Contents
Classification in biology, is the identification, naming, and grouping
of organisms into a formal system. The vast numbers of living forms are
named and arranged in an orderly manner so that biologists all over the
world can be sure they know the exact organism that is being examined
and discussed. Groups of organisms must be defined by the selection of
important characteristics, or shared traits, that make the members of
each group similar to one another and unlike members of other groups.
Modern classification schemes also attempt to place groups into
categories that will reflect an understanding of the evolutionary
processes underlying the similarities and differences among organisms.
Such categories form a kind of pyramid, or hierarchy, in which the
different levels should represent the different degrees of evolutionary
relationship. The hierarchy extends upward from several million species,
each made up of individual organisms that are closely related, to a few
kingdoms, each containing large assemblages of organisms, many of which
are only distantly related.
Carolus Linnaeus is probably the single most dominant figure in
systematic classification. Born in 1707, he had a mind that was orderly
to the extreme. People sent him plants from all over the world, and he
would devise a way to relate them. At the age of thirty-two he was the
author of fourteen botanical works. His two most famous were Genera
Plantarum, developing an artificial sexual system, and Species
Plantarum, a famous work where he named and classified every plant known
to him, and for the first time gave each plant a binomial.
This binomial system was a vast improvement over some of the old
descriptive names for plants used formerly. Before Linnaeus, Catnip was
known as: “Nepeta floribus interrupte spicatis pedunculatis” which is a
brief description of the plant. Linnaeus named it Nepeta
cataria–cataria meaning, “pertaining to cats”. The binomial
nomenclature is not only more precise and standardized; it also relates
plants together, thus adding much interest and information in the name.
For instance, Solanum relates the potato, the tomato and the Nightshade.
Binomial Classification
Early on in naming species taxonomists realized that there would have to
be a universal system of nomenclature. A system that was not affected by
language barriers, and would also classify the millions of species
throughout the world. Binomial classification in its simplest form is a
way of naming a species by means of two names both in Latin. Latin was
originally used because it was the language of the founders of the
classification system, like Carolus Linnaeus, but it continues to be
used presently because it is a “dead language”. This means that it is no
longer changing or evolving, so it stays the same and can be used
universally, without confusion. Carolus Linnaeus (see Appendix A, Image
1) first introduced binomial classification, which is why he is known as
the father of the modern day classification system.
In Binomial classification the first name, which begins with a capital
letter is known as the Genus it is always capitalized. The genus is a
group of species more closely related to one another than any other
group of species. The genus is more inclusive than the species because
it often contains many species. The second part of the binomial
represents the species itself and is always printed with all letters in
lower case. A species is a group of individuals that are alike in many
different ways. Individuals are in the same species if they are:
1. Are able to mate with those similar to themselves.
2. Produce young that are themselves able to reproduce.
As an example, in the cat family, the genus Panthera is coupled with the
species leo to form Panthera leo, the Lion. Likewise, Panthera is
coupled with tigris, to form Panthera tigris the Tiger. In simplified
terns both the Lion(see Appendix A, image 2) and Tiger share common
traits and a common genus – Panthera, whilst clearly remaining separate
species. To allow further subdivision, the prefixes sub- and super- may
be added to any category. In addition, special intermediate
categories-such as branch (between kingdom and phylum), cohort (between
class and order), and tribe (between family and genus)-may be used in
complex classifications.
Closely related species are a genus, closely related genera (plural form
of genus) are grouped together in a family. Closely related families are
grouped into an order, and so on, into more inclusive categories, or
levels in the classification hierarchy.
Taxonomic Hierarchy
Approximately one and a half million species have been classified and
there are estimates that over five million species remain to be
discovered. For biologists to order this mass of information, a
scientific system called taxonomy was introduced. The basic idea is to
group species with similar characteristics together into families, and
to group the families together into broader groupings. To this end, the
taxonomic categories where devised, and they create the taxonomic
hierarchy. The hierarchy goes (with an example):
*Categories Example
Kingdom Animalia
Phylum (Plural = Phyla) Cordata
*In plants, this category is often called a division*
Class Mammalia
Order Carnivora
Family Canidae
Genus Canis
Species Lupus (the Wolf)
Every species is in only one genus. Similarly, every genus is in only
one family, and so forth up the hierarchy. The most inclusive category
for classifying groups of similar organisms is the Kingdom. It is argued
exactly how many Kingdoms there are though. Up until recently, only two
kingdoms were generally used, the plant and animal kingdoms. Now however
there are 5 established kingdoms and one controversial unofficial
kingdom.
The 5 kingdoms:
1. Kingdom Animalia (The Animal Kingdom)
ex: Multi-cellular motile organisms, which feed heterotrophically
(Humans)
2. Kingdom Plantae (The Plant Kingdom)
ex: Multi-cellular organisms, which feed by photosynthesis (Tulips)
3. Kingdom Protista (The Protist Kingdom)
ex: Protozoa and single-celled algae
4. Kingdom Fungi (The Fungus Kingdom)
ex: Yeast
5. Kingdom Monera (The Monera Kingdom)
ex: Bacteria and blue-green algae
Parallel to these Kingdoms, but not included, are the Viruses. These
are acellular entities with many of the properties of other life forms,
but are genetically and structurally too dissimilar to the species
categorized above to fit into that scheme of taxonomy.
Although this system is complex and intricate at times, its
universality makes it a necessity. With out the system presently in use
the world would be years and years behind in their task to name all of
the living organisms on earth. This system is great but it is always
possible that some new finding could cause the system to evolve to
become more inclusive. This system is by no means set in stone, and
Linnaeus would probably be astounded to see the way that it has evolved
since his original system.
Appendix A
Carolus Linnaeus (Image
1) Panthera leo (Image 2)
Bibliography
Berkely University. www.ucmp.berkeley.edu/history/linnaeus.html/
Galbraith, Don. Understanding Biology. John Wiley and Sons. Toronto.
1989,
Microsoft. Encarta Encyclopedia 97. Microsoft Corporation. 1997
