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Chapter 15
Tracing Evolutionary History
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
PHYLOGENY AND
THE TREE OF LIFE
© 2012 Pearson Education, Inc.
Phylogenies based on homologies reflect
evolutionary history
 Phylogeny is the evolutionary history of a species.
 Phylogeny can be inferred from
– the fossil record,
– morphological homologies, and
– molecular homologies.
© 2012 Pearson Education, Inc.
Phylogenies based on homologies reflect
evolutionary history
 Homologies are similarities due to shared
ancestry.
 However, some similarities are analogies
 due to similar adaptations favored by a common
environment, a process called convergent evolution.
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The Bones Are Homologous, the Wings Are Not
Systematics connects classification with
evolutionary history
 Systematics is a discipline of biology that focuses
on
– classifying organisms and
– determining their evolutionary relationships.
 Carolus Linnaeus introduced taxonomy, a system
of naming and classifying species.
 Biologists use phylogenetic trees to depict
evolutionary history of species
Animation: Classification Schemes
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Figure 15.15A
Species:
Felis catus
Genus: Felis
Family: Felidae
Order: Carnivora
Class: Mammalia
Phylum: Chordata
Kingdom: Animalia
Bacteria
Domain: Eukarya
Archaea
Reading and constructing phylogenetic trees
Shared ancestral characters relate organisms to common ancestors.
TAXA
CHARACTERS
Hair,
mammary
glands
Frog
Iguana
Duck-billed
platypus
Kangaroo
Beaver
Amnion
Frog
0
1
1
1
1
Iguana
Duck-billed
platypus
Amnion
0
0
1
1
1
Gestation
0
0
0
1
1
Long
gestation
0
0
0
0
1
Kangaroo
Hair,
mammary
glands
Gestation
Beaver
Long gestation
Character Table
Phylogenetic Tree
Derived characters distinguish new lineages and form the branch points in
the tree of life
Reading and constructing phylogenetic trees
TAXA
CHARACTERS
Hair,
mammary
glands
Frog
Iguana
Duck-billed
platypus
Kangaroo
Beaver
Amnion
Frog
0
1
1
1
1
Iguana
Duck-billed
platypus
Amnion
0
0
1
1
1
Gestation
0
0
0
1
1
Long
gestation
0
0
0
0
1
Kangaroo
Hair,
mammary
glands
Gestation
Beaver
Long gestation
Character Table
Phylogenetic Tree
 A clade is a monophyletic group of species that
includes the ancestral species and all of its
descendants.
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Phylogenetic trees allow us to make hypotheses
about evolutionary relationships
 The phylogenetic tree of reptiles shows that
crocodilians are the closest living relatives of birds.
– They share numerous features, including
– four-chambered hearts,
– “singing” to defend territories, and
– parental care of eggs within nests.
– These traits were likely present in the common ancestor
of birds, crocodiles, and dinosaurs.
© 2012 Pearson Education, Inc.
Figure 15.16B
Lizards
and snakes
Crocodilians
Pterosaurs*
Common
ancestor of
crocodilians,
dinosaurs,
and birds
Ornithischian
dinosaurs*
Saurischian
dinosaurs*
Birds
Phylogenies based on homologies reflect
evolutionary history
 Phylogeny is the evolutionary history of a species
or group of species.
 Phylogeny can be inferred from
– the fossil record,
– morphological homologies, and
– molecular homologies.
© 2012 Pearson Education, Inc.
Using molecular homologies to establish
evolutionary relationships
 Molecular homologies: DNA or protein sequences are
compared to establish ancestry.
 More recently two species are related the more similar their DNA
sequences should be.
 More distantly related, the more their DNA should have diverged.
 Advantage of molecular homologies:

Can sort out relationships among closely related, or distantly related
species when morphologies alone are difficult or not sufficient
© 2012 Pearson Education, Inc.
Amino Acid Sequences of Cytochrome c
Amino Acid Sequence Alignment
Figure 15.17
Red
panda
Weasel
Raccoon
Giant panda
Spectacled bear
Sloth bear
Sun bear
American
black bear
Asian black
bear
Polar bear
35
30
25
20
15
10
Oligocene
Miocene
Millions of years ago
Pliocene
Pleistocene
Brown bear
Using molecular homologies allows us to understand both
close and distant relationships
 Different genes evolve at different rates.
– DNA coding for ribosomal RNA (rRNA)
– changes slowly and
– is useful for investigating relationships between taxa that
diverged hundreds of millions of years ago.
– Example: fungi vs animals; relationships among prokaryotes
– In contrast, DNA in mitochondria (mtDNA)
– evolves rapidly and
– is more useful to investigate more recent evolutionary events.
– Example: hominid and primate evolution
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Figure 15.17
Red
panda
Weasel
Raccoon
Giant panda
Spectacled bear
Sloth bear
Sun bear
American
black bear
Asian black
bear
Polar bear
35
30
25
20
15
10
Oligocene
Miocene
Millions of years ago
Pliocene
Pleistocene
Brown bear
Assigning time to evolutionary events
 Molecular clocks
– Assumption: genes exhibit a constant rate of change
– Must be calibrated by graphing the number of
nucleotide differences against the dates of evolutionary
branch points known from the fossil record
© 2012 Pearson Education, Inc.
A Molecular Clock of the Protein Hemoglobin
Figure 15.UN05
Outgroup