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Biology. Chapter 15: Darwin’s Theory of Evolution. Chapter 15: The Theory of Evolution 15.1 The Puzzle of Life’s Diversity. Evolution – change in a population of organisms over time Charles Darwin English Scientist Considered to be the father of evolutionary theory Born Feb 12 1809.

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Chapter 15:

Darwin’s Theory of Evolution


Chapter 15: The Theory of Evolution

15.1 The Puzzle of Life’s Diversity

  • Evolution – change in a population of organisms over time
  • Charles Darwin
    • English Scientist
    • Considered to be the father
    • of evolutionary theory
    • Born Feb 12 1809

Voyage of the H.M.S. Beagle

    • 1831 Darwin traveled on the Beagle
    • A 5-year expedition to South America and
    • South Pacific for mapping and collecting specimens
    • His job was to collect, study and store biological specimens
    • His observations in the Galapagos Islands were among his most important
    • Compared the anatomy of many species of reptiles, insects, birds, plants

Darwin’s observations

    • He noticed organisms were unique yet similar to species seen in other parts of the world
    • Grasslands in some regions were similar to one another but were inhabited by very different animals.
    • The Galapagos Islands were close together but had very different climates.
    • The shape of the giant tortoises shell and neck length can identify which island a tortoise inhabited
    • The shape of the finches beak varied from island to island

By the end of his trip he was convinced that evolution occurs, that species can and do change

  • He knew that many species produce large numbers of offspring and since Earth was not covered with many species he suspected that there must be a struggle for existence among individuals
  • Only the strongest survive and the weak die

15.2 Ideas that Shaped Darwin’s Thinking

  • Hutton
    • Earth is shaped by geological forces over long periods of time
    • Estimates earth to be millions, not thousands of years old
  • Lyell
    • Processes occurring now have shaped Earth’s geological features over long periods of time


    • Inheritance of Acquired Traits
      • Also called use and disuse theory
      • Selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime
      • Those traits could be passed on to offspring
      • Ex. Long necks of giraffes
      • Big muscles
  • Evaluating Lamarck’s Hypotheses
    • Lamarck’s hypotheses of evolution are incorrect in several ways.
    • Lamarck did not know how traits are inherited
    • However, he paved the way for the work of later biologists.


    • If the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
    • This information was central to Darwin’s explanations of evolutionary change.

15.3 Darwin Presents his Case

  • Publication of Origin of Species
    • Darwin wrote all of his ideas down, but did not publish them.
    • He struggled with his ideas because they went against scientific thought at the time
    • Wallace was a naturalist that had the same ideas as Darwin and was going to publish them.
    • This forced Darwin to publish his ideas
    • On the Origin of Species publish in 1859

Inherited Variation and Artificial Selection

  • One of Darwin’s most important ideas was that organisms of the same species vary from one another
  • Darwin thought that variation mattered
  • Artificial Selection – a breeder selects particular traits. This had been done by farmers for years
  • Darwin wondered if nature selected particular traits

The struggle for existence

    • Individuals with characteristics that are not well suited to their environment either die or leave few offspring.
    • Individuals that are better suited to their environment survive and reproduce most successfully.
  • Natural Selection – organisms with favorable variations survive, reproduce and pass those variations on to the next generation
  • Darwin also called this “Survival of the Fittest”
evidence for evolution
Evidence for Evolution
  • Fossil Record
    • Darwin saw fossils as a record of the history of life on Earth

Homologous Body Structures

    • Structural features with a common evolutionary origin
    • Similar in structure and/or function
    • Example: whale forelimb, crocodile forelimb, bird wing, human arm









Analogous Structure

    • Do not have a common evolutionary origin
    • Any body structure that is similar in function but different in structure
    • Example: butterfly wing and bird wing
    • Can’t be used to indicate evolutionary relationships, but they do provide evidence of evolution

Vestigial Structure

    • Any body structure that is reduced in function in a living organism but may have been used in an ancestor
    • Example: appendix, wisdom teeth, tail bone

Similarities in Embryology

    • The early stages, or embryos, of many animals with backbones are very similar
    • Similarities among vertebrate embryos suggest evolution from a common ancestor
    • These common cells and tissues, growing in similar ways, produce homologous structures

BIRD (chicken)

MAMMAL (human)



adult shark

Early human embryo (three millimeters in length)

Fig. 20.7, p. 317