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  • 1. S Darwin’s Theory of Evolution Chapter 16
  • 2. 16.1 Darwin’s Voyage of Discovery S Charles Darwin S Born Feb 12, 1809 S The first person to publish convincing evidence that species evolve, and propose a reasonable mechanism explaining how evolution occurs. S Modern organisms evolved over long periods of time through decent from common ancestors.
  • 3. Science Before Darwin S In Darwin’s time, most people and scientists believed that each species exists, unchanged as it has for all time. S However, views were beginning to change dramatically S The Earth had changed along with all living things on Earth S With the discovery of more and more fossils scientists began to propose various mechanisms to explain how these species change over time.
  • 4. S Jean Baptiste Lamarck, in 1809, proposed a hypothesis of the inheritance of acquired characteristics. S This hypothesis stated that by use or disuse of a body part could cause change in that feature within the lifetime of the organism. S These changes would then be passed on to offspring. S Lamarck’s hypothesis is now known to be incorrect.
  • 5. Darwin’s Epic Journey S In 1831, at age 22, Darwin took a position as a naturalist on a voyage of the HMS Beagle. S On the Beagle’s 5-year journey it sailed around the world to map the coast of South America. S During the voyage Darwin found evidence that challenged the belief that species are unchanging.
  • 6. Observations S Three patterns of biological diversity: 1. Species vary globally 2. Species vary locally 3. Species vary over time
  • 7. Species Vary Globally S Similar animals live in separate, but similar habitats. Rheas – South America Ostrich - Africa
  • 8. Species Vary Locally S Different, yet related species occupied different habitats in the same area. Isabella Island Hood Island
  • 9. Species Vary Over Time S Fossils of extinct animals are similar to living species.
  • 10. Putting it Together S Darwin noticed that the finches on each of the Galápagos islands had differently shaped beaks, and were similar to those in South America. S He spent years researching his ideas after he returned. S He began to wonder if the animals living on the different islands had come from a common ancestor.
  • 11. 16.3 Darwin Presents His Case S In 1858 Darwin published his ideas in the book “On the Origin of Species.” S This book outlined Darwin’s ideas of evolution based on natural selection focusing on three principles: S The struggle for existence S Variation and Adaptation S Survival of the fittest
  • 12. Struggle for Existence S Though every organism has the potential to produce many offspring, only a limited number of those survive and reproduce. 1 in 1000 survive to adulthood 50% survive past 1 year
  • 13. Variation and Adaptation S Individuals in a population vary in heritable characteristics S Adaptations increase an organism’s ability to survive and reproduce. S Camouflage S Mimicry S Behaviors
  • 14. Survival of the Fittest S Fitness is how well an organism can survive and reproduce in its environment. S Individuals with a high fitness are well suited for their environment and are more likely to survive and reproduce. S Individuals with low fitness are not as well suited to their environment therefore will either die or leave few offspring.
  • 15. Natural Selection S These mechanisms allow for natural selection to occur. S Each generation populations continue to change as more individuals are born with favorable traits for the environment. S It is important to remember that if environmental conditions change faster than a species can adapt to the changes, the species may become extinct. S Example p. 462
  • 16. 16.4 Evidence of Evolution The Age of the Earth and The Fossil Record S Earth is 4.5 billion years old S Fossils provide the most direct evidence that evolution takes place. S Fossils are preserved or mineralized remains or imprint of an organism that lived long ago. S Fossils provide an actual record of Earth’s past life forms. S Fossils are used to trace the evolution of modern species from extinct species.
  • 17. S Although the fossil record is not, and will never, be complete it presents strong evidence that evolution has taken place. S Paleontologists analyze fossils by dating the rocks and minerals around it. S They can arrange the fossils from oldest to youngest, and in this, orderly patterns of evolution can be seen.
  • 18. Comparing Anatomy and Embryology S Homologous Structures S Similarities in bone structure suggest that all vertebrates share a common ancestor.
  • 19. S Vestigial structures also provide evidence for evolution. S Ex: hind limbs of whales and dolphins
  • 20. Embryology S At some time in their development all vertebrate embryos have a tail, a notochord, and pharyngeal pouches. S Suggesting common ancestry
  • 21. Genetics and Molecular Evidence S Similarities in gene sequences can be linked to common ancestry. S Today we now know that genes are responsible for inherited traits. S Traits become more common in a population because more individuals in the population carry the alleles for those forms. S Mutations and the recombination of alleles that occurs during sexual reproduction provide endless sources of new variations for natural selection to act upon. S Analyzing Data p.470
  • 22. Examples of Evolution Natural Selection at Work S The key lesson scientists have learned about evolution by natural selection is that the environment dictated the direction and amount of change. S Ex: The polar bear’s white fur enables it to hunt successfully in its snowy environment. In a warmer environment, having white fur would no longer be an advantage. Examples of Natural Selection S Bacteria that cause disease evolve to have resistance to antibiotics. S Ex: TB, Staff