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What is a species?

Read time: 2 mins 15 June, 2019 - 08:00

We often hear or read that ‘some species of a bird or animal is going extinct’, or ‘a new species of an amphibian or reptile was discovered in the jungles of the Western Ghats’. However, what exactly do we mean by ‘species’?

The term ‘species’ refers to a group of organisms similar to each other and can produce a fertile offspring through sexual reproduction. While this definition holds true for most plants and animals around us, there are several cases in which defining a species can be a lot harder. Take for example bacteria, which reproduce asexually with a single cell dividing into two. Strictly speaking, the above definition of species is violated here.

Sometimes, individuals of two species are so similar in appearance that it’s hard to tell them apart, like the Common Mormon and the Crimson rose butterflies. In reptiles like snakes, individuals of the same species from different regions may look entirely different. In a few cases, individuals who seem distinctly different may interbreed wherever their ranges overlap, like the rhesus and bonnet macaques—both found in India.

A recent breakthrough in species identification and classification is the use of DNA to analyse the genetic similarities and differences. The DNA is used to construct evolutionary trees which display how closely an organism is related to another. If a group of plants or animals are almost identical genetically, then they are considered to belong to a new species. This genetic approach of defining species helps us overcome problems presented by outward appearances of organisms and can be applied across different modes of reproduction.