Health and the avoidance of macroparasites: a preliminary cross-cultural study

Discriminating between sick and healthy faces based on early sickness cues: an exploratory analysis of sex differences

Background and objectives

It has been argued that sex and disease-related traits should influence how observers respond to sensory sickness cues. In fact, there is evidence that humans can detect sensory cues related to infection in others, but lack of power from earlier studies prevents any firm conclusion regarding whether perception of sickness cues is associated with sex and disease-related personality traits. Here, we tested whether women (relative to men), individuals with poorer self-reported health, and who are more sensitive to disgust, vulnerable to disease, and concerned about their health, overestimate the presence of, and/or are better at detecting sickness cues.

Methodology

In a large online study, 343 women and 340 men were instructed to identify the sick faces from a series of sick and healthy photographs of volunteers with an induced acute experimental inflammation. Participants also completed several disease-related questionnaires.

Results

While both men and women could discriminate between sick and healthy individuals above chance level, exploratory analyses revealed that women outperformed men in accuracy and speed of discrimination. Furthermore, we demonstrated that higher disgust sensitivity to body odors is associated with a more liberal decision criterion for categorizing faces as sick.

Conclusion

Our findings give strong support for the human ability to discriminate between sick and healthy individuals based on early facial cues of sickness and suggest that women are significantly, although only slightly, better at this task. If this finding is replicated, future studies should determine whether women's better performance is related to increased avoidance of sick individuals.

Adaptive host responses to infection can resemble parasitic manipulation

Using a dynamic optimisation model for juvenile fish in stochastic food environments, we investigate optimal hormonal regulation, energy allocation and foraging behaviour of a growing host infected by a parasite that only incurs an energetic cost. We find it optimal for the infected host to have higher levels of orexin, growth and thyroid hormones, resulting in higher activity levels, increased foraging and faster growth. This growth strategy thus displays several of the fingerprints often associated with parasite manipulation: higher levels of metabolic hormones, faster growth, higher allocation to reserves (i.e. parasite-induced gigantism), higher risk-taking and eventually higher predation rate. However, there is no route for manipulation in our model, so these changes reflect adaptive host compensatory responses. Interestingly, several of these changes also increase the fitness of the parasite. Our results call for caution when interpreting observations of gigantism or risky host behaviours as parasite manipulation without further testing.

Disease, perceived infectability and threat reactivity: A COVID-19 study

Using a two-wave online experiment, we investigate whether COVID-19 exposure changes participants' threat-detection threshold. Threat reactivity was measured in a signal detection task among 277 British adults who also reported how vulnerable they felt to infectious diseases. Participants' data were then matched to the local number of confirmed COVID-19 cases announced by the NHS every day. We found that participants who perceive themselves as more likely to catch infectious diseases displayed higher threat reactivity in response to increased COVID-19 cases.

Food Disgust Scale: Spanish Version

INTRODUCTION

The Food Disgust Scale (FDS) was recently developed and validated in Swiss adult population. This study aims to: (1) validate the FDS for the first time in a Spanish-speaking Mexican population, (2) correlate food disgust sensitivity with picky eating measures, and (3) explore the association between food disgust sensitivity and body mass index (BMI).

MATERIALS AND METHODS

A Spanish version of the FDS (FDS-Sp) and its short version (FDS-Sp short) were tested with confirmatory factor analysis (CFA) in order to test the original item/factor structure. Bivariate correlations were performed to determine the association between FDS-Sp/FDS-Sp short scores and picky eating. Lastly, hierarchical linear regression analysis was carried out to determine the relationship between food disgust sensitivity and BMI.

RESULTS

The factor structure of the FDS was replicated and acceptable internal consistency values were observed for FDS-Sp subscales (α varied between 0.781 and 0.955). Moreover, FDS-Sp subscales and FDS-Sp short were correlated with picky eating. Higher score in VEGI subscale of the FDS-Sp was a significant predictor for higher BMI, explaining 4% of the variance.

CONCLUSION

FDS-Sp is a useful, reliable and robust psychometric instrument to measure the sensitivity to unpleasant food situations in a Mexican adult Spanish-speaking population. A relationship between food disgust sensitivity and picky eating, selective eating behaviors and neophobia in Mexicans was confirmed. BMI is multifactorial and only one subscale of FDS-Sp is a significant predictor for BMI status. These results are helpful to continue exploring food disgust in diverse populations.

