Thursday, March 31, 2022

Rolf Degen summarizing... Christians value receiving a prayer in a hardship from a Christian stranger at an average of $2.34, while non-believers are willing to pay $1.56 not to be prayed for

Thunström L, Noy S (2022) What we think prayers do: Americans’ expectations and valuation of intercessory prayer. PLoS ONE 17(3): e0265836. Mar 31 2022.

Abstract: Praying for others in the wake of a disasters is a common interpersonal and public response to tragedy in the United States. But these gestures are controversial. In a survey experiment, we elicit how people value receiving a prayer from a Christian stranger in support of a recent hardship and examine factors that affect the value of the prayer. We find that people who positively value receiving the prayer do so primarily because they believe it provides emotional support and will be answered by God. Many also value the prayer because they believe it will improve their health and wealth, although empirical support of such effects is lacking. People who negatively value receiving the prayer do so primarily because they believe praying is a waste of time. The negative value is particularly large if people are offended by religion. Finally, the hardship experienced by the prayer recipient matters to the intensity by which recipients like or dislike the gesture, suggesting the benefit of prayers varies not only across people, but also across contexts.

Reasons people positively value prayers from religious strangers.

Participants who stated a positive WTP for receiving a prayer from a stranger (Christian: N = 375/451; non-believers: N = 56/166), were asked about the factors that contributed to the value of the prayer.

Large majorities of both Christians and non-believers who value the prayer do so because it gives them emotional comfort to know that the stranger is thinking of them. The answers to the open ended question provide additional information on the comfort people experience from receiving the prayer–e.g., one non-believer noted that they valued prayers positively because “someone is acknowledging the hardships I am going through and wishes for me to get through them successfully” (R_161) while a Christian participant explained: as “a Christian, prayer is invaluable and a source of personal comfort through faith” (R_282).

Further, a large majority of Christians (82 percent) believe that the prayer will result in God intervening to ease their emotional pain. While shares are smaller, many Christians also value the prayer because they believe God will help materially (36 percent) or improve their health (55 percent). Such expectations appear to be misplaced, given previous research shows that prayers for others have no effect on the recipient’s health [23], and therefore might bias the value of prayers upwards. They might also explain why prayers may reduce material aid [8]–if God is expected to intervene materially in response to prayers, the perceived need for material aid may be lower.

We also asked Christians who positively value prayers (N = 375/451) about the probability that the prayer from the stranger would be answered by God. Their average response was 78 percent. Amongst these participants, those who were more religious (as measured by frequency of church attendance), Republicans and those with low income (compared to high income) stated a higher probability that God would answer the prayer. For details, see Supplemental Online Material.

The share of non-believers who value the prayer and believe the prayer will result in help from God (whether emotional, material, or health) is not statistically significantly different from zero, i.e., even though some non-believers positively value receiving a prayer, they do not expect the prayer to generate benefits due to divine intervention. Finally, a large majority of both Christians and non-believers positively value the prayer because they think sending the prayer is a meaningful activity for the stranger. Hence, altruism could be an important part of the prayer’s value, to both Christians and non-believers–the recipient believes the sender of the prayer will benefit from undertaking the prayer.

While the results shown in Fig 2 indicate why people positively value prayers, it does not show how intensely each factor affects the positive value. Next, we examined the extent to which these factors, and covariates, affect the positive WTP. To do so, we regressed WTP for the prayer from the Christian stranger on agreement with each statement in Fig 2, a set of common demographics—gender, age, conservatism, religious belonging, religiosity (measured as frequency of church attendance) income and college attendance–as well as the type of hardship (issue) described in the experimental survey.


Fig 3 shows that the highest positive value for a prayer is generated if the recipient expects emotional comfort from the prayer. Although Fig 2 shows that many participants value the prayer because it benefits the sender to pray (altruism), the benefit to the sender does not contribute to the average positive value of a prayer (if anything, it brings down the mean positive value of the prayer). Further, beliefs that the prayer generates material help or improved health do not affect the mean positive value of the prayer.


