1. Evidence of Evolution by Natural Selection
Dodo bird

2. Evidence supporting evolution
Fossil record
transition species
Anatomical record
homologous & vestigial structures
embryology & development
Molecular record
protein & DNA sequence
Artificial selection
human-caused evolution

3. Fossil record Layers of sedimentary rock contain fossils
new layers cover older ones, creating a record over time
fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

4. Fossil Record

5. Fossil record
A record showing us that today’s organisms descended from ancestral species

6. Evolutionary change in horses
550
500
450
Equus
400
350
Body size (kg)
300
250
Merychippus
increase in size, loss of toes, increase in size of molars
20-25 mya grasslands became widespread in Norh America
molars = easer to eat grass
hoof = faster locomotion on grassland
200
Mesohippus
150
Hyracotherium
100 50
Nannippus 60 55 50 45 40 35 30 25 20 15 10 5
Millions of years ago

7. Evolution of birds Archaeopteryx lived about 150 mya
links reptiles & birds
The avian nature of the brain and inner ear of Archaeopteryx (Alonso et al. 2004) - Archaeopteryx, the earliest known flying bird from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. Alonso et al. (2004) investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. A reconstruction of the braincase and endocasts of the brain and inner ear suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. Alonso et al. (2004) concluded that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability.
Smithsonian Museum, Washington, DC

8. Where are the transitional fossils?
Land Mammal ?
Where are the transitional fossils?
There are innumerable intermediate & transitional forms
Whales as land creatures returning to the water….
Where are the intermediate forms of whale ancestors?
Cartoon making fun of this idea.
The cartoons disappeared years ago when this fossil was found.
Ambilocetic natans = “Walking whale who likes to swim”
4-5 intermediate forms all found in last 2 decades
Indus River valley in between India & Pakistan.

9. 2006 Fossil Discovery of Early Tetrapod
Tiktaalik
“missing link” from sea to land animals

10. Study of Paleontology ( Three scientists)
Older sediments are below younger sediments.
Georges Cuvier ( )

11. Gradualism James Hutton (1726-1797) 2005-2006
Earth’s geologic features — profound change formed as product of slow but continuous & cumulative processes

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

13. II. Anatomical record Looking at morphological divergence and morphological convergence

14. morphological divergence
Proof in Homologous structures
Have similarities in characteristics resulting from common ancestry
BUT Diverge into separate species

15. Homologous structures
Similar structure
Similar development
Different functions
Evidence of close evolutionary relationship
recent common ancestor

16. Homologous structures
spines
leaves
succulent leaves
tendrils
needles
colored leaves

17. Example of Morphological divergence (text)
All modern vertebrates share a ‘stem reptile’ who crouched low to the ground (common ancestor)
Descendents of this stem reptile diversified in new habitats and became bird, reptiles, mammals
Its 5-toed limbs became many things

18. Stem reptile: walked crouching on the land

19. Morphological convergence: Proof: Analogous structures
Separate evolution of structures
Look alike in different lineages
But…
different internal structure & development
different origin
no evolutionary relationship
Don’t be fooled by their looks!
Solving a similar problem with a similar solution

20. Example of…Convergent evolution
Flight evolved in 3 separate animal groups
evolved similar “solution” to similar “problems”
Have analogous structures
Does this mean they have a recent common ancestor?

21. Example of Convergent evolution
Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to life in the sea
not closely related
Those fins & tails
& sleek bodies are analogous structures!

22. Parallel Evolution Convergent evolution in common niches marsupial
filling similar ecological roles in similar environments, so similar adaptations were selected
but are not closely related
marsupial
mammals
placental
mammals

23. Parallel types across continents
Niche
Placental Mammals
Australian Marsupials
Burrower
Mole
Anteater
Mouse
Lemur
Flying
squirrel
Ocelot
Wolf
Tasmanian “wolf”
Tasmanian cat
Sugar glider
Spotted cuscus
Numbat
Marsupial mole
Marsupial mouse
Nocturnal
insectivore
Climber
Glider
Stalking
predator
Chasing

24. This is not LaMarck’s loss from “disuse”!
Vestigial organs
Modern animals may have structures that serve little or no function
remnants of structures that were functional in ancestral species
deleterious mutations accumulate in genes for non-critical structures without reducing fitness
snakes & whales — remains of pelvis & leg bones of walking ancestors
eyes on blind cave fish
human tail bone
This is not LaMarck’s loss from “disuse”!

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

26. III. Comparative embryology
Similar embryological development in closely related species
all vertebrate embryos have similar structures at different stages of development
gill pouch in fish, frog, snake, birds, human, etc.

