Pepper & Nettle (P&N) use a life-history framework to integrate a large body of work on psychological consequences of socioeconomic status (SES). They argue that many behaviors that at first appear irrational or self-destructive are, in fact, adaptive responses to the ecologies faced by low-SES people. We agree that such differences likely are adaptive responses to ecological conditions. However, we note that P&N have restricted their focus to a small range of SES-related findings, thereby missing an opportunity to integrate a larger literature on social-class differences in psychological phenomena. We propose that ecological and evolutionary frameworks provide key explanations for how the broad range of social-class differences represent adaptations to particular ecological threats and affordances. Such explanations include but are not exclusive to life-history strategies.

SES systematically affects a wide range of psychological and behavioral phenomena beyond those discussed in the target article. These effects involve different attentional foci, reasoning, and attunement to others. We briefly review this body of literature and propose how these SES-linked differences may reflect adaptations to different ecologies.

Many studies suggest that lower-SES people are relatively more attentive to contextual information than those who are of higher SES, as demonstrated on tasks concerning the reproduction of abstract shapes (Grossmann & Varnum Reference Grossmann and Varnum2011) and memory recall (Na et al. Reference Na, Grossmann, Varnum, Kitayama, Gonzalez and Nisbett2010). Beyond differences in attention, there is evidence of SES differences in types of inferences people draw from their environments. Some of this evidence concerns reasoning about causality, revealing that when compared to higher-SES individuals, lower-SES individuals are more likely to explain their behavior in terms of environmental constraints rather than intentions or stable dispositions (Grossmann et al. Reference Grossmann, Karasawa, Izumi, Na, Varnum, Kitayama and Nisbett2012; Grossmann & Varnum Reference Grossmann and Varnum2011; Kraus et al. Reference Kraus, Piff and Keltner2009). Recent work also suggests that lower-SES people are also more likely to employ nonlinear, dialectical reasoning when predicting change in the trajectory of social (Na et al. Reference Na, Grossmann, Varnum, Kitayama, Gonzalez and Nisbett2010) and societal events (Grossmann & Varnum Reference Grossmann and Varnum2011).

Studies have also revealed SES differences in the degree to which people are attuned to others. Lower SES is associated with a greater likelihood of defining one's self and personal goals through relationships with others (Grossmann & Varnum Reference Grossmann and Varnum2011; Stephens et al. Reference Stephens, Fryberg and Markus2011; Stephens et al. Reference Stephens, Markus and Phillips2014). It is also associated with greater accuracy in determining (Kraus et al. Reference Kraus, Côté and Keltner2010) and showing compassion toward others' emotions (Stellar et al. Reference Stellar, Manzo, Kraus and Keltner2012). Eye-tracking studies show that low-SES individuals are more likely to focus on other people in their environments (Dietze & Knowles Reference Dietze and Knowles2016). Consistent with behavioral studies, EEG/ERP studies assessing neural responses to other emotions and movements suggest that lower-SES individuals show heightened responses to others' expressions of pain (Varnum et al. Reference Varnum, Blais, Hampton and Brewer2015) and that their mirror neuron systems appear to be more reactive to others' actions (Varnum et al. Reference Varnum, Blais and Brewer2016). Both of these effects may be useful from the standpoint of self-protection. Indeed, consistent with this idea, recent fMRI studies have suggested enhanced vigilance to threats among those of lower SES (Gianaros et al. Reference Gianaros, Horenstein, Hariri, Sheu, Manuck, Matthews and Cohen2008; Muscatell et al. Reference Muscatell, Morelli, Falk, Way, Pfeifer, Galinsky, Lieberman, Dapretto and Eisenberger2012).

Why might social class have these effects on processes ranging from neural responding to attention to reasoning about causality? We propose that these differences reflect adaptations to specific features of low- versus high-SES ecologies. Lower-SES ecologies are characterized by numerous threats, including resource scarcity, physical dangers, and greater prevalence of infectious decease. Under such circumstances, broader patterns of attention may be adaptive, helping people identify threats and spot fleeting resources and opportunities (Gallo et al. Reference Gallo, Bogart, Vranceanu and Matthews2005; Taylor & Seeman Reference Taylor and Seeman1999). Second, lower-SES ecologies are characterized by greater unpredictability. Thus, more dialectical forms of reasoning, which acknowledge the role of uncertainty and view processes in a nonlinear fashion (Grossmann, Reference Grossmann, Spencer-Rogers and Pengin press), may provide better guidance for decision making in such environments (Grossmann Reference Grossmann2017; Grossmann et al. Reference Grossmann, Brienza and Bobocel2017). Third, when reasoning about the causes of others' behavior in a setting of limited and feeling resources and a wide range of threats, one would arrive at more accurate inferences and predictions by giving greater weight to external causes (Stellar et al. Reference Stellar, Manzo, Kraus and Keltner2012). Finally, to avoid or better cope with potential threats common in low-SES environments, one may become more attuned to other people, including their feelings, intentions, and actions, enabling efficient in-group coordination of threat-specific responses (Pickett & Gardner Reference Pickett, Gardner, Williams, Forgas and Hippel2005; Taylor Reference Taylor2006). Given a backdrop of scarcity, these attentional, cognitive, and social strategies are of greater survival relevance for lower- versus higher-SES people. Beyond vigilance to and management of threats and uncertainty, greater attunement to others may also help alert individuals to potential mating opportunities, consistent with a faster life-history strategy. However, life-history theory alone cannot sufficiently account for SES differences illustrated here, including differences in nonsocial attention, dialectical reasoning, and many features of social attunement (e.g., self-definition through relationships with close others).

To conclude, a serious consideration of ecological affordances and constraints may provide a framework to understand not only SES-linked differences in behaviors linked to short- versus long-term focus but also a range of other tendencies that have been shown to vary as a function of SES. Although life-history provides a powerful lens to understand how social class shapes some aspects of cognition and behavior, we do not believe that life-history theory allows for ready explanations of a range of other ways in which those who are of higher versus lower SES differ. There are numerous ways in which SES differences may reflect ecology-specific adaptations. A complete account of how social class shapes minds and behavior must address ecological adaptations (Grossmann & Varnum Reference Grossmann and Varnum2015), the sociocultural environments they create (Grossmann & Huynh Reference Grossmann and Huynh2013; Kraus et al. Reference Kraus, Piff and Keltner2011; Stephens et al. Reference Stephens, Fryberg and Markus2011), and the interaction of ecological and cultural factors with processes discussed by P&N's model.