The type of hardship addressed by the prayer also matters to the intensity by which a person values receiving a prayer. Around 30 percent of participants reported a health issue (for self or a loved one) as the hardship, around 30 percent reported a financial issue, between 15 and 20 percent reported a relationship issue, and around 20 percent an issue that does not fall into any of those categories. Recipients value the prayer more if the hardship they experience consists of a health or relationship issue (for themselves or a loved one), compared to if they or a loved one experience a financial issues (the benchmark in the model underlying Fig 3). These results are robust to the inclusion of covariates. Note that while being conservative significantly affects whether a prayer is positively valued (see above), more conservative people who value prayers do not assign a particularly high positive value to the prayer. This result is stable across our measurements of conservatism—it does not matter whether we use the SEC scale (the conservatism measure in Fig 3), the liberal-conservatism scale or political party belonging as a measure of conservatism.

The stability of beliefs in conspiracy theories is comparable to or higher than some of the most stable psychological attributes

Williams, Matt N., Mathew Ling, John R. Kerr, Stephen R. Hill, Mathew Marques, Hollie Mawson, and Edward J. R. Clarke. 2022. “To What Extent Do Beliefs in Conspiracy Theories Change over Time?.” PsyArXiv. March 31. doi:10.31234/

Abstract: Recent years have seen an explosion in psychological research on beliefs in conspiracy theories. This research has produced a significant body of knowledge about the antecedents and consequences of inter-individual belief in conspiracy theories. What is less clear, however, is the extent to which individuals’ beliefs in conspiracy theories vary over time (i.e., intra-individual variation). In this descriptive and exploratory study we therefore aimed to describe intra-individual variability in belief in conspiracy theories. We collected data from 498 Australians and New Zealanders using an online longitudinal survey, with data collected at monthly intervals over six months (March to September 2021). Our measure of conspiracy theories included items describing ten unfounded conspiracy theories with responses on a 5-point Likert scale. While there was substantial variability in beliefs between different participants (i.e., inter-individual variability), there was much less intra-individual variability (intraclass r = 0.91). Indeed, it was common for participants to give exactly the same response to a given theory at every time point. Via power analyses, we demonstrate that the small quantity of intra-individual variation in beliefs in conspiracy theories has important consequences for sample size planning in longitudinal studies.

Wednesday, March 30, 2022

Parasites: Male psychopaths are not set against fatherhood, as long as someone else takes on the effort of raising the kids

Cads in Dads’ Clothing? Psychopathic Traits and Men’s Preferences for Mating, Parental, and Somatic Investment. Kristopher J. Brazil & Anthony A. Volk. Evolutionary Psychological Science, Mar 30 2022.

Abstract: Psychopathic traits are sometimes viewed as an alternative reproductive strategy that prioritizes mating over parental investment, particularly in men. Two aspects of this research receiving less attention are (1) the inclusion of somatic investment, which refers to the growth and maintenance of oneself, and (2) measuring perceptions of investment domains in addition to behavior and attitude outcomes. In this study, we used a sample of 255 young adult men from MTurk (Mage = 29.55, SD = 2.97) to examine how the three domains of investment (mating, parental, and somatic) relate to individual differences in men’s psychopathic traits, relationship/parental status, and age using outcome measures of (1) behavioral attitudes and (2) perceptions of stimuli associated with each investment domain (e.g., attractive women’s faces and cute infants). Results showed that while they were associated with being a parent, psychopathic traits were associated with higher mating and lower parental and somatic behavioral attitudes. Psychopathic traits were associated with negative perceptions of indirect somatic cues (e.g., working and forming friendships), positive perceptions of mating cues, and no relationship with perceptions of direct somatic (e.g., exercising) or parental cues. Our results agree with previous research but extend them by showing that while they engage in lower somatic behavior, men higher in psychopathic traits do not appear to have aversive reactions towards infant stimuli and are more likely to be parents themselves. We argue that these patterns are consistent with a parasitic parenting strategy that focuses on mating while depending on others to invest in their children.

