Biological Classification

Biodiversity is the variety of all living things on Earth. We have learnt that living organisms adapt to different environments, like where they live, what they eat, and how they protect themselves. Even members of the same species can have differences.

Scientists have discovered that there are around 87 million different species of living organisms on our planet, both in water and on land (as of the 2011 census). With so many species, it is necessary to organise them into groups to study them better. By grouping organisms based on their similarities and differences, scientists make it easier to understand and learn about them. This grouping system is called biological classification.

Historical Development of Biological Classification:

• Carl Linnaeus in 1735 divided the living world into 2 kingdoms: Vegetabilia and Animalia.
• Haeckel in 1866 considered 3 kingdoms: Protista, Plants, and Animals.
• In 1925, Chatton created two groups: prokaryotes and eukaryotes.
• In 1938, Kopland divided living organisms into 4 kingdoms: monera, protozoa, plants, and animals.

1) For a systematic study, we need to classify organisms

Aristotle classified animals according to whether they lived on land, in water, or in the air. This cannot give a clear idea, though, as organisms living in water have nothing in common except their habitat. So nowadays classification is based on the following characteristics:

1. Prokaryote or eukaryote
2. Unicellular or multicellular
3. Autotrophs or heterotrophs
4. Level of organization
5. Specialized organ

2) Classification helps in understanding evolution

1. Primitive/lower organisms: The group of organisms that have ancient body designs that have not changed very much.
2. Advanced/higher organisms: The group of organisms that have acquired their particular body designs relatively recently.

Classification presented by Aristotle:

He classified animals on the basis of their habitats-land, water, and air. But it can be easily observed that the animals that live in a particular habitat are still so different from each other. Therefore, it was decided to classify the living organisms on the basis of a hierarchy. This hierarchical classification was based on the similarities and dissimilarities in the characteristics of living organisms. Organisms having similar characteristics were placed in a similar category.

Classification of organisms is essential as it simplifies the study of the vast diversity of life forms. It aids in understanding the evolutionary relationships among different species and provides insights into their development over time. Additionally, classification helps in identifying how organisms are interconnected and the reasons for their distribution across various geographical conditions. This systematic organisation facilitates a deeper comprehension of biodiversity and ecological patterns.

• Evolution: Over the course of time, the living organisms accumulate changes. These changes could be in their body type or size or their features. These changes allow them to survive better with the change in environment. This is called Evolution. This concept was introduced by Charles Darwin.
• Classification: The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification.
• Primitive organisms are the ones that have an ancient body design. Their bodies haven't undergone many changes with time. They are called ‘lower’ organisms as well.
• The advanced organisms are those who have recently acquired body changes. They are also called 'higher' organisms.