17.1 The Linnaean System of Classification
KEY CONCEPT
Organisms can be classified based on physical
Pangolian ↓
similarities.
17.1 The Linnaean System of Classification
Linnaeus developed the scientific naming system still
used today.
• Taxonomy is the science of naming and classifying
organisms.
White oak:
Quercus alba
• A taxon is a group of organisms in a classification system.
17.1 The Linnaean System of Classification
Aristotle
• Grouped the types of creatures
according to their similarities:
animals with blood and animals
without blood, animals that live on
water and animals that live on
land.
• Hierarchical classification. He
assumed that creatures could be
grouped in order from lowest to
highest, with the human species
being the highest.
17.1 The Linnaean System of Classification
Aristotle 384 BC – 322 BC
• Greek philosopher and a student of Plato.
• His writings cover many subjects, including poetry,
theater, music, logic, linguistics, politics, government,
ethics, biology, and zoology.
• In the zoological sciences, some of his observations were
confirmed to be accurate only in the 19th century.
• All aspects of Aristotle's philosophy continue to be the
object of active academic study today.
17.1 The Linnaean System of Classification
Carl Linnaeus 1707-1778
• was a Swedish botanist,
physician, and zoologist,
who laid the foundations for
the modern scheme of
binomial nomenclature.
• He is known as the father of
modern taxonomy, and is
also considered one of the
fathers of modern ecology.
17.1 The Linnaean System of Classification
• Binomial nomenclature is a two-part scientific naming
system.
– uses Latin words
– scientific names always written in italics or underlined
– two parts are the genus name and species descriptor
17.1 The Linnaean System of Classification
• A genus includes one or more physically similar species.
– Species in the same genus are thought to be closely
related.
– Genus name is always capitalized.
• A species descriptor is the second part of a scientific name.
– always lowercase
– May refer to a trait of the
species, scientist who first
Tyto alba
described it or native location
White barn owl
17.1 The Linnaean System of Classification
Advantages
• Scientific names help scientists to communicate.
– Some species have very similar common names.
– Some species have many common names.
17.1 The Linnaean System of Classification
Linnaeus’ classification system has seven levels.
• Each level is
included in the
level above it.
• Levels get
increasingly
specific from
kingdom to
species.
17.1 The Linnaean System of Classification
Seven levels of classification
•
•
•
•
•
•
•
Kingdom
Phylum/Division
Class
Order
Family
Genus
Species
17.1 The Linnaean System of Classification
The Linnaean classification system has limitations.
• Linnaeus taxonomy doesn’t account for molecular
evidence.
– The technology didn’t exist during Linneaus’ time.
– Linnaean system based only on physical similarities.
17.1 The Linnaean System of Classification
• Physical similarities are
not always the result of
close relationships.
• Genetic similarities more
accurately show
evolutionary relationships.
Red panda →
More related to raccoons
17.1 The Linnaean System of Classification
Cladistics is classification based on common ancestry.
• Phylogeny is the evolutionary history for a group of species.
– evidence from living species, fossil record, and molecular
data
– shown with branching tree diagrams
17.1 The Linnaean System of Classification
17.1 The Linnaean System of Classification
• Cladistics is a common method to make evolutionary trees.
– classification based on common ancestry
– species placed in order that they descended from
common ancestor
17.1 The Linnaean System of Classification
• A cladogram is an evolutionary tree made using
cladistics.
– A clade is a group of species that shares a common
ancestor.
– Each species
in a clade
shares some
traits with the
ancestor.
– Each species
in a clade has
traits that have
changed.
17.1 The Linnaean System of Classification
• Derived characters are traits shared in different degrees by
clade members.
1 Tetrapoda clade
– basis of arranging
species in
cladogram
– more closely
related species
share more
derived characters
– represented on
cladogram as hash
marks
2 Amniota clade
3 Reptilia clade
4 Diapsida clade
5 Archosauria clade
FEATHERS &
TOOTHLESS
BEAKS.
SKULL OPENINGS IN
FRONT OF THE EYE &
IN THE JAW
OPENING IN THE SIDE OF
THE SKULL
SKULL OPENINGS BEHIND THE EYE
EMBRYO PROTECTED BY AMNIOTIC FLUID
FOUR LIMBS WITH DIGITS
DERIVED CHARACTER
17.1 The Linnaean System of Classification
• Nodes represent
the most recent
common ancestor
of a clade.
CLADE
1 Tetrapoda clade
2 Amniota clade
3 Reptilia clade
4 Diapsida clade
• Clades can be
identified by
snipping a branch
under a node.
