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AP Biology
Fall 2005
Lecture 21: Darwin’s view of the world
Campbell, Chapter 22.
Introductory Statements: Forget about “Survival of the fittest” (social Darwinism) and think
about these 2 main ideas:
1) Decent with Modification
2) Natural Selection is the mechanism of evolution
a) It’s an editing process, not a creative process
b) It happens over “huge tracts of time”
I. Pre-Darwinian world Views
A. Plato/Aristole (300 B.C.) - Scala Natura, linear hierarchy
B. Carolus Linneaus (1700s) Taxonomy, Classfication of related organisms, nested
heirarchy but the relationships are fixed!
1. Also responsible for binomial nomenclature (e.g. Homo sapiens)
C. 1st clue: Fossil Record showed that there were changes among species
D. Three ways of looking at it (the fossil record):
1. Georges Cuvier: saw changes in fossil record, older dif than younger, some
fossils disappear. Catastrophism. late 1700s
2. James Hutton: Gradualism. 1795
3. Charles Lyell (father of modern Geology): Uniformitarianism
E. Lamark : also looked at the fossil record and saw that organisms
changed throughout history. (1809)
1. “Use it or loose it”: species reflect beneficial traits
2. Mechanism: phenotypic changes can be passed on. Sounds
foolish now, but at least he proposed a mechanism.
II. Darwin’s View
A. Darwin’s “CV”
B. Voyage on the HMS Beagle
C. What he saw
1. Initial observation: different continents have different spp.
2. Temperate S.A. animals have more in common with tropical S.A.
animals than temperate European animals.
2.5
3. Adaptive radiation:
a. Islands have endemic spp. (NOT FOUND ANYWHERE ELSE)
(pg. 442, the end of the intro, but an important pt.)
b. these populations have characteristics ideally suited to
their environment
c. organisms on islands close to the mainland looked more like animals
from the mainlaind that organisms on islands further out. And all
organisms had more in common with mainland animals than with
eachother.
4. Changes were also reflected in the fossil record (traveled with Lyell’s Principles of
Geology)
5. These changes must have happened of over 100s or 1000s of generations.
III. Darwin’s Ideas in a bit more detail
A. Decent with modification: spp. Diverge from a common ancestor:
1. Examples: elephants (Fig. 22.7), lobe finned fish (Tiktolic), segmentation.
B. This all occurs very gradually. (Evolutionary time spans millions of years and 1000s
of generations)
C. Closely related organisms should be taxonomically similar, but these classifications
are in flux. More closey related organisms (spp.) diverged more recently than less
closely related organisms (orders, classes, phyla).
D. Natural Selection (Mayer’s Table)
1. Table 1: Observations 1-5, Examples
2. Table 2: Darwin’s Inferrences, your own words
E. Summary:
1. Differential success in reproduction
2. Natural selection occurs through interaction between the environment and
variability inherent in a population.
3. The product of NS is adaptation of a population to a particular environment.
F. Mr. Reardon’s Take
1. Natural Selection is the editor
2. Time is the driver. This happens over 1000s of generations
3. From Campbell: if an advantage is small, over time the advantageous trait will
accumulate within a population while a disadvantageous trait will disappear. This
is gradualism.
G. In Darwin’s view of the world evolution works on the level of the population.
Individual don’t evolve. Populations evolve, therefore species can evolve.
1. Further, these advantageous traits have to be passed onto successive
generations. How?
IV. Evidence for evolution
A. Artificial selection
B. Insecticides: small dose kills 99.9% of the population, but you select for resistant
strains.
C. Antipbiotics work on the same principle
D. Bacterial Plasmids
E. HIV Resistance
1. 3TC resistant strains replicate more slowly, but if you treat an HIV patient with
3TC you wipe out the non-resitant strains and 3TC strains replicate like mad (see
figure).
F. CAM plants (catus and other desert succulents)
F. Homology
1. Anatomical Homology
2. Vestigial organs
3. Embryological homologies
4. Molecular homology
a. Genetic code
b. amino acids
c. four main biological monomers
d. similar organisms share similar molecules (e.g. B-globin)
G. Biogeography --- adaptive radiation
H. Fossil Record
1. Prokaryotes show up before eukaryotes
2. Common body types (algae, dinoflagelates) show up before more specialized
algae.
3. mosses before ferns, before gymnosperms, before angiosperms
4. Transitional (extinct) spp. Exist.
5. In fact, 99% of every spp. That has existed is no longer extant (living)
V. Why is it called a threory
A. It’s an overarching set of testable hypotheses that show how organisms have
become so diverse yet respond to the environment in similar fashion and retain similar
molecular machinery.
B. Natural Selection is a smoking gun, but it’s not the only force at work. That is the
subject of the next few chapters.
1. EVOLUTIONARY BIOLOGISTS ARE INTERESTED IN…
THE HOW (the process, the mechanisms)
THE Product: adaptation, species survival, species selection, behavior,
mutualism, predator avoidance strategies, etc.)