Trust and deceit
in the animal kingdom
Liesbeth Sterck
Animal Ecology, UU
Ethology Research, BPRC
Trust
Nature in tooth and claw
• Monkey business
• Sly as a fox
Cooperation in theory
• Evolution on level individual
• Altruism:
benefit for other,
costs for individual
• Problem with cheaters
Cooperation in theory
• Mutualism: simultaneous exchange of benefits
• Altruism: donor incurs cost; recipient benefits
– Kin selection
– Reciprocal altruism
Kin selection (Hamilton 1964)
• Altruism when:
• C < r*B
• Costs < relatedness * Benefits
Kin selection (Hamilton 1964)
• C < r*B
r=1/2
r=1/4
r=1/8
Kin selection (Hamilton 1964)
• C < r*B
Animals can be nice to kin
Cooperation with non-kin?
http://www.youtube.com/watch?v=o2B1AJ3ZaUA
Reciprocal altruism (Trivers 1971)
• ‘If you scratch my back, I’ll scratch yours’
• Non-kin
• Not simultaneous
Prisoners Dilemma
• Cooperate or cheat (defect)
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
Humans
• Humans are a group-living species
– Family / kin
– Friends / acquaintances / colleagues
-- Warfare
Groups are diverse
• Size
– From 2 - 100 - 10.000s individuals
• Composition
– Changing- fixed
• Recognition group members
– Anonymous –categories – individuals
• Reproduction
– One female (+ male) - everyone
Cooperation in practice 1
• Why do primates live in groups?
Group living: advantages
• Warning against predators (van Schaik 1989)
Group living: disadvantages
• Competition (Wrangham 1980; Sterck et al. 1997}
Females:
– Food
Males:
– Matings
Group living: advantages
• Infanticide avoidance (Sugiyama 1965; 1966; Hrdy 1977; Sterck et
al. 1997)
Balance in costs and benefits
Protection against
predators and
infanticide
Competition
Primate peculiarity:
groups contain
both females and males
Cooperation in practice 2
• How do primates live in groups?
How primates live in groups
• How complex is living in a primate group
• Do they take benefit others into account
Methods
• From individual to group:
• Observations
• Behavioural experiments
Methods
• From individual to group:
• Observations
• Behavioural experiments
• Computer simulations
How primates live in groups
• How complex is living in a primate group
– Dominance
– Good relationships
Bob (29)
Relationships in group
(Massen, Sterck & de Vos 2010)
1.6
Sitting together
1.4
1.2
20
29
Timon (20)
1
0.8
0.6
0.4
0.2
0
verwant
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18niet
19familie
20 21 22 23 24 25 26 27 28 30 31 32 33 34 35
Kin
Dominance
Friendship
Good relationships
Advantages male – female relationships
Advantages
Friendship and mating success
Grooming by males (sec/hour)
(Massen, Sterck et al. 2012)
120
*
Mating
wel
paren
100
niet
No paren
mating
80
60
40
20
0
2006/07
2007/08
Mating season
Friendship and paternity
(Massen, Sterck et al. 2012)
Proximity of male (rank)
6
*
5
4
3
2
1
0
otheralle
male
vader
father
males
Friendship
• Do they know their friends?
Computer simulation of behaviour
(Hemelrijk 1998, 2000; Evers, Sterck et al. 2011, 2012, 2014)
Computer simulation of behaviour
(Evers, Sterck et al. MS)
Dominance
Grooming= friendship
Dominance
Computer simulation of behaviour
(Evers, Sterck et al. MS)
1.6
1.4
1.2
1
0.8
0.6
Dominance
Grooming = friendship
Dominance
0.4
0.2
0
niet
verwant
familie
Primate group living
• Compete and cooperate in group
• Relationships
– Kinship
– Dominance
– Friendship = ‘trust’
• Friendships take time to build and last long
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
Cooperation: pro-social behaviour
35
(Massen, vd Berg, Spruijt en Sterck
2010: PlosOne 5(3): e9734)
• Do primates bestow other a favor?
Cooperation: pro-social behaviour
(Massen, vd Berg, Spruijt en Sterck
2010: PlosOne 5(3): e9734)
• To kin
• To high-ranking animals
Bestow
Neutral
Withhold
High rank
36
Low rank
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
Inequity Aversion
• Negative inequity aversion
– React to getting less than other
• Positive inequity aversion
– React to getting more than other
38
Inequity Aversion
(Brosnan & de Waal 2003)
http://www.youtube.com/watch?v=KSryJXDpZo
capuchin monkey refuses food
39
Inequity Aversion (IA): critisism
• Newer data: no IA
40
The task for macaques
41
The Conditions
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
42
O,35 kg
2,
kg
O,35 kg
2,
kg
Proportion of acceptance/performance
of all equity conditions for all animals
Friedman test: n = 19, 2 = 15.84, df = 2, p = 0.001
Post-hoc
Wilcoxon
ranks tests:
Significant
dropsigned
in performance
(for low value
reward) with
increasing
workload
Provisioning
vs. 0,5
kg: n = 19,
T+=62.5, pexact= 0.115
Provisioning vs. 2,3 kg: n = 19,
T+= 152, pexact< 0.001
43
0,5kg vs. 2,3 kg:
n = 19, T+= 117.5, pexact= 0.008
Proportion of acceptance/performance
of dominant subjects
Wilcoxon signed ranks tests:
Disadvantageous
Inequity
in =small
Provisioning:
n = 12, aversion
T+= 21, pexact
0.719effort test
Small Effort:
n = 12, T+= 34, pexact= 0.023
Large Effort (reward):
n = 12, T+= 8.5, pexact= 0.211
Large Effort (reward & effort):
n 44
= 12, T+= 15.5, pexact= 0.250
AIA: Proportion of acceptance/
performance of subordinate partners
Wilcoxon
signed
Performance
forranks
low tests:
value reward decreases when workload
increases
Provisioning:
n = 9, T+= 3, p
= 0.156
T +=
exact
Small
Effort:
n = 9,
4, high
pexact=
0.219reward
At high
workload, performance
for
value
Large Effort (reward):
n = 9, T+= 0, pexact= 0.008
significantly better then for low value
reward
Large Effort (reward & effort):
n 45
= 9, T+= 4, pexact= 0.055
--> no advantageous inequity aversion
Nature in tooth and claw?
• Monkey business
• Sly as a fox
Care and friendship
• C < r*B
Conclusion
• Deceit kept in limits: otherwise no cooperation
• Competition and cooperation in group
– Dominance and friendship
• Trust and friendship crucial for cooperation
Thank you
Humans are smart and have large
brains
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
Social intelligence
• Evidence in favour:
• Group size and brain size are correlated in
primates, cetaceans and carnivores (Dunbar 1998)