Principles of Evolutionary Reasoning

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Principles of Evolutionary Reasoning
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Just-So Stories

• One of humans great abilities is to make sense
  of things
• . . . Even when they do not make sense.
• One can make an evolutionary argument for
  virtually everything (remember Gentlemen prefer
  blondes).

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The Spandrel
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The Spandrel (Gould Lewontin)

• The spandrel is the inadvertent result of
  building a dome on rounded arches.
• Biological structures may likewise be the
  inadvertent result of evolutionary processes.

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Example of Spandrel

• Anthropologist Michael Harner (1977) proposed
  that Aztec human sacrifice arose as a solution to
  chronic shortage of meat.
• E. O. Wilson (1978) used this explanation as a
  example of an adaptive, genetic predisposition
  for carnivory in humans.
• Alternative H human sacrifice developed as part
  of elaborate cultural fabric of Aztec cosmology
  (Sahlins, 1978)
• Evidence
• Only people of high status cannibalized and only
  limbs.
• Other sources of protein NOT in short supply
  (Ortiz de Montellano, 1978).

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How We Need to Pay Attention to Spandrels

• Testosterone increases size of nose and chin.
• Evolutionary argument is large nose and chin is
  marker for reproductive health.
• Testable hypothesis women more attracted to men
  with large noses and chins.
• If hypothesis is confirmed, can we conclude that
  evolutionary H is correct?
• No
• Large nose and chin might be spandrel.
• Women may be attracted to high-testosterone
  males because they are more aggressive and
  therefore better protectors .
• Does it matter?

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Homologous and Analogous Traits

• Homologous traits
• Two species have similar traits because same
  evolutionary path
• Eyes in chimps and humans
• Analogous traits
• Two species have similar traits that
  independently evolved.
• Saber-toothed marsupial cat and saber-toothed
  tiger
• Walking octopi

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Emergent Properties

• Be wary of hypothesizing high-level construct
  when lower level construct is sufficient (Occams
  razor).
• Remember our discussion of chimps cooperating in
  hunting monkeys.
• Boids

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• Take-home lessons
• Be choosy in your hypotheses.
• If you start with hypotheses that map a cultural
  bias, it will be more difficult to test