EVOLUTION

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EVOLUTION

• Transformation of the Biological Paradigm

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Evolution

• Charles Darwin
• BUT, the history of Evolutionary Thought
  pre-dates Darwin considerably

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The Aristotlean-Christian World View

• Aristotle (350 BC)
• Greek
• Special Creation Fixety of Species
• Every creature has its place, and all have been
  created in a specific and perfect form by an
  omnipotent omnipresent creator.
• No change each organism is created in its most
  ideal form.

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The Aristotlean-Christian World View

• Aristotle observes lifes complexity
• Suggests a Hierarchy of Life

Complexity
The scala naturae
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The Aristotlean-Christian World View

• Following Aristotle (and all the way up into the
  1700s), this is the unchallenged world view.
• Taxonomy (Identification Naming of organisms)
  centers around placing newly discovered species
  properly into the pyramid (Linnaeus).

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Naturalists begin to find problems

• Some organisms were not fitting properly into the
  hierarchy.
• Due to Variations
• Viewed as imperfections of an idealized form.
• Which characteristics of an organism are most
  important for placing it in the hierarchy?
• How much variation should be viewed as normal
  within a species?

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Georges Louis LeClerc DeBuffon

• (1707-1788)
• Wrote a huge Natural History
• Observed much Variation.
• Suggested the possibility of Descent with
  Modification
• As organisms descend through time, modifications
  of the basic form occur due to differences in
  environment, geographic isolation, overcrowding,
  etc.
• Offered no mechanism for such modification.
• Suggested the Earth was only 168,000 years old.

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Erasmus Darwin

• (1731-1802)
• Charles Darwins Grandfather
• Physician
• Examined the Anatomy of many organisms.
• Found Vestigial Organs (non-functional).
• Why would these be present in a perfectly-adapted
  organism?
• Examined changes during development (Ontogeny).
• Suggested some sort of Common Descent
• Currently living organisms have descended from
  ancestors of similar (but slightly different)
  form.
• Offered no mechanism for such modification.

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James Hutton

• (1726-1797)
• Geologist
• Suggested Gradualism
• Changes to the Earth occur gradually through
  continuous processesthe same processes that are
  occurring right now
• Erosion
• Volcanic activity
• Earthquakes

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Charles Lyell

• (1797-1875)
• Geologist
• (father of modern Geology)
• Suggested Uniformitarianism
• Following Huttons ideas, Lyell suggested that
  the rate at which geologic events occur is both
  slow and uniform (gradual).
• The same processes are responsible for both past
  and present geologic eventsthe geologic
  processes occurring now have been occurring over
  many millions of years.
• Leads to the conclusion that the Earth is very
  old many millions of years old.

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Georges Cuvier

• (1769-1832)
• Zoologist.
• Comparative Anatomy of bones muscles.
• Similarities in structure, despite function.
• Fossils (impressions of dead organisms in rock).
• Slight differences in fossil forms found in
  different rock strata (layers of different age).
• Was firmly entrenched in the Aristotlean-Christian
  View, so introduced Catastrophism as an
  explanation.
• Sporatic catastrophies in the Earths history
  killed off certain species those not found
  currently.

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Jean-Baptiste de Monet de Lamarck

• (1744-1829)
• Naturalist
• Examined Rock Stratigraphy.
• Fossils from the oldest strata appeared simpler,
  while those from more recent strata appeared more
  complex.
• 1st to fully support Common Descent and suggest
  a link between biological diversity and
  adaptation to the environment.
• Proposed a mechanism

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Jean-Baptiste de Monet de Lamarck

• Suggested that CHANGE in organisms took place by
  Inheritance of Acquired Characteristics.
• Characteristics acquired during an organisms
  life were passed on to offspring.
• Giraffe Necks became longer and longer as each
  generation stretched higher into the trees for
  food.
• Problem

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Jean-Baptiste de Monet de Lamarck

• Lamarcks hypothesis was never supported by
  experiments.
• Why?
• An environmentally-induced phenotype cannot be
  passed on to the next generationonly genotype
  can!
• Lamarks mechanism has long since been DISPROVED,
  but he is still remembered for this mistaken
  hypothesis!

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Charles Darwin

• (1809-1882)
• British Naturalist
• Supporter of the Aristotlean-Christian Worldview.
• Began science in Medical School at Edinburgh
• Became more interested in nature (birds
  particularly), and quit Medical School.
• Enrolled at Christs College at Cambridge to
  become a prieststill more interested in nature
  (especially collecting beetles).

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Charles Darwin

• Finished School and planned to start a church in
  the countryside.
• Before graduation, though, he gained an avid
  interest in Geology.
• Was invited by former professors to become a
  Naturalist aboard the HMS Beagle a ship
  destined for a sailing trip around the world.

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Charles Darwin

• 5 year voyage (1831-1836)
• Lots of DATA!
• 1. Geologic
• He saw first hand what Hutton had suggested
  (Gradualism), and agreed with Lyells premise
  that the Earth must be very old.
• He examined many fossils some resembling modern
  (current) organisms, but not exactly.
• Saw the possibility for Descent with Modification
  (modern forms having descended from now-extinct
  forms), and for organisms changing over time.

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Charles Darwin

• DATA
• 2. Biogeography
• He found similar organisms in far-reaching
  places, but in similar habitats.
• Suggested that organisms may be adapting to the
  same types of environment, despite the distance
  between them.
• He found slight variations in organisms found in
  slightly different habitats (but separated from
  each other Finch Bills, Tortoise Necks, etc.)
• Suggested that a common ancestor gave rise to the
  different varieties, which each adapted to
  slightly different environments.

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Darwins Biogeography
(Australia)
(S. America)
(Africa)
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Darwins Biogeography
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Charles Darwin

• Returned from the voyage andPUBLISHED!
• Saw that adaptation to environment was indeed
  real, and eventually formulated a mechanism for
  it, but
• He did not want to jeopardize his scientific
  status, so didnt publish it.
• Along came Alfred Russel Wallace

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Alfred Russel Wallace

• (1823-1913)
• Naturalist
• Studied and admired Darwins work.
• Wrote Darwin to see what he thought about a
  hypothesis regarding a mechanism for adaptation
  to the environment.
• This hypothesis was virtually the same as
  Darwins (unpublished) ideas about how change
  could take place!

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Darwin Wallace

• 1858 -- Presented their hypotheses at a meeting
  of the Linnaean Society (London)
• "The Variation of Organic Beings under
  Domestication and in their Natural State"
• "On the Variation of Organic Beings in the State
  of Nature on the Natural Means of Selection
  on the Comparison of Domestic Races and true
  Species"

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Darwin

• Later (1859) published his famous essay

I have called this principle, by which each
slight variation, if useful, is preserved, by the
term Natural Selection. - Charles Darwin, The
Origin of Species
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