Prosocial Emotion, Adolescence, and Warfare
Examining the costs and motivations of warfare is key to conundrums concerning the relevance of this troubling phenomenon to the evolution of social attachment and cooperation, particularly during adolescence and young adulthood—the developmental time period during which many participants are first recruited for warfare. The study focuses on Samburu, a pastoralist society of approximately 200,000 people occupying northern Kenya’s semi-arid and arid lands, asking what role the emotionally sensitized, peer-driven adolescent life stage may have played in the cultural and genetic coevolution of coalitional lethal aggression. Research in small-scale societies provides unparalleled opportunities for sharply defined variables, particularly in age generation societies in which all young men are initiated into “warriorhood.” Proposing an epigenetic and component behavior approach, we examine whether raiding activities such as number of raids, killing, and sparing enemy lives associate with DNA methylation in two candidate genes: MAOA, linked to mood and arousal, and NR3C1, linked to stress and immune response. We report statistically significant associations between the epigenetic variables and the combat (exposure) variables of overall raiding activity and reportedly showing mercy to enemies. In contrast, epigenetic variables did not associate with post-traumatic stress disorder (PTSD) symptom scores (a potential outcome measure), and the only combat variable associated with PTSD (but not DNA methylation) was losing one’s own livestock in a raid. These findings raise important questions concerning the mechanisms driving warfare’s paradoxical mix of violent and altruistic behaviors.
KeywordsWarfare adolescence prosocial emotion cooperation epigenetics Kenya
In Kenya, the authors would like to thank the Kenyan Ministry of Education for permission to conduct research, University of Nairobi and Laikipia University for affiliation and collegial interaction in Kenya, and the Samburu participants and their families for supporting and participating in the research. In the United States the authors are grateful to Western Michigan University Office of the Vice President for Research and College of Arts and Sciences for kind support of the research. Additional appreciation is extended to Richard and Yamilette Chacon for organizing the 2015 and 2017 Warfare, Environment, Social Inequality and Peace Studies (Pro-Socialty) (WESIPS) Conferences; to the participants for their incisive comments, especially Stephen Beckerman, Paul Valentine, and Charles Hilton; to Larry Schell for encouragement, and to anonymous reviewers of the manuscript whose excellent and constructive comments enhanced the final paper. Background research on Samburu warriors and coalitional gun violence was supported by National Science Foundation Senior Grant 0413431 (Jon Holtzman, co-PI), with additional support from National Science Foundation Senior Grant 1430860.
BS conceived the study’s pre-DNA phase, conceived and designed the culturally specific instrumentation including combat screens, supervised and checked translations, carried out the ethnographic interviews. BN and BS conceived the DNA methylation study component. AN and BS scored and interpreted standard psychosocial instrumentation. BS, CR, and JF supervised Kenyan translators and administered questionnaires to participants. TB and BS extracted the DNA. CL performed the bisulfite conversion, PCR, and supervised mass spectrometry. GO and PW performed the statistical analyses. CO and SL provided field support. BS wrote the paper, and BN, GO, TB, AN, CR, JF, CO, and SL commented on drafts.
Compliance with ethical standards
Human Rights and Informed Consent
All procedures performed in studies involving human participants were in accordance with the ethical standards of the Western Michigan University Human Subjects Institutional Review Board and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.
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