The target article proposes that expressions of heightened fearfulness by infants facilitate care-based responding from mothers and others. It also stipulates that the emergence of stable fearfulness traits facilitates cooperation across the lifespan. I am making no claims about caregiving in response to heightened fearfulness in infants. Rather, this commentary draws on three literatures to claim that experienced, expressed, and perceived fear is often associated with lower levels of cooperation in adults. Taken together, the empirical evidence coming from research on social decision making, defensive aggression, and social hierarchy suggests that heightened fearfulness may promote competitive behavior in social interactions.

Consider first a broad class of social decision-making situations in which mutual trust is required to achieve a shared goal, such as the successful completion of a joint project (Skyrms, Reference Skyrms2004). To the extent that experiencing heightened fearfulness is associated with distrust of others and concerns about the possibility of being exploited (i.e., worrying that others may shirk, defect, or free-ride one's efforts), it may undermine cooperation with others (Kramer, Reference Kramer1998; Wildschut, Pinter, Vevea, Insko, & Schopler, Reference Wildschut, Pinter, Vevea, Insko and Schopler2003). Fear of the other's fearfulness, in turn, may result in mutual defection as partners timidly choose a risk-averse strategy to avoid unilateral exploitation (i.e., choosing to work alone on a small challenge rather than collaborating with others to tackle a great challenge together; Halevy & Katz, Reference Halevy and Katz2013; Kuwabara, Reference Kuwabara2005). Hence, experiencing fear and perceiving fear in another may result in interaction partners settling for a suboptimal equilibrium attained through mutual defection in situations that require high levels of reciprocal trust to achieve the optimal equilibrium.

Consider next the particular case of preemptive strikes, a form of fear-based aggression (Simunovic, Mifune, & Yamagishi, Reference Simunovic, Mifune and Yamagishi2013). A preemptive strike occurs when an individual attacks another in an attempt to eliminate or disable a perceived threat (Halevy, Reference Halevy2017). Schelling (Reference Schelling1980) provides the example of an interaction between an armed burglar and an armed homeowner. Fear that the other person may use their gun can propel the burglar, the homeowner, or both of them to shoot even if everyone prefers the burglar to leave quietly. This form of aggression is motivated by self-defense, and is particularly likely to emerge when interaction partners experience a “reciprocal fear of a surprise attack” (Schelling, Reference Schelling1980, p. 207). Heightened fearfulness can promote preemptive strikes through the personal experience of fear as well as through the perception of fear in another. The fearful person may choose to launch a preemptive strike to eliminate or disable a perceived threat. Additionally, observing heightened fearfulness in another person may promote a preemptive strike when the perceiver worries that the fearful person may attack them. Hence, both experienced fear and perceived fear may increase the likelihood of defensive aggression.

Finally, consider situations that involve one or more individuals who seek to gain or maintain power by dominating others. Ruling by dominance (e.g., by using intimidation or coercion) means feeding off others' fear (Cheng, Tracy, Foulsham, Kingstone, & Henrich, Reference Cheng, Tracy, Foulsham, Kingstone and Henrich2013; Maner & Case, Reference Maner and Case2016). Perceiving heightened fearfulness in others may reinforce power-seeking individuals' tendencies to use dominance strategies as means to gain or maintain an elevated social rank. The expression of fear signals to the power-seeking individual that the fearful individual perceives their own level of power to be substantially lower than that of the power-seeking individual (Balliet, Tybur, & Van Lange, Reference Balliet, Tybur and Van Lange2017, p. 373). This signal, in turn, propels the power-seeking individual to seize the opportunity to gain or maintain their power by acting dominantly. Research also suggests that dominant leaders' competitive behavior is often fueled by fear of losing their (unstable or illegitimate) position of power (Maner & Case, Reference Maner and Case2016). Therefore, experiencing fear as well as perceiving fear in others may increase dominant behavior by power-seeking individuals.

The idea that power-seeking individuals who encounter heightened fearfulness in others are likely to dominate and subjugate them rather than treat them with compassion and care recurs across two distinct literatures. First, research on dominance complementarity shows that people typically behave in a way that contrasts with the behavior of their counterparts on the dimension of interpersonal control. Hence, individuals tend to respond to submission with dominance and to dominance with submission (Tiedens & Fragale, Reference Tiedens and Fragale2003; Tiedens & Jimenez, Reference Tiedens and Jimenez2003). Second, analyses of social behavior in brinkmanship situations, such as those modeled with the risky game of chicken (Halevy & Phillips, Reference Halevy and Phillips2015; Schelling, Reference Schelling1980), suggest that power-seeking individuals are likely to compete with a timid counterpart. The expressed fearfulness of the timid counterpart leads power-seeking individuals to conclude that they can safely keep course and count on the timid counterpart to change course as a means to avoid the disastrous outcomes associated with a head-on collision (Halevy, Chou, & Murnighan, Reference Halevy, Chou and Murnighan2012; Rapoport & Chammah, Reference Rapoport and Chammah1966). Both of these literatures suggest that, upon encountering an individual showing heightened fearfulness, a power-seeking individual is likely to respond with self-serving dominance rather than with prosocial care.

In sum, accumulated evidence across multiple streams of research on social decision making, defensive aggression, and social hierarchy suggests that experienced, expressed, and perceived fear is often associated with lower levels of cooperation in adults. This evidence requires a thoughtful consideration of potential boundary conditions to the target article's claim for “a link between human fearfulness traits and enhanced levels of cooperative behavior” (target article, sect. 4, para. 9) in adults.