Descent With Modification: A Darwinian View of Life

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Chapter 22

• Descent With Modification A Darwinian View of
  Life

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Jean Baptiste Lamarck

• Lamarck (1809) proposed a mechanism by which
  specific adaptations evolve, which included two
  related principles
• 1. Use and disuse Body organs used
  extensively to cope with the environment become
  larger and stronger while those not used
  deteriorate.
• 2. Inheritance of acquired characteristics
  Modifications an organism acquired during its
  lifetime could be passed along to its offspring.
• Ex birds wings, giraffes necks.
• Experiments and new knowledge have disproven
  Lamarck (mice tails experiment)

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Charles Darwin

• Darwin, serving as ships naturalist on the
  H.M.S. Beagle, observed unique species on the
  South American coast including the Galapagos
  Islands.
• Published On the Origin of Species by Means of
  Natural Selection in 1859.
• Made two major points
• 1. Species evolved from ancestral species due
  to inheritable variations.
• 2. Natural selection is a mechanism that could
  result in this evolutionary change.

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Darwins Theory

• Natural selection Due to survival of the
  fittest, organisms with certain traits survive to
  reproduce this results in changes in inherited
  characteristics of a population over time.
• Transmutation (descent with modification)
  species have descended, with changes, from other
  species over time.

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Evidence Presented

• Fossil record shows how organisms on earth have
  changed over time.
• Record has gaps difficulty finding accurate
  age.

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Evidence Presented cont.

• Homologous structures -- organisms have similar
  structures used for similar purposes.
• Did they have a common ancestor?

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Evidence Presented cont.

• Vestigial structures -- organs that serve no
  purpose, but resemble those found in other
  organisms.
• Scientists are still discovering functions.

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Evidence Presented cont.

• Comparative embryology -- embryos of vertebrates
  look similar in early stages.
• Did they have a common ancestor?
• Early sketches were exaggerated.

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Evidence cont. Biogeography
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The New Frontier

• Comparative biochemistry --The DNA revolution has
  disproven and supported some old ideas.
• Similar DNA sequences may tell which species are
  more closely related.

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More on Natural Selection

• Variations in a population arise by chance
  through mutation and recombination during sexual
  reproduction.
• Darwins view of Gradualism
• Life evolved by a gradual accumulation of small
  changes over vast spans of time.
• Or Punctuated equilibrium (S.J. Gould)
• Species have long periods of no change, then
  short periods of drastic change, due to intense
  environmental pressure.