All organisms are shaped by evolution in ways that make disease almost inevitable. These diseases can, in turn, impose pressures on social behavior. This could mean that cross-cultural differences in general human behavior is contingent on pathogen prevalence in local ecology, and that patterns of human behavior could consistently be explained by these factors.
For example, Navarette et al. (2006) argued that inter- and intra- group attitudes can be understood in terms of the cost and benefit of interacting with the in-groups versus the out-groups. In-group interactions would be preferred in ancestral environments because individuals would have possessed antibodies to in-group pathogens rather than out-group pathogens. Accordingly, ethnocentric attitudes were found to increase as perceived disease vulnerability increased.
However, there are reasons to suspect that in-group attraction may be just as important as out-group avoidance when considering the psychological states that affect adaptive responses to disease threat. Since networks of alliances are the only health insurance policy available in small-scale societies, we not only expect people to be motivated to avoid out-groups in response to disease threats but also to find the in-group more attractive. In a 2006 study, Navarette and Fessler found that the disease-avoidance system triggered enhancement of positive social evaluation of the in-group. In addition, a 2010 study by Schaller et. al found that the mere visual perception of disease-connoting cues promotes a more aggressive immune response. We decided to perform our own study based loosely on these for this class.
Participants and Design
Fourty-one participants (29 females, 12 males) were involved in a control and experimental condition. In the control condition, participants watched a slide show depicting furniture. In the experimental condition, participants watched a disease slide show depicting people who displayed morphological and behavioral characteristics associated with infectious diseases (e.g., pox, skin lesions, sneezing). In each condition, participants watched a slide show of 10 human faces (5 male, 5 female) after the first slide show. Participants were asked to rate the attractiveness of the faces on a scale of 0 to 3, with 0 being the least attractive and 3 being the most attractive. We also assessed participants’ self-reported emotional state following each slide show.
Each slide show comprised 10 photographs. When displayed, a photograph appeared for 8 seconds, followed by 4 seconds of blank screen before the next photograph appeared. Statistical analyses were conducted on an index indicating the percentage of change in attraction levels from pretest to posttest, computed as (posttest – pretest)/pretest.
Subjective emotional state was assessed immediately following each attraction questionnaire. On 4-point scales ranging from 0 to 3, participants rated the extent to which each of 18 adjectives accurately described their mood. Composite measures of four specific emotional states were computed as mean ratings of 3 adjectives each: stressed (stressed, tense, overwhelmed), relaxed (relaxed, calm, at ease), scared (scared, afraid, fearful), and disgusted (disgusted, repulsed, revolted).
Overall, attraction to the humans faces increased when primed with the disease slide show (the only exception was male 3). All participants rated male 1 as 54% more attractive after the disease slide show than after the neutral slide show, t(38)= -4.224, p= 0.000. Males rated male 1 as 100% more attractive, t(9)= -2.714, p= .024. Females rated male 1 as only 44% higher, t(28)= -3.266, p= .003.
All participants rated female 1 as 36% more attractive after the disease slide show than after the neutral slide show, t(40)= -4.735, p= 0.000. Female ratings were the only ones which were significant. Females rated female 1 as 50% higher, t(29)= -4.785, p= .000.
All participants rated male 2 as 160% more attractive after the disease slide show than after the neutral slide show, t(40)= -3.194, p= 0.003. Not all males rated male 2, so the analysis was dropped. Females rated male 2 as 105% higher, t(29)= -2.536, p= .017.
All participants rated female 2 as 37% more attractive after the disease slide show than after the neutral slide show, t(40)= -2.012, p= 0.051. Male ratings were the only ones which were significant. Males rated female 2 as 42% more attractive, t(10)= -1.936, p= .082.
All participants rated male 3 as 27% less attractive after the disease slide show than after the neutral slide show, t(40)= 1.861, p= 0.070. Female ratings were the only ones which were significant. Females rated male 3 as 33% lower, t(29)= 2.249, p= .032.
Ratings of female 3, male 4, and female 4 were insignificant.
All participants rated male 5 as 77% more attractive after the disease slide show than after the neutral slide show, t(40)= -4.398, p= 0.000. Males rated male 5 as 811% more attractive, t(10)= -2.667, p= .024. Females rated male 5 as 49% higher, t(29)= -3.496, p= .002.
All participants rated female 5 as 17% more attractive after the disease slide show than after the neutral slide show, t(39)= -2.236, p= 0.031. Female ratings were the only ones which were significant. Females rated female 5 as 14% higher, t(28)= -1.797, p= .083.
This study shows that the mere visual perception of other people’s disease symptoms can cause a difference in the visual cues of attraction. Overall, attraction increased after the experimental condition involving the disgust slide show. Even more interesting, faces in which there was a significant difference from the control to the experimental condition in both sexes had a higher percentage change among participants of the same sex. This may be an example of the in-group attraction which Navarette and Fessler (2006) found in their study. After all, these were pictures of out-group faces, as none of the faces in the slide shows were in the class. However, the in-group may have instead been perceived as the same sex, rather than the same co-ed group. Finally, previous research has suggested that the effect of disgust on attraction is primarily found in female, but this study showed that attraction was affected across the board, or either among males or females (e.g. the strong percentage change among males when rating male 5).
Limitations and Future Studies
After discussing the results, the class came up with a few problems with the study design. The demographic survey did not take sexual orientation into account, which could affect the way individuals rate the attractiveness of another person. In addition, the pictures themselves could have affected the level of attraction. The quality of the photos was not excellent, and the black background in which they stood sometimes made it difficult to distinguish the face. In addition, the unhappy facial expressions of some of the faces could have affected how attractive the faces were rated.
In the future, the class suggested that the survey incorporate a self-rating of the race/ethnicity of the faces. This can then be used to test how perceived in-group and out-group distinctions based on race affects attraction.
Navarrete, C. D., and Fessler, D. M. T. (2006). Disease avoidance and ethnocentrism: the effects of disease vulnerability and disgust sensitivity on intergroup attitudes. Evolution of Human Behavior, 27: 270–282.
Schaller, M., Miller, G. E., Gervais, W. M., Yager, S., & Chen, E. (2010). Mere visual perception of other people’s’ disease symptoms facilitates a more aggressive immune response. Psychological Science, 21, 649-652.