Darwin's Evidence:  Morphology
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© 1997
David H.A. Fitch
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Lecture notes

Darwin's evidence for evolution:  Morphology

I.  How to explain similarity in Body Plan?
( "Unity of Type" = members of a group share homologous characters)

II.  In these groups, structures for very different functions are often constructed on the same underlying pattern
A.  Inexplicable by "design" (i.e., special creation)  (Why?)
B.  Is explained by descent with successive slight modificaitons without a redesign of the entire pattern
C.  Sometimes homologies can be difficult to discern because the modifications are so great:  e.g., modifications can obscure, lose, or multiply the pattern (as in "serial homologs")

III.  Redefinition of "Transformation" (p. 438, 1st ed.)
Not a transformation between existing forms of a character, but from a shared character in an ancestor

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  1. What are the differences between "homologous" organs and "analogous" organs?  Find some examples of your own.
  2. What is the Darwinian explanation for homology and analogy?  Does special creation predict the patterns of homologous parts in different species?  How might transformist predictions (if any) about homology be different from those of branching evolution?
  3. One of the greatest debates in the history of biology occurred (before Darwin) between the great paleontologist/comparative anatomists George Cuvier and Etienne Geoffroy St. Hilaire.  Geoffroy argued that body plans constrain how organ functions will be manifested ("function follows form"), whereas Cuvier argued that functions determined how particular organs were designed ("form follows function").  How would you resolve this debate using the principle of descent with modification?

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 Variation  Fossils  Geographic
Distribution  Morphology  Classification  Vestigial
Organs  Embryology
[Variation] [Fossils] [Geographic Distribution] [Morphology] [Classification] [Vestigial Organs] [Embryology]


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