Homologous Structures

1. Homologous Structures Erica, Nao, Christian and Justine

2. What are Homologous Structures? • Structures derived from a common ancestor or same evolutionary or developmental origin • May not perform the same function but they share a common ancestral origin. • The forelimbs of humans and bats are homologous structures. • Although they are used differently, the basic skeletal structure is the same. • Taken from the same embryonic origin. • Evolution from a common ancestor.

3. These similarities between these structures are evidence that life on Earth has a common ancestor that the present species have evolved from over time. • The common ancestry of the species can be seen in the structure and development of homologous structures, even if their function is different. • The more closely the organisms are related, the more similar the homologous structures between organisms.

4. Evidence for Homologous Structures

5. Pentadactyl Limb

6. What is it? • 5 digits on the hand and foot • Specific pattern of bones. • Typical limb of mammals, birds, reptiles, and amphibians.

7. Origins • Vertebrates (animals with backbones) evolved from primitive amphibians • Amphibians immediate ancestors were fleshy-finned fish. • The limb in amphibians had 3 parts: hand/foot, with five digits (fingers/toes), a lower limb containing two bones, and an upper limb containing one bone. • This pattern has persisted in all terrestrial vertebrates, and aquatic vertebrates such as seals.

8. Animals with pentadactyl limb.

9. Charles Darwin • 'What could be more curious than that the hand of man formed for grasping, that of a mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should all be constructed on the same pattern and should include similar bones and in the same relative positions?’ • Shows how widespread the limb is. Animals completely different from each share the same similarities for different functions.