Descent with Modification: A Darwinian View of Life

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Descent with Modification A Darwinian View of
Life

• Chapter 22

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Historic Context

• Plato and Aristotle believed that organisms were
  perfectly formed and adapted to the world
• Judeo Christian theology believed
• that the world is 6,000 years old
• species were created individually
• Natural Theologians searched for Gods plan
  through the study of nature

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• Carolus Linnaeus founder of taxonomy and binomial
  nomenclature
• Clustered similar organisms into categories, he
  did not assume any evolutionary relationship
  based on this classification scheme
• Paleontology developed by Cuvier (1769-1832)
• He noticed that species appear and disappear in
  the fossil record
• He did not use this to support evolution, but
  developed catastrophism

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Principles of Populations

• Thomas Malthus (1798) published that populations
  increase faster than environment can handle
• Capacity to over-reproduce is seen in all species
• Eventually populations stop increasing in size
  and reach a steady state (carrying capacity)

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Geology

• Hutton (1795) theory of gradualism that major
  changes are the result of slow small changes
• Lyell (1830) geological changes throughout time
  have been subjected to the same forces
• Conclusions
• If geological changes are slow, earth is older
  than 6,000 years old
• the slow changes can build and result in profound
  environmental changes over time

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Relating geological evolution to biological
evolution

• Theories of biological evolution begin in the
  late eighteenth century
• Lamarck was the first to propose a mechanism that
  related environment to biological changes (1809)
• Use and Disuse
• Inheritance of Acquired Characteristics

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Darwin

• Sails on Beagle at 22
• Noted that flora and fauna of islands off of
  South America were more like continental species
  than those of other islands with similar climate
  and habitats
• Contributions of Lyell and Malthus along with his
  observations lead him to his mechanism for
  evolution

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Evolution

• What is evolution?
• All of the accumulated changes that have occurred
  over time
• Darwins definition Descent with modification
• Lifes history is a tree with different branches
• Forks of the tree represent common ancestors
• Most closely related organisms share common paths
  on the branching tree

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• Darwin used Linnaeus taxonomic classification
  scheme to connect diversity of life
• Kingdom gt phylum gt class gt order gt family gt genus
  gt species

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Mechanism Natural Selection

• Fact 1 Over-reproduction occurs in nature
• Fact 2 Populations do not increase
  exponentially
• Fact 3 There are limited natural resources
  (food, shelter)
• These facts are seen in Malthus works on
  populations

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• Inference 1
• struggle for survival ensues
• Fact 4 Variation exists in populations
• Fact 5 Much of the variation is heritable
• Fact 4 was physically observed. Darwins
  weakness was the 5th fact
• Inference 2
• Organisms with the best variations survive the
  struggle for life
• Inference 3
• Unequal survival of organisms with different
  variations leads to favorable variations
  accumulating over time

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Key Concepts

• What is the raw material necessary for the
  mechanism of Natural Selection?
• Heritable variations
• What is the smallest unit of evolution?
• Populations
• Darwin incorporated Lyells gradualism into
  biological evolution combined with Malthus
  observations regarding populations

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Examples of Natural Selection

• Grants on the island of Daphne Major
• observed shifts in the frequency of beak sizes
  over short periods of time
• Peppered moths
• Antibiotic resistance in bacteria
• How do the genetic variations arise in nature?

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Evidence for Evolution

• Artificial selection
• Island biogeography
• Fossil record
• Taxonomy
• Comparative Anatomy
• Vestigial Structures
• Comparative Embryology
• Molecular Biology

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Eye sockets in blind salamanders
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