Over thousands and millions of years, a wide variety of species has evolved on the earth. The life forms around us range from small ants to huge trees, colorless worms/insects to brightly coloured flowers and birds. For ease of study and identification, the idea of biological classification was put forward. But for the relevant classification, a fundamental basis of classification is necessary. Let’s learn about biological classification and basis of classification in details.
Since time immemorial, attempts of classification of things have been made. At first, things around us were classified into living and non-living things. Later, when the diversity of living things began to grow, it called for the necessity of biological classification. Biological classification is the classification of living organisms based on their similarities and dissimilarities. Many biologists worked on it. Each one of them classified organisms into different groups according to different criteria. It took years for researchers to decide the most fundamental characteristics for the classification. Let’s take a glance of biological classification by different biologists and their basis of classification.
Basis of Classification
History of biological classification begins with Aristotle, the Greek thinker. He described animal classification based on their habitat i.e., air, water and land. But classification wasn’t justified. Animals in each group have nothing in common, other than their habitat (except few). A fish and turtle can’t be in the same group. Hence, habitat can’t be a criterion for classification.
Later, scientists started to work on classification of living organisms based on their characteristics. Characteristics can be explained in many ways. A group of organisms are similar enough to be thought of together by certain characteristics. Hence, we need to define characteristics. Characteristics are the appearance/form and behaviour/function of something. These characteristics decide which organism will be in which group. For example, a dog has limbs but a snake doesn’t. A dog and a snake can move but a plant cannot.These are characteristics of different organisms. These behaviors classify them into different groups. But which characteristic should be the fundamental form or function? In above example, how should a dog be classified- on the basis of body design or its locomotion? Which of these characteristics is more fundamental?
Every classification starts from a single point. Fundamental characteristic will decide the broadest divisions i.e., main groups among living organisms. It is like the shapes and sizes of stones in the lowermost layer decide the shape and size of the top layer. The characteristics at the next level will decide sub-groups based on the fundamental one. Thus, a hierarchy of classification is built.
Some of the characteristics which are used today to classify organisms are as follows:
- Prokaryotic or Eukaryotic cell.
- Unicellular or Multicellular.
- Autotrophs (Photosynthetic) or Heterotrophs (Non-photosynthetic).
- The level of organization and development of organs.
The fundamental characteristic to classify a plant and an animal is their body design. The next level of the hierarchy is, whether the plant is a tree or a shrub. Based on different characteristics, more subgroups will be formed.
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