The Evolutionary Origins of Altruistic Behavior

The Evolutionary Origins of Altruistic Behavior
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This article explores whether selection at the individual level is enough to explain the origins of altruistic behavior. The authors discuss the anomaly of altruism in the animal world and the role of cooperation as the basis of human societies.

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PowerPoint presentation about 'The Evolutionary Origins of Altruistic Behavior'. This presentation describes the topic on This article explores whether selection at the individual level is enough to explain the origins of altruistic behavior. The authors discuss the anomaly of altruism in the animal world and the role of cooperation as the basis of human societies.. The key topics included in this slideshow are altruism, evolution, selection, cooperation, human societies,. Download this presentation absolutely free.

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1. On the evolutionary origins of altruistic behavior: can selection at the individual level be enough? On the evolutionary origins of altruistic behavior: can selection at the individual level be enough? Jos A. Cuesta & Anxo Snchez Jos A. Cuesta & Anxo Snchez GISC/Matemticas GISC/Matemticas Universidad Carlos III de Madrid Universidad Carlos III de Madrid 8th Granada Seminar Modelling Complex Social Systems 8th Granada Seminar Modelling Complex Social Systems

2. Cooperation: the basis of human societies Cooperation: the basis of human societies Occurs between genetically unrelated individuals Occurs between genetically unrelated individuals Anomaly in the animal world: Anomaly in the animal world:

3. Cooperation: the basis of human societies Cooperation: the basis of human societies Shows high division of labor Shows high division of labor Anomaly in the animal world: Anomaly in the animal world:

4. Cooperation: the basis of human societies Cooperation: the basis of human societies Valid for large scale organizations Valid for large scale organizations Anomaly in the animal world: Anomaly in the animal world: as well as hunter-gatherer groups as well as hunter-gatherer groups

5. Cooperation: the basis of human societies Cooperation: the basis of human societies Valid for large scale organizations Valid for large scale organizations Anomaly in the animal world: Anomaly in the animal world: or setting up nice events! or setting up nice events!

6. Cooperation: the basis of human societies Cooperation: the basis of human societies Some animals form complex societies Some animals form complex societies but their individuals are genetically related but their individuals are genetically related

7. Altruism: key to cooperation Altruism: key to cooperation Altruism: Altruism: fitness-reducing act that benefits others fitness-reducing act that benefits others Pure altruism is ruled out by natural selection acting on individuals la Darwin Pure altruism is ruled out by natural selection acting on individuals la Darwin

8. He who was ready to sacrifice his life (), rather than betray his comrades, would often leave no offspring to inherit his noble nature Therefore, it seems scarcely possible () that the number of men gifted with such virtues () would be increased by natural selection, that is, by the survival of the fittest. Charles Darwin (Descent of Man , 1871) How did altruism arise? How did altruism arise?

9. Altruism is an evolutionary puzzle Altruism is an evolutionary puzzle

10. A man who was not impelled by any deep, instinctive feeling, to sacrifice his life for the good of others, yet was roused to such actions by a sense of glory, would by his example excite the same wish for glory in other men, and would strengthen by exercise the noble feeling of admiration. He might thus do far more good to his tribe than by begetting offsprings with a tendency to inherit his own high character. Charles Darwin (Descent of Man , 1871) Group selection? Cultural evolution? Group selection? Cultural evolution?

11. Answers to the puzzle Answers to the puzzle Kin cooperation (Hamilton, 1964) Kin cooperation (Hamilton, 1964) common to animals and humans alike common to animals and humans alike Reciprocal altruism in repeated interactions (Trivers, 1973; Axelrod & Hamilton, 1981) Reciprocal altruism in repeated interactions (Trivers, 1973; Axelrod & Hamilton, 1981) primates, specially humans primates, specially humans Indirect reciprocity (reputation gain) (Nowak & Sigmund, 1998) Indirect reciprocity (reputation gain) (Nowak & Sigmund, 1998) primates, specially humans primates, specially humans None true altruism: individual benefits in the long run None true altruism: individual benefits in the long run

12. but only partial! but only partial! Strong reciprocity Strong reciprocity (Gintis, 2000; Fehr, Fischbacher & Gchter, 2002) (Gintis, 2000; Fehr, Fischbacher & Gchter, 2002) typically human (primates?) typically human (primates?) altruistic rewarding: predisposition to reward others for cooperative behavior altruistic rewarding: predisposition to reward others for cooperative behavior altruistic punishment: propensity to impose sanctions on non-cooperators altruistic punishment: propensity to impose sanctions on non-cooperators Strong reciprocators bear the cost of altruistic acts even if they gain no benefits Strong reciprocators bear the cost of altruistic acts even if they gain no benefits Hammerstein (ed.), Genetic and cultural evolution of cooperation (Dahlem Workshop Report 90, MIT, 2003)

