Unveiling Evolution: Fossil Records & Homologous Structures

1. http://www.johnkyrk.com/evolution.html

2. Palaeontology • Life has existed for more than 500 million years • Very different than today • None of the top predators we have around today were around at the time of the dinosaurs

3. Fossils as evidence for evolution • First organisms were simple in structure (matches the expected sequence) • Life forms have increased in size and complexity • Life forms are constantly changing • Evolutionary dead ends • Punctuated equilibrium vs gradualism

4. Palaeontology many living organisms today have no identical form in the fossil record (Apart from organisms such as certain types of sharks, cockroaches or ferns)

5. Evidence of Evolution • Sequence also fits with ecology of the groups – plants before animals, land plants before land animals, plants suitable for insect pollination before insects • Many known sequences that link together existing organisms with their ancestors (Equus)

6. Evidence of Evolution: Fossil Record • Strong evidence that evolution HAS occurred • Does not reveal mechanism for evolution

7. Cladogram activity

8. Adaptive Radiation

9. Textbook definition: • Emergence of numerous species from a common ancestor into an environment that presents a diversity of new opportunities and challenges  Is this divergent or convergent evolution????

11. Homologous • Similar due to inheritance • Modified structure seen among different groups of descendants

12. Homologous Structures: Tetrapod Limb • They are all built from many individual bones. • They are all spin-offs of the same basic bone layout: one long bone attached to two other long bones.

13. Pentadactyl limbs

14. The difference? • Homologous: look superficially different, serve different purposes but structures are anatomically similar b/c of shared ancestry…not necessarily used the same way…variations on a structural theme…divergent evolution!)

15. Homology: Evidence for Evolution • http://evolution.berkeley.edu/evolibrary/article/similarity_hs_01

16. Analogous: • serve the same function, but not constructed similarly, no common ancestry (an example of convergent evolution)

17. For these four critters, identify and explain whether the structures are homologous, analogous, or neither.

19. Importance of homology to evolution • Similar construction = evidence that organisms in question have a common ancestor…”unity of plan” • Linked to embryological development as well… • Don’t prove anything – but difficult to explain without evolution • Presence of vestigial structures also linked – traces of an organism’s evolutionary history

20. Differing sizes and variations in morphology • Basic shape and position of the limb bones = same • Suggests common ancestry • **Not just limited to structures – also applies to DNA!!! (molecular homologies) • http://www.pbs.org/wgbh/evolution/educators/teachstuds/unit3.html

21. Vestigial Structures

22. Florida Sand Skink

23. Vestigial Structures • A structure of little or no importance to an organism • Historical remnants of structures that had important functions in ancestors. • Evolution MODIFIES existing structures. Anatomical remodeling…

25. Embryological Development • Compare early stages of development • Reveals other homologies not seen in adult forms • Example: vertebrate tails • Example: vertebrate pharyngeal pouches

26. Molecular Homologies • All forms of life use the same genetic machinery of DNA and RNA • Genetic code is universal • Organisms share many genes • Many of the gene products (proteins) are the same too  Analysis of DNA and proteins: as number of similarities increases, do does the degree of relatedness.

27. Human, Chimpanzee, and Gorillas…who is more closely related? Activity