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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 • • • • • 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!
