1. Possible Modes of Natural Selection
Sexual- leads to differences in the sexes
Diversifying/Disruptive- favors extremes over intermediates
Directional- shifts the variation toward one extreme.
Stabilizing- Leads to reduced variation, uniformity

2. Possible Modes of Natural Selection

3. Evidence of Evolution

4. Evidence of Evolution Fossil records Fossils are more then just bones
Tracks
Insects trapped in tree sap
Impressions of leaves
Animals buried in tar
Fossils become more complex over time
The age of fossils are determined by radioactive dating
Carbon 14 – has a half life of 5,730 years
Earth = 4.6billion yrs old
Oldest fossils=bacteria traces 3.5billion yrs old

5. Evidence of Evolution

6. Nature's Whale Ancestors
Evidence of Evolution
Transition forms
Skeletons showing animals that are similar but change over time and can be dated using radioactive dating and
position in the rock layers.
Nature's Whale Ancestors

7. Evidence of Evolution

8. Evidence of Evolution DNA and protein patterns
If species have changed over time then their DNA should have also changed
Thus more closely related species would have more similar DNA and amino acids
Example of one amino acid sequence humans and chimps are identical, dogs have 91/104 identical and rattlesnakes have 84/104 identical

9. Evidence of Natural Selection
Many species and locations
Peppered moths experiment by Kettlewell

10. Evidence of Natural Selection
Sickle cell anemia
HH – normal / Hh - normal but low blood oxygenation / hh - sick with sickle cell
1/100 have sickle cell (hh) in central Africa
1/500 (African Americans)have sickle cell (hh) in the US
Hh – reduces the risk of catching Malaria but makes it possible to pass sickle cell on to your offspring
In the US it is directional selection against sickle cell
In Africa it is balancing selection

11. Species Formation
Ecological races are populations of the same species that differ genetically to adapt to their conditions

12. Species Formation
Divergence is the increase of these differences over time
At some point they may become a different species
The different races of humans are extremely closely related genetically.

13. Two theories of evolutionary rates
Gradualism
Slow and steady over time
Punctuated equilibrium
Irregular rates
Less transitional species