Why war is a man's game

Abstract

Interest in the evolutionary origins and drivers of warfare in ancient and contemporary small-scale human societies has greatly increased in the last decade, and has been particularly spurred by exciting archaeological discoveries that suggest our ancestors led more violent lives than previously documented. However, the striking observation that warfare is an almost-exclusively male activity remains unexplained. Three general hypotheses have been proposed, concerning greater male effectiveness in warfare, lower male costs, and patrilocality. But while each of these factors might explain why warfare is more common in men, they do not convincingly explain why women almost never participate. Here, we develop a mathematical model to formally assess these hypotheses. Surprisingly, we find that exclusively male warfare may evolve even in the absence of any such sex differences, though sex biases in these parameters can make this evolutionary outcome more likely. The qualitative observation that participation in warfare is almost exclusive to one sex is ultimately explained by the fundamentally sex-specific nature of Darwinian competition—in fitness terms, men compete with men and women with women. These results reveal a potentially key role for ancestral conditions in shaping our species' patterns of sexual division of labour and violence-related adaptations and behavioural disorders.

Warfare in an evolutionary perspective

“…If humans have an evolved propensity for acting aggressively toward outgroup individuals, war should be an adaptive response, that is, it should be observed under specific ecological conditions where the fitness benefits of aggression out‐weight the potential costs . For war, and more broadly for aggression, these ecological conditions are: (a) fitness‐enhancing resources (e.g., mating partners, water or shelter) are a limiting factor, that is, they cannot be shared among all of the agents (be these cells, individuals, groups or states) in a given area; (b) agents cannot access those resources by moving to another area or by depleting the same resource at different times (scramble competition); (c) there are small differences (or small perceived differences) in the fighting ability of the agents competing for the same resource.…”

“…It is important to point out that these studies do not imply that war is an unavoidable consequence of the conditions described above, or that those conditions are the only factors eliciting warfare. 34 Indeed, a positive relationship between taking part in battle and reproductive success may not be observed, for example, due to mate choice of individuals who did not fight or to cultural norms (e.g., social exclusion of individuals who committed violent acts at war). Social groups at every level of socio-political complexity, from family units to large states, can still peacefully resolve competitive interactions over limited resources.…”

“…Some authors argue that human ancestors faced an extensive period of warfare, dating back to at least 200,000 year BP, and probably much earlier, which has significantly shaped human social evolution . According to this view, war is an adaptive response that mostly emerges under specific socio‐ecological conditions (e.g., scarcity of valuable resources) and that has fitness consequences . Conversely, other authors propose that warfare is a relatively recent phenomenon in human evolution, appearing (or becoming common) around or after 15,000–8,000 years BP .…”

“…Stemming from the controversy over the early/late emergence of warfare in human evolution, some researchers suggest that war is mainly due to culture, because warfare is a recent phenomenon in evolutionary terms and often occurred at low frequency before state‐level societies. Therefore, warfare has not exerted significant evolutionary pressure on humans . Moreover, differences on whether, how often, why and how pre‐state human societies wage war are too extensive to be explained by an innate propensity to be aggressive toward outgroup individuals .…”

“…[29][30][31][32][33] According to this view, war is an adaptive response that mostly emerges under specific socio-ecological conditions (e.g., scarcity of valuable resources) and that has fitness consequences. 20,34 Conversely, other authors propose that warfare is a relatively recent phenomenon in human evolution, appearing (or becoming common) around or after 15,000-8,000 years BP. 3,35 According to this view, the late emergence of warfare and/or its low frequency in prehistoric times suggests that warfare played a minor role in human evolution.…”