Classification and biology

Abstract

If two kinds of animals differ constantly from each other in some definite but relatively minor structural character or characters, they are said to be distinct species. The structural differences are presumed or, in some cases, are known to be indicators of a barrier to interbreeding between the two kinds. Species are then grouped into genera, a genus being an assemblage of species showing evidence in common characters of close relationship. Genera in turn are arranged in the higher category of a family, whose components share many important characters. An order consists of all those families that show major features that link them together into a single natural assemblage. To continue ascending this hierarchical scheme, orders collectively form a class, while classes are grouped on the basis of common fundamental characters into a phylum. Certain intermediate taxonomic categories are also adopted, the most widely used being the subfamily or group of genera forming a section of a family; the superfamily, or group of families smaller than an order; and the suborder. It will suffice to give one example showing the systematic position of the ant Formica rufa Linnaeus.