Sijilmassi et al. present compelling evidence for the possibility that historical myths draw attention to cues of positive fitness interdependence which, in turn, enables humans to engage in large-scale collective action and to prevail in intergroup conflicts. Their analysis not only explains why humans – across time and space – so often celebrate a long-gone past, but also generates new questions and hypotheses about coalition formation, the historical roots of group solidarity, and the dynamics of intergroup conflict. Here we develop one hypothesis by considering that behavioural ecologies in themselves can create variation in fitness interdependencies and hence modulate the functionality of invoking historical myths.

Some coalitions form to protect against environmental threats and to survive attacks from hostile neighbours (viz. defence; De Dreu & Gross, Reference De Dreu and Gross2019; Rusch, 2014). In such behavioural ecologies, failure to avert threat results in significant losses for all individuals involved, including economic losses, physical injury, and, in extremis, death. Individuals share a “common fate” – they have positive fitness interdependence – and this not only enhances in-group solidarity (Boyer, Firat, & van Leeuwen, Reference Boyer, Firat and van Leeuwen2015) but also promotes coordination and cooperation (Aktipis et al., Reference Aktipis, Cronk, Alcock, Ayers, Baciu, Balliet and Muñoz2018; Balliet, Tybur, & Van Lange, Reference Balliet, Tybur and Van Lange2017; De Dreu, Gross, & Romano, Reference De Dreu, Gross and Romano2024). Conversely, some coalitions form to subordinate and exploit neighbours, that is for raiding and offensive warfare (viz. attack; De Dreu & Gross, Reference De Dreu and Gross2019; Rusch, 2014). All else equal, coalitions for attack exhibit lower levels of interdependence than coalitions for defence because during attacks also those individuals who do not (fully) engage in participation, and “lay low” to avoid losses and injury, may still benefit from victory and share in the spoils of war. Moreover, when attacks and collective attempts at subordination and exploitation fail, those who laid low suffer less from the waste of conflict than those who contributed.

Recent intergroup contest experiments (Fig. 1a) revealed three core consequences of this stronger free-rider problem faced by coalitions for attack rather than defence. First, attacker groups display lower levels of in-group identification and solidarity (De Dreu & Gross, Reference De Dreu and Gross2019). Second, individuals in attacker groups invest fewer personal resources in conflict than defenders (Fig. 1b). Third, attackers coordinate their conflict contributions less well than defenders – within-group variance in contributions to conflict is larger (Fig. 1c). As a result of these three behavioural patterns, attacker groups disproportionally often fail to defeat their enemies (De Dreu et al., Reference De Dreu, Gross, Méder, Giffin, Prochazkova, Krikeb and Columbus2016).

Figure 1.

The intergroup attacker–defender contest. (a) Six participants in two groups of three are assigned the role of attackers (red) or defenders (blue). In each round, participants decide how many units to contribute to attack (the “sword” symbolizes the total number of units contributed by the attackers to the conflict pool) or defence (the “shield” symbolizes the total number of units contributed by the defenders). Units contributed to conflict are non-recoverable, yet if combined contributions to attack exceed contributions to defence, attackers win and receive all non-contributed units from the defenders (i.e., defenders earn nothing); otherwise, individuals on both sides earn whatever they did not contribute to conflict. (b) Weighted average of contributions to out-group attack and in-group defence (based on De Dreu et al., Reference De Dreu, Gross, Méder, Giffin, Prochazkova, Krikeb and Columbus2016, Reference De Dreu, Gross and Reddmann2022; Gross, De Dreu, & Reddmann, Reference Gross, De Dreu and Reddmann2022; Snijder, Gross, Stallen, & De Dreu, Reference Snijder, Gross, Stallen and De Dreu2024; Yang, Zhang, Ni, De Dreu, & Ma, Reference Yang, Zhang, Ni, De Dreu and Ma2020). (c) Weighted average of within-group variance in contributions as a measure of within-group coordination failures (based on De Dreu et al., Reference De Dreu, Gross, Méder, Giffin, Prochazkova, Krikeb and Columbus2016, Reference De Dreu, Gross and Reddmann2022; Gross et al., Reference Gross, De Dreu and Reddmann2022; Snijder et al., Reference Snijder, Gross, Stallen and De Dreu2024; Yang et al., Reference Yang, Zhang, Ni, De Dreu and Ma2020). Error bars indicate the standard error of the mean (total N = 245 attacker and 245 defender groups of three individuals each).

Individual members, and their leaders, seem aware of these asymmetries. To make offensive warfare and raids more likely to succeed, coalitions form around friendships and invest in building interpersonal bonds among its members (Glowacki et al., 2016; Macfarlan, Walker, Flinn, & Chagnon, Reference Macfarlan, Walker, Flinn and Chagnon2014), for example, by using cultural rituals such as war dances (Fischer, Callander, Reddish, & Bulbulia, Reference Fischer, Callander, Reddish and Bulbulia2013; Whitehouse & Lanman, Reference Whitehouse and Lanman2014). From Sijilmassi et al., it follows that precisely here, for coalitional attacks, invoking historical myths may be pivotal both to recruit members and to motivate recruits to fight rather than free-ride. Evidence for these possibilities would fit anecdotal evidence. For example, during the expansion of the Roman Empire, soldiers were often motivated by tales of past conquests and legendary leaders like Julius Caesar (Taylor, Reference Taylor2003), and political myths have also been used to legitimize attacks like the “war on terror” (Esch, Reference Esch2010). Crucially, however, it also follows that historical myths are less needed, and hence less likely to be invoked, for coalitions for defence and protection where the inherent positive fitness interdependencies among affected individuals already motivate cooperation and coordinated collective action.

Sijilmassi et al.'s treatise alongside theory and research on the form and function of conflict suggests that (i) historical myths are functional for coalitional warfare that aims to subordinate and exploit more than for coalitional defence and protection; and therefore (ii) historical myths are invoked more readily – and should be seen more often – in coalitions for unprovoked aggression rather than more reactive defence. If true, whenever community leaders or high-raking politicians invoke historical myths, followers and outsiders should be “on guard” not to protect against impending hostilities but rather to avoid being recruited for otherwise unprovoked conflicts that may serve leaders more than citizens.