Robert Aunger

Evidence that disgust evolved to protect from risk of disease

Disgust is a powerful human emotion that has been little studied until recently. Current theories do not coherently explain the purpose of disgust, nor why a wide range of stimuli can provoke a similar emotional response. Over 40 000 individuals completed a web–based survey using photo stimuli. Images of objects holding a potential disease threat were reported as significantly more disgusting than similar images with little or no disease relevance. This pattern of response was found across all regions of the world. Females reported higher disgust sensitivity than males; there was a constant decline in disgust sensitivity over the life course; and the bodily fluids of strangers were found more disgusting than those of close relatives. These data provide evidence that the human disgust emotion may be an evolved response to objects in the environment that represent threats of infectious disease.

Planned, motivated and habitual hygiene behaviour: an eleven country review

Handwashing with soap (HWWS) may be one of the most cost-effective means of preventing infection in developing countries. However, HWWS is rare in these settings. We reviewed the results of formative research studies from 11 countries so as to understand the planned, motivated and habitual factors involved in HWWS. On average, only 17% of child caretakers HWWS after the toilet. Handwash ‘habits’ were generally not inculcated at an early age. Key ‘motivations’ for handwashing were disgust, nurture, comfort and affiliation. Fear of disease generally did not motivate handwashing, except transiently in the case of epidemics such as cholera. ‘Plans’ involving handwashing included to improve family health and to teach children good manners. Environmental barriers were few as soap was available in almost every household, as was water. Because much handwashing is habitual, self-report of the factors determining it is unreliable. Candidate strategies for promoting HWWS include creating social norms, highlighting disgust of dirty hands and teaching children HWWS as good manners. Dividing the factors that determine health-related behaviour into planned, motivated and habitual categories provides a simple, but comprehensive conceptual model. The habitual aspects of many health-relevant behaviours require further study.

Disgust as an adaptive system for disease avoidance behaviour

Disgust is an evolved psychological system for protecting organisms from infection through disease avoidant behaviour. This ‘behavioural immune system’, present in a diverse array of species, exhibits universal features that orchestrate hygienic behaviour in response to cues of risk of contact with pathogens. However, disgust is also a dynamic adaptive system. Individuals show variation in pathogen avoidance associated with psychological traits like having a neurotic personality, as well as a consequence of being in certain physiological states such as pregnancy or infancy. Three specialized learning mechanisms modify the disgust response: the Garcia effect, evaluative conditioning and the law of contagion. Hygiene behaviour is influenced at the group level through social learning heuristics such as ‘copy the frequent’. Finally, group hygiene is extended symbolically to cultural rules about purity and pollution, which create social separations and are enforced as manners. Cooperative hygiene endeavours such as sanitation also reduce pathogen prevalence. Our model allows us to integrate perspectives from psychology, ecology and cultural evolution with those of epidemiology and anthropology. Understanding the nature of disease avoidance psychology at all levels of human organization can inform the design of programmes to improve public health.

Mitochondrial DNA analysis reveals diverse histories of tribal populations from India

We analyzed 370 bp of the first hypervariable region of the mitochondrial DNA (mtDNA) control region in 752 individuals from 17 tribal and four nontribal groups from the Indian subcontinent, to address questions concerning the origins, genetic structure and relationships of these groups. Southern Indian tribes showed reduced diversity and large genetic distances, both among themselves and when compared with other groups, and no signal of prehistoric demographic expansions. These results probably reflect enhanced genetic drift because of small population sizes and/or bottlenecks in these groups. By contrast, northern groups exhibited more diversity and signals of prehistoric demographic expansions. Phylogenetic analyses revealed that southern and northern groups (except northeastern ones) have related mtDNA sequences albeit at different frequencies, further supporting the larger impact of drift on the genetic structure of southern groups. The Indian mtDNA gene pool appears to be more closely related to the east Eurasian gene pool (including central, east and southeast Asian populations) than the west Eurasian one (including European and Caucasian populations). Within India, northeastern tribes are quite distinct from other groups; they are more closely related to east Asians than to other Indians. This is consistent with linguistic evidence in that these populations speak Tibeto-Burman languages of east Asian origin. Otherwise, analyses of molecular variance suggested that caste and tribal groups are genetically similar with respect to mtDNA variation.

Independent origins of Indian caste and tribal paternal lineages

The origins of the nearly one billion people inhabiting the Indian subcontinent and following the customs of the Hindu caste system are controversial: are they largely derived from Indian local populations (i.e. tribal groups) or from recent immigrants to India? Archaeological and linguistic evidence support the latter hypothesis, whereas recent genetic data seem to favor the former hypothesis. Here, we analyze the most extensive dataset of Indian caste and tribal Y chromosomes to date. We find that caste and tribal groups differ significantly in their haplogroup frequency distributions; caste groups are homogeneous for Y chromosome variation and more closely related to each other and to central Asian groups than to Indian tribal or any other Eurasian groups. We conclude that paternal lineages of Indian caste groups are primarily descended from Indo-European speakers who migrated from central Asia approximately 3,500 years ago. Conversely, paternal lineages of tribal groups are predominantly derived from the original Indian gene pool. We also provide evidence for bidirectional male gene flow between caste and tribal groups. In comparison, caste and tribal groups are homogeneous with respect to mitochondrial DNA variation, which may reflect the sociocultural characteristics of the Indian caste society.

