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BIOLOGY
Chapter 19
Phylogeny and Systematics
Phylogenetic trees strive to represent
evolutionary history
• Phylogeny is the evolutionary history of a group
of organisms. Phylogenies are based on
common ancestries inferred from fossil,
morphological, and molecular evidence.
• Systematics is utilizing an analytical approach
to understanding the diversity and relationships
of organisms, both present day and extinct.
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Morphological and molecular homologies
• Morphological and
molecular similarities are
often used to determine
phylogenetic histories.
• Organisms that share
similar morphologies or
similar DNA sequences
are likely to be closely
related.
• However, morphological
differences can be great,
while genetic divergence is
small.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Human
gorilla, chimpanzee
common fruit fly
domestic pig
lab mouse
Plant
Roundworm
Yeast
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40
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Tracing Phylogeny

Fossil Record
Fossil record is incomplete
 It is often difficult to determine the phylogeny
of a fossil
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
Homology
Refers to features that stem from a common
ancestor
 Homologous structures are related to each
other through common descent


Analogy

Similarity due to convergence
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Homology vs. Analogy
• Homologous
structures suggest
shared ancestry.
• Analogy is the
result of
convergent
evolution. Similar
environmental
pressures produce
analogous
adaptations.
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CONVERGENT EVOLUTION
and Analogous structures
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DIVERGENT EVOLUTION
and Homologous structures
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Phylogenetic Trees




Systematics is the study of diversity of organisms using
information from cellular to population levels
One goal of systematics is to determine phylogeny
(evolutionary history) of a group
Phylogeny is the evolutionary history of a group of
organisms.
Phylogeny often represented as a phylogenetic tree


A diagram indicating lines of descent
Each branching point:


Is a divergence from a common ancestor
Represents an organism that gives rise to two new groups
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An unexpected family tree
Molecular systematics
has revealed thatdespite appearancesanimals, including
humans, and fungi, such
as mushrooms are more
closely related to each
other than either are to
plants.
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Classification and Phylogeny
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monkeys
apes
common
ancestor
(mobile limbs)
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reindeer
monkeys
apes
common ancestor
(placental mammal)
PHYLOGENETIC
TREE
PHYLOGENY
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Felis
catus
(domestic
cat)
Mephitis
mephitis
(striped
skunk)
Lutra
lutra
(European
otter)
GENUS
Felis
Mephitis
Lutra
FAMILY
Felidae
SPECIES
ORDER
Mustelidae
Canis
familiaris
(domestic
dog)
Canis
lupus
(wolf)
Canis
Canidae
Carnivora
Figure 15.10
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Phylogenetic Trees

Classification lists the unique characters of
each taxon and is intended to reflect
phylogeny

Primitive characters:
Present in all members of a group, and
 Present in the common ancestor


Derived characters:
Present in some members of a group, but
 Absent in the common ancestor

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Cladistics

Members of a species share quite specific
characters.

A character is any structural, chromosomal, or molecular feature
that distinguishes one group from another
• Patterns of shared characteristics can be
depicted in a cladogram.
• Within a phylogenetic tree, a clade is defined as
a group of species that includes an ancestral
species and all its descendants.
• The analysis of how species are grouped into
clades is called cladistics.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Terms Used in Cladistics
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Cladistic Systematics

Cladistics analyze primitive and derived characters and
constructs cladograms on the basis of shared derived
characters.


Arrange taxa into a cladogram
A cladogram is a special type of phylogenetic tree

A clade is an evolutionary branch that includes:




A common ancestor, together with
All its descendent species
It traces the evolutionary history of the group being studied.
Constructing a Cladogram



First step: construct a table of characters of the taxa being
compared.
Any character found in the outgroup as well is a shared primitive
character.
Homologies shared by certain lineages are shared derived
characters.
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A valid clade is monophyletic (“single tribe”)
• Paraphyletic and polyphyletic clades lack
information.
The ancestral species (B)
and all of its descendants
are included in this clade.
Consists of an ancestor (A)
and some, but not all, of the
descendants.
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Lacks the common ancestor (A)
of the species in the group.
Constructing a Cladogram
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tuna
frog
lizard
crocodile
finch
dog
ingroup
chimpanzee
Outgroup is a
species that
is closely
related to the
ingroup, but
is less
closely
related than
any of the
ingroup
Traits

lancelet (outgroup)
Species
mammary glands
hair
gizzard
epidermal scales
amniotic egg
four limbs
vertebrae
notochord in
embryo
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Constructing a Cladogram:
Phylogenetic Tree
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enlarged brain
common ancestor
hair, mammary glands
Amniotic
egg
chimpanzee
long canine teeth
terrier
feathers
gizzard
four limbs
finch
crocodile
epidermal
scales
lizard
vertebrae
frog
common
ancestor
tuna
lancelet (outgroup)
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Parsimony
Cladists are guided by the principle of
parsimony—the minimum number of
assumptions is most logical.
 The best cladogram is one in which the
fewest number of shared derived
characters are left unexplained or that
minimizes the number of assumed
evolutionary changes.
 Reliability of cladograms is dependent on
the knowledge and skill of a investigator.

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SYSTEMATICS AND PHYLOGENETIC BIOLOGY
Phylogenetic systematics connects classification
with evolutionary history
• Aristotle classified life into 14 groups (e.g., mammals, birds,
etc.),
• Ray grouped animals and plants according to how he
thought they were related.
• Systematics dates back to the 18th century with Linnaeus,
and his taxonomic classification of plants and animals.
• Taxonomists assign a two-part name to each species
(binomial nomenclature)
– The first name, the genus, covers a group of related species
– The second name refers to a species within a genus
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• Hierarchical classification
Table 15.10
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Three-Domain System
Domain Eukarya
 Unicellular and multicellular organisms
 Cells with a membrane-bounded nucleus

Sexual reproduction common
 Contains four kingdoms





Kingdom Protista
Kingdom Fungi
Kingdom Plantae
Kingdom Animalia
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Tree of Life Showing The Three Domains
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fungi
animals
plants
EUKARYA
protists
heterotrophic
bacteria
protists
cyanobacteria
BACTERIA
ARCHAEA
common ancestor
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Major Difference of Three Domains
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The Three Domains of Life
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Domain Eukarya
Protists
Paramecium, Paramecium
Domain Eukarya
Kingdom Fungi
Mushroom, Hygrocybe
Domain Eukarya
Kingdom Plantae
Black-eyed Susan, Rudbeckia
Domain Archaea
Methanosarcina
Domain Bacteria
Escherichia
Domain Eukarya
Kingdom Animalia
Grey wolf, Canis
(Bacteria): © David M. Phillips/Visuals Unlimited; (Archaea): © Ralph Robinson/Visuals Unlimited; (Flower): © Ed Reschke/Peter Arnold, Inc.;
(Paramecium): © M. Abbey/Visuals Unlimited; (Mushroom): © S. Gerig/Tom Stack & Associates; (Wolf): © Art Wolf/Stone/Getty Images
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