This opening chapter asks what distinguishes the living from the non-living and how biologists make sense of the enormous diversity of life, with between 1.7 and 1.8 million species described so far. Because local names vary from place to place, a universal system of naming is needed; this is nomenclature, and it works only after an organism is correctly identified. Each scientific name has two parts under binomial nomenclature, given by Carolus Linnaeus: a generic name and a specific epithet, written in Latin and in italics, as in Mangifera indica for mango. Plant names follow the ICBN and animal names the ICZN. Classification groups organisms into convenient categories called taxa, and the study of classification with its underlying rules of identification, naming and arrangement is taxonomy, while systematics additionally considers evolutionary relationships. The chapter then builds the taxonomic hierarchy from species upward through genus, family, order, class, phylum or division, and finally kingdom. As one moves up this ladder the number of shared characters decreases, so higher categories are harder to relate. Worked examples for man, housefly, mango and wheat show how each organism occupies a definite place at every rank.
Diversity in the living worldNeed for nomenclature and identificationBinomial nomenclature and its rulesTaxonomy, classification and systematicsTaxonomic categories: species to kingdomTaxonomic hierarchy with examples
Key terms
Taxonomy
The branch of biology dealing with identification, nomenclature and classification of organisms based on their characters.
Binomial nomenclature
The two-word naming system, given by Linnaeus, in which a name has a generic name and a specific epithet.
Taxon
A unit or group of classification at any rank, such as a species, genus or family.
Taxonomic hierarchy
The arrangement of categories from species up to kingdom in ascending order of rank.
Species
A group of individual organisms with fundamental similarities, distinguishable from closely related species by morphological differences.
Systematics
The study of the diversity of organisms and their relationships, taking evolutionary relationships into account.
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The two-word naming system for organisms, given by Linnaeus, is called:
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