Ever since Darwin (Reference Darwin1871), scientists have puzzled over why some people, such as heroes and martyrs, willingly self-sacrifice, even when facing overwhelming odds and apparent defeat. The global advent of suicide attacks has transformed the issue into a paramount policy challenge for governments and their publics. Whitehouse's article is informative and timely, focusing its explanation of violent extremism on an interrelated complex of cognitive and emotional means for binding groups (perceptions of shared essence, actual and imagined kinship, shared episodic memories, and intense emotional experiences), while offering general understanding of self-sacrifice applicable to many cultural contexts and times. However, Whitehouse risks overstating his case by claiming that identity fusion is the primary, if not unique, driver of extreme sacrifice.

In the last decade, experiments performed on five continents have shown identity fusion is a reliable predictor of willingness to fight, kill, and die for one's group. Identity fusion theory originated with William Swann and Ángel Gómez in 2005. It was initially conceived to help explain the September 11, 2001 attacks and March 11, 2004 Madrid train bombings (Europe's worst terrorist attack to date). It was then empirically validated in several publications (Gómez et al. Reference Gómez, Brooks, Buhrmester, Vázquez, Jetten and Swann2011a; Swann et al. Reference Swann, Gómez, Seyle, Morales and Huici2009). Whitehouse subsequently joined the effort (Swann et al. Reference Swann, Jetten, Gómez, Whitehouse and Bastian2012), applying the theory with colleagues to an impressive set of field settings from initiation rites in New Guinea to the Libyan insurgency against Gaddafi (Whitehouse et al. Reference Whitehouse, McQuinn, Buhrmester and Swann2014b).

The target article is compelling when extending fusion theory to explain the group-binding functions of intense, dysphoric experiences in painful rituals or other emotional life-shaping experiences (e.g., frontline combat). Whitehouse convincingly relates such experiences to kin psychology: attitudes and feelings associated with immediate familial ties, which can be extended to larger groups – from tribes to transnational movements – via participation in intensely emotional rituals or attention to symbols that evoke shared intense experiences. Previous fusion research supports the connection between these mechanisms and fusion. For example, individuals diagnosed with gender dysphoria (i.e., transsexuals), when fused with their preferred gender, are willing to suffer painful experiences (e.g., major surgery) to belong to their desired sex group (Swann et al. Reference Swann, Gómez, Vázquez, Guillamón, Segovia and Carillo2015). Other studies also show that fusion promotes self-sacrifice, including dying for a group, by fostering perception of familial ties (Swann et al. Reference Swann, Buhrmester, Gómez, Jetten, Bastian, Vázquez, Ariyanto, Besta, Christ, Cui, Finchilescu, González, Goto, Homsey, Sharma, Susianto and Zhang2014a).

Less compelling is Whitehouse's argument that identity fusion is generally the principal determinant of willingness to self-sacrifice. Other anthropological and psychological research indicates that commitment to so-called sacred values can motivate extreme and costly behaviors (Baron & Spranca Reference Baron and Spranca1997; Graham & Haidt Reference Graham, Haidt, Shaver and Mikulincer2013; Rappaport Reference Rappaport1971; Tetlock Reference Tetlock2003). Whitehouse dubiously acknowledges sacred values by assimilating them to identity fusion. Thus, “extreme beliefs [may] become so closely linked to the group that they take on an aura of sacredness”; however, “what connects those values to acts of self-sacrifice may well be fusion with the group rather than commitment to any kind explicit belief system” (sect. 2, para. 6).

