The kiss of death: three tests of the relationship between disease threat and ritualized physical contact within traditional cultures

The direct adaptive impact of rituals and other forms of behavior dictated or shaped by culture may be one factor influencing their persistence or lack thereof over time. Given that physical contact is a common means through which transmissible disease is spread, we explored the possibility that levels of normative physical contact would be negatively associated with levels of infectious disease prevalence. We tested this prediction across three domains of such behavior - greetings, romantic kissing, and mortuary rituals - by compiling ethnographic information on normative behavior in traditional cultures and comparing it with epidemiological estimates of pathogen prevalence. We find small but significant negative correlations between pathogen prevalence and both greetings and romantic kissing. Ancillary analyses suggest that these relationships are driven by human-transmitted pathogens. The relationship between pathogen prevalence and mortuary rituals is non-significant. Causal mechanisms that may account for these results, as well as implications and limitations, are discussed.