History of Evolutionary Thought

1
History of Evolutionary Thought

• Prior to Darwin
• View of nature determined by deep-seated beliefs
• Biological thought had slowly begun to be
  accepted
• Various ideas of evolution
• Similarities between living things reflect recent
  common ancestry
• Dissimilarities between living things reflect
  ancient common ancestry

2
Mid-Eighteenth Century

• Taxonomy matured during mid-eighteenth century
• Linnaeus believed in
• The fixity of species
• That each species had
• An ideal structure and function, and
• A place in the scala naturae (scale of
  complexity)
• Count Buffon
• Wrote 44-volume catalog of all known plants and
  animals
• Suggested descent with modification

3
Late Eighteenth Century

• Lamarck
• First biologist to
• Propose evolution
• Link diversity with environmental adaptation
• Concluded more complex organisms are descended
  from less complex organisms
• Charles Lyell
• Earth is subject to slow but continuous cycles of
  erosion and uplift
• Proposed uniformitarianism, rates and processes
  of change are constant

4
Darwins Theory of Evolution

• Geological observations consistent with those of
  Lyell
• Biogeographical observations
• The study of the geographic distribution of life
  forms on earth
• Darwin saw similar species in similar habitats
• Reasoned related species could be modified
  according to the environment

5
Galápagos Islands

• Tortoises
• Darwin observed tortoise neck length varied from
  island to island
• Proposed that speciation on islands correlated
  with a difference in vegetation
• Finches
• Darwin observed many different species of finches
  on various islands
• Speculated they could have descended from a
  single pair of mainland finch

6
Natural Selection and Adaptation

• Individuals have heritable variations
• Some individuals have adaptive characteristics
• Enables increased survival and reproduction
• Increasing proportion of succeeding generations
  will have these characteristics
• Populations become adapted to their local
  environment through change in individuals

7
Organisms Have Variations

• Darwin emphasized that individuals from a
  population vary in their
• Functional characteristics
• Physical characteristics
• Behavioral characteristics
• Proposed that these variations
• Are essential
• Allow adaptation to the environment over time

8
Organisms Struggle to Exist

• Each generation has the same reproductive
  potential as the previous generation
• Reproductive potential is greater than
  environment can support
• Death, disease, and famine were inevitable if
  population were to have stability
• Individuals experience a constant struggle for
  survival

9
Organisms Differ in Fitness

• Fitness is the relative reproductive success of
  an individual
• Interactions with the environment determine which
  individuals reproduce the most
• Adaptation
• Changes that help a species become more suited to
  its environment
• Product of natural selection

10
The Evidence of EvolutionAnatomical

• Vertebrate forelimbs
• Homologous - All contain the same sets of bones
  in similar ways
• Yet they are modified extensively to meet various
  adaptive needs
• Darwin interpreted this as support for a
  hypothesis of common descent
• Embryological development Vertebrates
• A postanal tail and
• Paired pharyngeal (gill) pouches

11
The Evidence of EvolutionAnatomical

• Homologous Structures
• Anatomically similar because they are inherited
  from a common ancestor
• May be functionally similar or not
• Analogous Structures
• Serve the same function
• Not constructed similarly
• Do not share a common ancestor
• Vestigal Structures
• Fully-developed anatomical structures
• Reduced or obsolete function

12
The Evidence of EvolutionFossil
Biogeographical

• Fossil Evidence
• Fossils record the history of life from the past
• Document a succession of life forms from the
  simple to the more complex
• Sometimes the fossil record is complete enough to
  show descent from an ancestor
• Biogeographical
• Distributions of plants and animals across earth.
  Consistent with origin in one locale

13
Biochemical Evidence

• Almost all living organisms
• Use the same basic biochemical molecules
• Utilize same DNA triplet code. Codon
• Utilize same 20 amino acids in their proteins