Whitehouse draws from several disciplines to propose a framework that helps explain violent self-sacrifice. We agree that cultural mechanisms appear to be co-opting evolved, kin-based, and tribal psychology, to facilitate readiness to sacrifice for the group. However, Whitehouse's theory is unable to answer questions concerning (a) processes leading individuals to sign up for these groups and (b) factors shaping martyrdom-promoting group norms. We suggest that such factors include environmental threats and ideology. Environmental threats can cause extreme reactions within individuals and urge them to join ideologically rigid groups engaged in self-sacrifice. Ideologies and environmental threats also help shape group norms that are conducive to violent self-sacrifice.

Environmental threats promote palliative zeal and extremity in attitudes and behavioral responses (Jonas et al. Reference Jonas, McGregor, Klackl, Agroskin, Fritsche, Holbrook, Quirin, Olson and Zanna2014), with the endorsement of martyrdom being a specific application of this general trend (Pyszczynski et al. Reference Pyszczynski, Abdollahi, Solomon, Greenberg, Cohen and Weise2006). Even minor, seemingly unrelated, threats induced in the lab can lead to ideological extremism: Attempts to understand an incomprehensible (vs. a simple) text passage that was said to be diagnostic of academic abilities resulted in greater endorsement of religious zeal on items such as “If I really had to, I would give my life for my religious beliefs” (McGregor et al. Reference McGregor, Nash and Prentice2010). Hundreds of similar experiments indicate that environmental threats move individuals toward diverse varieties of ideological zeal, with or without involvement of group processes, to help dampen threat-induced distress (McGregor Reference McGregor, Spencer, Fein, Zanna and Olson2003; reviewed in Jonas et al. Reference Jonas, McGregor, Klackl, Agroskin, Fritsche, Holbrook, Quirin, Olson and Zanna2014), an effect that holds when controlling for macro-level factors such as political and economic grievances (Rink & Sharma Reference Rink and Sharma2018).

In a similar vein, in response to environmental threats in the surrounding ecology (such as scarce resources), groups often turn toward stricter norms to deal with the threat (Gelfand et al. Reference Gelfand, Harrington and Jackson2017; Thornhill & Fincher Reference Thornhill and Fincher2014; Varnum & Grossmann Reference Varnum and Grossmann2016; for a review, see Varnum & Grossmann Reference Varnum and Grossmann2017). This increased rigidity is fertile ground for more tribal and dogmatic norms conducive to jingoistic expressions of violent self-sacrifice, thereby making environmental threats an important precursor to the group dynamics that Whitehouse takes for granted. For example, when resources are scarce, costly displays of loyalty might be more valued by the group to ensure lack of free-riding. The stakes are higher, and therefore, people need to jump through more hoops to prove themselves as invested, contributing group members. In turn, norms like those promoting binding ritualistic experiences described by Whitehouse become more valued, leading to a greater willingness to self-sacrifice.

Why would some people be attracted to groups that are extreme and demand intense conformity? Research indicates that, under threat, individuals are attracted to well-defined and active groups with highly purposeful and moralistic ideologies (Fritsche et al. Reference Fritsche, Jonas, Ablasser, Beyer, Kuban, Manger and Schultz2013; Hogg et al. Reference Hogg, Sherman, Dierselhuis, Maitner and Moffitt2007; Kruglanski et al. Reference Kruglanski, Jasko, Webber, Chernikova and Molinario2018). Groups with ideologies that provide a clear purpose and moralistic call to action are attractive to potential recruits, especially those feeling threatened, as they provide unambiguous conviction; this conviction would help excite the same, basic, agency-based motivational processes that relieve distress for individuals outside of group settings (Jonas et al. Reference Jonas, McGregor, Klackl, Agroskin, Fritsche, Holbrook, Quirin, Olson and Zanna2014; Kruglanski et al. Reference Kruglanski, Jasko, Webber, Chernikova and Molinario2018).

Notably, Whitehouse explicitly discounts the role of ideologies in shaping violent self-sacrifice: “[sacrifice to the group] is not motivated by doctrines and ideologies, religious or otherwise, but by a particularly intense love of the group” (sect. 2, para. 7). For Whitehouse, it seems that intense love for the group is sufficient to explain motivation for self-sacrifice. But are all groups equally likely to encourage extreme self-sacrifice? Research suggests that certain ideological beliefs are maintained culturally because they encourage behaviors that promote group interests (Norenzayan Reference Norenzayan2016; Norenzayan et al. Reference Norenzayan, Shariff, Gervais, Willard, McNamara, Slingerland and Henrich2016; Vail et al. Reference Vail, Rothschild, Weise, Solomon, Pyszczynski and Greenberg2010). Moreover, being active and engaged with a group in a religious context can lead to greater pro-sociality (Putnam & Campbell Reference Putnam and Campbell2012), but also greater endorsement of suicide (Ginges et al. Reference Ginges, Hansen and Norenzayan2009). Reminders of religious beliefs associated with magnanimous ideals led adherents to greater pro-sociality when exposed to threats (Schumann et al. Reference Schumann, McGregor, Nash and Ross2014), but those associated with jingoism encouraged extremism under threat (Rothschild et al. Reference Rothschild, Abdollahi and Pyszczynski2009). These divergent outcomes are partly explained by different ideological beliefs within the group, whether religious or otherwise, shaping what it is that groups find sacred and valuable – a tendency that likely extends to the group norms governing the appropriateness of self-sacrifice and how it can be expressed (Gómez et al. Reference Gómez, López-Rodríguez, Sheikh, Ginges, Wilson, Waziri, Vázquez, Davis and Atran2017; McGregor et al. Reference McGregor, Hayes and Prentice2015).

Self-sacrifice can happen outside of a group setting, as in the case of celebrity suicide imitation (Stack Reference Stack1987). It can also happen in a group setting in response to collective threats, but in a nonviolent way, as in the case of self-immolation (Biggs Reference Biggs and Gambetta2005; Somasundaram et al. Reference Somasundaram, Tejus Murthy and Raghavan2016). A violence-justifying ideological narrative is needed to help shape expressions of self-sacrifice toward terrorism and other violence-inflicting acts for the sake of the group (Kruglanski et al. Reference Kruglanski, Jasko, Webber, Chernikova and Molinario2018). Evidence suggests that specific scriptural passages help encourage violence (Bushman et al. Reference Bushman, Ridge, Das, Key and Busath2007), and religious beliefs have been found to play a key role in explaining religious extremism (Appleby Reference Appleby1999; Dawson Reference Dawson2018; Dawson & Amarasingam Reference Dawson and Amarasingam2017; Wood Reference Wood2016). In some cases, religiosity has been found to correlate with the increased endorsement of violent self-sacrifice (Cinnirella et al. Reference Cinnirella, Lewis, Ansari, Loewenthal, Brooke-Rogers and Amlot2010; Rink & Sharma Reference Rink and Sharma2018).

In conclusion, Whitehouse's model can be enriched with the acknowledgments (1) that environmental threats can lead individuals to become extreme outside of a group setting and predispose them to dogmatic ideologies, and (2) that environmental threats and ideologies can shape group norms that help facilitate readiness to violently self-sacrifice within groups. Integration of these factors would enrich Whitehouse's model, informing scientific understanding of the broader context of self-sacrificial acts and informing practical interventions oriented toward preventing suicide terrorism.