1. Homologous Structures: Structures that are similar because
they were inherited from a common ancestor

2. The process of evolution isn’t able to completely throw out an old design and start from scratch, it can only modify what is already there

3. The original skeleton was tinkered with over time.
The first Tetrapods evolved into amphibians, then reptiles, then mammals.
The original skeleton was tinkered with over time.

5. AMPHIBIANS
REPTILES

6. DOG
POLAR BEAR
MOUSE

7. COW
DEER
RHINO

8. REPTILE (lizard)
MARSUPIAL (opossum)
PRIMATE (monkey)
RODENT (squirrel)

9. MACAQUE
BONOBO
SAKI MONKEY
SQUIRREL MONKEY
SPIDER MONKEY
LANGUR

12. HUMAN HAND and TIGER PAW

13. MOUSE ARM

14. HOMOLOGOUS PENTADACTYL LIMBS

16. IDENTIFY THE KNEES ON THIS COW

18. Cows don’t have 4 legs, they have two arms and two legs.
They use their wrists and ankles like knees.

23. Some humans walk with elevated ankle bones

24. Homologous structures: have the same basic structure, but can perform different functions, like holding, swimming, or flying.
Example: Human hand and bat wing. The pentadactyl limb was inherited from a common mammal ancestor
Analogous structures: perform the same function, but the underlying structure is different.
Example: Whale fin vs. Shark fin. Whales and sharks did not both get their fins from a common ancestor. Whales evolved them independently as an adaptation for swimming.
Analogous structures evolve due to similar environments, not common ancestors. This is also known as convergent evolution.