The male warrior hypothesis: how has between-group conflict shaped human psychology?
Intergroup conflict and competition have been seemingly prevalent in human society for nearly as long as human society itself has existed (McDonald, Navarrete, & Van Vugt, 2012). Therefore, it might stand to reason that a propensity for this should have some form of long-term psychological impact (Bowles, 2009). However, it is important to not make presumptions in this regard, and to analyse the phenomenon closer to determine whether there might be a relationship or not. A combination of social and evolutionary psychology may provide valuable insight for this.
Specifically, Van Vugt, De Cremer, & Janssen (2007) coined the ‘male warrior hypothesis’ as one such model to explain how conflict might have impacted human psychology. The hypothesis suggests that intergroup conflict is routed in the interplay between social identity and sex differences in parental investment (Van Vugt, De Cremer, & Janssen, 2007; McDonald, Navarrete, & Van Vugt, 2012). Specifically, the social identity aspect overlaps with social identity theory (Tajfel & Turner, 1979). As social identity theory suggests; one’s own self-concept is derived from group membership, which can in turn lead to “us” and “them” categorisations that may serve as catalysts for conflict where one group perceives the other as a “threat” (Tajfel & Turner, 1979; Al Ramiah, Hewstone, & Schmid, 2011; Böhm, Rusch, & Baron, 2020).
However, the male warrior hypothesis incorporates the potential role of sex differences in how individuals process social identity; and how they then approach possible intergroup conflict scenarios (Van Vugt, De Cremer, & Janssen, 2007). Specifically, the hypothesis argues that males within a group face greater competition for mates than females which ultimately leads to a greater likelihood of partaking in conflict. This is primarily due to the fact that females invest more in producing offspring so tend to be more selective in mates; while males can reproduce with relatively low expenditure, however risk being unable to reproduce if they do not present themselves as “worthy” (McDonald, Navarrete, & Van Vugt, 2012). This may partially serve to explain why males are particularly inclined to play a more active, dangerous role in intergroup conflict (Muñoz-Reyes et al., 2020).
This effect may further be exacerbated by the effect of patrilocality. That is the tendency for social norms to favour wives relocating to their husbands’ in-groups as opposed to the other way around. As a result, males tend to demonstrate a greater degree of investment and commitment to their own in-group as the women will have not had sufficient time to form such a connection (Van Vugt, De Cremer, & Janssen, 2007; McDonald, Navarrete, & Van Vugt, 2012). Subsequently, males may also perceive the risks of intergroup conflict as being less significant when weighed against the potential loss of resources and in-group identity.
Evidence for how the male warrior hypothesis (and related phenomena) might have shaped human psychology throughout history may be found in modern-day social psychological trends. For example, men tend to demonstrate beliefs that are ethnocentric or xenophobic in nature with greater prevalence than women (Ekehammar, 1985). This is further linked with a more prolific use of dehumanisation when describing outgroup members; for example, in harbouring negative attitudes towards immigrant populations (Costello & Hodson, 2009; Van Vugt, 2009). Additionally, males also seem to exhibit a more intense degree of identification with their in-groups, and a stronger inclination for in-group cooperation against a perceived threat (Van Vugt, De Cremer, & Janssen, 2007; Van Vugt, 2009). Testosterone itself has been implicated, with experiments featuring the intentional administration of the hormone linking it to increased competition and in-group cooperation in conflict scenarios (van Honk et al., 2012; Muñoz-Reyes et al., 2020). Chang et al. (2011) ran an experiment which lent support to these trends, and subsequently to the male warrior hypothesis itself. In their study, male participants answered various conflict-related questions. Some of these participants were exposed to conventionally attractive images of the opposite sex, while some were not. Those that were exposed to these images demonstrated a greater likelihood to endorse statements that were in support of engaging in intergroup conflicts. This effect was not observed on questions pertaining to trade conflicts however, suggesting that disagreements of a more civilised focus are not typically affected.
Lindner (2018) argued that further evidence in support of the male warrior hypothesis can be found in perceptions of men and women in the context of conflict scenarios. Using the more extreme example of terrorism specifically; it was found that males are more likely to condone measures such as torture where offenders are also male and belong to an out-group. This suggests that men often view other men as the more likely aggressors, and subsequently the greater threats. For females’ respondents, Lindner could not identify and statistically significant likelihood towards the same trends, further supporting the view that this phenomenon is largely male-driven.
Interestingly, Barber (2009) found that the frequency of violent crimes often negatively correlates with the percentage of men in any given country. If the male warrior hypothesis were to provide valuable insight into the shaping of human psychology via in-group conflict, then one might reasonably assume that the opposite trend might be true – that more men should equate to more violent offences. However, further research has indicated that this surprising trend might actually provide yet more support for the impact of the male warrior hypothesis. This may be due to the fact that an abundance of women leads men to be less dutiful and engage in more risk-taking behaviours that ultimately fuel conflict with other men (Barber, 2009; Filser et al., 2021).
