1. Evidence for Evolution
SBi3U BioLogy

2. What lines of Evidence help us understand Evolution?
Fossils
Anatomy
Embryology
Biogeography
Biochemistry
Artificial Selection

3. The FossiL Record
Fossils = mineralized remains of organisms, or their imprints.
Form only under very specific conditions!

4. The FossiL Record
Impression fossils form when an organism dies, and before entirely decomposing is covered by silt, mud or ash.
The flesh decomposes inside this casing of minerals, leaving a ‘negative imprint’
Parts of the organism may mineralize

5. The FossiL Record
Cast fossils start off similarly, but large, tough structures such as bones remain after decomposition.
Over time, minerals seep in, replacing the CaPO4 in the bones.
The remains are now petrified, or ‘made of stone’.
A fossil is really a rock shaped like an organism.

6. The FossiL Record
Paleontologists can place fossils by their location in specific strata
Stratigraphy = study of fossils in strata
Deeper strata = older fossils = more unusual organisms
Some fossils tend to be found in certain minerals (granite, limestone…)
Others can be linked to other species; this is called faunal correlation

7. The FossiL Record In Darwin’s time, fossils were a new thing
Tangible evidence of change over time
For some organisms, we have a very complete & continuous fossil record; for example, the horse.
Virtually any organism can fossilize, from microbes through plants to animals.

8. Example: Horses

9. Example: The Felidae

10. Example: Elephants

11. Fossil Problems
Fossilization needs a specific set of conditions; if not everything fossilizes, what have we missed?
Incomplete or fragmented fossil records: we have some fossils in some strata, then none in several others…what was in the gap?
Limited numbers of fossils: only one of a certain type of fossil is found; does it accurately represent the whole species?

12. Comparative Anatomy Similar body structures indicate similar origins
Homologous Organs: similar structure, different use (related!)
Analogous organs: same use, different structure. (not related!)
Vestigial organs: still present, function lost; i.e. appendix & coccyx in humans; hip bone in whales.

13. Homologous Organs

14. Analogous Organs
homologous
analogous

15. Vestigial Organs

16. Plesiomorphies & Synapomorphies

17. Embryology
Vertebrate embryos all start out very similar, then diverge in form
The longer the similarity lasts, the more closely related two organisms are.
In Darwin’s time, they thought embryonic development was a ‘mini-evolution’ of sorts
‘Ontogeny recapitulates Phylogeny’ = Embryo development imitates species evolution

18. Embryology
Ernst Haeckel, 1874

19. Biogeography
Similar environments cause similar selective pressures on species
A selective pressure is any biotic or abiotic factor that influences your survival.
Similar selective pressures direct evolutionary change toward similar adaptations
Parallel evolution
Convergence

20. Biogeography All antelopes, all grassland dwellers… Africa Europe
North America
Asia - India
All antelopes, all grassland dwellers…
Asia - Tibet

21. Biochemistry Darwin didn’t have this technology…too bad!
DNA analysis: Humans & Chimpanzees are 98% similar
Hemoglobin analysis: Human & chimp Hb is identical; human & horse is 80% similar
Cytochrome proteins in the mitochondrion…
Histone proteins in the cell nucleus…

22. Biochemistry: Comparing DNA

23. Biochemistry: Cytochromes

24. Biochemistry: Hemoglobin

25. Artificial Selection
Darwin was a pigeon breeder, so he knew this well!
Domestication: Humans have changed many species by selective breeding.
Demonstrates the possibility for change in much shorter time
Sometimes, the traits we select are not the ones nature would!

26. Example: Corn

27. Example: Cows & Dogs