This is an exciting new chapter in game theory. We agree with the authors that we should “view biases and motivated reasoning as adaptations to recurrent problems that humans repeatedly faced in the past” (sect. 3.6, last para.) As evolutionary psychologists specializing in the social cognition of threat, we see at least three opportunities for testable hypotheses based on evolutionary theory: (1) sex differences in actions taken; (2) complementary biases in how the sexes are perceived; and (3) the ways in which facial expressions of prosociality and threat have coevolved with human perception to facilitate attack and defense.
Triver's (Reference Trivers and Campbell1972) theory of differential parental investment states that the lower investing sex (typically the male) will compete more intensely for access to the higher investing sex (typically the female). Consequently, a male's reproductive fitness (number of offspring produced in a lifetime) is often more variable than a female's. These selection pressures have endowed many species, including humans, with sexually dimorphic traits and behaviors. For example, men are taller and have greater upper body strength, are more competitive and aggressive (Archer Reference Archer2004), and take greater risks compared with women (Wilson & Daly Reference Wilson and Daly1985). Such adaptations may help men directly defeat same-sex rivals, as well as acquire resources and status, which women find attractive in mates (Buss Reference Buss1989). Taken together, men stand to benefit more from pursuing low-probability, high-reward strategies compared with women, because the potential gains in resources or social standing can increase a man's mating success. Women, on the other hand, tend to pursue a more cautious, self-protective strategy (Campbell Reference Campbell1999). For example, women report a greater fear of crime and victimization, and take actions to prevent or avoid victimization (May et al. Reference May, Radar and Goodrum2010). On the basis of these differences, it can be predicted that male attackers will invest more in attacking (compared with females), whereas female defenders should invest more in defense (compared with males). These sex differences are easily tested and may already exist in previous work.
Although these hypotheses are straightforward, a more nuanced set of predictions arises with contextual moderators. Research reveals that men take more risks when exposed to attractive women (Baker & Maner Reference Baker and Maner2008; Ronay & von Hippel Reference Ronay and von Hippel2010), and this relationship has been shown to be mediated by an increase in testosterone levels (Ronay & von Hippel Reference Ronay and von Hippel2010). In line with these results, men exposed to attractive female images should be more inclined to attack than normal.
Although men are generally the lower investing sex, fathers can, and often do, provide extensive care and resources to their offspring (Geary Reference Geary2000). Thus, both genders have an incentive to compete for access to high-quality mates (Campbell Reference Campbell1999). Given this, when primed with a potential romantic rival, both men and women may increase their investment in attacking. Although, for women, this may be true only when primed with images of potential romantic rivals, as opposed to playing against a rival in person. While women behave negatively toward their “sexy peers” (Valliancourt & Sharma 2011), they tend to use indirect tactics, such as gossip, social exclusion, and derogation, as a means of aggression (Valliancourt Reference Valliancourt2013). If women are interacting with a physically attractive rival face-to-face, they might become more inhibited when playing the role of the attacker, because women may not be as comfortable with direct aggression. It is also possible that women may attribute more hostile intentions to a female rival, believing that she is more malicious than she actually is (a hostile attribution bias). Considering that women's competitive tactics tend to be subtle, this cognitive bias makes sense, because it might benefit women to err on the side of defending against potential attacks. Women who are pregnant or with young children may also be more prone to defense.
A related opportunity lies in a deeper consideration of how out-group stigmatizations show complementary sex differences. Men have historically been the attackers in intergroup conflict (van Vugt Reference Van Vugt2009; van Vugt et al. Reference Van Vugt, De Cremer and Janssen2007), and it is the formidability of the males of the out-group that should calibrate our decisions to attack or defend. Some work suggests that activating a self-protective motive, plausibly the same as the BIS system the authors evoke as the defensive network, leads both men and women to devote more cognitive processing to out-group men than in-group men or women of either group (Becker et al. Reference Becker, Anderson, Neuberg, Maner, Shapiro, Ackerman, Schaller and Kenrick2010). Arousing a self-protective motive also enhanced biases to see out-group members as enemies in a signal detection task, and a complementary bias to see in-group men as allies (even though 50% had detectable signs of threats; Becker et al. Reference Becker, Mortensen, Ackerman, Shapiro, Anderson, Sasaki, Maner, Neuberg and Kenrick2011). It thus seems plausible that priming self-protection will increase aggression against out-group men but decrease aggression toward in-group men, and perhaps enhance our tolerance for their acts of aggression against the men of the out-group. The methods of the target article could easily test such ideas.
Thus far, we have discussed new experimental directions for the conflict paradigm. At a theoretical level, the author's arguments are consilient with new ideas about the evolution of facial expressions that signal aggression (anger) and prosociality (happiness). Mounting evidence suggests that the angry expression masculinizes a face, whereas happiness has features of neotony and femininity; modern forms of these expressions may be partially scaffolded on preexisting gender recognition systems (Becker Reference Becker2017). The conflict game could formalize the mechanism of such signal convergence. The form of the happy face also seems to have evolved to be highly discriminable at short durations and great distances (Becker & Srinivasan Reference Becker and Srinivasan2014), whereas anger holds attention after it has been seen (Becker et al. Reference Becker, Mortensen, Anderson and Sasaki2014). Anger and happiness may thus be instrumental to the dynamics that play out within a conflict, suggesting additional research trajectories.
These possibilities are merely the beginning of what a more evolutionary approach can bring to the theses advanced here. Importantly, these points also emphasize that evolutionary psychology is not a set of “just so” stories, but that it makes testable predictions based on first principles of evolutionary biology.
