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 1 Methods 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 1 Methods 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 1 Results 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 1 Results

Experiment 2 Methods 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 2 Results 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 3 Methods 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 3 Methods 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 3 Methods 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 3 Results 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 3 Results

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 Application Boston 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