Scientific classification

Scientific classification refers to how biologists group and categorize
extinct and living species of organisms. Modern classification has its roots
in the system of Carl Linnaeus, who grouped species according to shared
physical characteristics. These groupings have been revised since Linnaeus
to improve consistency with the Darwinian principle of common descent.
Genomic DNA analysis has driven many recent revisions and is likely to
continue to do so. Scientific classification belongs to the science of
taxonomy or biological systematics.

Early Systems

The earliest known system of classifying forms of life comes from the Greek
philosopher Aristotle.

The next major advance in developing scientific classification was by the
Swiss professor, Conrad Gessner (1516 - 1565). GessnerŐs work was a critical
compilation of life known at the time.

The exploration of parts of the New World next brought to hand descriptions
and specimens of many novel forms of animal life. In the latter part of the
16th century and the beginning of the 17th careful study of animals
commenced, which, directed first to familiar kinds, was gradually extended
until it formed a sufficient body of knowledge to serve as an anatomical
basis for classification. Advances in using this knowledge to classify
living beings bears a debt to the research of medical anatomists, such as
Fabricius (1537 - 1619), Severinus (1580 - 1656), Harvey (1578 - 1657), and
Tyson (1649 - 1708). Advances in classification due to the work of
entomologists and the first microscopists is due to the research of people
lile Malpighi (1628 - 1694), Swammerdam (1637 - 1680), and Hook (1635 - 1702).

John Ray (1627 - 1705) was an English naturalist who published important
works on plants, animals, and natural theology. His classification of plants
in his Historia Plantarum was an important step towards modern taxonomy. Ray
rejected the system of dichotomous division by which species were classified
according to a pre-conceived, either/or type system, and instead classified
plants according to similarities and differences that emerged from observation.

Linnaean taxonomy

Two years after John RayŐs death Carolus Linnaeus (1707 - 1778) was born.
His great work, the Systeina natisrae, ran through twelve editions during
his lifetime (1st ed. 1735). He is best known for his introduction of a
method of modern classification; he created systematic zoology and botany in
their present form. Linnaeus adopted RayŐs conception of species, but he
made species a practical reality by insisting that every species shall have
a double Latin name - the first half to be the name of the genus common to
several species, and the second half to be the specific name. This
convention is now referred to as binomial nomenclature, and the genus and
species names together are known as the scientific name of a species.

Previously to Linnaeus long many-worded names had been used, sometimes with
one additional adjective, sometimes with another, so that no true names were
fixed and accepted. Linnaeus' system made it possible to write with accuracy
of any given species of plant or animal. He proceeded further to introduce
into his system a series of groups: genus, order, class.

The Linnaeus's System works by placing each organism into a layered
hierarchy of groups. Each group at a given layer is composed of a set of
groups from the layer directly below. Therefore, in theory, one needs know
only the lowest layer (species) of a particular organism in order to
uniquely determine the other six layers. In practice, however, many species
actually have the same species designation, so when specifiying a species,
scientists use the bottom two layers.

The groupings (taxa) of taxonomy from most general to most specific are:

   * Kingdom
   * Phylum (animals) or Division (plants)
   * Class
   * Order
   * Family
   * Genus
   * Species

Several acronym mnemonics have been made for these, for instance King
Phillip called out for good soup, or Kings Play Chess On Funny Green
Squares.

Intermediate ranks may be created by adding prefixes, for instance:

   * Superorder
   * Order
   * Suborder
   * Infraorder

In husbandry, horticulture and other activities outside scientific biology,
people still assume the truth of the traditional Linnaean system. The term
varieties is sometimes used in place of subspecies. In horticulture, for
example, it refers to populations modified by selective breeding, for
instance the Peace Rose, a hybrid Tea Rose.

Modern developments

The approach Linnaeus took to classifying species and the majority of his
taxonomic groupings remained the standard in biology for at least two
centuries. Since the 1960s, however, a trend called cladism or cladistic
taxonomy, has emerged and is expected to supplant Linnaean classification.
In classifying species, cladists place a priority in achieving coherence
with the Darwinian principle of common descent.