Meta-analysis: Cognitive abilities are not related to the willingness to take financial risks

Cognitive abilities affect decision errors but not risk preferences: A meta-analysis. Tehilla Mechera-Ostrovsky, Steven Heinke, Sandra Andraszewicz & Jörg Rieskamp. Psychonomic Bulletin & Review, Mar 30 2022.

Abstract: When making risky decisions, people should evaluate the consequences and the chances of the outcome occurring. We examine the risk-preference hypothesis, which states that people’s cognitive abilities affect their evaluation of choice options and consequently their risk-taking behavior. We compared the risk-preference hypothesis against a parsimonious error hypothesis, which states that lower cognitive abilities increase decision errors. Increased decision errors can be misinterpreted as more risk-seeking behavior because in most risk-taking tasks, random choice behavior is often misclassified as risk-seeking behavior. We tested these two competing hypotheses against each other with a systematic literature review and a Bayesian meta-analysis summarizing the empirical correlations. Results based on 30 studies and 62 effect sizes revealed no credible association between cognitive abilities and risk aversion. Apparent correlations between cognitive abilities and risk aversion can be explained by biased risk-preference-elicitation tasks, where more errors are misinterpreted as specific risk preferences. In sum, the reported associations between cognitive abilities and risk preferences are spurious and mediated by a misinterpretation of erroneous choice behavior. This result also has general implications for any research area in which treatment effects, such as decreased cognitive attention or motivation, could increase decision errors and be misinterpreted as specific preference changes.


We conducted a Bayesian meta-analysis with a total of 30 studies and examined whether a potential meta effect size is better explained by the risk-preference hypothesis, which assumes a correlation between cognitive abilities and risk aversion because cognitive abilities affect the evaluation of risky options and, consequently risk-taking behavior, or by the error hypothesis, which assumes that mixed results are the product of a relationship between cognitive abilities and decision errors resulting from a bias of the architectural properties of the risk-preference-elicitation task. Our results show that the correlation between cognitive ability and risk aversion is noncredible. Notably, we find that when studies applied unbalanced choice sets, they reported a stronger negative (or positive) correlation between cognitive abilities and risk aversion depending on the direction of this unbalance. The effect of the RCRT bias was robust across all meta-analytical model specifications and thus provides strong evidence for the error hypothesis. That is, our findings support the claim that previous mixed evidence of a correlation between cognitive abilities and risk aversion is mainly driven by the important interaction between the architecture of the risk-preference-elicitation task and errors in decision making. In addition, we found an effect of task framing, where including losses in risk-preference-elicitation tasks only weakly moderates the relation between cognitive abilities and risk aversion. Note that this effect was not robust across all meta-analytical model specifications and appears to be highly correlated with the RCRT bias of the choice set, where the latter has a higher explanatory power. We found no mediating effects of the type of cognitive ability test applied or of the number of decisions. We conclude that a potential correlation between cognitive abilities and risk aversion is moderated by the link between cognitive abilities and the probability of making unsystematic decision errors.

A recent meta-analysis by Lilleholt (2019) similarly explored the link between cognitive abilities and risk preferences. However, in contrast to our work, Lilleholt’s analysis did not directly test whether the mixed findings regarding the link between cognitive abilities and risk preferences could be explained by the error hypothesis and the bias in the architecture of most risk-preference-elicitation tasks. There are other important differences. First, Lilleholt had a broader literature search scope, leading to a larger set of examined studies. For instance, the author included experience-based risk-preference-elicitation tasks, which we excluded from our analysis. In such tasks, people have no information about the outcomes of gambles and the probabilities with which the outcomes occur but learn this from feedback. Thus, in these tasks, learning plays a major role in how people make their decisions, thereby making the interpretation of a potential link between cognitive abilities and risk preferences more complicated. In general, it has been argued that description-based and experience-based tasks differ in both architecture and interpretation (Frey et al., 2017). Therefore, in contrast to Lilleholt, we have focused on a description-based task that makes it easier to code all relevant task-architecture information precisely.

