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 Beagle1831-1836

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 EvolutionDescent 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.

• 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 Theory of EvolutionDescent With Modification

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?

Those individuals that produces the most offspring that survive to reproduction

Mayfly: short life, high fecundity

Sequ

oia:

long

life

, low

fecu

ndit

y

Where is the Evidence?

• Biogeography• Fossil record• Taxonomy• Comparative anatomy• Comparative embryology

• Molecular Biology

Sunbird: Old W

orldH

umm

ingbird: New

World

Darwin’s

Now

human...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...

yeast ...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...

corn...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAAT...

Genetic HomologyA striking confirmation of evolutionary theory

Alfred Russel Wallace1823-1913

Independently derived the theory of evolution by natural selection

Evolution is a Fact!

Natural Selection is a (well-supported) Theory to Explain this

Fact!