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Classification
… of organisms
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Scientists discover new species of
organisms nearly every day.
Most these species live in regions
difficult to access, such as tropical
forests and the oceans.
It is necessary to classify these
organisms in order to better
understand them.
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Classification is the action of
grouping objects in useful units.
Taxonomy is the science of
classifying organisms. It consists in
classifying organisms according to
different sources of information.
The methods of classification can
vary.
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Aristotle (384-322 BC) was one of
the first taxonomists. He classified
the plants into grasses, bushes, and
trees.
He classified the animals depending
on whether they lived on the earth,
in water, or in air. (It didn't explain
the fact that some birds were in
water and air.)
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One of the objectives of the modern
taxonomy is to establish a natural
classification founded on evolution.
One supposes that the related
organisms have more features in
common than the distantly related
organisms.
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To identify an animal, it is not
necessarily useful to know that it has
some wings.
It would be artificial to group the
animals while only focusing on the
fact that they have wings.
Carolus Linnaeus
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A Swedish botanist
who elaborated a
classification that is
used again today.
Linnaeus established
binomial
nomenclature.
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The binomial nomenclature is a set of
scientific names formed of two words.
The first term designates the Genus (a
group of similar species), and the second
designates the species.
Ex. sugar maple  Acer saccharum
The Genus is written with a capital and
the species with a lower-case letter and
the two names are in italic or underlined.
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As binomial nomenclature is in Latin,
all scientists can understand it,
whatever their maternal language.
In taxonomy, the organisms are
grouped in a set of categories. Each
of these categories includes the
previous category.
Categories
Example
English
kingdom
Animalia
Animal
phylum
Chordata
Chordates
sub-phylum
Vertebrata
Vertebrates
class
Mammalia
Mammalian
order
Primates
Primates
family
Pongidae
Pongidae (big monkeys)
genus
Gorilla
Gorilla
species
Gorilla Gorilla
Gorilla
subspecies
Gorilla Gorrilla
beringei
mountain Gorilla
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A family is therefore a group of
related Genus, an order is a group
related families, a class is a group
related orders, a phylum is a group
of related classes, and a kingdom is a
group of related phyla.
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Phylogeny is the history of the evolution of
the species.
Scientists compared some modern shapes to
fossils of similar shapes. According to the
biologists, new species appeared as the
organisms adjusted (evolved) and the
populations changed.
The representation of this classification
looks like a tree
A Phylogenetic Tree
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The representation of this
classification looks like a tree, the
modern species are indicated at the
end of the branches.
The groups closer in the tree have a
lot of common features ; the distant
groups are very different and they
are probably not closely related.
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The periphery of the tree
represents the present time. Some
groups, such as the mammals,
appeared relatively later in the
history of life.
More the two groups of are
separated later in the tree, more
they are similar. And closely related.
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To determine the relations,
taxonomists compare the appearance,
the internal structures, the stages of
development, the chemical
composition, etc.
One can classify a plant in a family
according to the number of petals of
the flower.
All organisms are related either
closely or quite distantly.