Science > Biology > General Biology > Diversity of Living Organisms > Need for Classification of Living Beings
Scientists have identified and named 1.7 to 1.8 million species of living organisms. Of these, about 1.2 million are animal species while 0.5 million are plant species. The group of insects is the largest group with 1.025 million species. According to biologists some 5 to 30 million species of organisms exist on the earth. The variety that we see in the living things that exist on the earth is called biological diversity or biodiversity. There is variety in their shapes, sizes, bodies apart and lifespan. We should remember here that as we explore new areas, and even old ones, new organisms are continuously being identified. In this article, we shall study the need for classification of living organisms.
Time Line of Classification:
Aristotle, Greek philosopher (384 – 322 B.C.):
Aristotle developed the first classification system, which divided all known organisms into two groups: plants and animals. Aristotle’s system of classification was not full proof because many animals were there they didn’t fit in the classification. Aristotle’s limited classification system was used for nearly 2000 years.
Parasara (Indian sage) (Before Christ):
On the basis of comparative morphology, he classified plants, whose detail is given in his compilation called Vrikshayurveda. He group families of plants under name ganas. These ganas, can be clearly distinguished and recognized even today.
Charaka Indian Doctor and Father of Ayurveda (first century A.D.):
In his book ‘Charak Sanhita’ he classified 200 kinds of animals and 340 kinds of plants.
John Ray British Botanist (1628-1705):
He introduced the term ‘species’. He collected plant species from all over Europe and give an improved form of classification of plants.
Carlous Linnaeus Swedish Naturalist (1707 – 1778) :
He introduced the binomial nomenclature system. He listed about 5900 species of plants in his book ‘Species Plantarum’ (1753). He listed about 4200 species of animals in his book ‘Systema Naturae’ (1758). He is called the father of taxonomy.
George Cavier American biologist (1769 – 1832):
He introduced the natural classification system. He took into account not only the structure but also the functions of various structures and the ancestral history of the organism. He studied related fossils.
Sir Julain Huxley (1940):
He introduced the term ‘New Systematics’ for the classification of living organisms based on the theory of evolution and phylogeny.
Classification and its Need:
The term classification was coined by A. P. de Condole. Classification is the process by which anything is grouped into convenient categories based on some easily observable characters. There are a large number of organisms found on Earth. They show variations in their shape, size, structure, habit, habitat, nutrition, etc. It is difficult to remember the characteristics of all the organisms without their proper arrangement.
The classification helps us to explain unity in the diversity of the organisms. The classification places an organism amongst those which have common characteristics.
Systematics and Taxonomy:
- Systematics: Systematics is a scientific study of similarities and differences among different kinds of organisms and also includes identification, nomenclature, and classification.
- Taxonomy: It is the branch of biology which deals with the collection, identification, nomenclature, description, and classification of plants and animals.
- Generally, the terms taxonomy, systematics and classification are used interchangeably. But Simpson said that these are three separate fields of study and should not be confused with each other.
- We know the plants and animals in our own area by their local names. These local names would vary from place to place, even within a country. Hence, there is a need to standardize the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.
Classical or Old Systematics:
Classical systematics is based on the study of mainly morphological traits of one or a few specimens with supporting evidence from other fields. In classical systematics, species were considered to be an independent and immutable (changeless) entity and work of the creator.
New Systematics or Modern Systematics:
The term new systematics was coined by Julian Huxley (1940). New systematics is the systematic study which takes into consideration all types of characters including those from classification morphology, anatomy, cytology, physiology, biochemistry, ecology, genetics, development (embryology), behaviour, etc. of the whole population instead of a few typological specimens.
Characteristics of New Systematics:
- The importance is given to subspecies and populations instead of species.
- The biological definition is replaced by a morphological definition. It considers other branches of biology like cytology, physiology, biochemistry, genetics, etc.
- New systematics is based on the study of all types of variations in the species.
- Along with morphological characters, other investigations are also carried out to know the variety of traits.
- Delimitation of species is carried out on the basis of all types of biological traits. It is also called biological delimitation.
- Statistical data and techniques are used to know the traits in the degree of primitiveness, advancement and to find Inter-relationships.
- According to new systematics, species are not fixed or static but highly dynamic.
Basics of Systematics:
- Characterization: The organism to be studied is described for all its morphological and other characteristics.
- Identification:
- Based on the studied characteristics, the identification of the organism is carried out to know whether it is similar to any of the known groups or taxa.
- Classification: The organism is now classified on the basis of its resemblance to different taxa. It is the arrangement of organisms into groups based on their relationship. If the organism cannot be classified under known groups, then a new group or taxon is created to accommodate it.
- Nomenclature: After placing the organism in various taxa, its correct name is determined.
Objectives of Systematics and Taxonomy:
- To know various kinds of plants on the earth with their names, affinities, geographical distribution, habit, characteristics, and their economic importance.
- To have a reference system for all organisms with which scientists can work.
- To demonstrate manifold diversities of organisms and their phylogenetic (evolutionary) relationship.
- To ascertain nomenclature.
Advantages of Systematics:
- It is used in a study of other disciplines of biology. The knowledge gained through systematics is assembled for use in the field of morphology, physiology, anatomy, pathology, genetics, evolution, medicine, agriculture, forestry, and industries.
- It gives an idea about the organic diversity, its origin, and evolution. Using a few representatives from each group we can acquire knowledge of other organisms.
- It helps in the identification of crop pests and in solving the problem of many epidemic diseases.
- It helps in finding out new food resources such as fishes, arthropods, algae, etc.
- Many organisms are indicators of pollution, fossil fuels and types of minerals present in the soil. This can be achieved using systematics.
Phylogeny:
The evolutionary history of a particular species is called phylogeny. Classification based on their phylogenic relationship or on the basis of evolution is called evolutionary or phylogenetic classification.
Many groups of organisms are now extinct, and without their fossils, we would not have a picture of how modern life is interrelated. We express the relationships among groups of organisms through diagrams called cladograms, which are like genealogies of species.
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