The domains of disgust and their origins: contrasting biological and cultural evolutionary accounts Paul Rozin 1 and Jonathan Haidt 2 1 University of Pennsylvania, Department of Psychology, 3720 Walnut Street, Philadelphia, PA 19104-6241, USA 2 New York University, Stern School of Business, 40 West 4th Street, New York, NY 10012, USA A recent paper by Tybur and colleagues presents a theory of the evolved functions of disgust based on biological evolution. This work furthers our understand- ing of disgust and is the first to detail the computational mechanisms involved in detecting and evaluating dis- gust-related risks. However, because this approach ignores the powerful role of cultural evolution, its ability to encompass the wide and culturally variable range of disgust is limited. How can one emotion – disgust – have elicitors as diverse as excrement, amputation, incest, and flag burning? Rozin, Haidt, and McCauley ([1]; hereafter RHM) proposed that disgust could be understood as a way of dealing with an expanding set of threats. They argued that disgust evolved – biologically and culturally – from the older distaste response by the process of preadaptation, a well-documen- ted process, by which a structure or system that evolved for one purpose is re-used in a new context. On this account, the elicitors of disgust expanded by preadaptation, but the outputs – expressive, physiological, and behavioral – were generally conserved. These included contamination sensi- tivity and a motivation to cleanse, avoid, or expel the contaminant. The elicitors expanded from a food rejection system related to pathogen avoidance to avoidance of reminders of humans’ animal nature, especially death, and then on to some aspects of the moral domain. Tybur, Lieberman, Kurzban and Descioli ([2]; hereafter TLKD) recently published an alternative theory of disgust that accepts the general framework of an expansion from oral defense (pathogen avoidance) to other domains, but uses the term ‘co-opted’ instead of ‘preadapted’. With a focus on problems faced by humans in their ancestral environment, they parse disgust into three fundamental domains: pathogen avoidance, sex/mating, and morality. They propose computational mechanisms for each domain, which detect and evaluate a particular risk, perform a cost–benefit analysis, and then program a response. Unlike RHM, TLKD rely strictly on biological evolution to account for the historical expansion of disgust. Yet, the nature of disgust and its spread to social practices is quite variable in the West over the past thousand years [3] and across cultures right now [4]. Cultural evolution seems to be playing a major role. We highlight here two instances of the expansion of disgust where we think cultural matters are particularly important. Animal reminder versus pathogen disgust TLKD present and dismiss the proposal for an animal- reminder domain of disgust, which includes inappropriate sexual acts, poor hygiene, violations of the ideal body ‘envelope’ or exterior form, and most critically, death. RHM specifically noted that ‘all four of these domains involve potential sources of biological contamination and infection [. . .] thus core disgust was preadapted and easily expanded to apply contamination sensitivity to these ad- ditional classes of threats’ ([1], p. 761). Disgust figures prominently in Norbert Elias’ [3] ac- count of the ‘civilizing process’, by which societies develop rules and practices of self-restraint – a ‘second nature’ – that distinguish them from primitive societies and ani- mals. The civilizing process is a cultural rather than a biological process. By contrast, TLKD argue that pathogen threat is sufficient to explain disgust elicited not only by poor hygiene but also by body envelope violation and death. TLKD present evidence that supports a link between pathogen avoidance and animal reminder disgust. (The most striking link, which they do not note, is that contami- nation sensitivity is present in both domains.) They weigh this evidence more heavily than RHM do, because, unlike TLKD, RHM see fear of death – the key feature of animal- reminder disgust – as a basic culture-derived human con- cern, potentially on a par with pathogen avoidance. Many scholars, including Ernest Becker [5] and terror manage- ment theorists, have placed mortality concerns at the center of understanding humans. Many religions seem to be motivated in part by providing a way to cope with mortality. It is true that pathogen risks arose millions of years prior to fear of mortality, but it is an open question whether animal-reminder disgust arose prior to humans realizing their own mortality. Moral disgust Both RHM and TLKD identify a distinct moral domain of disgust. For RHM, disgust maps to a particular subset of moral concerns – originally described by Richard Shweder [6] and elaborated by Haidt [7] – that involve sanctity, divinity, and the protection of what are perceived to be sacred values and objects. Examples include consumption of beef for religious Hindus, incest, blasphemy, treason, betrayal, and actions that are seen to be ‘sleazy’ or ‘subhu- man’. Violators are seen as ‘polluted’: people often do not want to touch them or touch things they have touched. RHM noted that many cultures conceive of a vertical dimension of social cognition, with gods at the top and demons and animals at the bottom. RHM argued that Spotlights Corresponding authors: Rozin, P. (rozin@psych.upenn.edu); Haidt, J. (jhaidt@stern.nyu.edu). 367