1. Evidence of Evolution by Natural Selection
Chapter 19
Evidence of Evolution by Natural Selection
Dodo bird

2. THINK:
Make a list of all the vestigial structures you can think of. Why do they exist?

3. Vestigial organs
Modern animals may have structures that serve little or no function
remnants of structures that were functional in ancestral species
evidence of change over time
some snakes & whales show remains of the pelvis & leg bones of walking ancestors
eyes on blind cave fish
human tail bone

4. Vestigial organs Hind leg bones on whale fossils
Why would whales have pelvis & leg bones if they were always sea creatures?

5. Comparative embryology
Similar embryological development in closely related species
all vertebrate embryos have a gill pouch at one stage of development
fish, frog, snake, birds, human, etc.

6. Molecular record Comparing DNA & protein structure
universal genetic code!
DNA & RNA
cytochrome C (respiration)
protein structure
hemoglobin (gas exchange)
Evolutionary relationships among species are documented in their DNA & proteins.
Closely related species have sequences that are more similar than distantly related species.

7. Comparative hemoglobin structure
Human
Macaque
Dog
Bird
Frog
Lamprey 8 32 45 67
125 10 20 30 40 50 60 70 80 90
100
110
120
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans

8. Building “family” trees
Closely related species (twigs of tree) share same line of descent until their recent divergence from a common ancestor

9. VIEW: http://www. pbs. org/wgbh/evolution/library/07/3/real/l_073_47

10. What data from whole genome sequencing can tell us about evolution of humans

11. Example: Evolutionary Hypothesis of Common Ancestry
Chromosome Numbers in the great apes:
human (Homo) 46
chimpanzee (Pan) 48
gorilla (Gorilla) 48
orangutan (Pogo) 48
Do we share a common ancestor with apes?
This has the potential of contradicting evolution
There are genetic similarities between humans & apes
But humans have 2 fewer chromosomes (24 pairs vs. 24 pairs)
Where’s the missing chromosome? can’t lose it = lethal
Change in chromosome number?
If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

12. Chromosome Numbers in the great apes (Hominidae):
Ancestral Chromosomes
Chromosome Numbers in the great apes (Hominidae):
human (Homo) 46 chimpanzee (Pan) 48 gorilla (Gorilla) 48 orangutan (Pogo) 48
Fusion
Homo sapiens
Inactivated centromere
Telomere sequences
Centromere
Telomere
Do we share a common ancestor with apes?
Must have been a fusing. So should be able to look at our genome & find the fusing. If we don’t find it then evolution is wrong.
Nifty little markers = centromeres & telomeres. Fusing would put telomeres in the middle of a chromosomes. If we don’t find this then evolution is wrong.
Testable prediction: If common ancestor had 48 chromosomes (24 pairs) then humans carry a fused chromosome; or If common ancestor had 46 chromosomes (23 pairs) then apes carry a split chromosome.

13. Inactivated centromere
Human Chromosome #2 shows the exact point at which this fusion took place
“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16: – ), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).”
Homo sapiens
Inactivated centromere
Telomere sequences
Do we share a common ancestor with apes?
Chr #2 was formed by head to head fusion of 2 primate chromosomes
The centromere that has been inactivated corresponds to chimp chromosome #13
Chr 2
Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

14. In case you had any doubts…

15. “descendants” of wild mustard “descendants” of the wolf
Artificial selection
Artificial breeding can use differences between individuals to create vastly different “breeds” & “varieties”
“descendants” of wild mustard
“descendants” of the wolf

16. THINK:
You’ve heard about MRSA? Methicillin Resistant Staphlococcus aureus.
Based on what you know about how natural selection happens, how might Staph infections (caused by a bacterium, S. aureus) become resistant to the antibiotics we use to kill them?

17. Natural selection in action
Insecticide & drug resistance
insecticide didn’t kill all individuals
resistant survivors reproduce
resistance is inherited
insecticide becomes less & less effective
The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action.
The results of application of new insecticide are typically encouraging, killing 99% of the insects.
However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases.
See:

18. Evolution of Drosophila
All of the 500+ endemic species of Drosophila in Hawaiian archipelago descended from common ancestor that reached Kauai over 5 million years ago

19. Witness to Evolution Peppered Moth dark vs. light variants

20. Peppered moth
Year % dark % light

21. Peppered moth Why did the population change?
early 1800s = pre-industrial England
low pollution
lichen growing on trees = light colored bark
late 1800s = industrial England
factories = soot coated trees
killed lichen = dark colored bark
mid 1900s = pollution controls
clean air laws
return of lichen = light colored bark
industrial melanism

22. Unity & Diversity
Only evolution explains both the unity & diversity of life
By attributing the diversity of life to natural causes rather than to supernatural creation, Darwin gave biology a strong, scientific, testable foundation

23. Any Questions??

24. Older sediments are below younger sediments.
Study of Paleontology
Older sediments are below younger sediments.
Georges Cuvier ( )

25. Gradualism James Hutton (1726-1797)
Earth’s geologic features — profound change formed as product of slow but continuous & cumulative processes

26. Uniformitarianism Charles Lyell (1797-1875)
geologic processes have not changed throughout Earth’s history
Conclusion: Earth must be much older than 6,000 years

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