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NATURAL SELECTION
Ch. 22
PRESENT: ~10,000,000 SPECIES EXTANT
RECENT PAST: EXTINCTION
Carolina Parakeet (1918)
Golden Toad (1989)
Baiji River Dolphin (2002)
P. Ibex (2000)
Ivory-billed (1940)
Quagga (1870)
PAST: ~5,000,000,000 SPECIES EXTINCT
SPECIES CHANGES OVER TIME
FUTURE: SPECIES CONTINUE TO EVOLVE
EVOLUTIONARY
THOUGHT
Ch 22.1
GORGES CUVIER’S CONTRIBUTION
 1796: Fossil Record
 Living elephant jaw vs. fossil (mammoth & mastodon) jaws
 The deeper the fossils, the more dissimilar to living organisms
JAMES HUTTON’S CONTRIBUTION
 1795: Gradualism
 profound geological change occurs through slow/continuous process
CHARLES LYELL’S CONTRIBUTION
 1830: Uniformitarianism
 geologic processes of today are the same as in the past
BIG PICTURE
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Layers of the Earth show a consistently aging planet
Organisms living during the past have been preserved
Nearly all fossilized species are extinct
Therefore: life evolves as the environment changes
LAMARCK'S CONTRIBUTION
 Mechanism: Use and disuse & acquired characteristics
CHARLES DARWIN’S CONTRIBUTION
 Mechanism: Natural Selection
ALFRED WALLACE’S CONTRIBUTION
 Mechanism: Natural Selection
 Co-published w/ Darwin
DARWIN EXPLAINS
NATURAL SELECTION
Ch 22.2
DARWIN’S LIFE
 1809-1831
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Lived in England & fascinated with nature
Went to school to became a physician
Dropped out (disgusted by surgery)
Became a clergyman
 1831-1836
 Invited on the HMS Beagle
 Hydrographic survey of South America
DARWIN OBSERVES
 Documented
 Kept a Journal: The Voyage of the Beagle
 Collected
 Thousands of plants, animals, & fossils
ON THE ORIGIN OF SPECIES
 1836-1859
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Thinks about the voyage, animal/plant collection, fossils, geology…
Begins to describe the most revolutionary idea in biology
Receives a letter from colleague Alfred Wallace with same idea
They publish their idea together
Then Darwin finishes his book
WE CHANGE ORGANISMS
 Artificial Selection:
 humans modify species over many generations by selecting and
breeding individuals with desired traits
 https://www.youtube.com/watch?v=aDmzzREXI_g
 http://www.hhmi.org/biointeractive/dog -breeding
WE CHANGE ORGANISMS
OBSERVATIONS FROM THE VOYAGE
 Galapagos islands, while close to each other, contained:
 Various ecosystems
 Organisms similar to, but different from each other
 Each had adaptations to fit the environment
OBSERVATIONS
1. For any species, population sizes would increase
exponentially if all individuals born reproduce successfully
2. Populations tend to be stable in size, except for seasonal
fluctuations
3. Resources are limited
INFERENCE #1
 Production of more individuals than the environment can
support leads to a struggle for existence among individuals of
a population, with only a fraction of their of fspring surviving
OBSERVATIONS
4. Members of a population vary extensively in their
characteristics
5. Much of this variation is heritable
INFERENCE #2
 Survival depends in part on inherited traits; individuals whose
inherited traits give them a high probability of surviving and
reproducing are likely to leave more of fspring than other
individuals
INFERENCE #3
 This unequal ability of individuals to survive and reproduce
will lead to a gradual change in a population, with favorable
characteristics accumulating over generations
SUMMARY OF EVOLUTION BY NATURAL
SELECTION
 Organisms better suited to the environment are more likely to
survive & reproduce than organisms less suited to the
environment
Mutation  Variation  Selection
Individuals do NOT change; populations change
EVOLUTION BY NATURAL SELECTION
There is a
grandeur in this
view of life…
CARL SAGAN EXPLAINS EVOLUTION
 http://www.youtube.com/watch?v=gZpsVSVRsZk