27. Similarity due to: Master Genes (Homeotic genes)
A set of genes that determine development in the embryo
Failure of one of these genes most often leads to devastating results in body plan
These genes are highly ‘conserved’ meaning that they have not changed over evolutionary time.

28. Embryos of many vertebrate species develop in similar ways
Example: All vertebrates go through a stage with four limb buds and a tail

29. Ex. Master Genes and Appendages
DLx gene expression leads to appendages

30. So, what controls where appendages grow on the body?
HOX master gene
When present, it suppresses the activity of Dlx
Example: embryonic pythons – Hox is expressed along the length of snake’s body – no appendages.
Read about this on page 306

32. Why compare these genes?
Molecular record
Comparing DNA & protein structure
universal genetic code!
DNA & RNA
compare common genes
cytochrome C and b (respiration)
hemoglobin (gas exchange)
Why compare these genes? 25 50 75
100
125
Millions of years ago
Horse/
donkey
Sheep/
goat
Goat/cow
Llama/
cow
Pig/
Rabbit/
rodent
Horse/cow
Human/rodent
Dog/
Human/
Human/kangaroo
Nucleotide substitutions
Closely related species have sequences that are more similar than distantly related species
DNA & proteins are a molecular record of evolutionary relationships

33. Comparative hemoglobin structure
Human
Macaque
Dog
Bird
Frog
Lamprey
Why does comparing amino acid sequence measure evolutionary relationships? 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

34. DNA and amino acid sequence differences...
...are greatest among lineages that diverged long ago,
...and less among recently diverged lineages

35. Comparing Cytochrome b Sequences
10 different species compared to the Honeycreeper (bird)
Differences shown in red
They tend to be neutral mutations and do not affect the overall sequence for the cytochrome b protein
(found in cellular respiration)

37. Building “family” trees
Closely related species (branches) share same line of descent until their divergence from a common ancestor

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

39. Example: the Evolutionary Hypothesis of Common Ancestry
Chromosome Numbers in the great apes:
human (Homo) 46 chimpanzee (Pan) 48 gorilla (Gorilla) 48 orangutan (Pogo) 48
Testable prediction:
If these organisms share a common ancestor, that ancestor had either 48 chromosomes (24 pairs) or 46 (23 pairs).

40. Chromosome Numbers in the great apes (Hominidae):
Testable prediction: Common ancestor had 48 chromosomes (24 pairs) and humans carry a fused chromosome; or ancestor had 23 pairs, and apes carry a split chromosome.
Ancestral Chromosomes
Fusion
Homo sapiens
Inactivated centromere
Telomere sequences
Chromosome Numbers in the great apes (Hominidae):
human (Homo) 46 chimpanzee (Pan) 48 gorilla (Gorilla) 48 orangutan (Pogo) 48
Centromere
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
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.
Chr #2 was formed by head to head fusion of 2 primate chromosomes
The centromere that has been inactivated corresponds to chimp chromosome #13
Telomere

41. 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
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
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.
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.

42. IV. Artificial selection
Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties”
“descendants” of wild mustard
“descendants” of the wolf

43. 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.

44. Evolution is "so overwhelmingly established that it has become irrational to call it a theory."
Born in 1904 in Germany, Mayr trained as a medical student but realized he had a greater passion for studying birds and biology. Emigrating to the United States, he became a curator at the American Museum of Natural History, working on bird classification while formulating his key ideas about evolution. In 1942 he published his most important work, Systematics and the Origin of Species. Mayr moved to Harvard University in 1953 and served as director of the school's Museum of Comparative Zoology from 1961 to Since then, he has published a number of books and chapters and received the prestigious Japan Prize for Biology in 1983.
In his landmark 1942 book, Mayr proposed that Darwin's theory of natural selection could explain all of evolution, including why genes evolve at the molecular level. On the stubborn question of how species originate, Mayr proposed that when a population of organisms becomes separated from the main group by time or geography, they eventually evolve different traits and can no longer interbreed.
It's this isolation or separation that creates new species, said Mayr. The traits that evolve during the period of isolation are called "isolating mechanisms," and they discourage the two populations from interbreeding.
Moreover, Mayr declared that the development of many new species is what leads to evolutionary progress. "Without speciation, there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress. The species, then, is the keystone of evolution."
-- Ernst Mayr What Evolution Is 2001
Professor Emeritus, Evolutionary Biology
Harvard University
( )

45. Don’t be a Dodo… Ask Questions!!