Comparative anatomy provides evidence for evolution through the identification of homologous structures, analogous structures, and vestigial structures. Homologous structures are body parts with similar structures but different functions, indicating a close evolutionary relationship. Analogous structures have similar functions but different structures and no direct evolutionary relationship. Vestigial structures are remnants of structures that had a use in ancestral species but serve little purpose in current species.

1. Evidence of Evolution:
Comparative Anatomy

2. Comparative Anatomy
Similarities in the basic pattern of anatomy is evidence of
inheritance from a common ancestor:
i) Homologous Structures
ii) Analogous Structures
iii) Vestigial Structures

3. Comparative Anatomy
i) Homologous Structures:
• Body parts of different species with similar structures
but different functions.
• Evidence of close evolutionary relationship (recent
common ancestor).

4. Comparative Anatomy Homologous Structures

5. Comparative Anatomy
ii) Analogous Structures:
• Body parts of different species with similar functions
but different structures.
• No evolutionary relationship.
Australian squirrel glider North American chipmunk

6. Comparative Anatomy
Though this marsupial and placental mammal look very
similar, they are distantly related. Their methods of
gestation and birth are analogous.
Australian squirrel glider North American chipmunk
Marsupial Placental mammal

7. Comparative Anatomy Analogous Structures
The coloured bones are homologous.
The thin membrane of an insect's wing is
analogous to feathers or leathery flesh.

8. Comparative Anatomy
iii) Vestigial Structures:
• Structures of little or no use.
• These are remnants of structures in an ancestral
species that had a use for them.
Humans no longer have an inner eyelid - a structure similar to the one on cats -
but we still have the remnants of one (don't worry, she's not hurting the cat).

9. Comparative Anatomy Vestigial Structures on Humans
plica semilunaris
+
goosebumps

10. Comparative Anatomy
iii) Vestigial Structures:
Some whale fossils have hind leg bones.

11. Comparative Anatomy
iii) Vestigial Structures:
The cave fish (on the right) is blind, yet it still has eyes.

12. How is Comparative Anatomy
Evidence of Evolution?