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Darwin’s Theory of Evolution

Darwin’s Theory of Evolution. Unit 5. Objectives. The Puzzle of Life’s Diversity Ideas That Shaped Darwin’s Thinking Darwin Presents His Case. Do Lima Beans Show Variation?. Turn to page 368 in your textbook and complete the inquiry activity

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Darwin’s Theory of Evolution

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  1. Darwin’s Theory of Evolution Unit 5

  2. Objectives • The Puzzle of Life’s Diversity • Ideas That Shaped Darwin’s Thinking • Darwin Presents His Case

  3. Do Lima Beans Show Variation? • Turn to page 368 in your textbook and complete the inquiry activity • Work with your lab partner and compare results with the other lab group at your table • You have 20 minutes

  4. Historical Figures • 1785: James Hutton – proposed Earth was formed by geological forces over a very long period of time • 1798: Thomas Malthus – predicted that human population will grow faster than supplies can sustain it • 1809: Jean-Baptiste Lamarck – published his hypothesis of the inheritance of acquired traits

  5. Historical Figures • 1833: Charles Lyell – Proposes that processes that are occurring on Earth now have occurred for a very long time • 1858: Alfred Wallace – supporter of Darwin and speculates on evolution by natural selection

  6. Voyage of the Beagle • 1831-1836 • Darwin spent one month making observations on the Galapagos Islands • Most important observations were on finches and tortoises

  7. Tower Marchena James Fernandina Santa Cruz Isabela Santa Fe Floreana

  8. Darwin’s Observations1. Patterns of Diversity • He was amazed how well plants and animals adapted to their environment • On further trips to Argentina and Australia and observed that grassland ecosystems were different from Europe • Why were there no rabbits in Australia? • Or kangaroos in England?

  9. Darwin’s Observations2. Living Organisms and Fossils • Living organisms only made up part of the puzzle • Darwin collected fossils of ancient organisms during his voyage • What was the relationship between the fossils and living species?

  10. Darwin’s Observations3. The Galapagos Islands • Located 1000km west of Ecuador • Collection of islands from a volcanic arc • Islands had unique climates • Small islands were hot and dry • Large islands had greater rainfall, more variety of organisms

  11. The Journey Home • Hypothesized that organisms living on the Galapagos would evolved from a South American ancestor and then isolated on the island

  12. Ideas That Shaped Darwin’s Thinking

  13. An Ancient, Changing Earth • Hutton proposed that the processes on Earth occur very slowly. • Some layers of rock are moved up by internal geological forces, others are buried

  14. Sedimentary rocks form in horizontal layers. When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers. As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed. New sediment is then deposited above the exposed older rock surface.

  15. Lamarck’s Evolution Hypothesis • Proposed that by selective use and disuse of organs, organisms acquire or lose traits • Traits can then be passed to offspring

  16. Lamarck’s Evolution Hypothesis1. Tendency Toward Perfection • All organisms strive toward perfection • Ex. The urge for birds wanting to fly until wings became more suitable for flying

  17. Lamarck’s Evolution Hypothesis2. Use and Disuse • Organisms can alter the size and shape of organs by using them in different ways • Ex. If a winged animal did not want to fly, wings would decrease in size every generation

  18. Lamarck’s Evolution Hypothesis3. Inheritance of Acquired Traits • Proposed that if an animal changed its body structure, that change would pass to its offspring

  19. Example of Lamarck’s Hypothesis Using Fiddler Crabs

  20. Population Growth • Thomas Malthus • Believed that only war, famine, and disease will control population

  21. Darwin Presents His Case

  22. Publication of On the Origin of Species • Darwin returned to England in 1836 • Received letter from Alfred Wallace in 1858 • Summarized what Darwin had been mulling over for 25 years • Late in 1859 Darwin publishes his work stating a mechanism for evolution by natural selection

  23. Inherited Variation and Artificial Selection • Darwin knew nothing of heredity, only variation • Plant and animal breeders would select certain traits to move to the next generation • In artificial selection, humans select from the naturally occurring genetic variations in a species

  24. Evolution by Natural Selection1. Struggle for Existence • Members of each species compete regularly to obtain: • Food • Living space • Other necessities • High birth rates and a shortage of life’s basic needs leads to struggle

  25. Evolution by Natural Selection2. Survival of the Fittest • How well suited an organism is to its environment • The ability to survive and reproduce in a specific environment is fitness • The concept of fitness was central to Darwin’s theory • Referred to the survival of the fittest as natural selection

  26. Evolution by Natural Selection3. Descent with Modification • Natural selection produces organisms that have different structures, habitats or niches • Implies all living organisms are related to one another • Common descent states that all species were derived from common ancestors • “Tree of life”

  27. Evidence of Evolution • Darwin believed living things have been evolving for millions of years • Evidence found in: • The Fossil Record • Geographic Distribution • Homologous Structures • Embryology

  28. The Fossil Record • Darwin saw fossils as a history of life on Earth • Gaps do not indicate weakness only uncertainty on how some species evolved

  29. Geographic Distribution • Similar animals in different locations were the product of different lines of evolutionary descent

  30. Beaver Beaver Muskrat Beaver andMuskrat Coypu Capybara Coypu andCapybara NORTH AMERICA Muskrat Capybara SOUTH AMERICA Coypu

  31. Homologous Body Structures • Limbs of reptiles, birds, and mammals vary in form and function, but are similar in structure Bird Mammal Alligator Turtle Ancient lobe-finned fish

  32. Vestigal Organs • Not all homologous structures serve important functions • These organs have been reduced in size to just vestiges or traces of organs • Ex. The human appendix

  33. Similarities in Embryology • Early stages of many animals with backbones are very similar • Ex. Embryos of chickens, turtles and rats look similar providing evidence of a common ancestor

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