1. Trust and deceit in the animal kingdom Liesbeth Sterck Animal Ecology, UU Ethology Research, BPRC

2. Trust

3. Nature in tooth and claw Monkey business Sly as a fox

4. Cooperation in theory Evolution on level individual Altruism: benefit for other, costs for individual Problem with cheaters

5. Cooperation in theory Mutualism: simultaneous exchange of benefits Altruism: donor incurs cost; recipient benefits – Kin selection – Reciprocal altruism

6. Kin selection (Hamilton 1964) Altruism when: C < r*B Costs < relatedness * Benefits

7. C < r*B r=1/2 r=1/4 r=1/8 Kin selection (Hamilton 1964)

8. C < r*B

9. Animals can be nice to kin http://www.youtube.com/watch?v=o2B1AJ3ZaUA Cooperation with non-kin?

10. Reciprocal altruism (Trivers 1971) ‘If you scratch my back, I’ll scratch yours’ Non-kin Not simultaneous

11. Prisoners Dilemma Cooperate or cheat (defect)

12. Reciprocal altruism (Trivers 1971) ‘If you scratch my back, I’ll scratch yours’ Non-kin Not simultaneous Repeated encounters Individual recognition, e.g. in a group

13. Humans Humans are a group-living species – Family / kin – Friends / acquaintances / colleagues -- Warfare

14. Groups are diverse Size – From 2 - 100 - 10.000s individuals Composition – Changing- fixed Recognition group members – Anonymous –categories – individuals Reproduction – One female (+ male) - everyone

15. Cooperation in practice 1 Why do primates live in groups?

16. Group living: advantages Warning against predators (van Schaik 1989)

17. Group living: disadvantages Competition (Wrangham 1980; Sterck et al. 1997} Males: – Matings Females: – Food

18. Group living: advantages Infanticide avoidance (Sugiyama 1965; 1966; Hrdy 1977; Sterck et al. 1997)

19. Balance in costs and benefits Protection against predators and infanticide Competition Primate peculiarity: groups contain both females and males

20. Cooperation in practice 2 How do primates live in groups?

21. How primates live in groups How complex is living in a primate group Do they take benefit others into account

22. Methods From individual to group: Observations Behavioural experiments

23. Methods From individual to group: Observations Behavioural experiments Computer simulations

24. How primates live in groups How complex is living in a primate group – Dominance – Good relationships

25. Relationships in group (Massen, Sterck & de Vos 2010) Kin Dominance Friendship 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 30 31 32 33 34 35 Sitting together 29 20 Timon (20) Bob (29)

26. Good relationships Advantages Advantages male – female relationships

27. Friendship and mating success (Massen, Sterck et al. 2012) Grooming by males (sec/hour) Mating season * Mating No mating

28. Friendship and paternity (Massen, Sterck et al. 2012) Proximity of male (rank) males * other malefather

29. Friendship Do they know their friends?

30. Computer simulation of behaviour (Hemelrijk 1998, 2000; Evers, Sterck et al. 2011, 2012, 2014)

31. Computer simulation of behaviour (Evers, Sterck et al. MS) Grooming= friendship Dominance

32. Computer simulation of behaviour (Evers, Sterck et al. MS) Grooming = friendship Dominance

33. Primate group living Compete and cooperate in group Relationships – Kinship – Dominance – Friendship = ‘trust’ Friendships take time to build and last long

34. Primate cooperation in practice 2 Do they take benefit others into account? – Other-regarding preferences – Inequity aversion Yerkes 1930’s: http://www.youtube.com/watch?v=zrv91Pa3jgs

35. Cooperation : pro-social behaviour Do primates bestow other a favor? (Massen, vd Berg, Spruijt en Sterck 2010: PlosOne 5(3): e9734) 35

36. To kin To high-ranking animals (Massen, vd Berg, Spruijt en Sterck 2010: PlosOne 5(3): e9734) Bestow Withhold Neutral High rankLow rank 36 Cooperation : pro-social behaviour

37. Inequity Aversion "Inequity exists for a person whenever his perceived job inputs and/or outcomes stand psychologically in an obverse relation to what he perceives are the inputs and/or outcomes of another" (Festinger 1957) 37

38. Inequity Aversion 38 Negative inequity aversion – React to getting less than other Positive inequity aversion – React to getting more than other

39. Inequity Aversion (Brosnan & de Waal 2003) http://www.youtube.com/watch?v=- KSryJXDpZo capuchin monkey refuses food 39

40. Inequity Aversion (IA): critisism 40 Newer data: no IA

41. The task for macaques 41

42. O, 5 kg 2, 3 kg 1.No effort (provisioning) Equity 2.No effort (provisioning) Inequity 3.Small effort Equity 4.Small effort Inequity 5.Large effort Equity 6.Large effort Inequity 7.Large effort Reward & effort inequity The Conditions 42

43. Friedman test:n = 19,  2 = 15.84, df = 2, p = 0.001 Post-hoc Wilcoxon signed ranks tests: Provisioning vs. 0,5 kg: n = 19, T + =62.5, p exact = 0.115 Provisioning vs. 2,3 kg: n = 19, T + = 152, p exact < 0.001 0,5kg vs. 2,3 kg: n = 19, T + = 117.5, p exact = 0.008 Proportion of acceptance/performance of all equity conditions for all animals Significant drop in performance (for low value reward) with increasing workload 43

44. Wilcoxon signed ranks tests: Provisioning: n = 12, T + = 21, p exact = 0.719 Small Effort:n = 12, T + = 34, p exact = 0.023 Large Effort (reward):n = 12, T + = 8.5, p exact = 0.211 Large Effort (reward & effort):n = 12, T + = 15.5, p exact = 0.250 Proportion of acceptance/performance of dominant subjects Disadvantageous Inequity aversion in small effort test 44

45. Wilcoxon signed ranks tests: Provisioning: n = 9, T + = 3, p exact = 0.156 Small Effort:n = 9, T + = 4, p exact = 0.219 Large Effort (reward):n = 9, T + = 0, p exact = 0.008 Large Effort (reward & effort):n = 9, T + = 4, p exact = 0.055 AIA: Proportion of acceptance/ performance of subordinate partners Performance for low value reward decreases when workload increases At high workload, performance for high value reward significantly better then for low value reward --> no advantageous inequity aversion 45

46. Nature in tooth and claw? Monkey business Sly as a fox

47. Care and friendship C < r*B

48. Conclusion Deceit kept in limits: otherwise no cooperation Competition and cooperation in group – Dominance and friendship Trust and friendship crucial for cooperation

49. Thank you

50. Humans are smart and have large brains

51. Social Intelligence Hypothesis Primates have relatively large brains Both cooperation and competition in group Several hypotheses – Primates ‘smart’ through social complexity Socially complex = socially intelligent

52. Social intelligence Evidence in favour: Group size and brain size are correlated in primates, cetaceans and carnivores (Dunbar 1998)