The Evolution of Cooperative Behavoir

1. The Evolution of Cooperative Behavoir An Evolutionary Puzzle…..

2. 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????

3. 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?

4. Challenge: Can natural selection account for cooperative behavior???

5. Possible Explanations • Kin Theory – • Reciprocity -

6. 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.

7. 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) 

8. What “should” you do? Your partner Cooperate Defect You Cooper. 2 years 10 years Defect 0 years 8 years (Why is this a “Dilemma”?)

9. Ready to play? Your partner Cooperate Defect You Cooper. 2 years 10 years Defect 0 years 8 years Get Index Cards. Make your move!

10. Results # of • CC = • CD = • DD =

11. Question In a single-interaction scenario of Prisoner’s Dilemma, what is the logical move? (Defect, better choice, regardless of what partner does)

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

13. Cost-Benefit Matrix

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

15. Normalized Cost-Benefit Matrix

16. 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!

17. Question • Which strategies seemed most beneficial for you & your classmates?

18. 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.

19. The Evolutionary Game • Competition between two “nice” and two “nasty” strategies • Tabulate and graph results for 4 generations

20. Evolutionary PD • Try these computer simulations: • http://bio150.chass.utoronto.ca/pdgame/evolution.html

21. Tit for Tat in Nature? • Predator inspection • Blood sharing • Trench warfare

22. Some Featured Ideas • See Hand out