History of Evolutionary Thought

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History of Evolutionary Thought

• Diane Philip

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I. What is Evolution?

• Evolution a gradual process by which the living
  world has been developing following the origin of
  life.

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II. 18th and 19th centuries

1. Species were thought to have a fixed form.
2. Species defined mostly by their morphology
   (appearance).
3. World was believed to be perfectly designed and
   earth was very young.

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II. 18th and 19th centuries

• Classification system based on assumption that
  species were static (unchanging).
• Carl Linnaeus (1708-1788) created hierarchical
  classification scheme with binomial naming (genus
  species).
• Classification used as a method of organizing,
  not a way to show relationships.

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III. Early Ideas of Evolution

• George Louis Leclerc (1707-1778) French
  naturalist who first suggested evolution.
• George Cuvier (1769-1832) Vertebrate zoologist
  who suggested Catastrophism (Mass extinction).
• James Hutton (1726- 1797) Proposed the
  Uniformatarian Theory of geology.
• Theory states that geologic processes happen at
  the same rate today that they have throughout the
  earths history.

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III. Early Ideas of Evolution

1. Jean Baptiste Lamarck (1744-1829) French
   naturalist and taxonomist. He proposed the Theory
   of Acquired Characteristics.

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IV. Enter Darwin (1809-1882)

• Early Life
• Charles Darwin (18091882) was born at Shrewsbury
  in northwestern England.
• He was sent to Edinburgh University at age 16 to
  study medicine.
• In 1827 he was sent to Cambridge University to
  become an Anglican clergyman.

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IV. Enter Darwin (1809-1882)

• Voyage of the H.M.S Beagle
• Asked by Capt. Robert FitzRoy on a voyage to
  chart South America coast in 1831.
• Read Principles of Geology by Charles Lyell,
  which discussed theory of uniformitarianism.
  Wanted to extend it to all animals.
• Noticed family resemblance between species
  (living and fossil) in areas he studied.

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IV. Enter Darwin (1809-1882)

• Galapagos Observations
• different islands, climates, vegetation
• differences in animals (tortoise finch)
• could these differences be the result of the
  differences among islands?
• could each animal have come from a common
  ancestor?

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IV. Enter Darwin (1809-1882)

• Development of Natural Selection
• Malthus said as the human population outgrows
  its resources, members must compete for what is
  available.
• Darwin thought the same principle might apply in
  nature.
• Individuals with favorable traits might have an
  advantage in survival and reproduction.
• Favored individuals would pass their traits on to
  their offspring.

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IV. Enter Darwin (1809-1882)

• Darwin and Alfred Russel Wallaces papers were
  presented as a scientific meeting in 1858 but
  received little fan fare.
• Darwins findings were published in a book On
  the Origin of Species in 1859.

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V. Neo-Darwinian Synthesis

• After about 1870, scientific evidence piled up
  against natural selection
• The Earth was too young.
• Apparent swamping of favorable variations.
• Lack of transitional forms in the fossil record.
• Biologists convinced that evolution had occurred
  but no longer saw natural selection as its chief
  mechanism
• The main scientific objections to Darwinian
  natural selection theory were answered by the
  1930s
• Discovery of radioactivity and later studies of
  decay rates showed age of earth to be 4 billion
  years.
• Swamping inheritance problem and lack of
  transitional forms in fossil record both resolved
  by Mendelian genetics.