Parasite-stress Theory Research Articles

Parasites and their implications for social and cultural psychology

Social/cultural psychologists have traditionally used the value systems of collectivism and individualism to explain differences across cultures but very little consideration has been given to the ultimate origins of these value systems. Parasite Stress Theory (PST) is a new evolutionary theory that aims to explain why overarching value systems develop differently throughout the world and how these value systems lead to variations across countries (e.g. in xenophobia, innovation, conformity and political attitudes). This paper will discuss how PST, in conjunction with the Behavioural Immune System (BIS) explains in-group and outgroup interactions and specifies the conditions that lead to heightened prejudice.

The Parasite-Stress Theory of Values and Sociality, Infectious Disease, History and Human Values Worldwide

The Parasite-Stress Theory of Values and Sociality, Infectious Disease, History and Human Values Worldwide

The parasite-stress theory of sociality, the behavioral immune system, and human social and cognitive uniqueness.

Parasite adversity was an important source of Darwinian selection in human evolutionary history because parasites selected for a diversity of human behavioral parasite-defenses in addition to the numerous defenses provided by the classical human immune system. We argue for a broader view of behavioral immunity than has been emphasized recently. We propose a new hypothesis for the evolution of the unique cognitive and social adaptations of humans. We argue that, in human evolutionary history, as weaponry and other technologies reduced the importance of the physical environment, typical ecological challenges, and predators as agents of selection shaping mental and social traits, parasites became more important selection agents on these traits. Also, we suggest that the reduction of natural selection in the context of predation in human evolutionary history resulted in selection favoring high pathogenicity in human parasites because predation is focused on debilitated prey and hence selects against pathogenicity in the parasites involved. The new hypothesis argues that, in human evolutionary history, temporal variation in local parasite adversity gave rise to frequent change and complexity in the values that are adaptive for individuals to use in their social navigation in relation to the degree of local disease stress, and that selection in this context accounts for the evolution of aspects of human uniqueness in cognitive ability and sociality. The new hypothesis is akin to the social brain hypothesis but is contrary to the version of that hypothesis deemphasizing parasites. Tests of the new hypothesis are addressed.

Fast life histories, not pathogens, account for state-level variation in homicide, child maltreatment, and family ties in the U.S.

Parasite stress theory has recently been used to account for an array of cross-cultural differences in human cognition and social behavior, including in-group bias, interpersonal violence, child maltreatment, and religious adherence. Here, we re-assess the apparently ubiquitous effects of parasite stress on behavior observed in the U.S., using the cross-sectional, cross-population approach implemented by prior pathogen stress studies. Our results raise two challenges to previous findings. First, we show that the observed effects of pathogen stress in the U.S. data are due exclusively to one type of infectious disease – sexually transmitted diseases (STD) – while non-STD infections have no effect. Second, we find that controlling for life history measures of extrinsic risk and a fast life history erases the observed associations with family ties, interpersonal violence, child fatalities, and religious adherence. Thus, after appropriate variable specification, stratification, and control, U.S. cross-state population differences provide no support for the pathogen stress hypothesis in these various domains of behavior. Rather, the findings are more consistent with predictions from life history theory.

Rethinking innovative designs to further test parasite-stress theory

Fincher & Thornhill's (F&T's) parasite-stress theory of sociality is supported largely by correlational evidence; its persuasiveness would increase significantly via lab and natural experiments and demonstrations of its mediating role. How the theory is linked to other approaches to group differences in psychological differences and to production and dissemination of cultural ideas and practices, need further clarification. So does the theory's view on the possible reduction of negative group interactions.

Extending parasite-stress theory to variation in human mate preferences

In this commentary we suggest that Fincher & Thornhill's (F&T's) parasite-stress theory of social behaviors and attitudes can be extended to mating behaviors and preferences. We discuss evidence from prior correlational and experimental studies that support this claim. We also reanalyze data from two of those studies using F&T's new parasite stress measures.

