1. The Story of Life on Earth
Unit VI - Evolution
The Story of Life on Earth

2. Introduction to Evolution
What does biological “evolution” mean?
Change in a population of organisms over time
How does this relate to the “origin of life”?
It doesn’t…two different topics!
Much more evidence to support evolution
Remember: science deals with natural world, not belief

3. Introduction to Evolution
How could “life” have started?
Old Idea:
“spontaneous generation” (abiogenesis)…nonliving matter makes living
Disproved by Redi and Pasteur
New Idea:
“biogenesis”…life comes from life

4. Introduction to Evolution
So, then where did the first cells come from?
Early earth
Very hot; volcanoes; violent storms/lightning
Miller & Urey experiment
Under early earth conditions, organic compounds form & group together into “protocells”

5. Introduction to Evolution
But, when did we actually get cells? And how?
Evidence of first cells
3.4 bln yrs ago
Most likely anaerobic bacteria (no O2 in air)
First photosynthetic cells
2.8 bln yrs ago
Increased O2 in atmosphere
Led to ozone layer that protects from UV rays = more cells
cells could make ATP better with aerobic respiration

6. Evolutionary Theory Charles Darwin (1809-1882)
“father” of evolutionary theory
1831 spent 5 years on HMS Beagle
Visited the Galapagos Islands were he made observations that would inspire his work
1859 published “On the Origin of Species by means of Natural Selection”

7. Darwin’s Big Idea Natural Selection/Survival of the Fittest
Organisms best suited for their environment are more likely to survive and reproduce, passing on the characteristics which helped them survive to their offspring. Gradually leading to change in the population over time.

8. Darwin’s Idea How did Darwin form ideas about evolution?
Fossils showed organisms changed over time

9. Darwin’s Idea How did Darwin form ideas about evolution?
Geologists showed that earth was very old

10. Darwin’s Idea How did Darwin form ideas about evolution?
Malthus noticed populations grow faster than their food supplies (they produce too many offspring)

11. Darwin’s Idea How did Darwin form ideas about evolution?
Artificial selection (breeding) has brought about many changes or modifications to species

12. Darwin’s Idea How did Darwin form ideas about evolution?
He saw diverse species (ex: finches on Galapagos Islands, all with variations isolated on each island)

13. Darwin’s Ideas What did Darwin conclude about populations?
He identified that populations change due to “natural selection” (nature selects who goes on)

14. Darwin’s Ideas What did Darwin conclude about populations?
Four assumptions:
Populations produce large #’s of offspring (more than can survive with given food)
Individuals in population have variations
Certain variations are more useful (these will survive better)
Over time, “good” genes prevail in the population, while “bad” ones fade out

15. Evidence for Evolution
What direct evidence supports this theory?
Changes in populations over time
Ex: peppered moth & MRSA

16. Evidence for Evolution
What direct evidence supports this theory?
Structural adaptations
Ex: camouflage

17. Evidence for Evolution
What direct evidence supports this theory?
Structural adaptations
Ex: mimicry

18. Evidence for Evolution
What direct evidence supports this theory?
Physiological changes
Ex: drug-resistant bacteria; MRSA
Ex: pesticide-resistant insects

19. Evidence for Evolution
Is there indirect evidence of evolution?
Fossils
show changes through time

20. Evidence for Evolution
Is there indirect evidence of evolution?
Anatomy

21. Evidence for Evolution
Is there indirect evidence of evolution?
Anatomy
Homologous structures
Similar origin, but may now have different function
Shows common ancestry
Ex: bird wing, whale flipper, human arm

22. Evidence for Evolution
Is there indirect evidence of evolution?
Anatomy
Analogous structures
Similar function, but very different structure
Shows separate development…not related
Ex: bird wing & butterfly wing

23. Evidence for Evolution
Is there indirect evidence of evolution?
Anatomy
Vestigial structures
A part that no longer serves a purpose
Ex: snake hip bones; human wisdom teeth

24. Evidence for Evolution
Is there indirect evidence of evolution?
Embryology
Early similarities may show relation

25. Evidence for Evolution
Is there indirect evidence of evolution?
Embryology
Early similarities may show relation

26. Evidence for Evolution
Is there indirect evidence of evolution?
Embryology

27. Evidence for Evolution
Is there indirect evidence of evolution?
Biochemistry
Similar chemicals in most life forms (DNA, ATP)
More similarities in genetic code means closer relationship

28. Mechanisms of Evolution
Can individuals evolve?
No!!!
An organism is born with the only genes it will ever have. These cannot be changed in that individual.
Only populations can evolve.
This occurs when there are changes in the gene frequencies (in the population)
Gene pool = sum of all genes in population

29. Mechanisms of Evolution
How do populations evolve?
Any factor that affects genes in gene pool may disrupt equilibrium…leads to change (evolution)
Mutations may cause a shift (due to chance).
Genetic drift may cause changes…especially in small isolated populations.
Gene flow – immigration/emigration into or out of population
Large populations not as affected by these factors

30. Modes of Selection

31. Stabilizing Selection
Pushes to average
Ex: cactus with few spines eaten by animals more; cactus with too many spines invaded by more parasites

32. Diversifying Selection
Pushes toward both extremes
Ex: small beak for soft seeds; large beak for hard seeds; medium beak is bad at both types of seeds so selected against

33. Directional Selection
Pushes toward ONE extreme or the other
Ex: in dry years, beak size pushed to larger

34. Mechanisms of Evolution
How do species evolve?
Called “speciation” - the development of a new species (members of same species can breed)
For speciation to occur…there are a few things that have to happen…
Geographic isolation
keeps individuals apart so cannot interbreed…over time they develop different traits (Ex: finches on islands)

35. Mechanisms of Evolution
How do species evolve?
Called “speciation” (same species can breed)
Geographic isolation

36. Mechanisms of Evolution
How do species evolve?
After geographic isolation …
Reproductive isolation
no longer capable of interbreeding (timing, parts, gametes differ,…)

37. Mechanisms of Evolution
How fast can species evolve?
Gradualism
Speciation occurs over long periods of time with gradual changes (takes millions of years)
Punctuated equilibrium
Speciation occurs in quick bursts with equilibrium in between (~10,000 years or less)

38. Mechanisms of Evolution
How fast can species evolve?

39. Mechanisms of Evolution
Does evolution show patterns?
Divergent evolution
Ancestral species evolves into many species that fit different habitats
Ex: finches; common on islands

40. Mechanisms of Evolution
Does evolution show patterns?
Convergent evolution
Distantly related organisms end up with similar traits
Occurs when have similar habitats
Ex: cactus in N. American & euphorbias in African deserts

41. Mechanisms of Evolution
Does evolution show patterns?
Convergent evolution

45. The End

46. Quiz – Evolution for use with Questions 1 & 2

47. Quiz – Evolution for use with Questions 3-5

48. Quiz – Evolution for use with Question 6

49. Quiz – Evolution for use with Question 7