13. Experiments Experiments experimenter experimenter subject 1 subject 1 subject 2 subject 2 2-3 months income 2-3 months income

14. Altruistic punishment: the Ultimatum Game Altruistic punishment: the Ultimatum Game (Gth, Schmittberger & Schwarze, 1982) (Gth, Schmittberger & Schwarze, 1982) experimenter experimenter proposer proposer responder responder M euros M euros M-u M-u u u OK OK u u M-u M-u NO NO 0 0 0 0

15. Experimental results Experimental results Proposers offer substantial amounts (50% is a typical modal offer) Proposers offer substantial amounts (50% is a typical modal offer) Responders reject offers below 25% with high probability Responders reject offers below 25% with high probability Universal behavior throughout the world Universal behavior throughout the world Large degree of variability of offers among societies (26 - 58%) Large degree of variability of offers among societies (26 - 58%) Proposers optimal strategy: offer the minimum Proposers optimal strategy: offer the minimum Responders optimal strategy: accept anything Responders optimal strategy: accept anything Results: Results:

16. Experimental results Experimental results Extraordinary amount of data Extraordinary amount of data Camerer, Behavioral Game Theory (Princeton University Press, 2003) Henrich et al. (eds.), Foundations of Human Sociality : Economic Experiments and Ethnographic Evidence from Fifteen Small-Scale Societies (Oxford University Press, 2004)

17. Experimental results Experimental results Paciotti et al. , American Scientist 93 , 58 (2005) Paciotti et al. , American Scientist 93 , 58 (2005) Ultimatum game as an interpreting tool

18. Altruistic rewarding Altruistic rewarding (Fehr, Kirchsteiger & Riedl, 1993) (Fehr, Kirchsteiger & Riedl, 1993) experimenter experimenter truster truster trustee trustee M M M M -u -u +2u +2u -v -v +2v +2v

19. Experimental results Experimental results More than 50% of trustees transfer money back, the more the higher the trusters transfer More than 50% of trustees transfer money back, the more the higher the trusters transfer Players often exchange M Players often exchange M Universal behaviour throughout the world Universal behaviour throughout the world Homo economicus vs. Homo reciprocans Review in Fehr & Fischbacher, Nature 425, 785 (2003) Review in Fehr & Fischbacher, Nature 425, 785 (2003) Both players gain the maximum by exchanging M Both players gain the maximum by exchanging M The trustee gains more by returning nothing The trustee gains more by returning nothing Results: Results: So trusters best strategy is to transfer nothing So trusters best strategy is to transfer nothing

20. Strong reciprocity Strong reciprocity Kin cooperation selfish genes Kin cooperation selfish genes Reciprocity tit-for-tat strategy (Axelrods experiments) Reciprocity tit-for-tat strategy (Axelrods experiments) Reputation gain altruism as sexual ornament (handicap principle) Reputation gain altruism as sexual ornament (handicap principle) Strong reciprocity sense of fairness requires other-regarding capabilities Strong reciprocity sense of fairness requires other-regarding capabilities Explanations for altruistic behaviour: Explanations for altruistic behaviour:

21. Strong reciprocity Strong reciprocity In experiments of public goods, the presence of a few cheaters quickly deteriorates cooperation In experiments of public goods, the presence of a few cheaters quickly deteriorates cooperation The introduction of a few altruistic punishers forces long term cooperation The introduction of a few altruistic punishers forces long term cooperation Strong reciprocity seems a crucial element to ensure cooperation in human societies Strong reciprocity seems a crucial element to ensure cooperation in human societies Importance of strong reciprocity: Importance of strong reciprocity:

22. Strong reciprocity Strong reciprocity Standard answer: cultural evolution through group selection Standard answer: cultural evolution through group selection Evidences in favour: Evidences in favour: Strong variability between cultures in altruistic patterns Strong variability between cultures in altruistic patterns Increase of altruistic behaviour in children as they grow Increase of altruistic behaviour in children as they grow Simulations of group selection models Simulations of group selection models Evolutionary origins of strong reciprocity: Evolutionary origins of strong reciprocity:

23. Is group selection unavoidable? Is evolutionary game theory correct?

24. Our model: setup Our model: setup ...... ...... N players N players player i player i t i : threshold (minimum share player i accepts) t i : threshold (minimum share player i accepts) f i : fitness (accumulated capital) f i : fitness (accumulated capital) M monetary units ( M =100) M monetary units ( M =100) A.S. & J. A. Cuesta, J. Theor. Biol., in press (2005) A.S. & J. A. Cuesta, J. Theor. Biol., in press (2005)

25. Our model: game step Our model: game step ...... ...... N players N players proposer proposer responder responder t p t p f p f p t r t r f r f r t p t r t p t r +M-t p +M-t p +t p +t p t p t r t p t r < <

