Charles Darwin ( ) Origin of Species among the most influential texts of this century

Charles Darwin ( ) Studied Medicine at Edinburgh Switched to become a clergyman at Christ’s College, Cambridge University Passionate interest in Natural History Reverend (&Professor) John Henslow encouraged him to pursue Biology In 1831 invited as a naturalist on the HMS Beagle, a ship sent by British Navy to chart the waters of South America

HMS Beagle off of South America  When Darwin left on the Beagle Evolution was already a popular idea for explaining the fossil record.  However, there were no known mechanisms  Darwin did not believe in Evolution, but Rev. Henslow gave him a book to take with him: Lyell’s Principles of Geology

Historical Context  By mid-1800s scientific context was in place for development of theory of Evolution.  Developments in Geology : Earth more than 6,000 years old Fossil Record showed change in species over time  The mechanisms for Evolution were missing, and were hotly debated

Influences on Darwin Geology: Darwin had Lyell’s Principles of Geology on board the HMS BeagleGeology: Darwin had Lyell’s Principles of Geology on board the HMS Beagle Lamarck ’s ( ) Theory of EvolutionLamarck ’s ( ) Theory of Evolution Inheritance of acquired characteristics Malthus ( ): Competition within species and struggle for survivalMalthus ( ): Competition within species and struggle for survival

Darwin had Lyell’s book on board the HMS Beagle, given to him by his botany professor, Reverend John Henslow Fossil record: the earth is old many animals that once existed are now extinct there are layers (strata) in the fossil record show a pattern of change Lyell’s Principles of Geology Influences on Darwin

Jean-Baptiste Lamarck ( ) n Proposed most influential mechanism of evolution before Darwin n Inheritance of acquired characteristics n Introduced the idea of adaptation, but got the mechanism wrong

Malthus ( ): Essay on the Principles of Population Influences on Darwin n Competition: not all individuals could survive Rate of population growth >> Rate of increase in food supply n Darwin concluded that individuals that are better adapted would be the ones that survive and leave more offspring

Darwin held on to his work on natural selection for 20 yrs without publishing Alfred Wallace ( ) came up with the idea of natural selection independently Darwin rushed to publish Origins in 1859 when he learned of Wallace’s work

“On the Tendency of Varieties to Depart Indefinitely from the Original Type” Based on his work in the Malay Archipelago Alfred Russel Wallace ( )

Darwin’s Main Points (1) Organisms Evolve (Darwin not first) (2) Common Descent : species arise from common ancestors (3) Gradualism : changes are gradual (still debated) (4) Population Speciation : change in proportions of individuals having a trait in a population (Darwin’s original idea) (5) Natural Selection : mechanism (Wallace also)

***Lamarck vs Darwin*** Lamarck: inheritance of acquired traits (not mutations)-- Individual evolution Evolution at the Population Level

Lamarck Individuals are evolving If you got a tan, you’d pass it on

Lamarck Individuals are evolving If you got a tan, you’d pass it on Balls get tan

Lamarck Individuals are evolving If you got a tan, you’d pass it on Tan balls have offspring that are also tan

Lamarck Individuals are evolving If you got a tan, you’d pass it on Some get more tan

Lamarck Individuals are evolving If you got a tan, you’d pass it on And then pass on their acquired traits

Darwin Natural Selection

Darwin A heritable change (now known as a mutation) Natural Selection

Darwin Selection favors Natural Selection

Darwin Greater Fitness Natural Selection

Darwin Greater Fitness Natural Selection The individuals themselves are not changing, but the population is the unit of evolution

unique Darwin’s unique contribution: Population Speciation as a result of Natural Selection More offspring are produced than can survive Limited resources and competition for resources There is variation in a population Individuals better adapted to environment survive Survivors leave more offspring (“Survival of the Fittest”) Thus, average character of population is altered

"My attention was first thoroughly aroused by comparing together the various specimens... of the mocking-thrush" ~ C. Darwin, The Voyage of the Beagle (1839) Darwin’s Mockingbirds (studied Tortoises and finches later) Galapagos Islands

Darwin’s Mockingbirds  Only one species of mockingbird in South America  But, on each island there was a different species  Mockingbirds on different islands shared traits that suggested a shared common ancestor--and were not independently created Galapagos Islands

So… Darwin did NOT originate the idea of Evolution… … BUT he provided a plausible Mechanism … and much evidence

But, Darwin’s theory was not complete Because Darwin knew nothing about mutation, he had no idea how variability was generated in populations (Lecture 5) Because Darwin knew nothing about genetics or genes, he had no idea how variability was passed on to offspring (Mendel) Darwin did not know about nonadaptive evolutionary forces, such as Genetic Drift (Lecture 3)

Mendel published in 1865… was ignored until 1900Mendel published in 1865… was ignored until 1900 Presented a mechanism for how traits got passed onPresented a mechanism for how traits got passed on “Individuals pass alleles on to their offspring intact” (the idea of particulate (genes) inheritance) Mendel’s work held part of the key to what was missing in Darwin’s Theory