1. LECTURE 9: Evidence for Evolution

2. Abandoned The Idea That Species Were Perfect & Unchanging
Observed Significant Variation in All Species Observed
Observed Farmers Use Variation To Improve Crops & Livestock
Called Selective Breeding 2 2

3. What is the difference between natural variation and Artificial Selection?
Differences Among Individuals Of A Species
Artificial Selection
Selective Breeding To Enhance Desired Traits Among Stock or Crops 3 3

4. Natural Variation and Artificial Selection
Key Concept:
In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful 4 4

5. Major Problem in Darwin’s Theory
No mechanism to explain natural selection
How could favorable variations be transmitted to later generations?
With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found . 5 5

6. What is the Evidence of Evolution?
Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In:
The Fossil Record
The Geographical Distribution of Living Species (BIOGEOGRAPHY)
Homologous Structures of Living Organisms
Similarities In Early Development 6 6

7. The Fossil Records
The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record
Paleontologists have discovered fossils of many such transitional forms

8. Fossil Record Earth is Billions of Years Old
Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time 8 8

9. Geographic Distribution of Living Species
Different Animals On Different Continents But Similar Adaptations To Shared Environments 9 9

10. LE 22-17
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Some similar mammals that have adapted to similar environments have evolved independently from different ancestors
Flying
squirrel 10

11. Another example: while the sugar glider and flying squirrel have adapted to the same mode of life, they are not closely related, genetically.
Instead, the sugar glider from Australia is more closely related to other marsupial mammals from Australia than to the flying squirrel, a placental mammal from North America.
The resemblance between them is an example of convergent evolution.
Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 11

12. Evidence for Evolution
Evolutionary relationships are determined from shared characteristics between groups of organisms
What are these characteristics called?
Homologous structures
are those that have the same evolutionary origin but may or may not have similar functions—
has been modified to best suit its particular function in each species.
DIVERGENT EVOLUTION
Analogous Structures: perform same function, evolved separately
CONVERGENT EVOLUTION

13. Homologous Structures13 13

14. Homologous Body Structures
Not All Serve Important Functions
Vestigial Organs
Appendix In Man
Legs On Skinks 14 14

16. What is Divergent Evolution?
Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues
Strong Evidence That All Four-Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor
Help Scientist Group Animals 16 16

17. Convergent Evolution Convergent Evolution:
The evolution of species from different ancestors toward a similar form

18. “New” Evidence for Evolution?
Molecular Biology
Similarities in DNA sequences
Developmental Biology

19. What are Molecular Homologies?
Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor
Ex: Homeobox

20. LE 22-16
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Species
Human
100%
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Frog
54%
Lamprey
14%

21. Similarities in DNA Sequence21 21

22. Similarities In Early Development
Embryonic Structures Of Different Species Show Significant Similarities
Embryo – early stages of vertebrate development 22 22

23. Similarities In Embryonic Development
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development 23 23

24. Evidence for the Theory of Evolution by Natural Selection
Even when homologies are not obvious in adults, they may be quite apparent in embryonic stages
Which one is the human? 24

25. Human Fetus – 5 weeks 25 25

26. Chicken
Turtle
Rat 26 26

27. Evolution of pesticide resistance in response to selection27 27

28. Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV 28 28