Meanwhile, at the top of the hierarchy of classification, there has movement
towards a three domain system. The domains originally were replacements for
the different kingdoms, but many scientists regard them as a groupings above
the formerly paramount kingdom level.

Cladistics

In grouping species, cladists look for "derived similarities," meaning those
aspects that species can be expected to share by virtue of a common
evolutionary ancestry. This approach differs from that of phenetics, which
does not address ancestry and associates species based on overall
similarity, and it differs also from classification based on ad hoc "key
characters." Cladists avail themselves of all types of information
avaliable, including DNA sequences and hybridization studies, biochemistry,
and traditional morphology. They often make use of computers to identify the
most likely phylogeny or "family tree" that relates the species they are
considering.

Cladistics requires taxa (groups of species) to be clades. A formal code of
phylogenetic nomenclature, the Phylocode[1], is currently under development
for a cladistic taxonomy that abandons the Linnaean structure.

More at: cladistics.

Could add a description of the difficulty in classifying microbes: their
features are derived from direct visual observation, but include such
procedural characteristics as Gram stain type, motility, ability to form
spores, etc. However, given an unknown bacterium with a given set of
characteristics, it is in general not possible to predict its phylogeny,
toxicity, etc. Other methods, using genes, their DNA, and several types of
RNA, are under development.

Examples

The fruit fly so familiar in genetics laboratories is Drosophila
melanogaster. Its usual classification, as well as that of humans, is as
follows

Fruit Fly (Drosophila)

Kingdom Animalia
Phylum  Arthropoda
Class   Insecta
Order   Diptera
Family  Drosophilidae
Genus   Drosophila
Species melanogaster

Human (Homo sapiens)

Kingdom   Animalia
Phylum    Chordata
Subphylum Vertebrata
Class     Mammalia
Subclass  Eutheria
Order     Primates
Suborder  Catarrhini
Family    Hominidae
Genus     Homo
Species   sapiens

Cucumbertree (Magnolia acuminata)

Kingdom  Plantae
Division Magnoliophyta
Class    Magnoliopsida
Order    Magnoliales
Family   Magnoliaceae
Genus    Magnolia
Species  acuminata

Note in this last example, that most of the taxa are named after the type
genus, Magnolia.

Group Suffixes

Taxa above the genus level are often given names derived from the type
genus. The suffixes used to form these names depend on the kingdom, and
sometimes the phylum and class, as follows:

         Taxon         Plants    Algae     Fungi    Animals
    Division/Phylum   -phyta   -phyta    -mycota
 Subdivision/Subphylum-phytina -phytina  -mycotina
         Class        -opsida  -phyceae  -mycetes
       Subclass       -idae    -phycidae -mycetidae
         Order        -ales    -ales     -ales
       Suborder       -ineae   -ineae    -ineae
      Superfamily     -acea    -acea     -acea      -oidea
        Family        -aceae   -aceae    -aceae     -idae
       Subfamily      -oideae  -oideae   -oideae    -inae
         Tribe        -eae     -eae      -eae       -ini
       Subtribe       -inae    -inae     -inae      -ina

How to - Physics - History - Companies - Internet - Video Games - List of Phobias - September 11, 2001
Radio - Timelines - Chemistry - Genealogy - Family - Film - SARS - Cancer - Medicine - DVD - Calendar
Countries - Disease - Health Science - Dentistry - Economics - AIDS - Law - Autism - Statistics - Bible
Recipes - Architecture - Computers - History of the Internet - Personal computer - Apple Macintosh
War - Presidents of the United States - United States Constitution - Universe - Philosophy - Animals
Biology - United States Constitution - Marketing Topics - Sports - Television - History of Computing

Flights - Mobile Phones - Credit Card Consolidation - Wedding rings - Art Prints