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Classification
Chapter 18
What’s Wrong Here?
Classification
 To
study the diversity of life, biologists use
a classification system to name organisms
and group them in a logical manner
 Taxonomy
is the discipline of classifying
organisms and assigning each organism a
universally accepted name
 What
is the benefit of having a universal
classification system?
Development of a Classification
System

Carolus Linnaeusdeveloped a two word
naming system that is
still in use today
 In Binomial
Nomenclature each
species is always
assigned a two-part
scientific name
 The
first part of the scientific name is the
genus. The first letter of this name is
always capitalized--- Ursus
 The
second part of the scientific name is
the species, which is never capitalized
---- maritimus
Now You Try
 Examples:
ursus maritimus
 homo sapiens
 canis familiaris

What’s in a Name
 When
written together, the scientific name
includes both the species and genus name
of the organism
 This should be italicized when typed or
underlined when written hand-written
Taxonomic Categories
Linnaeus’s system of
classification uses 7
taxonomic categories.
 Genus is a group of
different species that
share common
characteristics

Kingdom
Phylum
Class
Order
Family
Genus
Species
Taxonomic Characteristics
 Families
are composed of different groups
of genera (genus) that share similar
characteristics
 Families are grouped into orders.
 Orders are grouped into classes.
 Classes are grouped into phyla (Phylum)
 Phyla (phylum) are grouped into a large
category called a kingdom
Modern Evolutionary Classification
 Linnaeus
compared structure and
anatomy
 Biologists now group organisms into
categories that represent lines of
evolutionary descent, not just physical
similarities
 Derived Characteristics are those that
“show up” in newer parts of a lineage but
are not in its older members
Modern Evolutionary Classification
 Cladograms
are diagrams
that show
evolutionary
relationships
between
groups of
organisms
Modern Evolutionary Classification
 The
genes of many organisms show
important similarities at the molecular
level. These similarities can be used as
criteria to help determine classification
 All organisms use RNA and DNA to pass
on information. All organisms use ATP as
an energy-carrying molecule. Similarities
in other important chemicals give us
another way to compare them
Modern Evolutionary Classification
 Molecular
clocks use DNA comparisons to
estimate the length of time that two
species have been evolving
independently.
 This
relies on the rate that neutral
mutations accumulate in the DNA of
different species
Kingdoms and Domains
 Using
new tools available today, scientists
have expanded upon Linnaeus’s system of
classification.
 The 6 kingdom system of classification
includes the kingdoms Eubacteria,
Archaebacteria, Protista, Fungi, Plantae,
and Animalia
Kingdoms and Domains
 Today,
most scientists are now recognizing
molecular evidence that requires the
addition of a category even larger than
kingdom: the domain
 Domains:



Archaea
Bacteria
Eukarya