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The Evolution of Cooperative Behavoir. An Evolutionary Puzzle…. If Darwin’s 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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The Evolution of Cooperative Behavoir

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The evolution of cooperative behavoir l.jpg

The Evolution of Cooperative Behavoir

An Evolutionary Puzzle…..


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If Darwin’s 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 another’s cub

  • Birds cleaning parasites from hippo’s 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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Prisoner’s 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 Prisoner’s 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


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Cost-Benefit Matrix(Cost = 2; Benefit = 4)


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Normalized Cost-Benefit Matrix


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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.html


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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


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