A multivariate analysis of women's mating strategies and sexual selection on men's facial morphology

The strength and direction of sexual selection via female choice on masculine facial traits in men is a paradox in human mate choice research. While masculinity may communicate benefits to women and offspring directly (i.e. resources) or indirectly (i.e. health), masculine men may be costly as long-term partners owing to lower paternal investment. Mating strategy theory suggests women's preferences for masculine traits are strongest when the costs associated with masculinity are reduced. This study takes a multivariate approach to testing whether women's mate preferences are context-dependent. Women (n = 919) rated attractiveness when considering long-term and short-term relationships for male faces varying in beardedness (clean-shaven and full beards) and facial masculinity (30% and 60% feminized, unmanipulated, 30% and 60% masculinized). Participants then completed scales measuring pathogen, sexual and moral disgust, disgust towards ectoparasites, reproductive ambition, self-perceived mate value and the facial hair in partners and fathers. In contrast to past research, we found no associations between pathogen disgust, self-perceived mate value or reproductive ambition and facial masculinity preferences. However, we found a significant positive association between moral disgust and preferences for masculine faces and bearded faces. Preferences for beards were lower among women with higher ectoparasite disgust, providing evidence for ectoparasite avoidance hypothesis. However, women reporting higher pathogen disgust gave higher attractiveness ratings for bearded faces than women reporting lower pathogen disgust, providing support for parasite-stress theories of sexual selection and mate choice. Preferences for beards were also highest among single and married women with the strongest reproductive ambition. Overall, our results reflect mixed associations between individual differences in mating strategies and women's mate preferences for masculine facial traits.

Microbes and masculinity: Does exposure to pathogenic cues alter women's preferences for male facial masculinity and beardedness?

Women's preferences for men's androgen dependent secondary sexual traits are proposed to be phenotypically plastic in response to exposure to pathogens and pathogen disgust. While previous studies report that masculinity in facial shape is more attractive to women who have recently been exposed to pathogenic cues and who are high in self-reported pathogen disgust, facial hair may reduce male attractiveness under conditions of high pathogens as beards are a possible breeding ground for disease carrying ectoparasites. In the present study, we test whether women's preferences for beardedness and facial masculinity vary due to exposure to different pathogenic cues. Participants (N = 688, mean age + 1SD = 31.94 years, SD = 6.69, range = 18-67) rated the attractiveness of facial composite stimuli of men when they were clean-shaven or fully bearded. These stimuli were also manipulated in order to vary sexual dimorphism by ±50%. Ratings were conducted before and after exposure to one of four experimental treatments in which participants were primed to either high pathogens (e.g. infected cuts), ectoparasites (e.g. body lice), a mixture of pathogens and ectoparasites, or a control condition (e.g. innocuous liquids). Participants then completed the three-domain disgust scale measuring attitudes to moral, sexual and pathogen disgust. We predicted that women would prefer facial masculinity following exposure to pathogenic cues, but would show reduced preferences for facial hair following exposure to ectoparasites. Women preferred full beards over clean-shaven faces and masculinised over feminised faces. However, none of the experimental treatments influenced the direction of preferences for facial masculinity or beardedness. We also found no association between women's self-reported pathogen disgust and their preferences for facial masculinity. However, there was a weak positive association between moral disgust scores and preferences for facial masculinity, which might reflect conservatism and preferences for gender typicality in faces. Women's preferences for beards were positively associated with their pathogen disgust, which runs contrary to our predictions and may reflect preferences for high quality individuals who can withstand any costs of beardedness, although further replications are necessary before firm conclusions can be made. We conclude that there is little support for pathogenic exposure being a mechanism that underpins women's directional preferences for masculine traits.

