Development of Evolution Theory

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Development of Evolution Theory
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What is a species?

• We need to define what a species is to understand
  evolution, the mechanisms, and diversity
• Species basic unit of taxonomic classification
  population of closely related and similar. In
  sexually reproducing organisms, the similar
  organisms must be able to breed and produce
  viable, fertile offspring

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History of Evolutionary Thought

• Early biological thought didnt include evolution
• Creationism
• Organisms remain fixed and unchanged
• 427-347 B.C. Plato
• 384-322 B.C. Aristotle Scala Naturae (ladder
  of Nature) categorized organisms into a linear
  hierarchy
• Until 1700s creationism was unchallenged

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New Evidence Eroded View of Creationism

• New lands
• revealed diversity of life
• Africa, Asia, Americas
• Many different species some closely resembled
  each other
• Fossil Discoveries
• Fossils remains of dead organisms (in rock,
  petrified bones and wood, shells, impressions of
  body forms
• showed life changed over time

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2. skin impression
3. bones
1. eggs in nest
4. fossilized feces (coprolites)
5. footprint
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(a)
(b)
(c)
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Nonevolutionary explanations for fossils

• Catastrophism
• Georges Cuvier (1769-1832)
• Proposed a vast of species was created and
  successive catastrophes produced layers of rock
  and destroyed many species, fossilizing them
• Problem some organisms that survived should have
  shown up in fossils because some would have died
  the majority of fossils are extinct species
• Louis Agassiz (1807-1873)
• Proposed there were new creations after each
  catastrophe

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Speculations Life Did Evolve

• Original creation produced a small of founding
  species and later species evolved through natural
  processes
• Georges Louis LeClerc (Comte de Buffon)
  (1707-1788)
• Problem couldnt prove a mechanism and also no
  one thought the earth was old enough to allow
  time for producing a new species

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Geological Evidence Earth is Old

• Uniformitarianism
• View of geologists Thomas Hutton and Charles
  Lyell
• Earth developed gradually through natural
  processes that occur over long periods of time
• Examples river flooding, volcanoes, geologic
  shift

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Pre-Darwin Biologists Proposed Mechanisms for
Evolution

• Jean Baptiste Lamarck (1744-1829)
• Hypothesized that organisms evolved through the
  inheritance of acquired characteristics
• Proposed that all organisms have an innate drive
  for perfection
• Example Giraffes
• Problem Acquired characteristics cannot be
  inherited
• Though he was wrong, Lamarcks evolution ideas
  influenced later biologists

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Darwin and natural selection
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The Voyage of the Beagle 1831 - 1836
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Darwins Voyage
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Galapagos islands

• Volcanic archipelago- geologically young.
• Several groups of closely related species found
  nowhere else.
• Mockingbirds, Finches, giant tortoises- distinct
  types on the different islands
• Diversification (adaptive radiation) from
  mainland ancestors

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14 Varieties of finches
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Darwin and Wallace Proposed a Mechanism of
Evolution

• 1858 Charles Darwin and Alfred Russel Wallace
  came up with the mechanism for evolution
• Worked separately
• 1859 Darwin published On the Origin of Species
  by Means of Natural Selection

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How Does Natural Selection Work?

• Overproduction
• Struggle for existence
• Variation
• Survival of fittest
• Origin of a new species

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Important Points Underlying Evolutionary Change

• Variations that natural selection works on are
  produced by chance mutations
• Mutations that produce traits occur spontaneously
  and are made common or rare by natural selection
• Natural selection selects organisms that are best
  adapted to a particular environment
• Conditions change in environments so the best at
  one point may not survive at another time