The Neuropeptide Oxytocin Regulates Parochial Altruism in Intergroup Conflict Among Humans

Carsten K. W. De Dreu, et al. (2010)

Thanh-Thao Truong and Erika Gajda

Abstract

• Parochial altruism – self-sacrifice to the in-group and aggression towards competing out-groups

• Oxytocin – neuropeptide produced in the hypothalamus, regulates intergroup conflict

• Double-blind placebo-controlled experiments• Results show a “tend and defend” response

Introduction

• Modern intergroup conflict includes prejudice, terrorism, ethnic cleansing, and interstate war

- ex. Genocides have killed >210 million people and terrorists killed >30,000 people

• Parochial altruism: self-sacrifice influences in-group love and out-group aggression

• Out-aggression may lead to out-group hate• “groups with a greater number of courageous,

sympathetic, and faithful members…would spread and be victorious over other tribes.” – Darwin

Introduction cont.

• Oxytocin is a neurotransmitter and hormone• Targets include amygdala, hippocampus,

brainstem, and regions of the spinal cord• Promotes trust and cooperation• More OXTR leads to greater empathy, generosity,

etc.• Hypothesis: “Oxytocin modulates parochial

altruism” via in-group trust/love and out-group hate/defensive aggression.

Experiment 1Methods

• Does oxytocin stimulate in-group love, out-group hate, or both?

• Participants: 49 healthy males• Given a placebo or oxytocin nasal spray 30

min. prior to game

Experiment 1Methods

• Each individual given €10* €1 kept = €1 for the individual* €1 contributed to within group = €0.50 to each in-group member + individual* €1 contributed to between group = €0.50 to each in-group member + individual, subtracts €0.50 from each out-group member

• Contributing nothing results in highest personal outcome regardless what others do

• Contributing to within group results in highest benefit to in-group (cooperative motivation and in-group love)

• Contributing to between-group reflects spiteful out-group hate

Experiment 1Results

• In-group love > out-group hate• Oxytocin maximized in-group love but had no

effect on out-group hate (25% oxytocin vs. 28% placebo)

• Placebo: 52% egoist and 20% in-group lovers• Oxytocin: 17% egoist and 58% in-group lovers• In-group trust exceeded out-group distrust

- Measured on a seven-point Likert scale (1 = low, 7 = high)

Experiment 1Results

Experiment 2Methods

• Do cooperative individuals respond more strongly to oxytocin than non-cooperative individuals?

• 67 males completed the standard social value orientations test (9 total choices)

• Cooperators made at least 6 out 9 cooperative choices (N=25)

• Non-cooperators made at least 6 out of 9 non-cooperative choices (N=42)

• Given placebo or oxytocin, same methods as Experiment 1

Experiment 2Results

• Oxytocin increased in-group love among both cooperators and non-cooperators

• Oxytocin does not work only on cooperative individuals

• Trust results similar to Experiment 1

Experiment 3Methods

• Does oxytocin modulate defensive aggression against out-groups?

• 75 males• Randomly assigned to one of four between-

group prisoner-dilemmas (BG-PD)• Four possible outcomes – temptation (T),

reward (R), punishment (P), and sucker (S)• T>R>P>S

Experiment 3Methods

• Mutual cooperation = reward of 1.00 (R) Mutual non-cooperation = reward of 0.60 (P)

• T and S values vary with fear and greed level• Greed = T – R• Fear = P – S• Greed and fear were set to high and low

values (0.40 vs. 0.10)

Experiment 3Methods

• B: high greed, high fear• C: high greed, low fear• D: low greed, high fear• E: low greed, low fear• Researchers prediction:– Higher non-cooperation in B/C may reflect greedy desire

to exploit out-group– Higher non-cooperation in B/D may reflect anxious desire

to protect the in-group against a possibly aggressive out-group.

Experiment 3Results

• Individuals given oxytocin are less likely to cooperate when fear is high.

• No effects involving greed were significant.• Those given oxytocin had stronger in-group

trust than placebo• Higher in-group trust• No effects on out-group distrust• “Tend and defend”

Experiment 3Results

Experiment 3Results

• A: non-cooperation (range 0-3 tries)• B: Motivation to protect

(range 1-7)• C: In-group trust (range 1-7)

Discussion

• In all three experiments, those given oxytocin display more in-group trust and in-group love.

• No effect on out-group hate and out-group distrust

• Defensive aggression and protection of in-group was higher among individuals given oxytocin.

• Parochial altruism evolved to increase individual survival via promotion of social life and protection against threats.

Limitations

• Used all males• Age limit (college student) Brain development Hormone levels

• OXTR number and sensitivity to response• Culture• Setting (no face-to-face interaction)• Unclear organization/format

Real World ApplicationBoston Bombings• Tsarnaev brothers planted two pressure

cooker bombs at the Boston Marathon in 2013

• "When you attack one Muslim, you attack all Muslims.“

• Great in-group love and out-group fear• What about out-group distrust?• Americans vs. Extremists