Individuals with trypophobia have an aversion towards clusters of roughly circular shapes, such as those on a sponge or the bubbles on a cup of coffee. It is unclear why the condition exists, given the harmless nature of typical eliciting stimuli. We suggest that aversion to clusters is an evolutionarily prepared response towards a class of stimuli that resemble cues to the presence of parasites and infectious disease. Trypophobia may be an exaggerated and overgeneralised version of this normally adaptive response. Consistent with this explanation, individuals with trypophobia, as well as comparison individuals, reported aversion towards disease-relevant cluster stimuli, but only the trypophobic group reported aversion towards objectively harmless cluster stimuli that had no relevance to disease. For both groups the level of aversion reported was predicted uniquely by a measure of disgust sensitivity. Scaled emotion ratings and open-ended responses revealed that the aversive response was predominantly based on the disease avoidance emotion, disgust. Many open-ended responses also described skin sensations (e.g. skin itching or skin crawling). These findings support the proposal that individuals with trypophobia primarily perceive cluster stimuli as cues to ectoparasites and skin-transmitted pathogens.

Behavioral-immune-system research has illuminated how people detect and avoid signs of infectious disease. But how do we regulate exposure to pathogens that produce no symptoms in their hosts? This research tested the proposition that estimates of interpersonal value are used for this task. The results of three studies ( N = 1,694), each conducted using U.S. samples, are consistent with this proposition: People are less averse to engaging in infection-risky acts not only with friends relative to foes but also with honest and agreeable strangers relative to dishonest and disagreeable ones. Further, a continuous measure of how much a person values a target covaries with comfort with infection-risky acts with that target, even within relationship categories. Findings indicate that social prophylactic motivations arise not only from cues to infectiousness but also from interpersonal value. Consequently, pathogen transmission within social networks might be exacerbated by relaxed contamination aversions with highly valued social partners.

Currently, disgust is regarded as the main adaptation for defence against pathogens and parasites in humans. Disgust's motivational and behavioural features, including withdrawal, nausea, appetite suppression and the urge to vomit, defend effectively against ingesting or touching sources of pathogens. However, ectoparasites do not attack their hosts via ingestion, but rather actively attach themselves to the body surface. Accordingly, by itself, disgust offers limited defence against ectoparasites. We propose that, like non-human animals, humans have a distinct ectoparasite defence system that includes cutaneous sensory mechanisms, itch-generation mechanisms and grooming behaviours. The existence of adaptations for ectoparasite defence is supported by abundant evidence from non-human animals, as well as more recent evidence concerning human responses to ectoparasite cues. Several clinical disorders may be dysfunctions of the ectoparasite defence system, including some that are pathologies of grooming, such as skin picking and trichotillomania, and others, such as delusory parasitosis and trypophobia, which are pathologies of ectoparasite detection. We conclude that future research should explore both distinctions between, and overlap across, ectoparasite defence systems and pathogen avoidance systems, as doing so will not only illuminate proximate motivational systems, including disgust, but may also reveal important clinical and social consequences.This article is part of the Theo Murphy meeting issue 'Evolution of pathogen and parasite avoidance behaviours'.

Benevolent sexism (BS) has detrimental effects on women, yet women prefer men with BS attitudes over those without. The predominant explanation for this paradox is that women respond to the superficially positive appearance of BS without being aware of its subtly harmful effects. We propose an alternative explanation drawn from evolutionary and sociocultural theories on mate preferences: Women find BS men attractive because BS attitudes and behaviors signal that a man is willing to invest. Five studies showed that women prefer men with BS attitudes (Studies 1a, 1b, and 3) and behaviors (Studies 2a and 2b), especially in mating contexts, because BS mates are perceived as willing to invest (protect, provide, and commit). Women preferred BS men despite also perceiving them as patronizing and undermining. These findings extend understanding of women's motives for endorsing BS and suggest that women prefer BS men despite having awareness of the harmful consequences.

Past research suggests that pathogen-avoidance motives (e.g., disgust sensitivity) relate to greater opposition to immigration. Two accounts have been proposed to explain this relationship, one of which emphasizes proximally avoiding outgroups, and the other of which emphasizes adherence to traditional norms. According to the former, immigrants are perceived as being more infectious because they carry novel pathogens due to their foreign ecological origins. According to the latter, immigrants' foreign norms are perceived as posing a pathogen threat. This study aimed to disentangle these accounts. Participants (N = 975) were randomly assigned to read a description of an immigrant who had high or low contact with locals and high or low assimilation to local norms. The effect of disgust sensitivity on sentiments toward the immigrant (and immigrants like him) was compared across conditions. Results supported the traditional norms account: disgust sensitivity related to anti-immigrant sentiments when the immigrant was described as not assimilating to local norms, but not when he was described as assimilating. Contrary to the outgroup avoidance account, the relationship between disgust sensitivity and anti-immigrant sentiments did not vary across the high-contact and low-contact conditions. Results suggest that resistance to foreign norms, rather than avoidance of novel pathogens, better explains the relationship between pathogen avoidance and outgroup prejudice.