1. Evidence of Evolution by Natural Selection
Chapter 21.
Evidence of Evolution by Natural Selection
Dodo bird

3. 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
( )

4. Support for Darwin’s ideas
_______________
change over time
___________________
Homologous structures
Analogous structures
embryology
_________________
measure of common ancestry
________________
induced evolution
Fossil Record
Comparative Anatomy
Molecular Analysis
Artificial Selection

5. 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

6. Formation of sedimentary strata containing fossils
1 Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the ocean floor.
2 Over time, new strata are deposited, containing fossils from each time period.
3 As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion reveals strata and fossils.
Younger stratum with more recent fossils
Older stratum with older fossils

7. A gallery of fossil types
(a) Dinosaur bones being excavated from sandstone
(g) Tusks of a 23,000-year-old mammoth, frozen whole in Siberian ice
(e) Boy standing in a 150-million-year-old dinosaur track in Colorado
(d) Casts of ammonites, about 375 million years old
(f) Insects preserved whole in amber
(b) Petrified tree in Arizona, about 190 million years old
(c) Leaf fossil, about 40 million years old

8. Fossil record Today’s organisms descended from ancestral species
Support for a very old earth

9. A dragonfly fossil from Brazil, more than 100 million years old

10. 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 10

11. Evolutionary Change in Horses

12. Where are the Intermediates?
Land Mammal ?
Where are the Intermediates?
There are innumerable intermediate & transitional forms
Wales as land creatures returning to other water….
Where are the intermediate forms of whale ancestors?
Cartoon making fun of this idea.
The cartoons disappeared years 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.

13. A transitional fossil linking past and present
Oh. Here they Are!

14. 2006 Fossil Discovery of Early Tetrapod
Tiktaalik
“missing link” from sea to land animals 14

16. Burgess Shale

17. Burgess Shale British Columbia
505 million years ago (Cambrian Explosion)
Period when animals rapidly diversified in body plan/anatomical feature
_________________
Taphonomic window

23. Anatomical record Homologous structures
similarities in characteristics resulting from _______________
common ancestry 23

24. Homologous structures
Similar _________
Similar ____________
Different _________
Evidence of close evolutionary relationship
_______ common ancestor
structure
development
functions
recent 24

25. Homologous structures
spines
leaves
succulent leaves
tendrils
needles
colored leaves 25

26. Don’t be fooled by their looks!
Analogous structures
Separate evolution of structures
similar ____________
similar ________________
_____________ internal structure & development
different_________
no ______________________
structure
external form
different
origin
evolutionary relationship
Don’t be fooled by their looks!
Solving a similar problem with a similar solution 26

27. Analogous structures 3 groups with wings
flight evolved 3 separate times =
evolving similar solutions to similar “problems”
Analogous structures
3 groups with wings
does this mean they have a recent common ancestor?

28. & sleek bodies are analogous structures!
Convergent evolution
Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to life in ______ environments
not closely related
similar
Those fins & tails
& sleek bodies are analogous structures! 28

29. Parallel Evolution marsupial mammals placental mammals
Convergent evolution in common niches
Similar ecological roles in ________environments, Similar adaptations were selected
but are not closely related
different
marsupial
mammals
placental
mammals 29

30. Convergent evolution of analogous burrowing characteristics
marsupial mole
placental mole

31. 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 31

32. Vestigial organs
Structures that serve _________________
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
little or no functions 32

33. Vestigial organs Hind leg bones on whale fossils
Why would whales have pelvis & leg bones if they were always sea creatures? 33

34. 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. 34

35. Anatomical similarities in vertebrate embryos
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo

36. Why compare these genes?
Molecular record
Comparing DNA & protein structure
universal genetic code!
DNA & RNA
compare common genes
cytochrome C (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
A molecular record of evolutionary relationships 36

37. Comparison of a protein found in diverse vertebrates
Species
Human
Rhesus monkey
Mouse
Chicken
Frog
Lamprey
14%
54%
69%
87%
95%
100%
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide

