SIMILARITY MEAN DESCENT?
New Light on the Concept of Homology
Legs of animals (as birds, frogs, turtles) and humans
Before Darwin: forms of life as modifications of great themes
For Darwin: similarity as evidence of relationship
DEFINED & ILLUSTRATED
Owen (1840s): "essential similarity" in
- relative position and
- adult structure
- embryonic development
Current popular definition: similarity based on descent from common
Homology contrasted with Analogy
- similarity in use, with no
prerequisites re/ structure
Thought of as powerful evidence for organic evolution
"The central task of evolutionary biology is the separation of
homologous from analogous likeness." (Gould, 1988, p 26)
For Christians: evidence of design by one Creator
Does homology mean ancestry or not?
Review of basic embryology
The trend of thought
- Darwin, 1872
- Ballard, 1976
- Denton, 1985
- "Homologous organs are arrived at by
routes." (p 146)
- Roth, 1988
- changed to view of
Pioneering work of Sir Gavin de Beer, 1971
"Homology of phenotypes does
not imply similarity of genotypes." (p 15)
Some examples supporting the concept that different genes lead to
diverse developmental pathways yet similar end products
- Vertebrate limbs
- Spinal cord
"in general the homology of structure
such as organs or
molecules cannot be ascribed to inheritance of homologous genes or sets
of genes. (Sattler, 1984, p 386)
Sequence similarities, yes; homologies, no
Suggestions for use of the term homology" in the future
- Morphology, yes
- Common ancestry, no
- Discontinue use in
"Evolutionary considerations are
considered as secondary.
What matters are the processes that realize a body plan, and not
whether a shared plan implies the same ancestry. Under this
perspective, perhaps a return to the pre-Darwinian concept of homology
will be more useful to biologists ... [homology] restricted to
morphology and not in molecular biology." (Aboitiz, 1988, p 28)
- naturalism vs. supernaturalism
- macroevolution vs abrupt appearance
will praise you because I am fearfully and wonderfully made; your
works are wonderful, I know that full well. Psalm 139:14
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Acta Biotheoretica 37:27-29.
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Berry A. and R.A. Jensen, 1988. "Biochemical evidence for phylogenetic
Boyden, A., 1935. "Genetics and homology."
Quarterly Review of Biology 10:448-451.
Boyden, A., 1943. "Homology and analogy: a century after the
definitions of 'homologue' and 'analogue' of Richard Owen."
Quarterly Review of Biology 18:228-241.
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meanings and implications of these concepts in biology."
American Midland Naturalist 37:648-669.
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serology: part ll."
Serological Museum Bulletin 34:1-4.
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Totowa, NJ: Rowman and Littlefield,
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Washington, DC: National Biomedical
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O.E. Lowenstein, eds.,
Oxford Biology Readers 11:1-16. London:
Denton, M., 1985. Evolution: a theoiy in crisis.
Kensington, MD: Woodbine House.
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Proceedings of the 11th Bible-Science
Assoc. National Conference,
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phylogeny -- why can't we decide?"
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Arbor, Ml: University
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ed., Ontogeny and
Systematics. New York: Columbia U.P.,
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Systematic Botany 9(4): 382-394.
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the ninth component of complement (C9)."