Quiz 10: Taxonomy and Phylogeny of Animals
Linnaeus' system of arranging organisms into a series of groups of ever-decreasing inclusiveness is a hierarchical system of classification. Major taxa, into which organisms are grouped, were given one of several standard taxonomic ranks to indicate the general degree of inclusiveness of the group. The list from most inclusive to least inclusive is: • kingdom • phylum • class • order • family • genus • species Higher taxa generally are more inclusive than lower-level taxa, although taxa at two different levels may be equivalent in content.
Linnaeus' system for naming species is known as binomial nomenclature because each species has a Latinized name composed of two words. The first word names the genus, which is capitalized; the second word is the species epithet which is peculiar to the species within the genus and is written in lower-case. The genus name is always a noun, and the species epithet is usually an adjective that must agree in gender with the genus. The species epithet never stands alone; the complete binomial must be used to name a species. The same species epithet may be used in different genera to denote different species.
The typological species concept: This concept considered species as a distinct and immutable entity. Scientists used to recognize species by naming them based on species present in museums. If the new species matched the one in the museum, it was put under the same species. Small differences were considered imperfections. This type of grouping was based on the external morphological features. The biological species concept: This concept considered species as - "a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature." Here a species is defined based on its reproductive qualities and not on its morphological features. A species is an interbreeding population of individuals having a common descent and sharing intergrading characteristics. The criterion of niche recognizes that members of a reproductive community are expected also to have common ecological properties. Evolutionary biologists prefer the biological species concept to typological species concept because according to them, species are historical entities whose properties are subject to change. They could not accept the typological concept as the morphological features of species in that concept were constant.