Do Symptoms of Illness Serve Signaling Functions? (Hint: Yes)

Abstract

Symptoms of illness provide information about an organism's underlying state. This notion has inspired a burgeoning body of research on organisms' adaptations for detecting and changing behavior toward ill individuals. However, little attention has been paid to a likely outcome of these dynamics. Once an organism's fitness is affected by others' responses to symptoms of illness, natural selection can favor individuals who alter symptom expression to influence the behavior of others. That is, many symptoms may originate as cues, but will evolve into signals. In this paper, I develop the hypothesis that symptoms of illness serve signaling functions, and provide a comprehensive review of relevant evidence from diverse disciplines. I also develop novel empirical predictions generated by this hypothesis and discuss its implications for public health. Signaling provides an ultimate explanation for otherwise opaque aspects of symptom expression, such as why symptoms fluctuate in social contexts, and can exist without underlying pathology, and why individuals deliberately generate symptoms of illness. This analysis suggests that signaling theory is a major organizing framework for understanding symptom etiology.

Why Care: Complex Evolutionary History of Human Healthcare Networks

“…This suggests that the process for recognizing when individuals need care requires more than simply activating offspring care behaviors. There is a growing consensus that the process of evaluating the health status of others is an aspect of social cognition (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018). The same brain pathways that enable animals to interpret behavioral, olfactory, vocal, or visual cues to discern the identities, motivations, and intentions of others can likely detect health cues such as lethargy or difficulties moving, odor changes due to immune responses, respiratory infections in vocalizations, or fevers and rashes on faces (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018).…”

“…There is a growing consensus that the process of evaluating the health status of others is an aspect of social cognition (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018). The same brain pathways that enable animals to interpret behavioral, olfactory, vocal, or visual cues to discern the identities, motivations, and intentions of others can likely detect health cues such as lethargy or difficulties moving, odor changes due to immune responses, respiratory infections in vocalizations, or fevers and rashes on faces (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018). This would suggest that recognizing health cues in others may be a key aspect of social cognition and/or that these pathways may have been co-opted for that use (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018).…”

“…The same brain pathways that enable animals to interpret behavioral, olfactory, vocal, or visual cues to discern the identities, motivations, and intentions of others can likely detect health cues such as lethargy or difficulties moving, odor changes due to immune responses, respiratory infections in vocalizations, or fevers and rashes on faces (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018). This would suggest that recognizing health cues in others may be a key aspect of social cognition and/or that these pathways may have been co-opted for that use (Fisher et al, 2014;Shakhar and Shakhar, 2015;Steinkopf, 2015;Tiokhin, 2016;Kessler et al, 2017;Kavaliers and Choleris, 2018;Steinkopf and de Barra, 2018). This is tentatively supported by the frequent observations of care in species with greater cognitive abilities and complex social relationships like the cetaceans (Bearzi et al, 2018), primates (Anderson et al, 2010), or carnivores (Davenport, 2010).…”

Financial alchemists and financial shamans

“…Thus, patients must convincingly communicate their need for care to others in their communities. This has a number of implications for the evolution of health and healing: The prosocial environment of humans should favor symptoms that signal suffering convincingly and motivate others to acknowledge the sick state and grant help and treatment (Steinkopf 2015;Tiokhin 2016). Marked displays of pain in humans might be selected for their effectiveness in mobilizing others' support (Finlay & Syal 2014;Steinkopf 2016;Williams 2002).…”

A ritual by any other name

“…The social environment of sick or injured humans is fundamentally different from the social environment of sick individuals of other species. In non-human animals, being recognized as sick or injured can lead to a loss of attractiveness as a mate or cooperation partner, to a challenge of social rank, to avoidance or exclusion from the group, or to preferential targeting by predators (Tiokhin 2016). Although all of this also could happen to sick or injured humans, a different response from the social environment is rare in other species and highly common in humans: social support and treatment (Steinkopf 2015).…”