Chapter 19
Homologous and Analogous
Structures
Need to Know
• The difference between homologous and
analogous structures and how this relates to
evolution.
• Convergent evolution
Concept 19.3: Evolution is supported by an overwhelming
amount of scientific evidence
• New discoveries continue to fill the gaps
identified by Darwin in The Origin of Species
• There are four types of data that document the
pattern of evolution
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Direct observations
Homology
The fossil record
Biogeography
Homology
• Evolution is a process of descent with
modification.
• Homology is similarity resulting from
common ancestry.
Example of homology
Example of homology
Video clip
• Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor.
Example of homologous structures
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Example of homologous structures
Pharyngeal
arches
Post-anal
tail
Chick embryo (LM)
Human embryo
• Vestigial structures are remnants of features that
served important functions in the organism’s
ancestors.
• Vestigial Structure example
• Vestigial Structure example
Example of Convergent Evolution
The wings are analogous.
Example of Convergent Evolution
Shark (Chondrichthyes)
Dolphin (mammal)
The fins and streamlined shape are analogous.
Example of Convergent Evolution
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
The side flaps of skin are analogous.