Question

Define the following in relations to each other?

1. Phylum
2. Class
3. Order
4. Family
5. Genus

Answer 1

Most of the words mentioned above were proposed to create a hierarchy for biological classification by Swedish naturalist Carl von Linne. He published a well acclaimed scientific style classification for living organisms, in his major work Systema Naturae (1735).

The fundamental nature of biological classification has not changed since his time, though the very basis of classification has changed from earlier emphasis on morphological/anatomical similarity to the more important consideration of common evolutionary lineage.

Linne wanted to reveal a system within natural diversity, hence:

• placed relatively similar species under one genera,
• slightly varying genera under one order,
• different related orders under one class,
• and classes were grouped together under kingdom.

So, a five level hierarchy was created where kingdom was the largest platform. A couple of platforms were added later:
one above class- Phylum,
another above genera- Family.

All these platforms are arbitrarily created ranks or categories, arranged in definite hierarchical order of which only species is naturally defined category.

Each category includes various taxa: i.e. actual biological objects. For example, mammalia, reptilia, aves are various animal taxa, all placed in category class.

• Linne defined species as 'natural' by which he meant created by God. Today species is defined as an entity of biological organisms which remains naturally separated from other such biological entities by reproductive barrier . (That is members of two different species will not engage in mating and reproduction. In case of asexually reproducing organisms, gene pool of each species remains completely separated from that of another.)
• Genus is taxonomic category which ranks just above species and below family in hierarchical classification.
• Similarly, definition of Family is- taxonomic category that ranks above genus but below order.
• This way, one can define Order, Class and Phylum according to their position in hierarchy. Please note, the word Phylum is synonymous to Division, latter word is commonly used in botany.