1. Homologous and Analogous Structures
Chapter 19
Homologous and Analogous Structures

2. Need to Know
The difference between homologous and analogous structures and how this relates to evolution.
Convergent evolution

3. There are four types of data that document the pattern of 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
Direct observations
Homology
The fossil record
Biogeography 3

4. Homology Evolution is a process of descent with modification.
Homology is similarity resulting from common ancestry.
Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor.
Homologous genes can be found in organisms as dissimilar as humans and bacteria. 4

5. Example of homology
All of these species carry a version of the gene Pac-6 that is used in eye formation. The human version of the gene can be inserted into a fly and still trigger the building of an insect eye.

6. Example of homology
Video clip

7. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor.
Related species can have characteristics with underlying similarity that function differently. 7

8. Example of homologous structures
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat 8

9. Example of homologous structures
Pharyngeal
arches
Post-anal
tail
Comparative embryology reveals anatomical homologies not visible in adult organisms.
Pharyngeal arches intimately develop into structures with vary different functions, such as gills in fishes and parts of the ears and throat in humans and other mammals.
Chick embryo (LM)
Human embryo 9

10. Vestigial structures are remnants of features that served important functions in the organism’s ancestors. 10

11. Vestigial Structure example

12. Vestigial Structure example

13. Example of Convergent Evolution
Convergent evolution is the evolution of similar, or analogous, features in distantly related groups.
Analogous traits arise when groups independently adapt to similar environments in similar ways.
Convergent evolution does not provide information about ancestry.
The wings are analogous. 13

14. Example of Convergent Evolution
Shark (Chondrichthyes) Dolphin (mammal)
The fins and streamlined shape are analogous.

15. Example of Convergent Evolution
NORTH AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
The side flaps of skin are analogous. 15