Transcript Evolution is a Fact!

The Pre-Darwinian Standard
Western World View
• Earth is young (6000 years)
• Earth is unchanged
• Creator (Great Engineer)
designed organisms ‘wisely’
• Different species exist because
of different functions & local
ecological conditions
Pre-Darwinian Challenges to the Classical View
• Stratigraphy suggests an old,
changeable earth
• Fossil organisms provide evidence
that species have disappeared from
their former ranges
• Some organisms must have become
extinct everywhere
• Many more organisms exist than
were known in the classical world
• Organisms can be classified by
anatomical & developmental
resemblances that transcend function
or ecology
Voyage of the Beagle
1831-1836
Darwin learned during his trip
• Geological change uniformitarian (same processes acting today
account for the past)
• Faunas are regional (South America different from Old World tropics)
• Extinct faunas resemble living regional faunas
• Nearby, similar islands have different species
After returning, Darwin learned
• Organisms produce many, many, many more
offspring than survive
• It is easy to modify organisms by artificial
selection - variation is heritable
Darwin after the Voyage of the Beagle
Darwin’s Theory of Evolution
Descent With Modification
• Fertility is so high that populations would
increase exponentially if all offspring survived
• Most species have stable numbers
• Natural resources are finite / limited
• Therefore, there is a struggle for existence, and
only a fraction of offspring survive.
Darwin’s Theory of Evolution
Descent With Modification
• Individuals in a population differ; no two are
exactly alike
• Much of the variation is heritable
• Survival in the struggle for existence is not
random, but tends toward those that have
inherited favorable variations
• Therefore, the unequal ability of individuals to
survive and reproduce leads to gradual
change in a population, with favorable
characteristics increasing in frequency
Darwin’s Main Points in the Origin
of Species
• Species evolve into new species gradually
over time
• All species share one (or a few) common
ancestor
• Natural selection is the mechanism by
which new species evolve (Darwin’s Theory)
Who are the fittest?
Sequoia: long life, low fecundity
Those individuals that produces the most
offspring that survive to reproduction
Mayfly: short life, high fecundity
Darwin’s
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Biogeography
Fossil record
Taxonomy
Comparative anatomy
Comparative embryology
• Molecular Biology
Sunbird: Old World
Now
Hummingbird: New World
Where is the Evidence?
Genetic Homology
A striking confirmation of evolutionary theory
human...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...
yeast ...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...
corn...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...
Alfred Russel Wallace
1823-1913
Independently derived the theory of evolution by
natural selection
Evolution is a Fact!
Natural Selection is a (wellsupported) Theory to Explain this
Fact!