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University of Oregon

War and Evolution Focus Group

Hosted by Holly Arrow (Psychology) and Marcela Mendoza (Anthropology), Institute for Cognitive and Decision Sciences


Intergroup violence has played a profound role in driving human history and continues to exert a powerful influence on people’s lives across the world. Evolutionarily informed perspectives of group processes can help us understand the power and persistence of war. We hope that this focus group will attract faculty members and graduate students in anthropology, evolutionary biology, history, political science, psychology, religious studies, sociology, and other fields who are interested in discussing the evolutionary roots of and broad impact of war, in the past and in modern times.


Marcela Mendoza recently presented a paper at a conference organized by Latin American developmental pediatricians, psychologists and neurologists in Asunción, Paraguay. This presentation is an outcome of the project on the war games of foragers. A pdf of her presentation is here.

Publication by Marcela Mendoza in The International Indigenous Policy Journal

Hunter-Gatherers’ Self-Governance: Untying the Traditional Authority of Chiefs from the Western Toba Civil Association




We will meet once a month, at a time to be determined based on member schedules. Please email Holly at for information about the next meeting and to get added to the mailing list for the group.

A little about the organizers:

Holly Arrow’s research focuses on the evolution of social capacities that help men and women cope with the challenges to survival and reproductive success posed by war.

Marcela Mendoza’s research explores hunter-gatherers social organization, including inter-group warfare and trophy-taking.

Please direct any questions to Holly at or Marcela at



Friday, May 15, 2015, 2:00 pm, 401 Straub Hall

Presenters: Marcela Mendoza and Michelle Scalise SugiyamaPlease come join us for a presentation of work in progress by two of our focus group members.  All are welcome!

War Games: Coalitional Play Fighting Among Forager Children

A large part of an organism’s development involves the assembly of adaptations.  As Tooby and Cosmides argue, “All mature adaptations depend upon the prior existence of adaptations designed to build them” (2001:15).  Thus, many cognitive adaptations are expected to have two modes, a functional mode and an organizational mode.  In the functional mode, the adaptation performs its evolved function; in the organizational mode, the adaptation is assembled.  During the assembly phase, the adaptation is provided with information and weightings that it needs to perform its function.  Some of this information may be reliably available in the external world, and the organizational mode of the adaptation may be designed to use this information rather than storing it in the genome.  Thus, the organizational mode is expected to have a motivational component that guides the organism to interact with its environment in ways that further the development of the adaptation.  We experience the effects of these motivational mechanisms, in part, as aesthetic responses, such as beauty, pleasure, fun, and excitement.  On this view, much of what is characterized as play behavior may be generated by adaptations operating in their organizational mode.  Each module of the human mind (e.g., language, vision, social intelligence, predator avoidance, sexuality) poses a different set of developmental problems.  Thus, each should come with its own aesthetic, designed to motivate the individual to engage in experiences (e.g., babbling, play chasing) that develop and/or calibrate the module.  We apply this hypothesis to coalitional play fighting (i.e., war play).  Specifically, we conceptualize war play as the operation of the module for coalitional intergroup aggression in its organizational mode.  To this end, we (1) delineate assessments that are specific to coalitional intergroup aggression, (2) describe war play (as documented in the ethnographic record) and the rules of engagement; and (3) discuss ways in which such play might provide information and weightings critical to readying the module for operation.



Friday, April 17, 2015, 2:00 pm, 401 Straub Hall

Topic of Discussion: Moral Injury

We will be discussing the attached short review of literature relevant to moral injury in veterans (Maguen & Litz 2012)
Several members of the group have read further into the reference list to expand input into the discussion:

Anne M. read Maguenet al. (2011). The impact of killing on mental health
symptoms in Gulf War veterans.

Marcela M. read the article on self-forgiveness (Hall & Fincham, 2005).

Holly Ah. read the Witvliet et al. (2004) on forgiveness and religious coping

Bill S. has read quite a few of the articles from the references, so he
can be our general lit review guy.

All are welcome, whether or not you have a chance to do look at the review article!  Our last discussion of moral injury was excellent and would be wonderful to have even more viewpoints for this next discussion.


Friday, March 6, 2015, 2:00 pm, 401 Straub Hall

The War and Evolution Focus Group will be meeting this Friday, March 6th at 2:00 PM in the ICDS Conference Room (401 Straub).  The reading, (Litz, B. T. et al. (2009). Moral injury and moral repair in war veterans: A preliminary model and intervention strategy.  Clinical Psychology Review, 29, 695-706) can be found here.

Those planning to attend are also encouraged (if they have time) to listen to or read the transcript of the following NPR  “Fresh Air” segment about moral injury:


Friday, February 13, 2015, 2:00 pm, 401 Straub Hall

The recently reconstituted War and Evolution Focus Group will be meeting Friday, February 13, 2015 at 2:00 pm. Ashleigh Landau (graduate student in Psychology) will be talking about her research in progress on genocide and we will also discuss the following article: “After the Genocide: Psychological Perspectives on Victim, Bystander, and Perpetrator Groups“.


Mendoza, M., (2007).
Hunter-Gatherers’ Aboriginal Warfare in Western Chaco. Pp.198-213. In Latin America Indigenous Warfare and Ritual Violence, edited by Richard Chacon and Ruben Mendoza. Tucson, AZ: University of Arizona Press.  Pdf

Mendoza, M., (2007).
Human Trophy Taking in the South American Gran Chaco. Pp. 575-590. In The Taking and Displaying of Body Parts as Trophies by Amerindians, edited by Richard J. Chacon and David H. Dye. NY: Springer. Pdf

Arrow, H., Smirnov, O., Orbell, J. & Kennett, D. (2007).
The selective consequences of war: A formal model. Pdf
In L. Thompson & K. Behfar (Eds.), Conflict in organizational teams: New directions in theory and practice (pp. 113-142). Evanston, IL: Northwestern University Press.

Smirnov, O., Arrow, H., Kennett, D., & Orbell, J. (2007).
Ancestral war and the evolutionary origins of ‘heroism.’ Pdf
Journal of Politics, 69 (4), 927-940.

Mendoza, M., (2006).
Skulls Collected for Scalping in the Gran Chaco. Pp. 113-118. In Skull Collection, Modification, and Decoration, edited by Michelle Bonogofsky. BAR International Series 1539. Oxford, UK: Archaeopress. Pdf

Arrow, H., & Burns, K. L. (2004).
Self-organizing culture: How norms emerge in small groups. Pdf
In M. Schaller & C. Crandall (Eds.), The psychological foundations of culture (pp. 171-199). Mahwah, NJ: Lawrence Erlbaum Associates.

Crosson, S. B., Orbell, J., & Arrow, H. (2004).
“Social poker”: A laboratory test of predictions from club theory. Pdf
Rationality and Society, 16(2), 225-248.

Arrow, H., & Crosson, S. B. (2003).
Musical chairs: Membership dynamics in self-organized group formation. Pdf
Small Group Research, 5, 523-556.