Since Lilleholt (2019) ran the meta-analysis for each domain separately, we compared Lilleholt’s results with our results by estimating our meta-analytic models on Lilleholt’s merged data set (see Appendix Table 8). In line with Lilleholt’s results, we find a credible metaeffect of −.05 with a 95% BCI ranging from −.07 to −.03 for the loss, gain, and mixed domains. Note that our restricted data set exhibits a comparable effect size of −.03, with a 95% BCI ranging from −.08 to .02. Additionally, the inclusion of losses as outcomes of the choice options had a credible effect on the correlation between cognitive abilities and risk preferences with a mean estimate of .12 and a 95% BCI ranging from .08 to .15 (see Appendix Table 8, Model Mf). The model comparison shows that the model that includes this variable is superior to a model that exclude it (see Appendix Table 8, Models Mf, M2). The effect of the RCRT bias towards risk aversion on the correlation between cognitive abilities and risk preferences was credible across all model specifications (see Appendix Table 8, Models Mf, M1, M2) and exhibited a mean estimate of −.17 and a 95% BCI ranging from −.25 to −.09 (see Appendix Table 8, Model Mf). More importantly, a regression model comparison procedure (see Appendix Table 8) shows that accounting for RCRT bias (Mf vs. M1 BF = 5.9×106) and the inclusion of losses (Mf vs. M2BF = 2.1×1010) improve the model fit substantially for the merged data set of Lilleholt (2019), replicating our results. However, given the larger set of studies in Lilleholt compared with ours, this replication should be interpreted with caution.

Our finding of a moderating effect of an RCRT-biased task architecture on the correlation between cognitive ability and risk aversion contributes to the discussion in the decision sciences and experimental economics literature. For instance, in line with the error hypothesis, Andersson et al. (2016) experimentally demonstrated that the link between cognitive abilities and risk aversion is spurious, as it is moderated by the link between cognitive abilities and random choice behavior (Andersson et al., 2016). In keeping with this result, Olschewski et al. (2018) reported that in risk-taking tasks, cognitive abilities correlated negatively with decision errors. We followed this work and rigorously tested the error hypothesis with a meta-analysis. Our results show that the correlation between cognitive abilities and risk aversion can be explained by the characteristics of the choice set (i.e., task architecture), implying an RCRT bias, a phenomenon that leads to misclassifying random choices as a specific risk preference.

Our findings support the view of the error hypothesis that cognitive abilities are linked to the probability of making unsystematic errors (Burks et al., 2008; Dean & Ortoleva, 2015; Olschewski et al., 2018; Tymula et al., 2013). Additionally, it is plausible to assume that people with lower cognitive abilities apply simpler decision strategies (i.e., heuristics) that reduce information-processing load. However, the use of heuristics does not necessarily imply more or less risk-taking behavior; only the interaction between the applied heuristic and the task architecture leads to a specific observed risk-taking behavior. As we discussed above, some heuristics lead to higher (or lower) observed risk-seeking behavior compared with more complex decision strategies, depending on the choice set. Therefore, one would not necessarily expect a specific correlation between people’s cognitive abilities and the observed risk-taking behavior across the different tasks, but instead expect some heterogeneity in the results. However, the use of specific strategies cannot explain the relationship between the observed average risk preferences in a task and the RCRT bias in the task. Thus, the link between cognitive abilities and the selected decision strategies does not imply a link between cognitive abilities and the latent risk preferences. Crucially, when examining the potential link between cognitive abilities, decision strategies, and risk preferences, it is necessary to first identify the specific strategies people apply in specific environments or task architectures (Olschewski & Rieskamp, 2021; Rieskamp, 2008; Rieskamp & Hoffrage, 19992008; Rieskamp & Otto, 2006). Future work should examine the different heuristics and decision strategies to arrive at a comprehensive understanding of whether and how those shape the correlation between cognitive abilities and risk preferences.

