Diversity in the Living World: What Is Biodiversity?

Step outside and look around: a garden may show you a handful of insects, a couple of bird species and a few kinds of plants, but walk into a forest, a river bank, or a paddy field in rural Bengal and the range of living things you meet multiplies many times over. Life on Earth is not a handful of types repeated everywhere — it exists in an astonishing range of forms, sizes and habits, from bacteria too small to see with the naked eye to towering banyan trees and blue whales. This enormous variety and abundance of living organisms found in a given region, or on the planet as a whole, is what biologists call biodiversity, a term built from "biological" and "diversity".

Biologists have so far formally described and given scientific names to somewhere between 1.7 and 1.8 million species of organisms — plants, animals, fungi and microbes together. This number itself is only the visible, catalogued fraction of what actually exists: enormous stretches of tropical forest, deep ocean floor and soil microbial communities remain barely explored, so working estimates of the true number of species on Earth run considerably higher, though the exact figure is genuinely uncertain and varies between studies.

Each distinctly different kind of organism recognised in this count is called a species — the basic, most fundamental unit in which biodiversity is measured and described. A mango tree (Mangifera indica), a house sparrow, a tiger and a Paramecium are all separate species, each with its own set of defining features that set it apart from every other kind of organism.

For West Bengal, one of India's most biodiversity-rich states — spanning the Sundarbans mangrove forests, the Himalayan foothills of Darjeeling, and the Gangetic plains — recognising and understanding this diversity is not an abstract exercise. It is the essential first step before any organism can be studied, conserved, or put to practical use, and it is exactly why biologists needed a systematic way to organise this diversity, which is the subject taken up in the sections that follow.