However, using the male warrior hypothesis to explain the development of human psychology has some significant limits. Notably, it is worth pointing out that it merely helps to explain one aspect (conflict) of human psychology more for males than for females. And while it addresses an increased likelihood of aggression for males (and a lack thereof for females), it does little to explain the minority of cases whereby females commit acts of violence (Simpson, 1991). In terms of explaining conflict behaviours, it also largely fails to consider the impact of other factors, such as the sociopolitical (Hewstone & Cairns, 2001). And in terms of an overall impact on shaping human psychology, the male warrior hypothesis might only be considered a “drop in the ocean” against such sheer complexity and a breadth of other factors.
Al Ramiah, A., Hewstone, M., & Schmid, K. (2011). Social Identity and Intergroup Conflict. Psychological Studies, 56, 44-52. https://doi.org/10.1007/s12646-011-0075-0
Barber, N. (2009). Countries with fewer males have more violent crime: marriage markets and mating aggression. Aggressive Behavior, 35(1), 49-56. https://doi.org/10.1002/ab.20291
Böhm, R., Rusch, H., & Baron, J. (2020). The psychology of intergroup conflict: A review of theories and measures. Journal of Economic Behavior & Organization, 178, 947-962. https://doi.org/10.1016/j.jebo.2018.01.020
Bowles, S. (2009). Did warfare among ancestral hunter–gatherer groups affect the evolution of human social behaviors. Science, 324 (5932), 1293-1298. https://doi.org/10.1126%2Fscience.1168112
Chang, L., Lu., H., Li., H., & Li, T. (2011). The Face That Launched a Thousand Ships: The Mating-Warring Association in Men. Personality and Social Psychology Bulletin, 37(7), 976-984. https://doi.org/10.1177%2F0146167211402216
Costello, K., & Hodson, G. (2009). Exploring the roots of dehumanization: The role of animal–human similarity in promoting immigrant humanization. Group Processes & Intergroup Relations, 13(1), 3-22. https://doi.org/10.1177%2F1368430209347725
Ekehammar, B. (1985). Sex Differences in Socio‐political Attitudes Revisited. Educational Studies, 11(1), 3-9. https://doi.org/10.1080/0305569850110101
Filser, A., Barclay, K., Beckley, A., Uggla, C., & Schnettler, S. (2021). Are skewed sex ratios associated with violent crime? A longitudinal analysis using Swedish register data. Evolution and Human Behavior, 42(3), 212-222. https://doi.org/10.1016/j.evolhumbehav.2020.10.001
Hewstone, M., & Cairns, E. (2001). Social psychology and intergroup conflict. In D. Chirot & M. E. P. Seligman (Eds.), Ethnopolitical warfare: Causes, consequences, and possible solutions (pp. 319–342). American Psychological Association. https://doi.org/10.1037/10396-020
Lindner, M. (2018). Public Reactions to Male Versus Female Terrorism: Experimental Evidence for the Male Warrior Hypothesis. Evolutionary Psychology, 16(2). https://doi.org/10.1177%2F1474704918764578
McDonald, M. M., Navarrete, C. D., & Van Vugt, M. (2012). Evolution and the psychology of intergroup conflict: the male warrior hypothesis. Philosophical Transactions of The Royal Society, 367, 670-679. https://doi.org/10.1098/rstb.2011.0301
Muñoz-Reyes, J. A., Polo, P., Valenzuela, N., Pavez, P., Ramírez-Herrera, O., Figueroa, O., Rodriguez-Sickert, C., Díaz, D., & Pita, M. (2020). The Male Warrior Hypothesis: Testosterone-related Cooperation and Aggression in the Context of Intergroup Conflict. Scientific Reports, 10(375). https://doi.org/10.1038/s41598-019-57259-0
Simpson, S. S. (1991). Caste, Class, and Violent Crime: Explaining Difference in Female Offending. Criminology, 29(1), 115-135. https://doi.org/10.1111/j.1745-9125.1991.tb01061.x
Tajfel, H., & Turner, J. C. (1979). An Integrative Theory of Intergroup Conflict. Organizational identity: A reader, 56(65), 9780203505984-16.
van Honk, J., Montoya, E. R., Bos, P. A., Van Vugt, M., & Terburg, G. (2012). New evidence on testosterone and cooperation. Nature, 484, 356-359. https://doi.org/10.1038/nature08711
Van Vugt, M., De Cremer, D., & Janssen, D. P. (2007). Gender Differences in Cooperation and Competition: The Male Warrior Hypothesis. Psychological Science, 18(1), 19-24. https://doi.org/10.1111%2Fj.1467-9280.2007.01842.x
Van Vugt, M. (2009). Sex Differences in Intergroup Competition, Aggression, and Warfare: The Male Warrior Hypothesis. Values, Empathy, and Fairness across Social Barriers, 1167(1), 124-134. https://doi.org/10.1111/j.1749-6632.2009.04539.x