Why a Mango in Maharashtra and One in Bihar Share the Same Scientific Name

Scientists have described well over a million kinds of living things, and many more remain unnamed. Without an agreed way to group and name them, a biologist in Kerala and one in Canada could discuss the same frog under different names and never realise it. Classification and scientific naming solve that problem.

This lesson covers taxonomy and its branches, species and the taxonomic hierarchy, binomial nomenclature, and systems of classification.

Taxonomy is the science of identifying, naming and classifying organisms; its modern branches decide relationships using many coded characters (numerical taxonomy), chromosome features (cytotaxonomy) and chemical constituents (chemotaxonomy).

Why classification is needed:

- It makes the huge variety of organisms manageable to study
- It shows how groups are related to one another
- It lets scientists everywhere refer to the same organism without confusion

Basic processes of taxonomy. Characterisation, identification, nomenclature and classification.

Modern branches:

- Numerical taxonomy — codes every observable character as a number and uses computers to compare many characters at once, giving each character equal weight
- Cytotaxonomy — uses cell features, especially chromosome number, structure and behaviour
- Chemotaxonomy — uses chemical constituents such as proteins, pigments and aromatic oils

An everyday example. Two kinds of tulsi that look almost the same but contain different aromatic oils can be separated with the help of chemotaxonomy.

The substance. Systematics is broader than taxonomy — it also studies the evolutionary relationships between organisms, not only their names and groups.

A species is a group of individuals with fundamental similarities that can interbreed to produce fertile offspring, and the taxonomic hierarchy arranges categories in descending order: kingdom, phylum or division, class, order, family, genus and species.

Moving up the hierarchy, each category contains more organisms that share fewer common characters. Plants use division in place of phylum.

Classification of four organisms (kingdom; phylum or division; class; order; family; genus; species):

- Man — Animalia; Chordata; Mammalia; Primata; Hominidae; Homo; sapiens
- Housefly — Animalia; Arthropoda; Insecta; Diptera; Muscidae; Musca; domestica
- Mango — Plantae; Angiospermae; Dicotyledonae; Sapindales; Anacardiaceae; Mangifera; indica
- Wheat — Plantae; Angiospermae; Monocotyledonae; Poales; Poaceae; Triticum; aestivum

An everyday example. A library that sorts books into floors, sections and shelves mirrors the hierarchy — the higher the level, the broader the group.

The substance. Man and housefly share only the kingdom — they part at phylum, which is why so few characters are common to both, while mango and wheat stay together down to division and part at class.

Binomial nomenclature gives every organism a two-part scientific name — a genus name followed by a specific epithet — written in Latin or Latinised form. Mango, for example, is Mangifera indica.

Rules:

- The name is in Latin or Latinised form, whatever its origin
- The first word is the genus and the second is the specific epithet
- The genus begins with a capital letter; the specific epithet begins with a small letter
- Printed names are in italics; handwritten names have each word underlined separately
- The name of the author may follow in abbreviated form, as in Mangifera indica Linn.

Worked example. Neem is Azadirachta indica — Azadirachta is the genus and indica is the specific epithet.

Advantages:

- Each name is unique, so it avoids confusion across languages and regions
- It is understood by scientists worldwide
- The genus name shows relationships, since species in one genus are closely related

An everyday example. Brinjal, baingan and eggplant are local names for one plant, but its scientific name, Solanum melongena, is the same everywhere.

The substance. Two species can share a specific epithet but never a full name — Mangifera indica and Azadirachta indica both end in indica, yet belong to different genera.

Artificial systems group organisms by one or a few easily seen features, natural systems use many characters including internal structure, and phylogenetic systems group organisms by their evolutionary relationships.

Artificial system:

- Based on a few external features, such as habit, colour or the number of stamens
- Gives equal weight to vegetative and sexual characters
- Can place unrelated organisms together, since vegetative features are easily affected by the environment

Natural system:

- Based on many characters, including external features, anatomy, embryology and phytochemistry
- Brings out natural affinities between organisms
- Example: the Bentham and Hooker system for flowering plants

Phylogenetic system:

- Based on evolutionary relationships, assuming that members of a group share a common ancestor
- Uses evidence from fossils, molecules and genetics

An everyday example. Grouping bats with birds because both fly is artificial; grouping bats with cats and cows because all are mammals with hair and milk glands is natural.

The substance. Flight evolved separately in bats and birds — a shared feature misleads when it arose independently, which is the central weakness of an artificial system.