SPECIES AND THE LINNAEAN HIERARCHY

When the Swedish naturalist Karl Linné, better known then as now under his Latinized name, Carolus Linnaeus, proposed a system for biological taxonomy in the first half of the eighteenth century, he could hardly have predicted that it would continue to form the backbone for biological classification and taxonomy over 250 years later. Two features of the system that Linnaeus proposed structure systematics today: the idea that biological nature was hierarchically organized, with higher levels in the hierarchy subsuming lower levels, and the Latinized binominal nomenclature that is still used in the naming of biological taxa. Reflecting Linnaeus's own debt to the Aristotelian distinction between species and genus, these binominals name species but also reflect the genus to which the species belongs. Thus, Homo sapiens uniquely names our own species and the name tells us that we belong to the genus Homo. Species and genus are distinct ranks in the Linnaean hierarchy, and both were taken by Linnaeus to be natural categories, part of the organization of nature itself.

The contemporary Linnaean hierarchy includes many more ranks than just species and genus. Linnaeus recognized higher ranks, such as the empire of all things, three kingdoms of animal, vegetable, and mineral, six classes of animal (mammals, birds, reptiles, fish, insects, and worms), and eight orders of mammals.