In biology, hierarchy refers to the taxonomical classification of living organisms in successive levels of complexity. The kingdom is the highest rank in such a classification while species is the lowest. The meaning of hierarchy is the arrangement of the categories in an increasing order from species to the kingdom or in a decreasing order from kingdom to species.
The hierarchy can be classified in two ways:
- Obligate hierarchy: A classification where the order is followed strictly from kingdom to species or vice-versa.
- Intermediary hierarchy: it does not follow the order and can be added to the categories in the obligate list like the subdivision, subspecies, superfamily, suborder, and superclass.
A taxonomical study has led to the formation of seven categories in which every living organism in this world can be categorized:
This is the first step on the ladder of the hierarchy of classification and shows exceptional similarities in the organisms who are in the same category. It can be defined as a group of living organisms who share similar forms, features and reproductive systems. One species can be differentiated from another species which is closely related to it based on the study of their individual morphology. Species can be further subcategorized into subspecies, races etc.
Genus (plural Genera)
A genus is a collection of very similar species. They share similar characteristics with each other but distinctly different from other genera.
Example: Tiger and lion are a part of the genus Panthera.
A collection of similar genera which share some characteristics with each other. However, the similarities are very limited as compared to genus and species.
Example: The genus Panthera (lions, tigers) and the genus Felis (cats) are grouped under the same family Felidae.
Families in the same order share some of their basic features with each other.
Example: Families Panthera and Felidae are included in the order Carnivora based on their eating habits.
A class is a group of orders which have some features in common with each other.
Example: Class Mammals contains orders Carnivora and Primates.
A major taxonomy category which ranks below kingdom and above class. A group of similar orders forms a phylum.
Example: It is the international code of nomenclature for algae, fungi, and plants accept the terms as equivalent.
This is the highest form of taxonomical classification. It groups similar phylums.
Example: All living animals are put under the Kingdom Animalia.
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