s Classification): Proposed by Carl Woese (1990) based on genetic sequencing:
1.Bacteria – Prokaryotic, unicellular organisms.
2.Archaea – Prokaryotic, but distinct from bacteria (extremophiles).
3.Eukarya – Eukaryotic organisms (animals, plants, fungi, protists).
6. Binomial Nomenclature: Proposed by Carl Linnaeus. Each species has two Latinized names:
Genus name (capitalized)
Species name (lowercase)
Example: Felis catus (domestic cat), Canis lupus (wolf).
7. Taxonomic Tools & Techniques
Morphology (study of structure)
Anatomy (internal structure)
Embryology (developmental stages)
Molecular Taxonomy (DNA sequencing)
Paleontology (fossil study)
Numerical Taxonomy (statistical classification)
8. Taxonomy in Other Fieldsz
Medical Taxonomy – Classification of microbes for disease identification.
Agricultural Taxonomy – Classifies crops and pests for better management.
Ecological Taxonomy – Helps in biodiversity conservation efforts.
Current systems of classification
Division of organisms into kingdoms
Whittaker five-kingdom classificationThe Whittaker five-kingdom classification of life
Kingdom Animalia (or Metazoa)
Subkingdom Parazoa (sponges)
Phylum Porifera (sponges)
Subkingdom Eumetazoa
Phylum Mesozoa (mesozoans)
Phylum Cnidaria (or Coelenterata; cnidarians)
Phylum Ctenophora (ctenophores)
Phylum Platyhelminthes (flatworms)
Phylum Nemertea (or Rhynchocoela; ribbonworms)
Phylum (or class) Acanthocephala (spiny-headed worms)
Phylum Aschelminthes
Phylum Priapulida (priapulids)
Phylum Annelida (annelid worms)
Phylum Tardigrada
Phylum Onychophora
Phylum Arthropoda (arthropods)
Phylum Mollusca (mollusks)
Phylum Bryozoa (or Ectoprocta; bryozoans)
Phylum Phoronida (phoronid worms)
Phylum Brachiopoda (brachiopods)
Phylum Sipuncula (sipunculid worms)
Phylum Chaetognatha (arrowworms)
Phylum Echiurida (spoonworms)
Phylum Echinodermata (echinoderms)
Phylum Hemichordata (hemichordates)
Phylum Pogonophora (beardworms)
Phylum Chordata (chordates)
cle Important of Taxonomy
Provides a universal naming system for organisms (Binomial Nomenclature)
Helps in understanding evolutionary relationships
Assists in biodiversity conservation
Supports fields like medicine, agriculture, and ecology
3. Principles of Taxonomy
1.Hierarchy of Classification – Organisms are arranged in a ranked system.
2.Binomial Nomenclature – A two-name system for naming species (Genus + species).
3.Taxonomic Ranks – Classification is divided into different ranks.
4.Identification & Description – New species are described and compared with known organisms.
4. Taxonomic Ranks (Hierarchy)
Living organisms are classified into a hierarchical system consisting of the following levels:
Rank Example (Human – Homo sapiens)
Domain Eukarya
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Primates
Family Hominidae
Genus Homo
Species Homo sapiens
Each rank narrows down the classification from broad groups to specific species.