Aristotle (384-322 BC) was the first to classify the organisms scientifically. He was first to divide the organisms into two groups – (i) Plant & (ii) Animals. The animals were further classified on the basis of presence or absence of RBC into two groups viz. (a) Aniama – absence of RBC and (b) Eniama – Presence of RBC.
The plants were divided on the basis of morphology as trees, bushes and herbs.Sweden scientist Carolus Linnaeus (18th century) classified plants and animals into two kingdom viz. – (i) Kingdom – Plantae and (ii) Kingdom – Animalia. It is popular as two kingdom classification. However, this system failed to differentiate eukaryotes, prokaryotes, unicellular & multiceullar, algae & fungi etc.
The classification systems putforth during 19th century were based on morphology, anatomy and geographical distribution of the organisms. Such characters are important even today. After the evolutionary theory given by Darwin (1859), phylogentic basis of the organism was included in the classification.
The genetical similarities and cytogenetic characters were the main basis. Two main fields viz. (i) Chemotaxonomy and (ii) Numerical taxonomy were developed in the taxomony after 1960. To include, many changes occurred in the classification systems as per requirement from time to time.