The Neuropeptide Oxytocin Regulates Parochial Altruism in Intergroup Conflict Among Humans

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