The results of this study also resonate with a recent empirical discourse on the validity of risk-preference-elicitation measures. For instance, Frey et al. (2017) and Pedroni et al. (2017) found behavioral risk-elicitation tasks to be less stable elicitations of risk preferences compared with self-reported measures. Importantly, the difference between behavioral and self-reported measures could disappear once measurement errors are accounted for (Andreoni & Kuhn, 2019) by applying better task architectures.

Our results also have implications for interpreting experimental results in other research domains. For example, when testing for a specific treatment effect it appears important to control for increased decision errors, so that a potential increase in errors is not misinterpreted as a specific treatment effect. Whether such misinterpretation is likely to occur depends on whether the task architecture has a bias, so that random choice behavior leads to a specific psychological interpretation. For instance, a potential effect of increased time pressure on people’s risk preferences could also simply be due to an increase in decision errors under high time pressure (e.g., Olschewski & Rieskamp, 2021). Likewise, the potential effect of cognitive load on people’s risk preferences, intertemporal time preferences, or social preferences could also simply be due to an increase in decision errors under cognitive load manipulations (e.g., Olschewski et al., 2018). Finally, the potential effect of increased monetary incentives on people’s preferences could also be due to lower decision errors with higher monetary incentives (e.g., Holt & Laury, 2002; Smith & Walker, 1993). In general, treatment effects on preferences have been observed in intertemporal discounting (e.g., Deck & Jahedi, 2015; Ebert, 2001; Hinson et al., 2003; Joireman et al., 2008) as well as social preferences (e.g., Cappelletti et al., 2011; Halali et al., 2014; Schulz et al., 2014). Across these domains, it is important to understand how changes in decision errors affect preference measurements. Failure to do so could potentially lead to misinterpretations of observed effects.

Consequently, addressing the issue of decision errors captured by the error hypothesis is of general importance to any research in behavioral economics and psychology with the objective to elicit individual preferences. There are two possible ways to address this matter. First, one can account for random errors ex ante by choosing an experimental design that controls for random errors. At the experimental design stage, researchers could apply a variety of measures to assess people’s preferences. In this way, they could cancel out systematic errors and minimize measurement errors in the associated biased classifications (Frey et al., 2017). For instance, Andersson et al. (2016) suggested choosing a symmetrical choice set when measuring risk preferences. However, this approach may not always be suitable for every preference-elicitation task. Leading to the second approach, one can account for error at the data analysis stage. For example, accounting for potential biases with an explicit structural decision-making model what includes an error theory at the data-analysis stage could be advantageous (Andersson et al., 2020). Recently, behavioral economists Gillen et al. (2015) and Andreoni and Kuhn (2019) proposed an instrumental variable approach to address this problem (see also Gillen et al., 2015).

It is important to note the task architecture determines the context in which a choice option is presented. Consequently, various theories relating to the context effect could also contribute to the fact that people with lower cognitive abilities are more prone to be influenced by the task architecture. For example, Andraszewicz and Rieskamp (2014) and Andraszewicz et al. (2015) demonstrated that pairs of gambles with the same differences in expected values and the same variances (i.e., risk) but various covariances (i.e., similarity) result in more unsystematic choices when the covariance between the two gambles is lower (Andraszewicz et al., 2015; Andraszewicz & Rieskamp, 2014). This effect called the covariance effect results from the fact that pairs of gambles with low covariances are more difficult to be compared with each other. Simonson and Tversky (1992) demonstrated that context effects can result from the available sample of choice options, such that extreme outcomes may appear as extreme in face of the available sample (Simonson & Tversky, 1992). Along the same lines, Ungemacht et al. (2011) demonstrated that people’s preferential choices depend on one’s exposure to hypothetical choice options.