26. Our model: every s steps Our model: every s steps ...... ...... N players N players minimum fitness minimum fitness maximum fitness maximum fitness t min t min f min f min t max t max f max f max new player new player t max t max f max f max mutation: t max = t max mutation: t max = t max (prob.=1/3) (prob.=1/3) +1 +1 -1 -1

27. Implemented features Implemented features Degree of altruism inherited from progenitor (with some error) Degree of altruism inherited from progenitor (with some error) No learning from experience No learning from experience No influence from other players (no culture) No influence from other players (no culture) No groups No groups Other-regarding behaviour with optimization (players offer the minimum they would accept) Other-regarding behaviour with optimization (players offer the minimum they would accept) Fitness (accumulated capital) is inherited Fitness (accumulated capital) is inherited

28. Small populations Small populations N =1000, 10 7 games, s =1, uniform initial condition

29. Slow selection Slow selection N =1000, 10 8 games, s =10 4 , t i =1 initial condition

30. Large populations Large populations N =10 6 , 2x10 7 games, s =1, uniform initial condition

31. Slow selection Slow selection N =10 5 , 1.28x10 11 games, s =10 4 , t i =1 initial condition

32. Why are reciprocators selected? Why are reciprocators selected? Higher threshold implies lower payoffs but higher acceptance rates for agents own offers Higher threshold implies lower payoffs but higher acceptance rates for agents own offers The presence of altruistic punishers increases rejection of selfish agents offers The presence of altruistic punishers increases rejection of selfish agents offers Mutations are small (darwinian), so newborn altruistic agents are just a little more altruistic Mutations are small (darwinian), so newborn altruistic agents are just a little more altruistic A quantitative description is still lacking A quantitative description is still lacking

33. Two thresholds (s small) Two thresholds (s small) N =1000, 10 6 games, s =1, uniform initial condition accept accept offer offer

34. Two thresholds (s middle) Two thresholds (s middle) N =1000, 10 8 games, s =1000, t i = a i =1 initial condition accept accept offer offer

35. Two thresholds (s large) Two thresholds (s large) N =1000, 10 9 games, s =10 5 , t i = a i =1 initial condition accept accept offer offer

36. Discussion Discussion Altruistic punishment is not necessarily a losing strategy when there are many agents Altruistic punishment is not necessarily a losing strategy when there are many agents Thus it may be established by individual selection alone Thus it may be established by individual selection alone Results reproduce the observed variability Results reproduce the observed variability One or two levels: not important for the arising of altruistic punishment One or two levels: not important for the arising of altruistic punishment Mutation rate might be relevant Mutation rate might be relevant

37. Mutation rate effect Mutation rate effect N =10000, 10 8 games, s =1, t i = 1 initial condition

38. Related results Related results

39. Related results Related results

40. Related results Related results Stag-hunt game: Two equilibria, S and R Round-robin gaming: S or R selected from x 0 ( x fraction of R) s games between death-birth S R C. P. Roca, J. A. Cuesta & A. S., in progress (2005) C. P. Roca, J. A. Cuesta & A. S., in progress (2005)

41. Related results Related results

42. Related results Related results Random death Death proportional to fitness

43. Discussion Discussion In general, evolutionary game theory studies a limit situation: s infinite! (every player plays every other one before selection) In general, evolutionary game theory studies a limit situation: s infinite! (every player plays every other one before selection) Number of games per player Poisson distributed Number of games per player Poisson distributed Fluctuations may keep players with smaller mean-field fitness alive Fluctuations may keep players with smaller mean-field fitness alive

44. Further discussion Further discussion Thresholds observed in neural activity measurements (Sanfey et al., 2003) (suggest that this threshold is an inheritable feature) Thresholds observed in neural activity measurements (Sanfey et al., 2003) (suggest that this threshold is an inheritable feature) Correlation with other-regarding behavior: also in different primates (capuchin monkeys) (Brosnan & de Waal, 2003) Correlation with other-regarding behavior: also in different primates (capuchin monkeys) (Brosnan & de Waal, 2003)

45. Main conclusions Main conclusions Altruism (altruistic punishment, as implemented in the Ultimatum Game) need not be an evolutionary losing strategy, so it may have arisen through standard individual selection Altruism (altruistic punishment, as implemented in the Ultimatum Game) need not be an evolutionary losing strategy, so it may have arisen through standard individual selection A new perspective in evolutionary game theory: more general dynamics, dictated by the specific application A new perspective in evolutionary game theory: more general dynamics, dictated by the specific application

46. Adam Smith on altruism Adam Smith on altruism How selfish soever man may be supposed, there are evidently some principles in his nature, which interest him in the fortunes of others, and render their happiness necessary to him, though he derives nothing from it, except the pleasure of seeing it. Adam Smith (The Theory of Moral Sentiments , 1854, Chapter 1)

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