1. Intergroup Conflict Intergroup conflict in the EEA:
Intergroup conflict in the EEA:
Selection pressures and psychological implications.
Potential threats to survival.
Implications for attitudes regarding intergroup conflict.
Potential threats to mate choice.
Implications for attitudes toward outgroups.
Potential opportunities to enhance mate value.
Implications for mate preferences.
Implications for attitudes regarding inter-group conflict.
Implications for within-group cooperation.

2. Implications for cognition and behavior in contemporary contexts
Intergroup conflict in the EEA.
If intergroup conflict was an enduring feature of ancestral ecologies, then specific selection pressures associated with intergroup conflict may have influenced the evolution of specific psychological mechanisms.
Selection pressures associated with intergroup conflict in ancestral ecologies
Psychological adaptations resulting from those specific selection pressures
Implications for cognition and behavior in contemporary contexts
Potential threats
to survival.
to mate choice.
Potential opportunities
to enhance mate value.

3. Potential threats to survival.
Within the EEA, interactions with outgroups posed a potential survival threat.
Psychological responses that may have been adaptive within EEA.
Stereotypic beliefs that outgroups are dangerous.
Fearful responses to outgroups.
Especially when people feel more vulnerable.
Avoidance of unexpected encounters with outgroup members
Perception that outgroup members are dangerous
Vulnerability

4. Potential threats to survival.
Additional implications, resulting from “fight-or-flight” response to threats.
Responses that that create (rather than avoid) intergroup conflicts
Responses that perpetuate (rather than resolve) existing conflicts.
Especially when people feel more vulnerable.
Avoidance of unexpected encounters with outgroup members
Perception that outgroup members are dangerous
Vulnerability
Aggressive behavior against outgroups and outgroup members

5. Potential threats to survival.
Additional implications, resulting from “fight-or-flight” response to threats.
Responses that that create (rather than avoid) intergroup conflicts
Responses that perpetuate (rather than resolve) existing conflicts.
Especially when people feel more vulnerable.
Application to contemporary conflicts in which everyone feels outnumbered.
For example: Intergroup conflict in Sri Lanka.
(Schaller & Abeysinghe, 2006)
When Sinhalese Sri Lankans felt like an outnumbered minority group, they…
Perceived Sri Lankan Tamils to be more aggressive.
Perceived Sri Lankan Tamils to be more capable.
Were less supportive of attempts to reach a peaceful resolution to the war.

6. Potential threats to mate choice.
Underlying evolutionary logic:
Within the EEA, intergroup conflict posed threat to female mate choice.
(Rape and sexual coercion within the context of intergroup conflict.)
Potential costs to female reproductive fitness.
Especially when most likely to conceive.
Psychological responses that may have been adaptive within EEA.
Menstrual cycle variation in female attitudes toward outgroups.
Some relevant research evidence:
(Navarrete et al., 2009)
This effect was strongest for women who felt most vulnerable to sexual coercion, and who perceived outgroup men to be especially aggressive.

7. Potential opportunities to enhance mate value.
Underlying evolutionary logic:
Choosy females and show-off-y males.
Within EEA, intergroup conflicts provided a domain within which males could potentially demonstrate their mate value to choosy females.
Psychological responses that may have been adaptive within EEA.
Female sexual attraction to successful male warriors.
Male attitudinal attraction to war.

8. Research on female sexual attraction to successful male warriors.
Anthropological research on Yanomamö tribal societies:
Male warriors had higher status and greater access to sexual partners.
Archival data on U.S. World War II veterans:
Compared to other veterans, “war heroes” produced more offspring.
Experimental evidence on perceived sexual attractiveness:
Women rated male “war heroes” to be especially sexually attractive.

9. British women presented with information about a male British soldier.
Three experimental conditions:
No War: “John has been in the military for 5 years now. He is the leader of a unit consisting of 4 men. John and his unit have not yet been to a war zone during their employment in the military. They have stayed in the UK and are responsible for the coordination of military personnel and equipment.”
War: “John has been in the military for 5 years now. He is the leader of a unit consisting of 4 men. John and his unit have been to Iraq recently. When they were there, their main job was the coordination of military personnel and equipment but they have also fought in a number of battles. After 6 months, John and his unit have returned home safely.”
War Hero: “John has been in the military for 5 years now. He is the leader of a unit consisting of 4 men. John and his unit have been to Iraq recently. When they were there their main job was the coordination of military personnel and equipment but they have also fought in a number of battles. After 6 months, John and his unit returned home safely. John was awarded a medal for individual bravery upon his return from Iraq.”
(Rusch, Leunissen, & Van Vugt, 2015)

10. Results: Perceived sexual attractiveness
(Rusch, Leunissen, & Van Vugt, 2015)

11. Research on male attitudinal attraction to war.
(Sex differences in “hawkish” attitudes toward intergroup conflict.)
Attitudes regarding real-life conflict situations:
Men more strongly support military interventions.
Men more strongly support continuation of ongoing wars.
Behavior in experiments that simulate war games:
Men are more likely to make unprovoked aggressive attacks.

12. Just a reflection of traditional gender roles?
Or does it reflect something deeper?
Prenatal environment
Development of nervous system
Attitudes and behaviors later in life

13. Just a reflection of traditional gender roles?
Or does it reflect something deeper?
Prenatal exposure to testosterone
Development of a “masculinized” nervous system
Prototypically “male” attitudes and behaviors later in life
For example:
Attitudes regarding war

14. Finger length ratio (“2D:4D”):
Indicates less prenatal
exposure to testosterone.
(More common among women)
Indicates more prenatal
exposure to testosterone.
(More common among men)
Behavior in experiments that simulate war games:
Smaller 2D:4D ratio associated with more unprovoked aggressive attacks.
(Masculinized nervous system produces “hawkish” attitudes.)
(Among both men and women.)
(McIntyre et al., 2007)

15. Potential opportunities to enhance mate value.
One additional implication…
Underlying logic:
Victory (rather than defeat) in an intergroup conflict is more show-off-y.
Victory is more likely under conditions of within-group cooperation.
Implication:
Intergroup competition may promote within-group cooperation (among men).
Some evidence:
(Van Vugt, De Cremer, & Janssen, 2007)

16. Masculinized nervous system produces “hawkish” attitudes.
Indicates less prenatal
exposure to testosterone.
(More common among women)
Indicates more prenatal
exposure to testosterone.
(More common among men)
Masculinized nervous system produces “hawkish” attitudes.

17. Less masculinized nervous system produces less hawkish attitudes.
Indicates less prenatal
exposure to testosterone.
(More common among women)
Indicates more prenatal
exposure to testosterone.
(More common among men)
Less masculinized nervous system produces less hawkish attitudes.

18. Menstrual cycle variation in female attitudes toward outgroups.
This effect was strongest for women who felt most vulnerable to sexual coercion, and who perceived outgroup men to be especially aggressive.

19. Menstrual cycle variation in female attitudes toward outgroups.
This effect was weakest for women who felt less vulnerable to sexual coercion, and who perceived outgroup men to be not-so-aggressive.

20. When Sinhalese Sri Lankans felt like an outnumbered minority group, they…
Perceived Sri Lankan Tamils to be more dangerous.
Were less supportive of attempts to reach a peaceful resolution to the war.

21. When Sinhalese Sri Lankans felt like less vulnerable, they…
Perceived Sri Lankan Tamils as less dangerous.
Were more supportive of attempts to reach a peaceful resolution to the war.