38. 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 38

39. Building “family” trees
Closely related species (branches) share same line of descent until their divergence from a common ancestor 39

40. “descendants” of wild mustard “descendants” of the wolf
Artificial selection
Artificial breeding can use variations in populations to create vastly different “________” & “__________”
breeds
varieties
“descendants” of wild mustard
“descendants” of the wolf 40

41. It’s Important To
Remember How Powerful
And Fast Selection
Can Be!!!

42. Natural selection in action
Insecticide & drug resistance
insecticide doesn’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. 42

43. Evolution of drug resistance in HIV
Patient
No. 1
Patient No. 2
Patient No. 3
Percent of HIV resistant to 3TC
Weeks

44. Evolution Misconceptions
A Brief Discussion

45. Evolution is not goal-oriented
An evolutionary trend does not mean that evolution is goal-oriented.
Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well
Remember that for humans as well!
Evolution is not the survival of the fittest. Rather it is the survival of the just good enough. 45

46. "Nothing in biology makes sense except in the light of evolution."
Theodosius Dobzhansky: Integrating Genetics and Evolution
Theodosius Dobzhansky, a Russian geneticist who moved to the United States, provided laboratory evidence for natural selection and variation where previously there had been only field observation. Dobzhansky's work with Drosophila, or fruit flies, provided new evidence that supported Darwin's theory that natural selection, acting on genetic variation in populations, is a driving force in evolution.
-- Theodosius Dobzhansky March 1973
Geneticist, Columbia University
( ) 46

47. I might be dead, but Perhaps you children would appreciate a bit of what you call the “rap” music?!?

48. Just Because Things Seem Obvious
Doesn’t Mean They Don’t Need To Be Supported

49. Peppered Moths Dark vs. light variants Year % dark % light 1848 5 95 49

50. Peppered moth What was the selection factor?
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 50

51. Genome sequencing
What can whole genome sequence data tell us about evolution of humans?

52. Primate Common Ancestry?
Chromosome Number in the Great Apes (Hominidae)
orangutan (Pogo) 48
gorilla (Gorilla) 48
chimpanzee (Pan) 48
human (Homo) 46
Could we have just lost a pair of chromosomes?
Hypothesis: Change in chromosome number?
If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

53. Chromosomal fusion
Testable prediction: If common ancestor had 48 chromosomes (24 pairs), then humans carry a fused chromosome (23 pairs).
Ancestral Chromosomes
Fusion
Homo sapiens
Chromosome Number in the Great Apes (Hominidae)
orangutan (Pogo) 48
gorilla (Gorilla) 48
chimpanzee (Pan) 48
human (Homo) 46
Inactivated centromere
Telomere sequences
Testable! This is what makes evolution science & not belief!
Centromere
Telomere

54. Test of the Human Genome
Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.
Ancestral Chromosomes
“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1, where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22. 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.”
Fusion
Homo sapiens
Inactivated centromere
Telomere sequences
Well I’ll be a monkey’s …or an ape’s… uncle!
Chr 2
Human Chromosome #2 shows the exact point at which this fusion took place

55. Geographic variation in chromosomal mutations1
2.4
3.14
5.18 6
7.15 XX 19
13.17
10.16
9.12
8.11
2.19
3.8
4.16
5.14
6.7
15.18
11.12
9.10

56. 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

57. Any Questions?? 57

58. 1. A complete fossil record
Exists because of the great preservation in ocean sediment
Exists because of the solidification of minerals around organisms
Is available because of the small location in which all organisms used to live
Exists because organisms that die become embedded in the soil to form rocks
Does not exist

59. 2. The similarity of insect wings and bird wings is an example of
Behavioral adaptations
Geographic isolation
Adaptive radiation
Convergent evolution
Divergent evolution

60. 3. The human appendix is an example of
A balanced polymorphism
Divergent evolution
Convergent evolution
A vestigial structure
A homologous structure

61. One piece of evidence that supports evolution from molecular biology is:
carbohydrate structure
amino acid sequence
lipid composition
nucleotide structure
cellulose chains

62. Any Questions?? 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