Yet, among Itza’ Maya in lowland Guatemala, we find strong commitment to spiritual values that summarize millennial experience – but no significant contemporary group bonding, ritualized or otherwise – driving very costly rainforest management (Atran et al. Reference Atran, Medin, Ross, Lynch, Vapnarsky, Ucan Ek', Coley, Timura and Baran2002). Studies in Western Europe, North Africa, and the Middle East reveal sacred values and identity fusion to be uncorrelated, independent predictors of willingness to engage in, and suffer, extreme violence. When individuals perceive a threat both to their fused group and to sacred values, identity fusion and sacred values interact, leading to greater willingness to sacrifice than for either factor alone (Atran et al. Reference Atran, Sheikh and Gómez2014; Sheikh et al. Reference Sheikh, Gómez and Atran2016). Sometimes identity fusion takes precedence over sacred values (Gómez et al. Reference Gómez, López-Rodríguez, Vázquez, Paredes and Martínez2016a). In other circumstances, sacred values prove more important. For example, in our study of frontline combatants in Iraq (Kurdish PKK and Peshmerga, Sunni Arab militia, Iraqi Army, captured Islamic State fighters), those most willing to make costly sacrifices (as verbally expressed and in terms of actually being wounded and voluntarily returning to fight) were ready to forsake their fused group, whether their genetic family or any other group with which they were fused, rather than their sacred values. This finding was replicated among subjects most willing to make costly sacrifices in a sample of more than 6,000 Western Europeans (Gómez et al. Reference Gómez, López-Rodríguez, Sheikh, Ginges, Wilson, Waziri, Vázquez, Davis and Atran2017) and with young men just emerging from Islamic State rule in the Mosul area of Iraq (Atran et al. Reference Atran, Waziri, Gómez, Sheikh, López-Rodríguez, Rogan and Davis2018).

Whitehouse questions these findings, arguing that “measures of sacred values … are related to similar measures of willingness to sacrifice for sacred values” (sect. 2, para. 6). Our sacred value measures chiefly concern unwillingness to trade the value against material gain or loss (Ginges et al. Reference Ginges, Atran, Sachdeva and Medin2011), although in some studies additional indicators of sacredness include insensitivity to discounting, immunity to peer pressure, and blindness to exit strategies (Sheikh et al. Reference Sheikh, Ginges and Atran2013). But in our frontline studies, for example, we see no support for Whitehouse's intimation that refusing material incentives for assessing sacred values, such as Sharia law, is conflated with outcome measures of costly commitments such as “dying, letting one's family suffer, undertaking a suicide attack, torturing women and children” (Gómez et al. Reference Gómez, López-Rodríguez, Sheikh, Ginges, Wilson, Waziri, Vázquez, Davis and Atran2017, p. 678).

Whitehouse surmises: “willingness to fight and die is not motivated by doctrines and ideologies, religious or otherwise, but by a particularly intense love of the group” (sect. 2, para. 7). Previous research suggests that even for some suicide attacks in the name of religion or for a political goal, group dynamics can be more important than confessional or ideological affiliation (Atran Reference Atran2010; Sageman Reference Sageman2004). But in other circumstances, devotion to sacred values may be primary (Atran et al. Reference Atran, Waziri, Gómez, Sheikh, López-Rodríguez, Rogan and Davis2018; Gómez et al. Reference Gómez, López-Rodríguez, Sheikh, Ginges, Wilson, Waziri, Vázquez, Davis and Atran2017) or be important even without any longstanding relationship to religious or ideological doctrine (e.g., right to nuclear capability among some Iranians [Dehghani et al. Reference Dehghani, Atran, Iliev, Sachdeva, Medin and Ginges2010]). Whitehouse (Reference Whitehouse2000) distinguishes ideologies and doctrines from the imagistic and emotion-laden aspects of ritual and dysphoric experiences that, by and large, distinguish spiritual life in small-scale societies (e.g., pre-state cultures, contemporary New Guinea tribes) from the “doctrinal” religions and political ideologies of large-scale societies (e.g., empires, nations). Sacred values, though, appear to have privileged connections to emotions and can be as imagistic and intensely felt (Atran & Ginges Reference Atran and Ginges2012; Durkheim Reference Durkheim1912; Ginges et al. Reference Ginges, Atran, Medin and Shikaki2007; Gómez et al. Reference Gómez, López-Rodríguez, Sheikh, Ginges, Wilson, Waziri, Vázquez, Davis and Atran2017), as they can be part of religious or ideological doctrine.

A general theory of extreme self-sacrifice should consider, at a minimum, that people can make extreme sacrifices for a group, but also, or even independently, for a cherished cause.