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15.3 Darwin Presents His Case. Darwin Presents His Case. The specimens Darwin brought back had the scientific community in a buzz Learned that Galapagos species are found nowhere else in the world They looked similar to South American mainland species but were clearly different.

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darwin presents his case
Darwin Presents His Case
  • The specimens Darwin brought back had the scientific community in a buzz
  • Learned that Galapagos species are found nowhere else in the world
  • They looked similar to South American mainland species but were clearly different
darwin s book
Darwin’s Book
  • Published his ideas about species diversity and evolution in On the Origin of Species
  • Proposed a mechanism for evolution called natural selection
  • Many agreed with Darwin while others strongly opposed him
natural variation
Natural Variation
  • Scientists used to believe species were perfect and unchanging
  • Darwin argued natural variation (differences among species) is found in all types of organisms
    • Some cows give more milk
    • Some plants give larger fruit
artificial selection
Artificial Selection
  • Darwin also studied English farmers and breeders
  • Used selective breeding to breed the “best” individuals
    • Largest hogs, fastest horses
  • Darwin called this artificial selection
  • Still used today!
evolution by natural selection
Evolution by Natural Selection
  • Darwin believed that evolution occurred through natural selection
  • Natural selection = the process by which only the organisms best adapted to their environment will survive and reproduce
  • 3 main parts to natural selection
1 the struggle for existence
1. The Struggle for Existence
  • There are more living things than resources
  • Results in competition
  • Competition = the struggle among living things to get their needs for life
2 survival of the fittest
2. Survival of the Fittest
  • Individuals that are better suited to their environments survive (high fitness)
  • Individuals not suited to their environment will die (low fitness)
  • Fitness – the ability of an individual to survive and reproduce in its environment
    • Is a result of adaptations
2 survival of the fittest1
2. Survival of the Fittest
  • Adaptation – any inherited characteristic that increases an organism’s chance for survival
    • Long necks in giraffes
    • Long toes / webbed feet in birds
    • Coloring / Camouflage
3 descent with modification
3. Descent with Modification
  • Each living species has descended, with changes, from other species over time
  • Implies all organisms are related to one another
    • Known as common descent
evidence for evolution
Evidence for Evolution
  • Fossil Evidence
    • When living things from the past are compared to living things today, we can see that change has occurred
evidence for evolution1
Evidence for Evolution
  • Geographic distribution of living things
    • Species are located in different parts of the world but share similarities
    • Beavers and capybara are similar
    • Muskrat and coypu are similar




Beaver andMuskrat



Coypu andCapybara






evidence for evolution2
Evidence for Evolution
  • Homologous body structures
    • Limbs (arms, wings, legs, flippers) have different form and function but are constructed from the same bones





Typical primitive fish

evidence for evolution3
Evidence for Evolution
  • Vestigial structures
    • Body parts that no longer have functions
    • i.e. Pink lump in corner of eye
      • Remnant of a third eyelid
      • Frogs and turtles have third eyelid to see underwater
    • Appendix
      • In many mammals the appendix is used to help digest food
evidence for evolution4
Evidence for Evolution
  • Embryology
    • Studying embryodevelopment to look for similarities and differences