Richerson et al. present an interesting take on the contemporary movement to understand the complexity of human behavior via multi-level selection forces. Their arguments in favor of multi-level selection by way of cultural group fitness, though speculative, highlight the potential application in evaluating the social structure as a potent mediator in the selection of characteristics of human psychology. It may in fact be the case that a multitude of basic biological systems have been influenced by both individual- and group-level selection forces due to the reciprocal nature on individual and group fitness outcomes. One domain of mental and physical health functioning that likely evolved within the constraints of embedded social communication is the experience and demonstration of visceral suffering in its various forms (e.g., anxiety, sadness) including pain. In this commentary, we propose to extend Richerson et al.'s thesis by showing how human pain perception could have been influenced by multi-level selection, a thesis that, if true, has broad implications for the future directions of evolutionary psychology and the clinical health sciences.

There is no doubt that the behavioral expression of physical discomfort has both intra- and interpersonal functions that directly impact the individual's fitness. Some intrapersonal functions of pain perception include the ability to detect and discriminate environmental threats, to serve as a warning system, to promote self-awareness (e.g., to attend to and protect an injured body-part), and to facilitate operant learning (e.g., to avoid dangerous stimuli; Eccleston & Crombez Reference Eccleston and Crombez1999). Relative to other species, these intrapersonal functions alone do not explain why humans express so many and such varied non-vital suffering behaviors, including those associated with chronic, psychosomatic, and emotion-induced pain conditions. One likely explanation for the adaptive benefits of pain expression lies in the social-signaling properties of pain behaviors (Vigil & Strenth Reference Vigil and Strenth2014).

The social-signaling perspective maintains that pain behaviors are a pinnacle demonstration of vulnerability, which humans use and direct toward selective social partners to gain logistical and emotional social support in times of need (Vigil Reference Vigil2009). Expressive pain behaviors also allow sufferers to assess the altruistic reliability of the targets of their expression (e.g., friends, domestic partners or health care providers). In other words, persons who respond to a solicitation evoked by a pain expression are perceived as potentially more reliable social partners. To date, this social-signaling perspective of pain perception has been used (with relative success) for predicting individual differences that influence the expression of pain in various social contexts, such as audience characteristics (Vigil & Alcock Reference Vigil and Alcock2014; Vigil & Coulombe Reference Vigil and Coulombe2011; Vigil et al. Reference Vigil, Rowell, Alcock and Maestes2014b) and the simulated presence of another person (e.g., the sound of a stranger's voice; see Vigil et al. Reference Vigil, Torres, Wolff and Hughes2014d).

Still, there is no reason to assume that the social-signaling functions of pain are limited to individual-level fitness incentives alone. Thus, additional selection forces acting at the group level may have played a secondary or coevolutionary role in the selection of pain's perception and expression. As Richerson et al. and others have noted (Geary Reference Geary2010; Geary et al. Reference Geary, Byrd-Craven, Hoard, Vigil and Numtee2003), humans evolved in an environment of coalitional competition whereby social cooperation was used to form alliances for protecting oneself from and competing against rival groups for control of ecologically relevant resources (e.g., food and mates). The coordination of group activities was such a predominant feature throughout human evolution that it may make sense to conceptualize the group as a valid unit of selection. This is especially true if the success of group activities depends on communication among members. Given that the expression of pain can be understood as an individual's perception of threat and state of debilitation, the aggregate effect of multiple individuals expressing pain should ultimately influence a group's behavior. Based on this, the selection of individual characteristics and attributes that bolster selective communication of pain within a group should enable improved group coordination and decision-making. Likewise, groups that are better able to assess external threats (predators, neighboring groups, or parasites) and in-group capabilities should have a greater chance of survival. From an evolutionary perspective, this hypothesis makes intuitive sense, given that humans are the quintessential social animal and competition between groups is dependent on achieving effective group-level consensus on resource expenditure and risk-taking (e.g., engaging in new hunting tactics, migration, coalitional warfare).

Complementary to this hypothesis is the role that empathy plays during interpersonal communication. Expressed empathy could be understood as a key behavioral mediator subserving the interpretation of individual-level vulnerability and threat (i.e., pain) in coalition members. Said differently, for pain's expression to find an effective target, the receiver must be able to internalize the current state (and changes in that state) of physical and mental prowess of the signaler. This combination of pain and empathetic signaling (e.g., behavioral mimicry) distributed among group members enables group coordination. This hypothesis is supported by recent findings suggesting that people express empathy systematically with the formation of social identities creating an intragroup empathy bias – the increasing empathy between in-group members greater than that of out-group members (Cikara et al. Reference Cikara, Bruneau and Saxe2011; Reference Cikara, Bruneau, Van Bavel and Saxe2014). The mutual expression of pain and empathy enables in-group members to use this information in making effective decisions. In line with this, our lab has found that momentary pain reporting is influenced by the quantity and quality of the individual's peer relationships (Vigil et al. Reference Vigil, Rowell, Chouteau, Chavez, Jaramillo, Neal and Waid2013), relationships with pair-bonding partners (Vigil et al. Reference Vigil, Strenth, Trujillo and Gangestad2014c), and other types of co-residents (Vigil et al. Reference Vigil, Pendleton, Coulombe, Vowels, Alcock and Smith2014a). These findings suggest that pain has been naturally selected to be expressed systematically within a broader social networking system. Further, recent work has explicated a neurobiological relationship between social and physical pain. Panksepp (Reference Panksepp1998) originally proposed the idea of social pain, and since then, numerous studies have demonstrated a cognitive and behavioral overlap between the shared aspects of physical and social pain (Eisenberger & Cole Reference Eisenberger and Cole2012; Macdonald & Leary Reference Macdonald and Leary2005).

On the balance, the diverse research findings from numerous lines of inquiry suggests a need for further empirical and experimental studies that would add to a developing framework for understanding how individual behavior is reciprocally shaped by both individual and group outcomes. Pain behaviors enjoy a rich variability that may not be attributed to individual factors alone, and this new framework may offer alternative means for generating predictions of the evolved nature of human suffering.