The Evolution of Cooperative Behavoir

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The Evolution of Cooperative Behavoir

• An Evolutionary Puzzle..

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If Darwins Theory is true

• Our very nature is based on competition . . . .
  There is no reason why human should live together
  civilly anarchy will ultimately rule
• Is this true????

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Examples of Cooperative Behavior
Observed in Nature

• Hyenas cooperating to hunt prey
• Lioness caring for anothers cub
• Birds cleaning parasites from hippos teeth
• others?

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Challenge

• Can natural selection account for cooperative
  behavior???

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Possible Explanations

• Kin Theory
• Reciprocity -

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Game Theory

• Developed by Nobel Laureate and mathematical
  genius Dr. John Nash
• Featured in award-winning movie, A Beautiful
  Mind
• Can be used to test Reciprocity explanation for
  Cooperative Beh.

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Prisoners Dilemna
               

• Scenario
• You and a partner have been caught with stolen
  goods a minor crime punishable with 2 years in
  jail. Police, however, think you did the robbery
  (a major crime with a prison term of another 8
  years ), but they have no evidence it was either
  of you. They bring you in separately for
  questioning.
• ? (Get two volunteers) ?

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What should you do?

• Your partner
• Cooperate Defect You Cooper.
  2 years 10 years Defect 0
  years 8 years
• (Why is this a Dilemma?)

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Ready to play?

• Your partner
• Cooperate Defect You Cooper.
  2 years 10 years Defect 0
  years 8 years
• Get Index Cards. Make your move!

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Results

• of
• CC
• CD
• DD

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Question

• In a single-interaction scenario of Prisoners
  Dilemma, what is the logical move?
• (Defect, better choice, regardless of what
  partner does)

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Multiple Move PD

• But in nature, often two organisms will interact
  on a regular basis.
• What does Game Theory tell us about this
  situation?

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Cost-Benefit Matrix
Cooperate Defect
Cooperate b c c
Defect b 0
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Cost-Benefit Matrix(Cost 2 Benefit 4)
Cooperate Defect
Cooperate b c2 C-2
Defect b4 0
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Normalized Cost-Benefit Matrix
Cooperate Defect
Cooperate 4 0
Defect 6 2
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Your turn!

• Get ready to play a multiple move version of PD
• You will interact with your partner chimp some
  number between 20 30 times
• Try to think of a strategy which will maximize
  your points!

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Question

• Which strategies seemed most beneficial for you
  your classmates?

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Some common strategies in the Prisoner's Dilemma
Game

• ALTERNATE The player alternates between C and D,
  starting with a C.
• ALWAYS COOPERATE The player always plays C, no
  matter what their partner has played in the past.
  Also known as sucker.
• ALWAYS DEFECT The player always plays D. Also
  known as cheat.
• GRUDGER The player starts playing C and
  continues to do so until the other player plays
  D. After that it plays D for the rest of the game
  with that particular partner.
• RANDOM The player chooses either C or D with
  equal probability.
• SNEAKER The player starts with a C and then
  plays whatever its partner play in the previous
  move. However, at random intervals it plays D.
• TIT FOR TAT The player starts playing C and then
  plays whatever its partner did in the previous
  move.
• TIT FOR TWO TATS The player plays C in the first
  and second moves. After that, if its partner
  played D in the two previous moves they play D,
  otherwise they continue to play C.
• TWO TITS FOR TAT The player starts with C, and
  then if its partner plays D, then plays D in the
  following two moves, otherwise plays C.

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The Evolutionary Game

• Competition between two nice and two nasty
  strategies
• Tabulate and graph results for 4 generations

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Evolutionary PD

• Try these computer simulations
• http//bio150.chass.utoronto.ca/pdgame/evolution.h
  tml

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Tit for Tat in Nature?

• Predator inspection
• Blood sharing
• Trench warfare

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Some Featured Ideas

• See Hand out