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Classification
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
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