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Darwin, Evolution, and Natural Selection. Scientific Theory. Social use of the word “theory” Not the same as in science Implies a hunch or a casual guess Scientific Theory 1. Highly probable explanation based on vast collections of scientific data

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scientific theory
Scientific Theory
  • Social use of the word “theory”
    • Not the same as in science
    • Implies a hunch or a casual guess
  • Scientific Theory

1. Highly probable explanation based on vast collections of scientific data

    • There are relatively few scientific theories
  • Examples of Scientific Theories
    • Cell Theory
    • Atomic Theory
    • Plate Tectonic Theory
    • Big Bang Theory
theories of evolution
Theories of Evolution
  • Lamarck (1800)
    • Similar species descended from a common ancestor – related to fossil record
    • Species change by ACQUIRING traits in their lifetime
    • Acquired traits are NOT genes; they are things that are learned
theories of evolution2
Theories of Evolution
  • Alfred Wallace (late 1800’s)

1. species were modified by natural selection

theories of evolution3
Theories of Evolution
  • Charles Darwin (late 1800’s)
    • Background
      • medical and clergy student  naturalist
      • HMS Beagle –goal was to survey the coast of S. America (1831-1836) –Darwin collected biological & geological specimens
      • Read Lyell’s Principles of Geology which influenced his thinking as he observed fossils—book proposed the earth was millions of years old
theories of evolution5
Theories of Evolution
  • On the Galapagos Islands
    • Different islands seemed to have their own slightly different varieties of animals
    • Finches had distinctive bills – 13 different species
    • Very similar – must have descended from a common ancestor
    • Related this to artificial selection
theories of evolution7
Theories of Evolution
  • Framework for Natural Selection (1840)

a. Individuals in a population show

differences

b. Variations are inherited

c. Organisms have more offspring than can

survive on available resources

d. Variations that increase reproductive success

will have a greater chance of being passed on

than those that do not increase reproductive

success

theories of evolution8
Theories of Evolution

Galapagos Turtle

theories of evolution9
Theories of Evolution
  • Wrote a book – Origin of Species (1859)

a. Compiled evidence for evolution and

explained how natural selection might

provide a mechanism for the origin of

species

b. 1858: another naturalist (Alfred Wallace)

proposed a theory almost identical to

Darwin’s—Darwin published his book a year

later; evolution is only used once: on the last

page!

summary
Summary
  • Over time, natural selection results in changes in the inherited characteristics of a population.
  • These changes increase a species fitness (survival rate)