1. Natural Selection
Ch. 22

2. Present: ~10,000,000 species extant

3. Recent Past: extinction
Ivory-billed (1940)
Carolina Parakeet (1918)
Baiji River Dolphin (2002)
P. Ibex (2000)
Quagga (1870)
Golden Toad (1989)

4. Past: ~5,000,000,000 species extinct

5. Species changes over time

6. Future: species continue to evolve

7. Evolutionary Thought
Ch 22.1

8. Gorges Cuvier’s contribution
1796: Fossil Record
Living elephant jaw vs. fossil (mammoth & mastodon) jaws
The deeper the fossils, the more dissimilar to living organisms

9. James Hutton’s Contribution
1795: Gradualism
profound geological change occurs through slow/continuous process

10. Charles Lyell’s Contribution
1830: Uniformitarianism
geologic processes of today are the same as in the past

11. Big Picture Layers of the Earth show a consistently aging planet
Organisms living during the past have been preserved
Nearly all fossilized species are extinct
Therefore: life evolves as the environment changes

12. Lamarck's contribution
Mechanism: Use and disuse & acquired characteristics

13. Charles Darwin’s contribution
Mechanism: Natural Selection

14. Alfred Wallace’s Contribution
Mechanism: Natural Selection
Co-published w/ Darwin

15. Darwin Explains natural Selection
Ch 22.2

16. Darwin’s Life
Lived in England & fascinated with nature
Went to school to became a physician
Dropped out (disgusted by surgery)
Became a clergyman
Invited on the HMS Beagle
Hydrographic survey of South America

17. Darwin Observes Documented Collected
Kept a Journal: The Voyage of the Beagle
Collected
Thousands of plants, animals, & fossils

18. On the Origin of Species
Thinks about the voyage, animal/plant collection, fossils, geology…
Begins to describe the most revolutionary idea in biology
Receives a letter from colleague Alfred Wallace with same idea
They publish their idea together
Then Darwin finishes his book

19. We change organisms Artificial Selection:
humans modify species over many generations by selecting and breeding individuals with desired traits

20. We change organisms

21. Observations from the voyage
Galapagos islands, while close to each other, contained:
Various ecosystems
Organisms similar to, but different from each other
Each had adaptations to fit the environment

22. Observations
For any species, population sizes would increase exponentially if all individuals born reproduce successfully
Populations tend to be stable in size, except for seasonal fluctuations
Resources are limited

23. Inference #1
Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

24. Observations
Members of a population vary extensively in their characteristics
Much of this variation is heritable

25. Inference #2
Survival depends in part on inherited traits; individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

26. Inference #3
This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations

27. Summary of Evolution by Natural Selection
Organisms better suited to the environment are more likely to survive & reproduce than organisms less suited to the environment
Mutation  Variation  Selection
Individuals do NOT change; populations change

28. Evolution by natural selection
There is a grandeur in this view of life…

29. Carl sagan Explains evolution