Skin-transmitted pathogens and the heebie jeebies: evidence for a subclass of disgust stimuli that evoke a qualitatively unique emotional response

Skin-transmitted pathogens have threatened humans since ancient times. We investigated whether skin-transmitted pathogens were a subclass of disgust stimuli that evoked an emotional response that was related to, but distinct from, disgust and fear. We labelled this response "the heebie jeebies". In Study 1, coding of 76 participants' experiences of disgust, fear, and the heebie jeebies showed that the heebie jeebies was elicited by unique stimuli which produced skin-crawling sensations and an urge to protect the skin. In Experiment 2,350 participants' responses to skin-transmitted pathogen, fear-inducing, and disgust-inducing vignettes showed that the vignettes elicited sensations and urges which loaded onto heebie jeebies, fear, and disgust factors, respectively. Experiment 3 largely replicated findings from Experiment 2 using video stimuli (178 participants). Results are consistent with the notion that skin-transmitted pathogens are a subclass of disgust stimuli which motivate behaviours that are functionally consistent with disgust yet qualitatively distinct.

Is a woman's preference for chest hair in men influenced by parasite threat?

Humans (Homo sapiens) are unique primates due to a lack of a thermally insulating fur covering, typical of all other primates. Our primary goal was to examine the "ectoparasite avoidance mediated by mate choice hypothesis" suggesting that women prefer men lacking chest hair in order to avoid ectoparasite loads. We predicted that women living in areas with high prevalence of pathogens (n = 161) would be less likely to show a preference for a male with chest hair in comparison with women living in areas with low pathogen prevalence (n = 183). We found that overall preference for man chest hair was low, but there were no significant associations between perceived vulnerability to diseases or disgust sensitivity and preference of men who have had experimentally removed chest hair. Women who lived in an environment with a high parasite prevalence rate (Turkey) showed a similar preference for man chest hair as did women from an environment with low parasite prevalence (Slovakia). The participants biological fathers' chest hair had no significant effect on their preference for men with chest hair. Women living in a high-parasite-prevalence environment reported a higher disgust score in the sexual domain and more recent experiences with illnesses, suggesting that parasites influence sensitivity to sexual disgust. These results provide no support for the ectoparasite avoidance hypothesis mediated by mate choice and suggest that shaved men bodies are preferred more by women.

Self-Protection Versus Disease Avoidance

Predators and pathogens are powerful natural selection tools that influence the evolution of two domain-specific management systems: self-protection and disease avoidance. Both systems are activated by specific ecological conditions and protect humans against physical harm or disease transmission. The perception of predators is associated with fear, and the perception of disease-relevant animals is associated with disgust. Fear of predators negatively correlated with the perceived physical condition of participants, suggesting that the self-protection system is activated particularly in people who are more vulnerable to predation threat. People vulnerable to infectious diseases rated predators as more dangerous, suggesting that the disease-avoidance system activates behavior-reducing contact with harmful animals. Females had a higher score in terms of fear, disgust, and perceived danger in particular when considering animals that pose physical harm and/or a disease threat. Our results support the adaptation view, suggesting that the self-protection and disease-avoidance systems are domain specific, and that both have been shaped by natural selection in order to protect humans against harmful animals or events.

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.

The Effect of Owning Animals on Perceived Vulnerability to, and Avoidance of, Parasitic Diseases in Humans

The evolutionary history of humans has always been influenced by pathogens because of their ability to cause both morbidity and mortality. Natural selection should favor behavioral strategies that minimize disease transmission and consequently increase human survival. Collectively such strategies are referred to as the behavioral immune system, which is thought to be more often activated in individuals with an impaired immune system who are most vulnerable to pathogens and infectious diseases. We investigated the associations between an individual’s perceived vulnerability to disease, whether they own any animals, and whether they carry out behavioral tactics to avoid parasite transmission. A sample of 285 Slovakian students participated in a questionnaire study. As predicted, antipathogen behavior was activated in individuals with a high perceived vulnerability to disease. Females showed higher antiparasitic scores than males especially when behaviors were most likely to transmit disease. Individuals who owned animals perceived themselves as less vulnerable to disease as well as less vulnerable to the perceptions of those who did not own any animals. Moreover, among animal owners scores for parasite-avoiding behaviors relevant to being in close contact with an animal (such as removing animal feces and worming animals) were higher than for parasite-transmitting behaviors relevant to being in close contact with an animal (such as allowing animals to lick). We discuss the results, further taking into account both the model of natural selection and the coevolutionary arms race model.