1. Evolution, Darwin and Evidence
Descent with Modification: A Darwinian View of Life

2. Evolution
Evolution: the change over time of the genetic composition of populations
Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success)
Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction
November 24, 1859

3. Evolutionary history Linnaeus: taxonomy Hutton: gradualism
Lamarck: evolution
Malthus: populations
Cuvier: paleontology
Lyell: uniformitarianism
Darwin: evolution
Mendel: inheritance
Wallace: evolution

4. Charles Darwin 1809-1882 British naturalist
Proposed the idea of evolution by natural selection
Collected clear evidence to support his ideas
What did Darwin say?
What evidence supports Evolution by Natural Selection?
What impact did Evolution have on biology?

5. Voyage of the HMS Beagle
Invited to travel around the world
(22 years old!)
makes many observations of nature
main mission of the Beagle was to chart South American coastline
Stopped in Galapagos Islands
500 miles off coast of Ecuador
After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world.
FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain.
Darwin noted that the plants and animals of South America were very distinct from those of Europe

6. Darwin found… birds
Collected many different birds on the Galapagos Islands.
Thought he found very different kinds…
Finch?
Finch?
Sparrow?
Woodpecker?
Warbler?
Sparrow?
Woodpecker?
Warbler?

7. But Darwin found… a lot of finches
Darwin was amazed to find out:
All 14 species of birds were finches…
But there is only one species of finch on the mainland!
Large Ground Finch
Small Ground Finch
Sparrow?
How did one species of finches become so many different species now?
Warbler Finch
Veg. Tree Finch
Woodpecker?
Warbler?

8. Darwin’s finches Differences in beaks
associated with eating different foods
survival & reproduction of beneficial adaptations to foods available on islands
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small insectivorous
tree finch
Small ground
finch
Warbler
finch
Large
insectivorous
tree finch
Cactus
eater
Tree finches
Medium ground finch
Ground finches
Insect eaters
Seed eaters
Vegetarian
tree finch
Large ground finch
Bud eater

9. Darwin’s finches Darwin’s conclusions
small populations of original South American finches landed on islands
variation in beaks enabled individuals to gather food successfully in the different environments
over many generations, the populations of finches changed anatomically & behaviorally
accumulation of advantageous traits in population
emergence of different species

10. Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends.

11. Darwin’s finches Differences in beaks allowed some finches to…
successfully compete
successfully feed
successfully reproduce
pass successful traits onto their offspring

12. Correlation of species to food source
More observations…
Correlation of species to food source
Whoa, Turtles, too!

13. Essence of Darwin’s ideas
Natural selection
variation exists in populations
over-production of offspring
more offspring than the environment can support
competition
for food, mates, nesting sites, escape predators
differential survival
successful traits = adaptations
differential reproduction
adaptations become more common in population

14. Evolution evidence: Biogeography
Geographical distribution of species
Examples: Islands vs. Mainland Australia Continents

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

16. 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

17. Evolution evidence: The Fossil Record
Succession of forms over time
Transitional links
Vertebrate descent

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

19. 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

20. 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

21. Evolution evidence: Comparative Anatomy
Homologous structures (homology)
Descent from a common ancestor

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

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

24. 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

25. Vestigial organs
Hind leg bones on whale fossils

26. Evolution evidence: Comparative Embryology
Pharyngeal pouches, ‘tails’ as embryos

27. Evolution evidence: Molecular Biology
Similarities in DNA, proteins, genes, and gene products
Common genetic code
Closely related species have sequences that are more similar than distantly related species
DNA & proteins are a molecular record of evolutionary relationships

28. 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

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

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

31. 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.

32. Final words…...
“Absence of evidence is not evidence of absence.”