To summarize, this meta-analysis highlights the importance of accounting for choice-set architecture, in particular, its interaction with random decision errors. Our applied methods and results go beyond the current research scope and suggest that neglecting the effect of random decision errors at the experimental design stage or at the data-analysis stage can lead to spurious correlations and the identification of “apparently new” phenomena (Gillen et al., 2019). The findings presented in this meta-analysis offer an important contribution to the scientific communities in judgment and decision making, psychology, experimental finance, and economics. In these fields of studies, measuring risk-taking propensity is particularly important. Therefore, findings of the current meta-analysis are very relevant to all researchers investigating risk-taking behavior using common risk-preference-elicitation methods.

A majority could well imagine undergoing psychotherapy via artificial intelligence, among other things because of the ability to comfortably talk about embarrassing experiences

Attitudes and perspectives towards the preferences for artificial intelligence in psychotherapy. Mehmet Emin Aktan, Zeynep Turhan, İlknur Dolu. Computers in Human Behavior, March 29 2022, 107273.


• We explored the factors of choosing AI-based psychotherapy.

• The less stigma and remote access were found as key in preferring AI-based therapy.

• Trust of the security of data in AI-based therapy were less than human therapists.

• The beliefs about limited ability to empathize in AI-based psychotherapy was found.

Abstract: The use of artificial intelligence (AI) in psychotherapy has been increased in recent years. While these technologies in psychotherapy are growing, the circumstances of accepting artificial tools during psychotherapy need to be explored to improve effective AI tools during the sensitive therapeutic environment. In this study, the factors around the preferences for AI-based psychotherapy were investigated. This cross-sectional study was conducted with a sample of 872 individuals who are highly educated, 18 aged and above. Attitude towards AI-based Psychotherapy, Attitude towards Seeking Professional Psychological Help Scale- Short Form, and Stigma Scale for Receiving Psychological Help Scale were used to examine the factors of participants' preferences for AI-based psychotherapy. While 55% of the sample preferred AI-based psychotherapy, the majority of participants trusted more human psychotherapists than AI-based systems when asked participants’ trust about the security of personal data. However, three important benefits of AI-based psychotherapy were identified as being able to comfortably talk about the embarrassing experiences, having accessibility at any time, and accessing remote communication. Importantly, factors of preferences for AI-based psychotherapy were related to the idea of AI-based psychotherapy systems can improve themselves based on the results from previous therapeutic experiences. Gender and the types of profession related to psychology and technical/engineering were also associated with choosing AI-based psychotherapy. The results suggest that both raising awareness of the benefits and effectiveness of psychotherapy as well as the trust to the artificial intelligence tools can improve the rate of the preferences for AI-based psychotherapy.

Keywords: Artificial intelligencePsychotherapyAccessibilityHelp-seeking behaviorStigma

Serial Sexual Murderers: Criminal paraphilia developed to reinforce positive emotions from sexual fantasies and helped to create a sense of intimacy to avoid being rejected

The Role of Child and Adult Sexual Fantasies and Criminal Paraphilia Involving Serial Sexual Murderers. Heather Brown. Walden University, PhD Dissertation. Mar 2022.

Abstract: Childhood trauma may be a reason a child develops maladaptive coping mechanisms such as sexual fantasies and paraphilia. These coping mechanisms increase in intensity, leading to sexual violence to gain a sense of power and control. Even though researchers have identified that serial sexual killers suffer from child and adult sexual fantasies and criminal paraphilia, details of the sexual fantasies and paraphilia have not been examined. The purpose of this qualitative exploratory case study was to explore the role of child and adult sexual fantasies and criminal paraphilia involving serial sexual murderers. Hickey’s trauma-control model and relational paraphilic attachment theory were used as the theoretical foundations. Data were collected from 12 U.S. male participants identified as serial sexual murderers. Four themes were identified from the thematic analysis and were linked to all 12 case participants. Findings indicated child and adult sexual fantasies began as a maladaptive coping mechanism to avoid feeling abandoned, which escalated to ways of feeling control and revenge. Criminal paraphilia developed to reinforce positive emotions from sexual fantasies and helped to create a sense of intimacy to avoid being rejected. Findings may assist law enforcement, school staff, and mental health professionals to promote positive social change by preventing future risk for behaviors that lead to and are incorporated into the sexual murders committed by serial killers.

