Charles Darwin (1809-1882)

1. Charles Darwin(1809-1882) Origin of Species among the most influential texts of this century

2. Charles Darwin (1809-1882) • 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

3. 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

4. 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

5. Influences on Darwin • Geology: Darwin had Lyell’s Principles of Geology on board the HMS Beagle • Lamarck ’s (1744-1829)Theory of Evolution Inheritance of acquired characteristics • Malthus (1766-1834): Competition within species and struggle for survival

6. Influences on Darwin Lyell’s Principles of Geology • 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

7. Influences on Darwin Jean-Baptiste Lamarck (1744-1829) • Proposed most influential mechanism of evolution before Darwin • Inheritance of acquired characteristics • Introduced the idea of adaptation, but got the mechanism wrong http://www.ucmp.berkeley.edu/history/lamarck.html

8. Influences on Darwin Malthus (1766-1834): Essay on the Principles of Population • Competition: not all individuals could survive Rate of population growth >> Rate of increase in food supply • Darwin concluded that individuals that are better adapted would be the ones that survive and leave more offspring

9. Darwin held on to his work on natural selection for 20 yrs without publishing • Alfred Wallace (1823-1913) came up with the idea of natural selection independently • Darwin rushed to publish Origins in 1859 when he learned of Wallace’s work

10. Alfred Russel Wallace(1823-1913) • “On the Tendency of Varieties to Depart Indefinitely from the Original Type” • Based on his work in the Malay Archipelago

11. 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)

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

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

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

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

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

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

18. Darwin • Natural Selection

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

20. Darwin • Natural Selection Selection favors

21. Darwin • Natural Selection Greater Fitness

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

23. 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 isvariationin a population • Individuals better adapted to environment survive • Survivors leave more offspring (“Survival of theFittest”) • Thus,averagecharacter ofpopulationis altered

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

25. 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

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

27. 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)

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