Fincher & Thornhill (F&T) extend both theory and evidence for a behavioral immune system theory of cognition and behavior to the level of cultural norms regarding family and religion. The theory posits the existence of an evolved psychological system that generates prophylactic, pathogen-avoidant response strategies to pathogen threat in the environment, which may consist of beliefs, attitudes, and psychological orientations that serve as the psychological substrates for avoiding potential disease vectors. Unlike the somatic immune system, which typically responds to pathogen attacks via the activity of pro-inflammatory cytokines, the behavioral immune system responds to perceptual threats – before infections occurs – which may include assortative biases for one's own group versus others as a defense against vectors of novel parasites.
In a bold extension of this framework, F&T hypothesize that the behavioral immune system may extend to beliefs and customs transmitted at the cultural or societal level, where norms regarding the tightness of family ties and religiosity (“assortative sociality”) are expected to be stronger in environments where pathogen loads have been historically prevalent. In an inter-regional and cross-national analysis, F&T demonstrate that such assortative sociality is indeed predicted by historical parasite stress in the region. These findings hold even when controlling for factors expected to covary with disease threat, such as economic development. There are many potential alternative explanations for why parasite threat might covary with assortative biases (such as more general existential fears). However, F&T find that their effects are strongest in environments where human-specific transferred diseases were most prevalent, relative to those transferred through other means. I don't think the importance of this last point about the disease specificity of this phenomenon can be underemphasized, because it is so compelling as to all but preclude the plausibility of any competing theory in explaining these findings. F&T have made a solid advance in the scientific understanding of some of the most fundamental domains of the human condition – families, groups, and religion – by extrapolating from a major theme in biology: disease, an adaptive problem for all life forms.
The arguments and findings of F&T are compelling in their conceptual clarity and theoretical integration, and are sweeping in their explanatory power. The authors have clarified and built on the ruminations of others (e.g., Curtis & Biran Reference Curtis and Biran2001; Fessler Reference Fessler2002; Navarrete & Fessler Reference Navarrete and Fessler2006; Schaller Reference Schaller2006; Wronska Reference Wronska, Drenth, Sergeant and Takens1990) to develop an enterprise that is maturing much faster and more convincingly than anyone would have imagined possible just a few years ago.
Given their success, I am tempted to push them even further. As F&T are aware, but do not emphasize, the behavioral immune system need not be relegated solely to a psychological system whose functions are only prophylactic. F&T rightly paraphrase Navarrete and Fessler (Reference Navarrete and Fessler2006) in noting that assortative sociality not only serves protective functions, but can also function as an “insurance policy” to facilitate the healing process after the fact. If this is indeed the case, might F&T be able to find evidence for greater prosociality relevant to helping the sick and weak within families and religious groups in response to disease threat cross-culturally? I'm not sure how readily testable this notion is compared with what the authors have already heroically demonstrated, but the challenge is put.
Along similar lines, one might push the notion even further that the behavioral immune system should generate not only behavioral prophylaxis, but should also include psychological mechanisms underlying behavioral responses to infection that allow the organism to heal and recover, should prophylaxis fail (sensu Hart Reference Hart1988). The action of pro-inflammatory cytokines not only serves to neutralize pathogens in the body, but also may play a role in neurological changes that increase the likelihood of sickness behaviors, which cause an organism to not over-exert itself while it is still vulnerable and on the mend. Research describes a syndrome associated with cytokine activity where diseased animals will show decreased motor activity and food intake, reduced foraging, less exploratory behavior, increased sleep, and decreased grooming behavior (Kelley et al. Reference Kelley, Bluthe, Dantzer, Zhou, Shen, Johnson and Broussarda2003).
Previously believed to be mere artifacts of exogenous cytokines, these changes in behavior are now widely believed to be an important part of the healing process, and can be considered to be the expression of a motivational state that resets an individual's priorities to promote resistance to pathogens and facilitate recovery from infection (Kelley et al. Reference Kelley, Bluthe, Dantzer, Zhou, Shen, Johnson and Broussarda2003). In humans, this may include an increase in relational cognition, designed to foster social or coalitional support when one is most vulnerable, as suggested elsewhere (Navarrete & Fessler Reference Navarrete and Fessler2006; Navarrete et al. Reference Navarrete, Fessler and Eng2007). Perhaps cross-geographic studies of emotions, attitudes, personalities, beliefs, and norms could be conducted that would shed light on the understudied phenomenon of the evolved psychology of sickness behavior as has been demonstrated across species. It would take considerable reflection on the animal literature to extrapolate what the relevant psychological or cultural expressions of pan-species chronic sickness behavioral strategies might look like. However, a straightforward instantiation might be along the lines of a study of the beliefs, attitudes, and norms regarding the function of calmness, quietude, and “taking it easy” compared to themes that emphasize assiduousness, industriousness, tenacity, and negative views of “idleness.” Sleep duration and daily activity patterns may be relevant as well. Such a scientific investigation could be politically sensitive to be sure, but may be as worthwhile as the present research; and it would be no more potentially sensitive than is F&T's bold and impressive work at hand.
