In historical context

1. In historical context • Other people’s ideas paved the path for Darwin’s thinking competition: struggle for survivalpopulation growth exceeds food supply land masses change over immeasurable time

2. The History Behind THE Theory • Aristotle • viewed species as fixed and arranged them on a scala naturae of increasing complexity • Linnaeus • interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • founder of taxonomy, the branch of biology concerned with classifying organisms by the use of binominal nomenclature (genus and species)

3. The History Behind THE Theory Cuvier Determined some past organisms differ greatly from living species by looking at fossils in various strata Some organisms became extinct Hutton Published his idea of gradualism: the Earth had been molded by several events over time

4. The History Behind THE Theory • Lyell • Lamarck • Simple life forms develop into more complex forms through use and disuse • Individuals can acquire traits during their lifetime and pass on those traits to their offspring (inheritance of acquired characteristics) • Uniformitarianism: Geologic processes that have changed the shape of the Earth’s surface in the past continue to work in the same ways.

5. The History Behind THE Theory • Wallace • Published the first essay discussing the process of natural selection that was identical to Darwin’s that had yet to be published

6. The History Behind THE Theory • Charles Darwin • 1809-1882 • British naturalist • Proposed the idea of evolution by natural selection • Collected clear evidence to support his ideas

7. Voyage of the HMS Beagle • Invited to travel around the world • 1831-1836 (22 years old!) • makes many observations of nature • main mission of the Beagle was to chart South American coastline Robert Fitzroy

8. Voyage of the HMS Beagle • Stopped in Galapagos Islands • 500 miles off coast of Ecuador

9. Glyptodont fossils are also unique to South America. Succession of types Armadillos are native to the Americas, with most species found in South America. Why should extinct armadillo-like species& living armadillos be found on the samecontinent?

10. Modern sloth (right) Mylodon (left) Giant ground sloth (extinct) “This wonderful relationship in the same continent between the dead and the living will…throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.”

11. Unique species

12. Darwin found… birds Collected many different birds on the Galapagos Islands. Thought he found very different kinds… Finch? Sparrow? Warbler? Woodpecker?

13. But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Small Ground Finch Finch? Sparrow? How didone species of finches becomeso many differentspecies now? Warbler Finch Veg. Tree Finch Warbler? Woodpecker?

14. Darwin’s Theory of Natural Selection • He described evolution with the phrase “descent with modification” meaning that all species descended from preexisting species but changed over time.

15. Essence of Darwin’s ideas • Natural selection • variation exists in populations • over-production of offspring • more offspring than the environment can support • competition • for food, mates, nesting sites, escape predators • differential survival • successful traits = adaptations • differential reproduction • adaptations become more common in population

16.  LaMarckian vs. Darwinian view • LaMarck • in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring • Darwin • giraffes born with longer necks survive better & leave more offspring who inherit their long necks

17. Tree Thinking Descendantspecies Ancestralspecies Large-seed eater? Large GroundFinch Small-seed eater? Small GroundFinch Warbler? Leaf-browser? Veg. Tree Finch Warbler Finch

18. Correlation of species to food source Seedeaters Flowereaters Insecteaters Rapid speciation:new species filling new niches,because they inheritedsuccessful adaptations. Adaptive radiation

19. Darwin’s finches • Differences in beaks • associated with eating different foods • survival & reproduction of beneficial adaptations to foods available on islands Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Small ground finch Warbler finch Large insectivorous tree finch Cactus eater Mediumground finch Tree finches Ground finches Insect eaters Seed eaters Vegetarian tree finch Large ground finch Bud eater

20. Darwin’s finches • Darwin’s conclusions • small populations of original South American finches landed on islands • variation in beaks enabled individuals to gather food successfully in the different environments • over many generations, the populations of finches changed anatomically & behaviorally • accumulation of advantageous traits in population • emergence of different species

21. Darwin’s finches • Differences in beaks allowed some finches to… • successfully compete • successfully feed • successfully reproduce • pass successful traits onto their offspring

22. Correlation of species to food source More observations… Whoa,Turtles, too!

23. Many islands also show distinct local variations in tortoise morphology… …perhaps these are the first steps in the splitting of one speciesinto several?