1. Descent with Modification Darwinian View of Life
Chapter 22

2. Why is Evolution So Controversial?
Often evolution (and science in general) is pitted against religion in “winner take all” stance
Modern debate mostly involves the teaching of evolution rather than the theory itself
And that means mixing science, religion and politics, etc.- --Never an easy combination!
Plenty of misconceptions and confusion surround evolution, adding to controversy

3. 3 Key Observations About Life
Organisms are suited for life in their environments.
Organisms share many characteristics of life (unity).
There is a rich diversity of life.
These observations led Charles Darwin to develop a scientific explanation for these observations.

4. Endless Forms Most Beautiful
Study of biology upended in 1859 when Darwin published The Origin of Species
Darwin proposed: Descent with modification
Species are descendants of ancestral species which were different from present day species
Evolution: change in genetic composition of population from generation to generation

5. Summary of Other Ideas
Many scientists before and during the time of Darwin theorized on what was the cause of the unity and diversity of living organisms
Some ideas supported Darwin’s theories while some did not

6. Intellectual Context of Darwin’s Ideas
1809
Lamarck publishes his
hypothesis of evolution.
1798
Malthus publishes
“Essay on the Principle
of Population.”
1812
1858
Cuvier publishes his extensive studies of vertebrate fossils.
1795
While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection.
Hutton proposes
his principle of
gradualism.
1830
Lyell publishes
Principles of Geology.
Figure 22.2 The intellectual context of Darwin’s ideas.
1790
1870
1809
183136
1859
Charles Darwin
is born.
Darwin travels around the world on HMS Beagle.
On the Origin of Species is published.
1844
Darwin writes his essay on descent with modification.
The Galápagos Islands

7. Not in Darwin’s “Camp” Aristotle viewed species as unchanging
Arranged them on a scala naturae, ladder of permanent “rungs”
Linneaus: Developed taxonomy and the binomial classification system
Believed in a divine placement of organisms in this classification, not necessarily changing either
Cuvier (geologist): Founded of modern paleontology (study of fossils)
Saw that fossils are deposited in strata (layers) of rocks with older layers containing fossils of species that may be extinct now
Believed in catastrophism, the sudden loss of local species due to disasters

8. Lamarck’s Hypothesis of Evolution
Other scientists were thinking about life forms evolving over time
Lamarck hypothesized:
Use and disuse of body parts could change organisms over their lifespan
These changes could be passed to offspring by Inheritance of Acquired Characteristics

9. Lamarck’s Hypothesis of Evolution
Lamarckism unsupported by much of genetic evidence
BUT emerging field of epigenetics may prove to support some of Larmarck’s ideas!

10. Scientists in Darwin’s “Camp”
Hutton and Lyell believed:
Earth’s surface changes from cumulative, SLOW continuous actions still operating today (uniformitarianism)
Strongly influenced Darwin’s thinking
He reasoned the Earth must be much older than previously believed
Also reasoned biological organisms may also have slow, continuous change
Malthus (economist):
Limited resources shape population sizes

11. Voyage of the HMS Beagle
Darwin in 1840, after his return from the voyage
HMS Beagle in port
Great
Britain
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
Figure 22.5 The voyage of HMS Beagle.
AFRICA
PACIFIC
OCEAN
Pinta
Genovesa
Equator
Marchena
Malay Archipelago
Equator
SOUTH
AMERICA
PACIFIC
OCEAN
Santiago
Daphne
Islands
Brazil
Chile
AUSTRALIA
Pinzón
Fernandina
PACIFIC
OCEAN
Andes Mtns.
Isabela
Cape of
Good Hope
Santa
Cruz
Santa Fe
San
Cristobal
Argentina
Tasmania 20 40
Florenza
Española
Cape Horn
New
Zealand
Kilometers

12. Darwin’s Focus on Adaptation
During the voyage, Darwin observed many adaptations:
Inherited characteristics of organisms which increase their survival and reproduction in different environments
Darwin saw how adaptation to environment and the origin of species is closely related
Theorized: Could new species arise from gradual accumulation of adaptations to different environments?

13. Darwin’s Focus on Adaptation
How do adaptations arise? Largely dependent on:
Natural selection: Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

14. Example of Speciation in Galapagos Finches
Figure 22.6 Three examples of beak variation in Galápagos finches.
(a) Cactus-eater
(b) Insect-eater
(c) Seed-eater

15. Artificial Selection
Humans have modified other species by selective breeding for 1000’s of years, a process called artificial selection

16. The Reason Why You Shouldn’t Procrastinate
In 1844, Darwin wrote an essay on natural selection--but did not publicize it
In June 1858, Wallace sent Darwin a paper to review with an almost identical theory of natural selection
Darwin quickly finished The Origin of Species by Means of Natural Selection and published it
Wallace graciously stepped away so now we call it “Darwinism” and not “Wallacism”!

17. Observations of Darwin
Observation #1: Members of a population often vary in their inherited traits

18. Observations of Darwin
Observation #2: All species can produce more offspring than the environment can support
Many offspring fail to survive and reproduce

19. Important Points About Natural Selection
Note that individuals do not evolve; but populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
If everyone is genetically identical, no basis for selection
Adaptations vary with different environments
Single adaptation not preferred for all environments

20. Direct Observations of Evolutionary Change
The bacterium Staphylococcus aureus is commonly found on people
One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen
S. aureus became resistant to penicillin in 1945 and resistant to methicillin in 1961

21. Direct Observations of Evolutionary Change
Methicillin works by inhibiting a protein used by bacteria in their cell walls
But MRSA bacteria use a different protein in their cell walls
When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains
MRSA strains are now resistant to many antibiotics

22. Homology Homology is similarity resulting from common ancestry
Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

23. Mammalian Forelimbs: Homologous Structures
Humerus
Figure Mammalian forelimbs: homologous structures.
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat

24. Embryonic Homologies
Pharyngeal pouches
Figure Anatomical similarities in vertebrate embryos.
Post-anal tail
Chick embryo (LM)
Human embryo
Comparative embryology reveals anatomical homologies not visible in adult organisms

25. Vestigial Structures
Vestigial structures are remnants of features that served important functions in the organism’s ancestors
Common human vestigial structures:
Appendix
Male nipples
Wisdom teeth
Body hair and goosebumps
Ear muscles

26. Evolutionary Tree Branch point Lungfishes Amphibians 1 Tetrapods2
Mammals
Digit- bearing
limbs
Amniotes
Figure Tree thinking: information provided in an evolutionary tree.
Lizards and snakes 3
Amnion 4
Crocodiles
Homologous characteristic 5
Ostriches 6
Birds
Feathers
Hawks and other birds

27. Different Cause of Resemblance: Convergent Evolution
Convergent evolution is the evolution of similar, or analogous, features in distantly related groups
Analogous traits arise when groups independently adapt to similar environments in similar ways
Convergent evolution does not provide information about ancestry

28. Examples of Convergent Evolution
Figure Convergent evolution.

29. Homology vs. Convergent Evolution
Both are evidence of evolution
Analogous features (convergent evolution) share similar function but not common ancestry
Homologous features (homology) share common ancestry but not necessarily similar function