Headhunting and Warfare in Austronesia: A Phylogenetic Comparative Analysis

Headhunting -- the practice of acquiring human heads for ritual purposes -- was historically widespread around the world. We hypothesize that headhunting represented a cultural response to frequent inter-tribal warfare and served as a mechanism to train warriors ready to defend their community. The practice was effective since, first, it allowed verification of warrior quality based on performance in headhunting raids and, second, it offered a system of rewards for men to develop and refine warfare skills. We use phylogenetic comparative methods and ethnographic data to empirically investigate this hypothesis in a sample of preindustrial Austronesian societies. Headhunting turns out to be substantially more prevalent in societies exposed to frequent warfare, accounting for shared cultural ancestry and a host of potentially confounding characteristics. Furthermore, Bayesian estimation of correlated evolution models suggests that, consistent with our hypothesis, the adoption of headhunting typically followed increases in warfare frequency and the decline of this practice was preceded by reduced intergroup conflict.