The Historical Development of a Theory of Evolution

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					     The Historical
Development of a Theory
      of Evolution
         What is “evolution”?
 Evolution,in the biological sense, is
 the process by which hereditary
 changes occur in one or more
 characteristics within a species over
 time.
These changes occur as a result of
 mutations.
          What is a Theory?
A scientific hypothesis is a statement
 that provides one possible
 explanation for an observation.

 Hypotheses must be tested to
 determine their validity through:
  – experimentation
  – observations
  – and developing models from data
 Hypotheses  that consistently lead to
 successful predictions or
 explanations are sometimes
 synthesized into a general statement
 called a theory.

 Thetheory of evolution is a set of
 ideas put forward that attempts to
 explain how life has evolved, and
 continues to evolve, on Earth.
"Nothing in biology makes
  sense except in the light of
  evolution."
Theodosius Dobzhansky, Geneticist
    Development of the Theory of
            Evolution
   Although Charles Darwin is the most
  well-known evolutionist, the theory of
  evolution is built on the work of many
  contributors and is based on several
  different lines of evidence.
 Many of the earliest ideas about the
  origins of life were strongly influenced by
  religion and philosophy. These ideas
  suggested that all life forms have existed
  unchanged since their creation.
    Georges-Louis Leclerc, Comte de
          Buffon (1707-1788)
   French naturalist
   Publicly challenged the
    idea that life forms
    are unchanging
   Noted similarities
    between humans and
    apes and speculated
    they might have a
    common ancestor
   Suggested that Earth
    was much older than
    6000 years
     James Hutton (1726-1797)
     Charles Lyell (1797-1875)




 UNIFORMITARIANISM
 The natural processes that change the
  Earth presently have operated in the past
  at the same gradual rate
Georges Cuvier (1769-1832)
                Largely credited with
                 developing the science
                 of paleontology –the
                 study of ancient life
                 through the
                 examination of fossils
                Found that each layer
                 of rock was
                 characterized by its
                 own unique group of
                 fossil species
                Deeper rock layers
                 had fossil species
                 most dissimilar to
                 modern life
    Cuvier: CATASTROPHISM
 Every extinction of
  species in the fossil
  record was due to
  a local catastrophe
 A new set of
  species moved in
  and colonized an
  area from another
  part of the world
  (rather than
  evolved in situ)
      Jean Lamarck (1744-1829)
   first to recognize key
    role played by the
    environment in
    evolution
   Each species gradually
    became more complex
    and new and simple
    species were being
    created by
    spontaneous
    generation
Lamarck: ACQUIRED
CHARACTERISTICS
             Organisms acquired
              characteristics as a
              result of interactions
              with their environment
             Body parts used
              extensively to cope
              with conditions in the
              environment would
              become larger and
              stronger; adaptations
              would be inherited by
              offspring
             Body parts not used
              would eventually
              disappear
             “use and disuse”
    Thomas Malthus (1766-1834)
   Plants and animals
    produce far more
    offspring than can be
    supported by their
    environments
   Population growth is
    limited by density-
    dependent factors
    such as disease, war,
    and starvation (food
    availability)
Limits to Population Growth
     Charles Darwin (1809-1882)
and Alfred Russel Wallace (1823-1913):




       NATURAL SELECTION
On the Origin of Species
    by Charles Darwin
                 Main Ideas:
   Organisms produce
    more offspring than
    can survive.
    Therefore, they
    compete for limited
    resources.
   Individuals of a
    population vary
    extensively, and much
    of this variation is
    heritable.
 Individuals that are better suited to local
  conditions survive to produce offspring.
  SURVIVAL OF THE FITTEST
 Processes for change are slow and gradual
   GRADUALISM
Natural Selection at Work
    Descent with Modification
 Natural selection does not demonstrate
  progress; it has no set direction with
  regards to the complexity of an organism.
  It is random and does not result from a
  “grand design or plan”.
 It results from the ability of certain
  individuals in any population to survive
  local environmental conditions and to pass
  on the trait that helped them survive.

				
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posted:1/21/2013
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