The parasite-stress theory may be a general theory of culture and sociality

In the target article, we presented the hypothesis that parasite-stress variation was a causal factor in the variation of in-group assortative sociality, cross-nationally and across the United States, which we indexed with variables that measured different aspects of the strength of family ties and religiosity. We presented evidence supportive of our hypothesis in the form of analyses that controlled for variation in freedom, wealth resources, and wealth inequality across nations and the states of the USA. Here, we respond to criticisms from commentators and attempt to clarify and expand the parasite-stress theory of sociality used to fuel our research presented in the target article.

Time allocation, religious observance, and illness in Mayan horticulturalists

Analysis of individual differences in religious observance in a Belizean community showed that the most religious (pastors and church workers) reported more illnesses, and that there was no tendency for the religiously observant to restrict their interactions to family or extended family. Instead, the most religiously observant tended to have community roles that widened their social contact: religion did not aid isolation - thus violating a key assumption of the parasite-stress theory of sociality.

Analyses do not support the parasite-stress theory of human sociality

Re-analysis of the data provided in the target article reveals a lack of evidence for a strong, universal relationship between parasite stress and the variables relating to sociality. Furthermore, even if associations between these variables do exist, the analyses presented here do not provide evidence for Fincher & Thornhill's (F&T's) proposed causal mechanism.

Parasite-stress promotes in-group assortative sociality: The cases of strong family ties and heightened religiosity

Throughout the world people differ in the magnitude with which they value strong family ties or heightened religiosity. We propose that this cross-cultural variation is a result of a contingent psychological adaptation that facilitates in-group assortative sociality in the face of high levels of parasite-stress while devaluing in-group assortative sociality in areas with low levels of parasite-stress. This is because in-group assortative sociality is more important for the avoidance of infection from novel parasites and for the management of infection in regions with high levels of parasite-stress compared with regions of low infectious disease stress. We examined this hypothesis by testing the predictions that there would be a positive association between parasite-stress and strength of family ties or religiosity. We conducted this study by comparing among nations and among states in the United States of America. We found for both the international and the interstate analyses that in-group assortative sociality was positively associated with parasite-stress. This was true when controlling for potentially confounding factors such as human freedom and economic development. The findings support the parasite-stress theory of sociality, that is, the proposal that parasite-stress is central to the evolution of social life in humans and other animals.

Parasite stress promotes homicide and child maltreatment

Researchers using the parasite-stress theory of human values have discovered many cross-cultural behavioural patterns that inform a range of scholarly disciplines. Here, we apply the theory to major categories of interpersonal violence, and the empirical findings are supportive. We hypothesize that the collectivism evoked by high parasite stress is a cause of adult-on-adult interpersonal violence. Across the US states, parasite stress and collectivism each positively predicts rates of men's and women's slaying of a romantic partner, as well as the rate of male-honour homicide and of the motivationally similar felony-related homicide. Of these four types of homicide, wealth inequality has an independent effect only on rates of male-honour and felony-related homicide. Parasite stress and collectivism also positively predict cross-national homicide rates. Child maltreatment by caretakers is caused, in part, by divestment in offspring of low phenotypic quality, and high parasite stress produces more such offspring than low parasite stress. Rates of each of two categories of the child maltreatment--lethal and non-lethal--across the US states are predicted positively by parasite stress, with wealth inequality and collectivism having limited effects. Parasite stress may be the strongest predictor of interpersonal violence to date.

Prenatal experience with low-frequency maternal voice sounds influences newborns' perception of female voices

Little research has tested the parasite-stress theory of sociality based on a well-framed model of personal values using a multilevel analysis conducted on multinational samples. To robustly examined the validity of this novel theory of cultural evolution, this study used multilevel data of European Social Survey (from 2002 to 2016, 32 countries, N = 374,730) and World Values Survey (from 2005 to 2014, 80 countries, N = 173,540) to investigate the relationships between pathogen prevalence and the conflicting values dimensions (Conservation versus Openness to change; Self-enhancement versus Self-transcendence) of the circular model of human values, accounting for the micro- (age, sex, religious belief, education, and income) and macro-level predictors (modernization and cultural similarity). Results did not support the parasite-stress theory at both the country and individual levels when controlling for a composite index of modernization. Across all analyses, modernization remained a significant predictor of values even when controlling for cultural similarity. No conclusions changed when using an alternative parasite stress estimate. These findings support the modernization theory of value-change but challenge the roles of infectious diseases in cultural evolution.