In this article we will discuss about the history of the classification of animals.
The history of classification and naming of animals can be traced before Aristotle. Simpson (1961) and Mayr (1982) have given excellent history of taxonomic development. Mayr and Ashlock (1991) described the history of taxonomy, and the same reflects the concept and trend in systematics.
Tribal natives are very apt in their local environments including fauna and flora. They were experts in habits and habitats of their local animals and could identify easily. Local tribes of New Guinea in S. E. Asia and other tribes in Asia and America used two parts for the naming of the animals before Linnaeus.
Democritus (470-380 B. C.) was the first Greek philosopher and scientist who attempted a classification of animals, based on presence or absence of red blood. Aristotle (384-322 B. C.) put forward the scheme of classification based on presence or absence of red blood, which followed Democritus’s pattern of classification.
He divided the animal kingdom into two major divisions:
I. Anaima:
This group included all the invertebrates which is characterised by the absence of red blood. He recognized 4 classes under Anaima and three of these are Malakia, Malacostraca and Ostracoderma. His ‘Malakia’ would be placed in present day’s Cephalopoda, and Malacostraca with the Crustacea, and Ostracoderma contained several miscellaneous molluscs and certain representatives of lower phyla.
II. Enaima:
This group included the vertebrates, having red blood.
The Enaima was again subdivided into two categories:
A. Oviparous:
It included the egg-laying vertebrates, e.g., the fishes, amphibians, reptiles and birds.
B. Viviparous:
This group on the other hand included the vertebrates where the young’s are born alive, e.g., the mammals.
Then Gesner (1516-1565), Belone (1517- 1564) and Aldrovandus (1522-1605) classified the animals in a little different way than that of Aristotle. John Ray (1627-1705) was the first naturalist to give the modern concept of species and tried to classify the animals.
He published Quadrupeds and Reptiles in 1693 and divided the two classes based on toes covered with horny hoofs and toes having only nails. He classified the living things based on structure rather than colour, size and habit. This approach was most important as compared with the approach of his predecessors.
Linnaeus (1707-1778) introduced a complete biological system of naming and classification of animals. Linnaeus divided the animal kingdom into several classes: Mammalia, Aves, Amphibia, Pisces, Insecta and Vermis. The class Vermis includes all invertebrates except the insects and is divided into the following orders: Intestina, Mollusca, Testacea, Lithophyta and Zoophyta.
Other scientists like Lamarck (1744-1829), Cuvier (1769-1832), Leuckart (1823-1898), Haeckel (1834-1919), Ray Lankestar (1847- 1929) threw much light to find out a general principle in biological classification and contributed much to the science of taxonomy. Both Cuvier and Lamarck distinctly separated the invertebrates and vertebrates.
Lamarck divided the invertebrates into: Mollusca, Cirripedia, Annelida, Crustacea, In-secta, Arachnida, Vermes, Radiata, Polypes and Infusoria. But Cuvier made some progress in systematics and classified the invertebrates into: Mollusca (including annelids and arthropods) and Radiata or Zoophyta (including rest of the invertebrates).
Leuckart’s contribution on systematic zoology is noteworthy. He recognised the phyla, Protozoa, Coelenterata (sponges are included), Echinodermata, Vermes, Arthropoda, Mollusca (Tunicates are included) and Vertebrata. The defects of the above systems were rectified by Carl Vogt (1851). He classified the Vermes into Annelida, Rotatoria, Platyelmia and Nematelmia.
Gegenbaur (1859) changed the names of the last two groups to Platy- helminthes and Nemathelminthes respectively. Of the various taxonomical names, Protostomia and Deuterostomia have been extensively used by many taxonomists.
The Bilateralia is divided into: Protostomia (Blastopore becomes the mouth) and Deuterostomia (Mouth is a new formation). But such groupings are not regarded as the true taxonomic divisions.
Linnaean System of Classification:
In order to place the known organisms in their proper systematic status Linnaeus (1758) employed 5 levels of classificatory categories in Systema naturae, called Linnaean hierarchy, such as
He used only 5 categories for zoological classification, such as Classis (Class), Ordo (Order), Genus, Species and Varietas (Variety). Later ‘Family’ was added by Butschli in 1790 between Genus and Order, and Phylum by Haeckel in 1886 between the two levels— Class and kingdom.
The term ‘Varietas’ (variety) has been discarded as a level from animal taxonomy but is now widely familiar in botany. The term ‘varietas’ was commonly used in the Linnaean period but after 1960 the use of ‘variety’ is not accepted by Zoological commission. Earlier taxonomists used variety instead of subspecies. There are no distinct criteria to differentiate a subpopulation as variety.
Linnaeus first placed closely resembling organisms in a species, then similar species under a genus and several genera under a family and so on. The taxonomists, before Linnaeus, were engaged in classifying animals only for the sake of identification. It is Linnaeus who, for the first time, suggested a scheme to establish kinship amongst different members.
With the increase of the large number of kinds of organisms several intermediate levels have been added in the hierarchy for zoological classification.
A complete hierarchy (sometimes called “extended Linnaean hierarchy”) with 21 categories used by Simpson (1945) in the classification of mammals, is as follows:
I. C. Z. N. has recognised the following hierarchial categories (17) for classification such as Kingdom, Phylum, Superclass, Class, Subclass, Cohort, Superorder, Order, Suborder, Superfamily, Family, Subfamily, Tribe, Genus, Subgenus, Species and Subspecies.
The following hierarchial categories are usually used for zoological classification, such as Kingdom, Phylum, Class, Order, Family, Genus and Species. These seven categories also represent as the basic levels of Linnaean hierarchy.