Fincher & Thornhill (F&T) extend both theory and evidence for a behavioral immune system theory of cognition and behavior to the level of cultural norms regarding family and religion. The theory posits the existence of an evolved psychological system that generates prophylactic, pathogen-avoidant response strategies to pathogen threat in the environment, which may consist of beliefs, attitudes, and psychological orientations that serve as the psychological substrates for avoiding potential disease vectors. Unlike the somatic immune system, which typically responds to pathogen attacks via the activity of pro-inflammatory cytokines, the behavioral immune system responds to perceptual threats – before infections occurs – which may include assortative biases for one's own group versus others as a defense against vectors of novel parasites.
In a bold extension of this framework, F&T hypothesize that the behavioral immune system may extend to beliefs and customs transmitted at the cultural or societal level, where norms regarding the tightness of family ties and religiosity (“assortative sociality”) are expected to be stronger in environments where pathogen loads have been historically prevalent. In an inter-regional and cross-national analysis, F&T demonstrate that such assortative sociality is indeed predicted by historical parasite stress in the region. These findings hold even when controlling for factors expected to covary with disease threat, such as economic development. There are many potential alternative explanations for why parasite threat might covary with assortative biases (such as more general existential fears). However, F&T find that their effects are strongest in environments where human-specific transferred diseases were most prevalent, relative to those transferred through other means. I don't think the importance of this last point about the disease specificity of this phenomenon can be underemphasized, because it is so compelling as to all but preclude the plausibility of any competing theory in explaining these findings. F&T have made a solid advance in the scientific understanding of some of the most fundamental domains of the human condition – families, groups, and religion – by extrapolating from a major theme in biology: disease, an adaptive problem for all life forms.
The arguments and findings of F&T are compelling in their conceptual clarity and theoretical integration, and are sweeping in their explanatory power. The authors have clarified and built on the ruminations of others (e.g., Curtis & Biran Reference Curtis and Biran2001; Fessler Reference Fessler2002; Navarrete & Fessler Reference Navarrete and Fessler2006; Schaller Reference Schaller2006; Wronska Reference Wronska, Drenth, Sergeant and Takens1990) to develop an enterprise that is maturing much faster and more convincingly than anyone would have imagined possible just a few years ago.
Given their success, I am tempted to push them even further. As F&T are aware, but do not emphasize, the behavioral immune system need not be relegated solely to a psychological system whose functions are only prophylactic. F&T rightly paraphrase Navarrete and Fessler (Reference Navarrete and Fessler2006) in noting that assortative sociality not only serves protective functions, but can also function as an “insurance policy” to facilitate the healing process after the fact. If this is indeed the case, might F&T be able to find evidence for greater prosociality relevant to helping the sick and weak within families and religious groups in response to disease threat cross-culturally? I'm not sure how readily testable this notion is compared with what the authors have already heroically demonstrated, but the challenge is put.
Along similar lines, one might push the notion even further that the behavioral immune system should generate not only behavioral prophylaxis, but should also include psychological mechanisms underlying behavioral responses to infection that allow the organism to heal and recover, should prophylaxis fail (sensu Hart Reference Hart1988). The action of pro-inflammatory cytokines not only serves to neutralize pathogens in the body, but also may play a role in neurological changes that increase the likelihood of sickness behaviors, which cause an organism to not over-exert itself while it is still vulnerable and on the mend. Research describes a syndrome associated with cytokine activity where diseased animals will show decreased motor activity and food intake, reduced foraging, less exploratory behavior, increased sleep, and decreased grooming behavior (Kelley et al. Reference Kelley, Bluthe, Dantzer, Zhou, Shen, Johnson and Broussarda2003).
Previously believed to be mere artifacts of exogenous cytokines, these changes in behavior are now widely believed to be an important part of the healing process, and can be considered to be the expression of a motivational state that resets an individual's priorities to promote resistance to pathogens and facilitate recovery from infection (Kelley et al. Reference Kelley, Bluthe, Dantzer, Zhou, Shen, Johnson and Broussarda2003). In humans, this may include an increase in relational cognition, designed to foster social or coalitional support when one is most vulnerable, as suggested elsewhere (Navarrete & Fessler Reference Navarrete and Fessler2006; Navarrete et al. Reference Navarrete, Fessler and Eng2007). Perhaps cross-geographic studies of emotions, attitudes, personalities, beliefs, and norms could be conducted that would shed light on the understudied phenomenon of the evolved psychology of sickness behavior as has been demonstrated across species. It would take considerable reflection on the animal literature to extrapolate what the relevant psychological or cultural expressions of pan-species chronic sickness behavioral strategies might look like. However, a straightforward instantiation might be along the lines of a study of the beliefs, attitudes, and norms regarding the function of calmness, quietude, and “taking it easy” compared to themes that emphasize assiduousness, industriousness, tenacity, and negative views of “idleness.” Sleep duration and daily activity patterns may be relevant as well. Such a scientific investigation could be politically sensitive to be sure, but may be as worthwhile as the present research; and it would be no more potentially sensitive than is F&T's bold and impressive work at hand.