UC Santa Barbara

This dissertation research addresses two central questions: 1) what conditions promote warfare? 2) how do people cope with conflict? I seek to answer these questions by developing and employing osteological, stable isotope, and statistical methods, and using theoretical models from Human Behavioral Ecology (HBE).

The four dissertation chapters presented here articulate distinct but related aspects of warfare and concern casual forces, subsistence trade-offs, and well-being. The dissertation builds towards the third and fourth chapters, which evaluate the two primary questions of this research: 1) what variables explain the emergence and persistence of warfare? and 2) how do individuals manage the tradeoff between the risk of food shortages and the risk of wartime violence? Chapter three will focus on the climatological, demographic, and sociopolitical conditions that explain variability in warfare, and how these conditions may promote violence from an evolutionary perspective. Chapter four explores the ways in which the risk of interpersonal violence (RIV) structures the costs and benefits of alternative subsistence strategies and their attendant health impacts. Further, it investigates the factors that influence individual variability in risk-preference. Chapters one and two set the stage for the latter half of the dissertation by investigating 1) evidence for internecine warfare in the study region, and heterogeneity in the risk of interpersonal violence, and 2) changes in pathology, mortality, and longevity by engaging with the osteological paradox using a multimethod approach.

These topics are explored using a case study population of agropastoralists from the Late Intermediate period (950 – 1450 C.E.; LIP) Nasca highlands of Peru. To accomplish dissertation goals, my research must demonstrate that 1) the LIP Nasca highland population experienced chronic, internecine warfare which produced high probabilities of interpersonal violence; 2) increasing pathological burden is the result of elevated biological stress rather than increasing longevity or robusticity; 3) variability in violent conflict can be explained by changes in socioecological and demographic variables, and 4) wartime changes in subsistence practices and dietary stress can be understood as optimal strategies that attempt to balance the risk of food insecurity with the risk of interpersonal violence.

Chapter one focuses on using osteological data and formal quantitative analyses to test various hypotheses concerning the character of conflict in the Nasca highlands region. This chapter develops and tests osteological expectations of what patterns should be observed if LIP violence is defined by intra-group violence, ritual conflict, intermittent raiding, or internecine warfare. This chapter will also highlight heterogeneity in violent mortality to assess whether certain subgroups were targeted for violence, or whether violence is best explained by the concept of social substitutability.

Chapter two assesses changes in morbidity, mortality, and longevity during the LIP. We leverage recent multimethod approaches to address the implications of the osteological paradox, which revealed profound equifinality in interpretations of health from skeletal samples. The goal of this chapter is to evaluate how conditions during the LIP impacted the general well-being of the population as well as variability in the risk of disease and death.

Chapter three investigates individual motivations for participating in warfare from an evolutionary perspective, and how they relate to the emergence and spread of conflict on large spatiotemporal scales. I derive and test hypotheses that predict how political transitions, climate change, dietary stress, and demographic pressure structure the payoffs for conflict and interact to promote warfare.

Chapter four develops and tests a risk sensitive HBE model that outlines how the local economy, while designed to reduce the risk of food shortages in the arid Andean environment, nevertheless puts individuals at increased risk of violence during wartime. The model specifies resource returns and violence avoidance as an explicit tradeoff, whereby the probability of violence can be mitigated at the cost of food security and vice versa. This chapter seeks to develop a model that can explain how populations and individuals cope with subsistence needs during times of war, especially when local environmental conditions promote subsistence strategies that put individuals at a high risk of interpersonal violence.