Climate change–induced population pressure drives high rates of lethal violence in the Prehispanic central Andes

Abstract

Significance Warfare and homicide are pervasive features of the human experience, yet scholars struggle to understand the conditions that promote violence. Climate and conflict research has revealed many linkages between climate change and human violence; however, studies often produce contrary findings, and the driving mechanisms remain difficult to identify. We suggest a solution is to identify conditions producing resource scarcity, which are necessarily a combination of climate and population dynamics. We examine patterns of lethal violence in the Prehispanic Andes and find that favorable climate conditions fostered rapid population growth within a circumscribed landscape, resulting in chronic warfare. Our work suggests that an increasingly unstable climate may promote future violence, where favorable climate regimes incentivize population growth and attendant resource strain.

1000 years of population, warfare, and climate change in pre-Columbian societies of the Central Andes

“…The spatially differentiated pattern in the mutual coupling between population growth and conflict detected here supports the notion that warfare was a localized process across the Central Andes Centers Area, and it was particularly relevant in the southern highland centers (e.g., [30, 66]. Conflict dynamics in this area have been attributed to the disintegration of sociopolitical networks [70], but more recently to increased population pressure on food production [35]. Alternatively, the increase in warfare intensity has been linked to the impact of a multicentennial drought that hit the Andean highlands between AD 900 and AD 1200 [e.g., 30, 31].…”

“…Although most of available evidence indicates that these demises were accompanied by increased warfare intensity [30][31][32][33][34], the interaction of internal conflicts has been poorly considered. Still, McCool et al [35] have recently explored the relationship between demography, hydroclimate and conflict in groups that dwelled mid-elevation valleys from the southern centers area at 700-1400 AD. Based on statistical causality analyses, these authors found that chronic conflict in the Nasca region was indirectly linked to climate, but directly to increased population size/pressure, which was ultimately set by the positive effect of wetter conditions on the food production in an arid region with limited availability of croplands.…”

Climate change intensified violence in the south-central Andean highlands from 1.5 to 0.5 ka

“…For those people who did perceive mobility as an acceptable solution to drought-induced resource scarcity, migration towards wetter regions may not have completely alleviated metabolic stress or conspecific competition over agricultural resources. McCool et al (McCool et al, 2022b) argued that the increased precipitation in the Nazca highlands may have acted as a pull factor, drawing more people to the area than the environment could support, leading to conflict over scarce resources. That these findings contradict each other requires explanation.…”

“…In a more region-specific study, McCool et al (2022b) found that violence rates in the Nazca highlands were, counter to expectation, greatest during periods of elevated precipitation. The authors hypothesized that the increased precipitation may have acted as a pull factor—drawing more people to the area than the environment could support (McCool et al, 2022b).…”

“…In a more region-specific study, McCool et al (2022b) found that violence rates in the Nazca highlands were, counter to expectation, greatest during periods of elevated precipitation. The authors hypothesized that the increased precipitation may have acted as a pull factor—drawing more people to the area than the environment could support (McCool et al, 2022b). These findings conflict with findings from other world regions indicating increased violence associated with increasingly dry conditions (Allen et al, 2016; Schwindt et al, 2016).…”