Science at a Distance

CLAS Hierarchical Ordering

Systems of biological classification did not make much significant progress for about 2,000 years after Aristotle's contribution, until a Swedish Professor of Botany devised a new organizing principle, and applied it to a taxonomy of plants, animals and later minerals and diseases.

CLAS Carl Linne Born on May 23, 1707 in Rashult Sweden, quickly found the major interest in his life in the gardens and fields around him. From a very young age he was called the "little botanist" a title he took with him all the way through school, university and medical training.

At Uppsala University he met and was influenced by the botanist Olof Celsius, who helped him get the position of lecturer in botany at Uppsala University, and two years later encouraged him to go on collecting explorations in Lapland. He published the results of his travels as the Flora Lapponica, and later (in 1735) published his famous Systema Naturae, which brought him a world wide reputation.

Human and Ape chromosomes Carolus Linnaeus (he loved Latin and used it for everything, including changing his name to the Latin version), is considered to be the founder of modern taxonomy. His work is the start of modern botanical and zoological classification. Like Aristotle before him, Linnaeus used logic in devising his classification scheme. But he introduced a new idea; a hierarchy of nested groups within groups, a system sometimes called hierarchical ordering.
An example of how this works is shown in the example below. Place your cursor over the buttons beside the "2D World" to see how groups nest within groups.

Hierarchical Ordering







CLAS At first, Linnaeus tried to use a "natural" classification or taxonomic ordering, for example, he divided up all living organisms in to two major groups (Kingdoms) which he called 'plants' and 'animals'. All newly discovered creatures, therefore had to be first to be placed in one of these groups. It seemed "natural".

But the attempt at a purely "natural" scheme quickly gave way to a much more arbitrary set of criteria, for plants, for example, he used differences in the nature and structure of small parts of the flower. These differences gave him a good delineation between groups, but the choice was not related to any obvious "natural" function of the plant, flower or flower parts.

CLAS His major groupings in the hierarchy of groups were, the kingdom, phylum, class, order, family, genus, and species; seven levels of groups within groups. This was arbitrary, and more levels have been added over the years since the time of Linnaeus.

But, no matter how many levels are involved, finally only one form of an organism occupies the last group at the last level. After that there is no point in making more levels. Linnaeus followed the practice, started by Aristotle, of naming each unique form of an organism by it's genus name followed by a differentia phrase. As today, the genus defined the second lowest group and was general a way of describing the set (for example 'canines').

The differentia phrase added more information and said what made that particular organism special. For example 'canine' that 'lives in woods'. This system of naming creatures worked well until it became overcrowded. As the list of different species within a genus expanded so did the length and complexity of the differentia ('lives in woods; dark coat in winter; found only in the north').

Eventually, in some of his works Linnaeus took to writing a short, easy to remember name in the margin. This name consisted of the genus and then either only one word from the longer differentia or some other word from a former name. This meant that every species could be unambiguously named using only 'two words'. He had invented the binomial system of naming creatures, or what can be considered to be a binary nomenclature.

The combination of an easy to remember binomial name (even if it was in Latin), and the ease with which new organisms could be identified, characterized and then fitted into their respective groups and grouping, gave the Linnaean system of classification a utility that greatly exceeded its artificiality. In highly modified form, it has persisted to this day and is still used.

CLAS The typical text book example of how humans are classified using the modern Linnaean system is given below:

  • Kingdom: Animalia
  • Phylum: Chordata
  • Subphylum: Vertebrata
  • Superclass: Tetrapoda
  • Class: Mammalia
  • Subclass: Theria
  • Infraclass: Eutheria
  • Cohort: Unguiculata
  • Order: Primata
  • Suborder: Anthropoidea
  • Superfamily: Hominoidae
  • Family: Hominidae
  • Subfamily: Homininae
  • Genus: Homo
  • Subgenus: Homo (Homo)
  • Specific epithet: sapiens

The binomial name would therefore be Homo sapiens.

In 1739 Linnaeus got married to the daughter of a physician, and was later appointed to the chair of medicine at Uppsala University. He did well in this post, but it was not his first love, and a year later he swapped the scalpel for the chair of the Botany Department.

He never gave up classifying things and after systematizing the plant and animal world, he went onto the mineral kingdom and even tried his hand at the known diseases of his day. He was a teacher and a writer who never stopped working.


Science at a Distance
© 1998 Professor John Blamire