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Chapter 15. Darwin’s Theory of Evolution. “…the single most important scientific idea that anyone has ever had…”. 15-1 The Puzzle of Life’s Diversity. Evolution : change over time p rocess by which modern organisms descended from ancient organisms Do you remember what a theory is?.

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chapter 15

Chapter 15

Darwin’s Theory of Evolution

“…the single most important scientific idea that anyone has ever had…”

15 1 the puzzle of life s diversity
15-1 The Puzzle of Life’s Diversity
  • Evolution: change over time
    • process by which modern organisms descended from ancient organisms
  • Do you remember what a theory is?
voyage of the beagle
Voyage of the Beagle

1831- England

Charles Darwin

Recorded observations

Collected data/specimens

Proposed evolutionary theory about how life changes over time

darwin s data
Darwin’s Data
  • Diversity
    • Galapagos Islands- different plants/animals on each island
  • Patterns
    • Reproductive, habitats, etc.
  • Fossils: preserved remains/evidence of ancient organisms
    • Connected old and new
15 2 ideas that shaped darwin s thinking
15-2 Ideas that shaped Darwin’s thinking
  • Old belief: Earth was “young” and hadn’t changed since life began
  • Discoveries in geology:
    • James Hutton
      • Geological change
      • Effects of natural forces (rain, wind)
      • Happens slowly/constantly
    • Charles Lyell
      • Wrote Principle’s of Geology
      • Earth has changed over time…could life?
jean baptiste lamarck
Jean-Baptiste Lamarck

Organisms adapt

If you use it, it will stay (get passed on)

If you don’t, it will go away

Tendency toward perfection

Inheritance of acquired traits*

population growth
Population Growth

Thomas Malthus- economist

More people are born than are dying

Uncontrolled population growth = high competition for resources

What makes some survive and others die?

15 3 darwin presents his case
15-3 Darwin Presents his case
  • 1859- publishes On the Origin of Species:
    • Evolution has been happening for millions of years and is still happening today
    • Mechanism of evolution = natural selection
variation and artificial selection
Variation and Artificial Selection
  • Genetic variation found everywhere
  • Breeders use it to make “the best”:
    • Fastest horses
    • Plants with biggest fruit
  • Artificial selection: selection by humans for breeding of desired traits from the natural genetic variation of organisms
evolution by natural selection
Evolution by Natural Selection

Darwin questioned: How does “selection” happen in nature?

Struggle for existence: competition among members of a species for food, living space, reproduction, etc.

survival of the fittest
Survival of the Fittest

Process by which individuals better suited to their environment survive and reproduce most successfully

Fitness: ability of an organism to survive and reproduce

Adaptation: inherited characteristic that increases an organisms chance of survival (structural, physiological, behavioral, etc.)

survival of the fittest natural selection
Survival of the Fittest = Natural Selection

Successful adaptations will increase fitness

If you survive/reproduce, you pass on genes = more of those genes in nature

descent with modification
Descent with Modification

Each living species has descended- with changes- from other species over time

Common descent: all living things come from a common ancestor

darwin s evidence 1
Darwin’s Evidence #1

fossil record- organisms have come and gone but can be related/connected to current organisms

darwin s evidence 2
Darwin’s Evidence #2
  • geographical distribution of living species- descent with modification
    • As organisms changed, they adapted to different habitats and spread out
darwin s evidence 3
Darwin’s Evidence #3
  • homologous body structures: structures that have different mature forms in different organisms but developed from the same embryonic tissue
    • Ex: limbs (arms, wings, flippers)
  • Increased similarities = more closely related
    • Ex: bats and humans, birds and reptiles
vestigal structures
Vestigal Structures

Structures that serve no useful function

Homologous structures that the organisms no longer needs

Ex: whale “legs”

darwin s evidence 4
Darwin’s Evidence #4

similarities in embryology- many embryos look the same

common cells growing in similar ways