History of Evolutionary Thought

Why is there a diversity of life?

Plato (427-347 B.C.)

• Real World Ideal• Perceived World

Imperfect via Senses

• **No need for evolution because organisms are already perfect.

Aristotle (384-322 B.C.)

• Scala Naturae All life organized on a scale, or ladder, of increasing complexity.

• Organisms are fixed at each “rung”.

• No evolution of species.

Old Testament

• Judeo-Christian culture

• Species individually designed and permanent

• No evolution of organisms

1700 A.D. Europe

• Natural Theology

• Adaptations or organisms evidence organisms were created with purpose.

• Taxonomy Reveal steps of scale of life created by God.

– Linnaeus System we use today

• K, P, C, O, F, G, S

Georges Cuvier (1769-1832)• Paleontology – study of

fossils in France.• Documented changes

in organisms present in each rock layer.

• **Catastrophism – boundary layers caused by local catastrophe and repopulated by organisms migrating in.

James Hutton (1726-1797)

• **Gradualism – geological features are cummulative products of slow, but continuous processes

• Canyons formed by rivers cutting through rocks as observed daily.

Charles Lyell (1797-1875)

• **Uniformitarianism – Geological processes, such as erosion, sediment deposition, volcanoes, earthquakes, have not changed throughout Earth’s history.

Hutton + Lyell to Biology

• 1) Geological change results from slow, continuous actions rather than sudden events and therefore, the Earth must be very old (older than 6000 years as proposed by theologians)

• 2) Very slow and subtle processes persisting over a long period of time can cause substantial change.

End of 1700’s

• Many naturalists suggested that life had evolved along with the evolution of Earth.

Jean Baptiste de Lamark(1744-1829)

• Invertebrate Collection in Paris

• Saw many lines of descent of older to younger fossils leading to modern

• Species move up the ladders to greater complexity

Lamark (cont.)

• Evolution was driven by an innate tendency toward perfection.

• Evolution responded to organisms needs.• Mechanism of Evolution:

– 1) Use and disuse – those parts used extensively to cope with environment enlarged and those not used reduced in size.

– 2) Passing on of Acquired Traits• Traits one develops in one’s lifetime – read,

music

Lamark (cont.)

• Nice theory…No evidence that Acquired Traits can be passed on.– Biceps of Blacksmith, removed tails of mice

• Deserves a lot of credit:– Evolution best explanation for both fossil

record and current diversity of life– Recognition of great age of Earth– Adaptation to Environment as product of

Evolution

Charles Darwin (1809-1882)

• 1) The occurrence of Evolution (Descent with Change) – Unity of life related by descent from some common prototype.

• 2) Mechanism is Natural Selection

Natural Selection

• 1) Species produce more offspring than can survive

• 2) Struggle for survival- limited environmental resources

• 3) Variation within a species – no two humans (except identical twins) alike.

• 4) Those best suited for the environment are selected by nature to produce more offspring.

Darwin (cont.)