Animal Information Plant and Garden

Classification and Taxonomy of Plants and Animals

Ideally, the taxonomic classification reflects evolutionary relationships among organisms. For example, it is accepted that all organisms included in the phylum Chordata descend from a common ancestor. Currently, many biologists are using DNA sequence data to verify taxonomic descriptions of organisms and determine the patterns of evolution within and between different groups.

The biological classification of plants and animals was first proposed by Aristotle, who virtually invented the science of logic, of which for 2,000 years classification was a part of.

Aristotle, Greek Aristoteles, (born 384 bce, Stagira, Chalcidice, Greece—died 322, Chalcis, Euboea), ancient Greek philosopher and scientist.

The 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 in separating invertebrate animals into different groups and was aware that whales, dolphins, and porpoises had mammalian characters and were not fish. Lacking the microscope, he could not, of course, deal with the minute forms of life.

The Aristotelian method dominated classification until the 19th century. His scheme was, in effect, that the classification of a living thing by its nature.

As against superficial resemblances requires the examination of many specimens, the discarding of variable characters (since they must be accidental, not essential), and the establishment of constant characters. These can then be used to develop a definition that states the essence of the living thing.

The model for this procedure is to be seen in mathematics, especially geometry, which fascinated the Greeks. Mathematics seemed to them the type and exemplar of perfect knowledge since its deductions from axioms were certain and its definitions perfect, irrespective of whether a perfect geometrical figure could ever be drawn.

But the Aristotelian procedure applied to living things and is not by deduction from stated and known axioms Rather, it is by induction from observed examples and thus does not lead to the immutable essence but to a lexical definition.

Theophrastus of Lesbos (c.371-c.287 BC), Greek philosopher. Known as the “father of botany”

Theophrastus described over 500 plant species and devised an advanced classification scheme for plants. Artwork from the 19th century book Vies des Savants Illustres.

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. Encyclopaedists also began to bring together classical wisdom and some contemporary observations.

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.

He 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.

Later, Whittaker proposed the current and more elaborate five kingdom classification of Monera, Protista, Fungi, Plantae, andAnimalia.

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 essence of each form.

The main criteria of the kingdom classification are cell structure, body organization, mode of nutrition and reproduction, and phylogenetic relationships based on the evolutionary development and diversification of a species.

At present, the biological classification includes:

  1. Kingdom Monera
  2. Kingdom Protista
  3. Kingdom Fungi
  4. Kingdom Plantae
  5. Kingdom Animalia
  6. Viruses, Viroids and Lichens

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.

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 things including, snake, earthworm, intestinal parasite, or dragon and to any swimming or aquatic thing.

Although the term fish is common to the names shellfishcrayfish, and starfish, there are more anatomical differences between a shellfish and a starfish than there are between a bony fish and a man. Vernacular names vary widely.

The American robin (Turdus migratorius), for example, is not the English robin (Erithacus rubecula), and the mountain ash (Sorbus) has only a superficial resemblance to true ash.

Biologists, however, have attempted to view all living organisms with equal thoroughness and thus have devised a formal classification.

A formal classification provides the basis for a relatively uniform and internationally understood nomenclature, thereby simplifying cross-referencing and retrieval of information.

How are organisms classified to the species level?

A hierarchical system is used for classifying organisms to the species level. This system is called taxonomic classification. The broadest classifications are by domain and kingdom. The most specific classification is by genus and species. The hierarchical groupings in between include phylum, class, family, and order.

What is a species?

Species are the basic unit of classification. While there are different views on what defines a species, in sexually reproducing organisms, a species has traditionally been defined by the ability of its members to reproduce together to form fertile offspring.

This definition is trickier in asexually reproducing organisms like bacteria, archaea, and protists, where scientists look at the similarity in DNA among individuals to tell whether they are in the same “species.”

When identifying an organism, familiar names like human, fruit fly, or maple tree are most likely the names you use. However, each type of organism has a scientific name such as humans are called Homo sapiens, for example.

Scientific names are derived from the genus and species names in a system known as binomial nomenclature (“bi” = two; “nom” = name). When species names appear in print, the genus is always capitalized and the species name is not, and both names appear in italics (or underlined).

This system allows for a common language with which biologists can both classify and compare organisms. It also provides a basis for biologists to communicate their findings with other scientists. A key aspect of taxonomy is the ability to characterize each level of description with unifying features, thus relaying information about the organism(s).

Particularly common in bacteria and plants, “subspecies” are described which can produce viable offspring but possess one or more features which distinguish them from other members of that species. In plants, these sub groups are referred to as different “varieties” or “subspecies,” while in single-celled organisms, they are referred to as “strains.” Within the animal kingdom, subspecies may be termed “races” or “breeds.”

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