Transcript The Tree of Life

THE TREE OF LIFE
WHY CLASSIFY?
• We classify to make organisms easier to
study.
• To study the diversity of life, biologists use a
classification system to name organisms and
group them in a logical manner.
• The field of taxonomy allows scientists to
classify organisms and assign each
organism a universally accepted name in
order to study the diversity of life.
LINNAEUS’S SYSTEM OF
CLASSIFICATION
• During the eighteenth century,
Swedish botanist Carolus Linnaeus
developed a two-word naming
system called binomial
nomenclature
• Linnaeus often classified organisms
based on similarities in structures and
details of anatomy
BINOMIAL NOMENCLATURE
• In binomial nomenclature, each species
is assigned a 2-part Latin name
• The name is always written in italics with
the 1st word is always capitilized
• Example: Homo sapiens (humans)
• The 1st part of the name is the genus
and the second part of the name is
unique to each species within that
genus
LINNAEUS’S SYSTEM OF
CLASSIFICATION
• Linnaeus’s system of classification uses 7
taxonomic categories (from largest to
smallest):
• Kingdom – largest & most inclusive
• Phylum – includes many different organisms that
share important characteristics
• Class – composed of similar orders
• Order – composed of similar families
• Family – genera that share many characteristics
• Genus – a group of closely related species
• Species – a group of individuals so similar that they
can breed and produce fit offspring
HUMAN CLASSIFICATION
• Kingdom: Anamalia
• Phylum: Chordata
• Subphylum: Vertebrata
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Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Homo
Species: Homo sapiens
KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos
PROBLEMS WITH TRADITIONAL
CLASSIFICATION
• During Linnaeus’s time, scientists classified organisms
based on their physical appearance…but today…we
know that doesn’t always work.
• Ex: Dolphins  Fish or Mammals?
• Remember Convergent Evolution  sometimes
organisms that are different from each other evolve
similar body structures, due to the change in the
environment.
• This does not mean they need to be classified in the same
group…maybe they only evolved similar body structures!
• These situations make it very difficult for scientists to classify.
EVOLUTIONARY CLASSIFICATION
• Biologists now group organisms into categories
that represent lines of evolutionary descent,
not just physical features
• Evolutionary classification (phylogeny) is the
strategy of grouping organisms together
based on their evolutionary history
TRADITIONAL V/S EVOLUTIONARY
CLASSIFICATION
CLASSIFICATION USING CLADOGRAMS
• To refine evolutionary classification, biologists
now prefer a method called cladistics
• Cladistics considers only those characteristics that
are new characteristics that arise as lineages evolve
over time
• Characteristics that appear in recent parts of a
lineage but not in its older members are called
derived characters
• Characteristics that are shared by all members of a
lineage are ancestral/primitive characters and
should not be used when building cladograms.
• Cladogram – a diagram that shows the evolutionary
relationships among a group of organisms; includes
new characteristics that arise as lineages evolve.
DERIVED CHARACTERISTICS
ANATOMY OF THE CLADOGRAM
Monophyletic group = clade
J
Taxon
I
F G H
C
D
E
Paraphyletic group
Lineage (represents a sequence
of ancestor-descendent
populations)
A B
Node (represents most recent
common ancestor of two or
more taxa)
Synapomorphy (shared derived character)
MONOPHYLETICGROUPS:
include ancestor & all descendents
PARAPHYLETIC GROUPS:
includes ancestor and some, but not
all descendent
MONOPHYLETIC CLADES
• A valid clade is monophyletic signifying that it consists
of the ancestor species and all its descendants.
OUTGROUPS
• Systematists use a method called outgroup
comparison
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To differentiate between shared derived and shared
primitive characteristics
• As a basis of comparison we need to
designate an outgroup
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which is a species or group of species that is closely
related to the ingroup, the various species we are studying
• Outgroup comparison
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Is based on the assumption that homologies present in
both the outgroup and ingroup must be primitive
characters that predate the divergence of both groups
from a common ancestor
PERFORMING OUTGROUP
COMPARISON
OUTGROUP COMPARISONS
• First, look at the animals we are studying and establish
which characteristics that they share & which are unique
to each individual species.
• Then use these derived characters to build your
cladogram.
CELLS
Slug
Catfish
Frog
Tiger
Human
BACKBONE LEGS
HAIR
OPPOSABLE
THUMB
THE THREE-DOMAIN SYSTEM
• Molecular analyses have given rise to the most
current classification system – the Three Domain
System
• The 3 Domain System is the most recent classification system
and includes:
• Bacteria
• Archaea
• Eukarya
DOMAINS ARE BIGGER/MORE INCLUSIVE THAN
KINGDOMS
Domains
Kingdoms
Bacteria
Eubacteria
Archaea
Archaebacteria
Eukarya
Protista
Fungi
Plantae
Animalia
These 2
kingdoms
used to be
combined
into one
called
“Monera”
REMEMBER - THERE ARE 3
METHODS OF CLASSIFYING
ORGANISMS
• The 3 Domain System (most current)
• Bacteria, Archae, & Eukarya
• The 5 Kingdom System (Whittaker)
• Monera, Protista, Fungi, Plantae, Animalia
• The 6 Kingdom System – still used in conjunction
with the 3 domain system
• Archaebacteria, Eubacteria, Protista, Fungi, Plantae,
Animalia
Section 18-3
Classification of Living Things
Go to
Section:
DOMAIN BACTERIA
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Kingdom: Eubacteria
Unicellular
Prokaryotic
Cell wall of peptidoglycan
Autotrophic or heterotrophic
Examples: Streptococcus, E. Coli
DOMAIN ARCHAEA
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Kingdom: Archaebacteria
Unicellular
Prokaryotic
Cell walls w/out peptidoglycan
Autotrophic or heterotrophic
Methanogens & halophiles
DOMAIN EUKARYA
WHITTAKER’S FIVE-KINGDOM SYSTEM
OUR CHANGING VIEW OF BIOLOGICAL DIVERSITY
THE THREE DOMAIN SYSTEM
Describes classification as:
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Not all prokaryotes are closely related (not
monophyletic)
Prokaryotes split early in the history of living
things (not all in one lineage)
Archaea are more closely related to Eukarya
than to Bacteria
Eukarya are not directly related to Eubacteria
There was a common ancestor for all extant
organisms (monophyletic)
Eukaryotes are more closely related to each
other (than prokaryotes are to each other)