Biology - Biological Classification

DescriptionSince the dawn of civilisation, there have been many attempts to classify living organisms. It was done instinctively not using criteria that werescientific but borne out of a need to use organisms for our own use - for food, shelter and clothing. Aristotle was the earliest to attempt a morescientific basis for classification.

He used simple morphological characters to classify plants into trees, shrubs and herbs. He also divided animalsinto two groups, those which had red blood and those that did not. In Linnaeus' time a Two Kingdom system of classification with Plantae and Animalia kingdoms was developed that included all plants and animals respectively.

This system did not distinguish between he eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) organisms. Classification of organisms into plants and animals was easily done and was easy to understand, but, a large number of organisms did not fall into either category. Hence the two kingdom classification used for a long time was found inadequate.

Besides, gross morphology a need was also felt for including other characteristics like cell structure, nature of wall, mode of nutrition, habitat, methods of reproduction, evolutionary relationships, etc. Classification systems for the living organisms have hence, undergone several changes over the time. Though plant and animal kingdoms have been a constant under all different systems, the understanding of what groups/organisms be included under these kingdoms have been changing; the number and nature of other kingdoms have also been understood differently by different scientists over the time.