How old is war? Is it a deep-seated propensity in the human species or is it a recent cultural invention? This article investigates the archaeological evidence for prehistoric war across world regions by probing two competing hypotheses. The "deep roots" thesis asserts that war is an evolved adaptation that humans inherited from their common ancestor with chimpanzees, from which they split around seven million years ago, and that persisted throughout prehistory, encompassing both nomadic and sedentary hunter-gatherer societies. In contrast, the "shallow roots" viewpoint posits that peaceful intergroup relations are ancestral in humans, suggesting that war emerged only recently with the development of sedentary, hierarchical, and densely populated societies, prompted by the agricultural revolution ~ 12,000-10,000 years ago. To ascertain which position is best supported by the available empirical evidence, this article reviews the prehistoric archaeological record for both interpersonal and intergroup conflict across world regions, following an approximate chronological sequence from the emergence of humans in Africa to their dispersal out of Africa in the Near East, Europe, Australia, Northeast Asia, and the Americas. This worldwide analysis of the archaeological record lends partial support to both positions, but neither the "deep roots" nor the "shallow roots" argument is fully vindicated. Intergroup relations among prehistoric hunter-gatherers were marked neither by relentless war nor by unceasingly peaceful interactions. What emerges from the archaeological record is that, while lethal violence has deep roots in the Homo lineage, prehistoric group interactions-ranging from peaceful cooperation to conflict-exhibited considerable plasticity and variability, both over time and across world regions, which constitutes the true evolutionary puzzle.