HomologyAnalogy

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Homology/Analogy
Botany 940 Evidence for evolution

• Natalia Alvarez
• Kevin Coleman
• 2006

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Homolog structure Similar structure and
position, but different function
Courtesy of Prof. Ken Sytsma
Analog structure Similar function, but different
origin
http//evolution.berkeley.edu
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Homology
Courtesy of Prof. Ken Sytsma
How can we explain this? Hypotheses??
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Homology

• Archetypal explanation
• The same organ in different animals under every
  variety of form and function. (Owen,1843)
  
• Common ancestry
• A structure is similar among related organisms
  because those organisms have all descended from a
  common ancestor that had an equivalent trait.
  (Darwin,1859)

Homology in character evolution. Staton, July 2000
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Wells Critique Circular definition

• Homology/Common ancestor
• Features are homologous because they are
  inherited from a common ancestor
  
• Common ancestry is inferred using homologous
  features.
  

Features can be tested by Multiple ad hoc
hypothesis of homology (Kluge 1997)
Origin of arthropod compound eye. Oakley,2002.
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How would you test common ancestry?
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How would you test common ancestry?

• Fossil record
• Structure and position
• behavioral patterns

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• Fossil record -Fossil intermediates
• Behavioral patterns

Bird
Alligator
Dinosaur
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How would you test common ancestry?

• Fossil record
• Structure and position
• behavioral patterns
• Genetics

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Wells Critique Genetics

• Assumption homologous features are programmed by
  similar genes
  
• Problems
• 1. Similar genes determine radically different
  structures.
  
• 2. Organisms with different genes produce similar
  structures.
  
• Example Pax6 in fruit flies, mice and humans

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• Genetics Homolog structures and genes
• Is there a correlation between genotype and
  phenotype?
  
• Pax6 in fruit flies, mice and humans
• "master regulator of eye development (qtd. in
  Displan,1997).
  
• Downstream genes are not the same, thus
  determines different structures.
  

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How would you test common ancestry?

• Fossil record
• Structure and position
• behavioral patterns
• Genetics
• Developmental pathways

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Wells Critique Developmental Pathways

• Assumption homologous features should develop in
  similar ways
  
• Problems
• 1. Similar pathways may produce very dissimilar
  features.
  
• 2. Similar features are often produced via very
  different pathways.

Haeckels drawings
Gilbert, S. F. 1997. http//7e.devbio.com/about.ph
p
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• Developmental pathways shared features, shared
  early developmental features ,presence and
  sequence of development stages.

http//www.natcenscied.org/icons/icon4haeckel.html
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How would you test common ancestry?

• Fossil record
• Structure and position
• behavioral patterns
• Genetics
• Developmental pathways
• others?

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Analogy

• Different structures which perform the same
  function (Owen, 1843)
  
• Convergence Similarities between organisms that
  evolved independently.

Tasmanian wolf
Mexican wolf
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Counterarguments

• Convergent evolution is used by evolutionists to
  explain homologies that do not line up with the
  evolutionary tree.
  
• The probability of a beneficial mutation is very
  low. In addition, the probability of two
  different organisms with the same configuration
  from the same mutation is astronomically low.

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Convergence directionality?

• Oakley and Cunningham 2002

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• -When you examine the tapestry of evolution you
  see the same patterns emerging over and over
  again. Gould's idea of rerunning the tape of life
  is not hypothetical it's happening all around
  us. And the result is well known to biologists
  evolutionary convergence. When convergence is the
  rule, you can rerun the tape of life as often as
  you like and the outcome will be much the same.
  Convergence means that life is not only
  predictable at a basic level it also has a
  direction. (Simon Conway Morris 2002)

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Design or Mere Accident?

• The mechanism of Darwinism is at last securely
  founded and as a consequence man has to
  understand that he is a mere accident. - Jaques
  Monod, 1970
• Two questions

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Design or Mere Accident?

• The mechanism of Darwinism is at last securely
  founded and as a consequence man has to
  understand that he is a mere accident. - Jaques
  Monod, 1970
• Two questions
• Why does a naturalistic mechanism preclude a
  divine scheme?
  
• Are just men an accident, or are women merely
  accidental as well?
  

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What is the PURPOSE of this seminar??
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What is the PURPOSE of this seminar??

• Understand evidence for evolution
• Allow scientists in different fields the
  opportunity to discuss their perspectives
  
• Circle the wagons against ID
• Critically discuss how we can best communicate
  evolution to a non-technical audience

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What is the PURPOSE of this seminar??

• Awareness of the limits of science the full
  range of the human experience cannot be explain
  by science alone
  
• Openness to questioning and inquiry, and
  accepting the possibility of being wrong.
  
• Reverence for life life is amazing, should we
  not all be in awe of biodiversity?

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Evolution vs. ID Does it matter? If so, why?

• How do we stop the current loss of biodiversity?
  
  
• Is this debate sucking energy away from the
  crisis at hand?
  
• Can we find common ground and work together
  toward protecting the planet?