Historical Background of classification
Now, today we would discuss the historical background of classification.
Human beings of ancient time started naming organisms as per their choice.
The first clue of the classification comes from Vedas and Upanishids between 1500 B.C to 600 B.C. The eminint scholars of India were CHARAKA and SUSRUTA. In Vedas several terms have been used for plants and their parts. The plants of medicinal importance were collected and studied during that period .
Greek scholars like HIPPOCRATES and DEMOCRITUS around 460B.C. to 370B.C., also contributed to the Taxonomy but their observations was not useful and record of their studies has also been in bits and pieces.
Aristotle(384BC to 322BC) developed the first widly accepted system of classification which remained effective for around 2000 years. He laid the foundations of classical taxonomy, though criterion of his classification was not scientific. He placed all living organisms in two broad groups; those which could move were called as ANIMALS and those which could not move were called as PLANTS. He further classified animals on the basis of habitats they lived in, their morphology and presence or absence of Red blood; as such the subgroups of animals identified were; aquatic, terrestrial and aerial. In this way Aristotle placed many unrelated animals together like fishes , amphibians and crocodiles were placed in one group i.e., aquatic, similarly the birds and bats were place in the same group i.e., aerial group. Also, he categorized plants on the basis of average size and structure into three groups viz herbs, shrubs, and trees.
After Aristotle, there was little innovation in the fields of the taxonomic sciences until the 16th century AD, however THEOPHRASTUS (372-287 BC), one of Aristotle's students continued the work which was started by Aristotle and went on to be known as the "father of botany." The fact is that he introduced no new principles of classification.
GASPARD BAUHIN(1560AD -1624AD) Classified the plants on the basis of texture and form. He was first to devise the binomial nomenclature all though it is credited to Carolus Linnaeus due to his vast contribution in it .
JOHN RAY'S (1627AD-1705AD) contribution is very significant. Prior to him the classification was baseless and there was no scientific background to it. He was first person who recognised difference between genus and species.
CAROLUS LINNAEUS(1707AD-1778AD) Linnaeus system of classification was first formal system of taxonomy. Linnaeus is credited for devising scientific method of naming organisms i.e., binomial nomenclature, which gives a scientific name to the organism that consists of two parts viz Generic (genus) name which represents first the part and Specific (Species) name which represents the second part of scientific name. This system of scientific nomenclature has an advantage over the common names as the common names were not universal and same organisms were having many common names which always added to the confusion. Rules of binomial nomenclature as were framed by him are being followed even now, all across the globe. These rules are as under:
1. Generic name always starts with a capital letter e.g., Homo
2. Specific name always starts with a small letter e.g., sapien
3. Scientific names are always in italics if they are in print form and they must be underlined if they are hand written.
4. After a complete scientific name has been written once , the generic name thereafter is written in abbreviated form e.g. H. sapien.
He was the first, in his book, System of Nature, to combine a hierarchical system of classification from kingdom to species with the method of binomial nomenclature, using it consistently to identify every species of both plants and animals then known to him.
The organisms having common features are placed in one group. Such a group is called as a Taxon (plural is Taxa)or taxonomic category. Further each taxon is contained in another taxon, such an arrangement of one taxon over another is called as taxonomic hierarchy. If we look at the hierarchy of taxonomic categories, we come across the fact that distantly related organism form a part of larger Taxon where as closely related organisms form the part of smaller Taxon. Various taxa of the taxonomic hierarchy are - Domain-Kingdom-Phylum- Class - Order- Family- Genus and Species. There may be many related species in one genus and many related genera in one family and so on. The organisms of two related genera are not as closer and hence don't share more common features, as are the organisms of different species of same genus, which share more common features and so on. A Domain contains one or more related kingdoms, a kingdom contains many related phyla ( plural of phylum) and so on.
Major works of Carolus Linnaeus went through a great deal of revision in his lifetime, eliminating errors and coming closer to the system that was eventually adopted by taxonomists world over. His methods of classifying plants have been completely superseded by a deeper scientific understanding. Originally, Linnaeus had only used binomial nomenclature to classify plants, but he later extended this system to include animals and even minerals. There were also errors, subsequently corrected. At first, for example, he had placed the whales among the fishes, but later moved them and placed them into the mammals. He was also the first taxonomist to place human beings among the primates and to give them the binomial nomenclature i.e. Homo sapiens.
If Linnaeus is now considered the father of taxonomy, his success rested on the work of his predecessors.
While he continued throughout his lifetime to revise and expand this great work, so his successors have continued to revise the principles of taxonomy.
JEAN BAPTIST MONET de LAMARCK(1744AD-1829AD) and CHARLES DARWIN(1809 -1882AD) also had a vast contribution to this field as prior to them the concept of evolution did not exist and the number of species were thought to be fixed but it were their studies which changed the vision of the whole world about the evolution of the new species from the pre-existing species and thus they completely rejected the pre-Lamarckian concept of fixity of species, according to which all the species living on the earth remain unchanged. Thus the concept of evolutionary relationship was first introduced by them. Though lamarckism holds no ground in present scenario but he was first to change the perception about the fixity of the species while the Darwinism holds its ground till date with some revision and addition of recent discoveries.
From Aristotle to Linnaeus all organisms were classified into two kingdoms viz PLANTAE and ANIMALIA
But ERNST HAECKEL(1866) Who was a German biologist proposed a third kingdom called as PROTISTA to accommodate bacteria and some microorganisms such as Euglena that did not fit into plants and animals.
Then COPELAND(1956) grouped all living organisms into four kingdoms which include MONERA, PROSTISTA, PLANTAE and ANIMALIA. Monera included bacteria and blue green algae.
ROBERT H. WHITTAKER(1969) an American ecologist proposed five kingdom classification. He separated fungi from plants and gave it the status of independent Kingdom. Thus 5 kingdoms included MONERA, PROTISTA, FUNGI, PLANTAE and ANIMALIA. Whittaker' system of classification takes into account complexity of the cell, complexity of the organism, mode of nutrition and major ecological role. This scheme of classification of living organisms is still widely accepted.
CARL WOESE, O.KANDLER and M.L. WHEELIS in 1990 divided the living organisms into three main Domains viz EUKARYA, BACTERIA and ARCHAEA and these domains have six kingdoms which included as EUBACTERIA, ARCHAEBACTERIA, PROTISTA, FUNGI, PLANTAE and ANIMALIA. Domain, Bacteria includs kingdom Eubacteria and domain, archaea includes kingdom Archaebacteria where as domain eukarya included rest four kingdoms. This classification is based on DNA and RNA sequencing methods.
Regard
Dr Rahul Kait
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