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This is an exciting new chapter in game theory. We agree with the authors that we should “view biases and motivated reasoning as adaptations to recurrent problems that humans repeatedly faced in the past” (sect. 3.6, last para.) As evolutionary psychologists specializing in the social cognition of threat, we see at least three opportunities for testable hypotheses based on evolutionary theory: (1) sex differences in actions taken; (2) complementary biases in how the sexes are perceived; and (3) the ways in which facial expressions of prosociality and threat have coevolved with human perception to facilitate attack and defense.
Triver's (Reference Trivers and Campbell1972) theory of differential parental investment states that the lower investing sex (typically the male) will compete more intensely for access to the higher investing sex (typically the female). Consequently, a male's reproductive fitness (number of offspring produced in a lifetime) is often more variable than a female's. These selection pressures have endowed many species, including humans, with sexually dimorphic traits and behaviors. For example, men are taller and have greater upper body strength, are more competitive and aggressive (Archer Reference Archer2004), and take greater risks compared with women (Wilson & Daly Reference Wilson and Daly1985). Such adaptations may help men directly defeat same-sex rivals, as well as acquire resources and status, which women find attractive in mates (Buss Reference Buss1989). Taken together, men stand to benefit more from pursuing low-probability, high-reward strategies compared with women, because the potential gains in resources or social standing can increase a man's mating success. Women, on the other hand, tend to pursue a more cautious, self-protective strategy (Campbell Reference Campbell1999). For example, women report a greater fear of crime and victimization, and take actions to prevent or avoid victimization (May et al. Reference May, Radar and Goodrum2010). On the basis of these differences, it can be predicted that male attackers will invest more in attacking (compared with females), whereas female defenders should invest more in defense (compared with males). These sex differences are easily tested and may already exist in previous work.
Although these hypotheses are straightforward, a more nuanced set of predictions arises with contextual moderators. Research reveals that men take more risks when exposed to attractive women (Baker & Maner Reference Baker and Maner2008; Ronay & von Hippel Reference Ronay and von Hippel2010), and this relationship has been shown to be mediated by an increase in testosterone levels (Ronay & von Hippel Reference Ronay and von Hippel2010). In line with these results, men exposed to attractive female images should be more inclined to attack than normal.
Although men are generally the lower investing sex, fathers can, and often do, provide extensive care and resources to their offspring (Geary Reference Geary2000). Thus, both genders have an incentive to compete for access to high-quality mates (Campbell Reference Campbell1999). Given this, when primed with a potential romantic rival, both men and women may increase their investment in attacking. Although, for women, this may be true only when primed with images of potential romantic rivals, as opposed to playing against a rival in person. While women behave negatively toward their “sexy peers” (Valliancourt & Sharma 2011), they tend to use indirect tactics, such as gossip, social exclusion, and derogation, as a means of aggression (Valliancourt Reference Valliancourt2013). If women are interacting with a physically attractive rival face-to-face, they might become more inhibited when playing the role of the attacker, because women may not be as comfortable with direct aggression. It is also possible that women may attribute more hostile intentions to a female rival, believing that she is more malicious than she actually is (a hostile attribution bias). Considering that women's competitive tactics tend to be subtle, this cognitive bias makes sense, because it might benefit women to err on the side of defending against potential attacks. Women who are pregnant or with young children may also be more prone to defense.
A related opportunity lies in a deeper consideration of how out-group stigmatizations show complementary sex differences. Men have historically been the attackers in intergroup conflict (van Vugt Reference Van Vugt2009; van Vugt et al. Reference Van Vugt, De Cremer and Janssen2007), and it is the formidability of the males of the out-group that should calibrate our decisions to attack or defend. Some work suggests that activating a self-protective motive, plausibly the same as the BIS system the authors evoke as the defensive network, leads both men and women to devote more cognitive processing to out-group men than in-group men or women of either group (Becker et al. Reference Becker, Anderson, Neuberg, Maner, Shapiro, Ackerman, Schaller and Kenrick2010). Arousing a self-protective motive also enhanced biases to see out-group members as enemies in a signal detection task, and a complementary bias to see in-group men as allies (even though 50% had detectable signs of threats; Becker et al. Reference Becker, Mortensen, Ackerman, Shapiro, Anderson, Sasaki, Maner, Neuberg and Kenrick2011). It thus seems plausible that priming self-protection will increase aggression against out-group men but decrease aggression toward in-group men, and perhaps enhance our tolerance for their acts of aggression against the men of the out-group. The methods of the target article could easily test such ideas.
Thus far, we have discussed new experimental directions for the conflict paradigm. At a theoretical level, the author's arguments are consilient with new ideas about the evolution of facial expressions that signal aggression (anger) and prosociality (happiness). Mounting evidence suggests that the angry expression masculinizes a face, whereas happiness has features of neotony and femininity; modern forms of these expressions may be partially scaffolded on preexisting gender recognition systems (Becker Reference Becker2017). The conflict game could formalize the mechanism of such signal convergence. The form of the happy face also seems to have evolved to be highly discriminable at short durations and great distances (Becker & Srinivasan Reference Becker and Srinivasan2014), whereas anger holds attention after it has been seen (Becker et al. Reference Becker, Mortensen, Anderson and Sasaki2014). Anger and happiness may thus be instrumental to the dynamics that play out within a conflict, suggesting additional research trajectories.
These possibilities are merely the beginning of what a more evolutionary approach can bring to the theses advanced here. Importantly, these points also emphasize that evolutionary psychology is not a set of “just so” stories, but that it makes testable predictions based on first principles of evolutionary biology.