Based on theory and empirical findings drawn from the fields of neuroscience, behavioral economics, social, and evolutionary psychology, De Dreu and Gross develop a framework to disentangle the neurobiological, psychological, and cultural characteristics that contribute to the nature of intergroup conflict. More specifically, they propose that potentially distinct psychological and cultural factors could be involved in what they conceptualize as “attacking” versus “defending” behavior at a group level. We agree with the argument that social affiliation, such as identification with and loyalty to in-group members, emerges more spontaneously within defender groups, whereas the formation and behavior of attacking groups may rely more heavily on cultural tools and arrangements (e.g., propaganda, cultural rituals, religious belief). However, research in developmental psychology that adopts a sociocultural lens to examine the origins of intergroup bias is critical to understanding these phenomena.

Children are motivated to affiliate with others from early in development (Carpenter et al. Reference Carpenter, Nagell and Tomasello1998; Over Reference Over2016) and particularly with individuals who belong to their own social group. A substantial number of studies have demonstrated that 4- and 5-year-old children are more likely to selectively befriend (Kinzler et al. Reference Kinzler, Dupoux and Spelke2007), stay loyal to (Misch et al. Reference Misch, Over and Carpenter2016), share more resources with (Renno & Shutts Reference Renno and Shutts2015), and trust the testimony of (Harris & Corriveau Reference Harris and Corriveau2011) in-group members. These social affiliative tendencies are observed in societies in which intergroup tension is relatively low and even when group membership is based on very minimal cues (i.e., shirt color; Dunham et al. Reference Dunham, Baron and Carey2011). De Dreu & Gross posit that the spontaneously coordinated and affiliative behavior witnessed within defense groups could be due, in part, to the earlier emergence of defense behavior in ancient societies. The early appearance of affiliative behavior in development also supports the evolutionary value of belonging to a group (Brewer Reference Brewer1999; Brewer & Caporael Reference Brewer, Caporael, Schaller, Simpson and Kenrick2006). Although the drive to affiliate with socially similar others is considered to be a fairly ubiquitous phenomenon (Meltzoff Reference Meltzoff2007), some researchers have emphasized the role of early sociocultural experiences in the development of in-group positivity. For example, minority race children can exhibit less favoritism for in-group members compared with majority (white) children (Margie et al. Reference Margie, Killen, Sinno and McGlothlin2005; Shutts et al. Reference Shutts, Kinzler, Katz, Tredoux and Spelke2011), and variability in socialization with and exposure to different racial groups can shape young children's social preferences (Chen et al. Reference Chen, Corriveau, Lai, Poon and Gaither2018; Gaither et al. Reference Gaither, Chen, Corriveau, Harris, Ambady and Sommers2014).

Other research in developmental psychology has suggested that negative out-group attitudes appear slightly later in development, typically after the age of 6 (Buttelmann & Böhm Reference Buttelmann and Böhm2014; McLoughlin & Over 2018). A recent body of work has illustrated that older children (ages between 6 and 11 years) can even hold dehumanizing out-group views, including the belief that out-group members possess fewer mental state capabilities (Dore et al. Reference Dore, Hoffman, Lillard and Trawalter2014; McLoughlin & Over Reference McLoughlin and Over2017) and uniquely human characteristics (Chas et al. Reference Chas, Betancor, Delgado and Rodríguez-Pérez2018; Costello & Hodson Reference Costello and Hodson2014). Yet, there is evidence to suggest that the developmental onset and trajectory of harmful out-group perceptions can vary widely, depending on different sociocultural factors, such as the cultural saliency of historical conflict between ethnic groups (Bennett et al. Reference Bennett, Barrett, Karakozov, Kipiani, Lyons, Pavlenko and Riazanova2004; Birnbaum et al. Reference Birnbaum, Deeb, Segall, Ben-Eliyahu and Diesendruck2010; Smyth et al. Reference Smyth, Feeney, Eidson and Coley2017), as well as the shared ideologies of the surrounding community (Rhodes & Mandalaywala Reference Rhodes and Mandalaywala2017; Segall et al. Reference Segall, Birnbaum, Deeb and Diesendruck2015). Taken together, these findings reinforce the importance of cultural learning and communication (Harris et al. Reference Harris, Koenig, Corriveau and Jaswal2018; Over & McCall Reference Over and McCall2018; Skinner & Meltzoff Reference Skinner and Meltzoff2019) and further speak to the relevance of social tools in motivating attacking behavior.

In sum, the potential divergence in the development of affiliation with the in-group and derogation of the out-group – at least in the cultural contexts studied thus far – supports the authors’ proposed framework but does indicate that more emphasis on early sociocultural input is required. One caveat to consider, however, is that it is sometimes not feasible to experimentally manipulate or measure parallel behaviors in research with children (e.g., extreme attacking intentions). Nonetheless, this field can provide valuable insight into the adaptive psychological mechanisms and the social learning processes contributing to intergroup conflict.