5 Archosauria clade
FEATHERS AND
TOOTHLESS
BEAKS.
SKULL OPENINGS IN
FRONT OF THE EYE AND
IN THE JAW
OPENING IN THE SIDE OF
THE SKULL
SKULL OPENINGS BEHIND THE EYE
EMBRYO PROTECTED BY AMNIOTIC FLUID
NODE
FOUR LIMBS WITH DIGITS
DERIVED CHARACTER
17.1 The Linnaean System of Classification
Clades can be identified by snipping a branch under a
node.
• Molecular data may confirm classification based on
physical similarities.
• Molecular data may lead scientists to propose a new
classification.
• DNA is usually given the last word by scientists.
17.1 The Linnaean System of Classification
Molecular clocks use mutations to estimate evolutionary
time.
• How they work
Mutations add up at a constant rate in related species.
– This rate is the ticking of the molecular clock.
– As more time passes, there will be more mutations.
Mutations add up at a fairly
constant rate in the DNA of
species that evolved from a
common ancestor.
DNA sequence from a
hypothetical ancestor
Ten million years later—
one mutation in each lineage
Another ten million years later—
one more mutation in each lineage
The DNA sequences from two
descendant species show mutations
that have accumulated (black).
The mutation rate of this
sequence equals one mutation
per ten million years.
17.1 The Linnaean System of Classification
• Scientists estimate mutation rates by linking molecular
data and real time.
– an event known to separate species
– the first appearance of a species in fossil record
17.1 The Linnaean System of Classification
Mitochondrial DNA and ribosomal RNA provide two types
of molecular clocks.
• Different molecules have different mutation rates.
– higher rate, better for studying closely related species
– lower rate, better for studying distantly related species
17.1 The Linnaean System of Classification
• Mitochondrial DNA is used to study closely related
species.
– mutation rate ten times faster than nuclear DNA
– passed down unshuffled from mother to offspring
grandparents
mitochondrial
DNA
nuclear DNA
parents
Mitochondrial DNA is
passed down only from
the mother of each
generation,so it is not
subject to recombination.
child
Nuclear DNA is inherited from both
parents, making it more difficult to
trace back through generations.
17.1 The Linnaean System of Classification
• Ribosomal RNA is used to study distantly related species.
– many conservative regions
– lower mutation rate than most DNA
17.1 The Linnaean System of Classification
Classification is always a work in progress.
• The tree of life shows our most current understanding.
• New discoveries can lead to changes in classification.
– Until 1866: only two kingdoms,
Plantae
Animalia and Plantae
Animalia
17.1 The Linnaean System of Classification
Classification is always a work in progress.
• The tree of life shows our most current understanding.
• New discoveries can lead to changes in classification.
– Until 1866: only two kingdoms,
Plantae
Animalia and Plantae
Animalia
– 1866: all single-celled
Protista
organisms moved to
kingdom Protista
17.1 The Linnaean System of Classification
Classification is always a work in progress.
• The tree of life shows our most current understanding.
• New discoveries can lead to changes in classification.
– Until 1866: only two kingdoms,
Plantae
Animalia and Plantae
Animalia
– 1866: all single-celled
Protista
organisms moved to
kingdom Protista
– 1938: prokaryotes moved
to kingdom Monera
Monera
17.1 The Linnaean System of Classification
Classification is always a work in progress.
• The tree of life shows our most current understanding.
• New discoveries can lead to changes in classification.
– Until 1866: only two kingdoms,
Plantae
Animalia and Plantae
Animalia
– 1866: all single-celled
Protista
organisms moved to
kingdom Protista
– 1938: prokaryotes moved
to kingdom Monera
– 1959: Fungi moved
to own kingdom
Monera
Fungi
17.1 The Linnaean System of Classification
Classification is always a work in progress.
• The tree of life shows our most current understanding.
• New discoveries can lead to changes in classification.
– Until 1866: only two kingdoms,
Plantae
Animalia and Plantae
Animalia
– 1866: all single-celled
Protista
organisms moved to
kingdom Protista
– 1938: prokaryotes moved
to kingdom Monera
Archea
– 1959: fungi moved to
Fungi
own kingdom
Eubacteria
– 1977: kingdom Monera
split into kingdoms Eubacteria and Archaebacteria
17.1 The Linnaean System of Classification
1977: Carl Woese discovered two genetically different
groups of prokaryotes, based on rRNA studies of
prokaryotes
• He proposed creating 3 domains above the kingdom level.
– domain model more clearly shows prokaryotic diversity