Men and women invested equally in improving their appearance if exercising and bodybuilding were included

Sex Differences in Physical Attractiveness Investments: Overlooked Side of Masculinity. Marta Kowal. Int. J. Environ. Res. Public Health 2022, 19(7), 3842; Mar 24 2022.


Background: Public opinion on who performs more beauty-enhancing behaviors (men or women) seems unanimous. Women are often depicted as primarily interested in how they look, opposed to men, who are presumably less focused on their appearance. However, previous studies might have overlooked how masculinity relates to self-modification among men. Methods: We explored this issue in depth by conducting a qualitative Study 1 aimed to establish how men and women enhance their attractiveness (N = 121) and a quantitative Study 2 aimed to test time spent on activities that increase one’s attractiveness in a longitudinal design (with seven repeated measures from 62 participants; N(total) = 367). Results: We observed no sex differences in beauty investments. Although women spent more time on make-up and cosmetics usage, men caught up with women in exercising and bodybuilding. Conclusion: Our study provides evidence that there may not be such wide sex differences in the intensity of enhancing one’s appearance as has been previously thought. We hypothesize that this might partly stem from changes in gender roles regarding masculinity.

Keywords: gender; diary study; enhancing beauty; self-modification; sex comparison

Tuesday, March 29, 2022

The cat parasite Toxoplasma gondii might boost people's sexual attractiveness, possibly thru changes in facial symmetry

Borraz-León JI, Rantala MJ, Krams IA, Cerda-Molina AL, Contreras-Garduño J. 2022. Are Toxoplasma-infected subjects more attractive, symmetrical, or healthier than non-infected ones? Evidence from subjective and objective measurements. PeerJ 10:e13122. Mar 2022.


Background: Parasites are among the main factors that negatively impact the health and reproductive success of organisms. However, if parasites diminish a host’s health and attractiveness to such an extent that finding a mate becomes almost impossible, the parasite would decrease its odds of reproducing and passing to the next generation. There is evidence that Toxoplasma gondii (T. gondii) manipulates phenotypic characteristics of its intermediate hosts to increase its spread. However, whether T. gondii manipulates phenotypic characteristics in humans remains poorly studied. Therefore, the present research had two main aims: (1) To compare traits associated with health and parasite resistance in Toxoplasma-infected and non-infected subjects. (2) To investigate whether other people perceive differences in attractiveness and health between Toxoplasma-infected and non-infected subjects of both sexes.

Methods: For the first aim, Toxoplasma-infected (n = 35) and non-infected subjects (n = 178) were compared for self-perceived attractiveness, number of sexual partners, number of minor ailments, body mass index, mate value, handgrip strength, facial fluctuating asymmetry, and facial width-to-height ratio. For the second aim, an independent group of 205 raters (59 men and 146 women) evaluated the attractiveness and perceived health of facial pictures of Toxoplasma-infected and non-infected subjects.

Results: First, we found that infected men had lower facial fluctuating asymmetry whereas infected women had lower body mass, lower body mass index, a tendency for lower facial fluctuating asymmetry, higher self-perceived attractiveness, and a higher number of sexual partners than non-infected ones. Then, we found that infected men and women were rated as more attractive and healthier than non-infected ones.

Conclusions: Our results suggest that some sexually transmitted parasites, such as T. gondii, may produce changes in the appearance and behavior of the human host, either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts. Taken together, these results lay the foundation for future research on the manipulation of the human host by sexually transmitted pathogens and parasites.


Limitations and future directions