Experimental Pretesting of Hand-Washing Interventions in a Natural Setting

OBJECTIVES We pretested interventions derived from different domains of behavior change theory to determine their effectiveness at increasing hand washing with soap in a natural setting. METHODS We installed wireless devices in highway service station restrooms to record entry and soap use. Two text-only messages for each of 7 psychological domains were compared for their effect on soap-use rates. We collected data on nearly 200 000 restroom uses. RESULTS The knowledge activation domain was most effective for women, with a relative increase in soap use of 9.4% compared with the control condition (P = .001). For men, disgust was the most effective, increasing soap use by 9.8% (P = .001). Disgust was not significantly better than the control condition for women, nor was knowledge activation for men. Messages based on social norms and social status were effective for both genders. CONCLUSIONS Our data show that unobtrusive observation of behavior in a natural setting can help identify the most effective interventions for changing behaviors of public health importance. The gender differences we found suggest that public health interventions should target men and women differently.

Three kinds of psychological determinants for hand-washing behaviour in Kenya

Washing hands with soap at the right times - primarily after contact with faeces, but also before handling food or feeding an infant - can significantly reduce the incidence of childhood infectious disease. Here, we present empirical results which substantiate a recent claim that washing hands can be the consequence of different kinds of psychological causes. Such causes can be divided into three kinds of control over behaviour: automatic or habitual responses, motivated or goal-driven behaviour to satisfy needs, and cognitive causes which reflect conscious concerns. Empirical results are based on 3-h-long structured observations of hand-washing behaviour in 802 nationally representative Kenyan households with children under five, and structured interviews with the primary female caretaker in these households, collected in March 2007. Factor analysis of questionnaire responses identified three psychological factors which are also significant predictors of observed hand-washing behaviour: having the habit of hand-washing at particular junctures during the day, the motivated need for personal or household cleanliness, and a lack of cognitive concern about the cost of soap use. These factors each represent a different kind of psychological cause. A perceived link between clean hands and sexual attractiveness also appeared in the factor analysis, but was not a determinant of actual behaviour. We also report evidence that those who express concern about the cost of soap use are those with relatively few economic resources. We suggest that those developing hygiene promotion programmes should consider the possible existence of multiple types of strategies for increasing hand-washing behaviour.

Forming a flossing habit: An exploratory study of the psychological determinants of habit formation

OBJECTIVES Habit formation has been proposed as a means to promote maintenance of healthy behaviours, but there have been few investigations into how habits are formed. This exploratory study sought to model determinants of the formation of a dental flossing habit, including placement of the behaviour within the routine (before vs. after tooth-brushing), past behaviour, prospective memory ability, and motivational factors. DESIGN AND METHOD All participants (N = 50) received a motivational intervention designed to initiate behaviour change and habit formation. Half of the participants were instructed to floss before brushing, and half after. Participants subsequently self-reported flossing behaviour daily and, 4 weeks later, flossing automaticity. Automaticity and flossing frequency were also measured at 8-month follow-up. RESULTS Participants with stronger prospective memory ability, higher levels of past behaviour, and a more positive attitude flossed more frequently during the study. Stronger automaticity was predicted by positive attitudes, and increased behaviour frequency during and prior to the study. Those who flossed after brushing (rather than before) tended to form stronger flossing habits and, at 8-month follow-up, had stronger habits and flossed more frequently. CONCLUSIONS Habit forming interventions might usefully consider features of everyday routines and how behaviour may be reinforced. Suggestions for further research using more methodologically rigorous designs are offered. STATEMENT OF CONTRIBUTION What is already known on this subject? The formation of habit - that is, a learnt automatic response to contextual cues - requires initiation of a behaviour and repetition in a constant context. A recent formation study showed variation in habit strength despite equal repetitions, indicating that factors other than repetition may be important in habit development. From studies of routine behaviour, the boundaries between sub-routines are characterized by different processes than the middle of sub-routines, suggesting that placement of behaviour within existing routines may affect the likelihood of habit formation. What does this study add? Greater prospective memory ability predicted more frequent dental flossing. Initiating flossing after rather than before tooth-brushing promoted stronger habits. Positive attitudes impacted directly on habit formation, independent of behaviour repetition.

Determinants of handwashing practices in Kenya: the role of media exposure, poverty and infrastructure

Background  To explore how structural constraints such as lack of reliable water supply, sanitation, educational and other socio‐economic factors limit the adoption of better hygiene.

Sensor recorded changes in rates of hand washing with soap in response to the media reports of the H1N1 pandemic in Britain

Objectives To examine how the frequency of information regarding a real disease threat influences hand washing with soap. Design and setting The authors installed wireless devices in highway service station lavatories in England to record the proportion of individuals washing hands with soap from May 2009 to January 2010. Participants Participants were users of mens and womens toilets. Combined there was an average of 6800 participant entrances into the lavatories daily. Primary outcome measure The primary outcome measure is the proportion of soap usage to the number of entries into the lavatories. Results Hand-washing rates were positively related to both H1NI coverage in blogs and the news; however, these relationships were stronger for men than for women. Conclusions Hand washing with soap increases proportionally to the frequency of media key words related to H1N1. Womens hand washing was more strongly associated with incidence of media keywords than mens.