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Never eat a Pigeon with a Pumpkin: a model for the emergence and fixation of unsupported beliefs

Anders Sandberg, Len Fisher

Abstract

A popular poster from Myanmar lists food pairings that should be avoided, sometimes at all costs. Coconut and honey taken together, for example, are believed to cause nausea, while pork and curdled milk will induce diarrhea. Worst of all, according to the poster, many seemingly innocuous combinations that include jelly and coffee, beef and star fruit, or pigeon and pumpkin, are likely to kill the unwary consumer. But why are these innocuous combinations considered dangerous, even fatal? The answer is relevant, not just to food beliefs, but to social beliefs of many kinds. Here we describe the prevalence of food combination superstitions, and an opinion formation model simulating their emergence and fixation. We find that such food norms are influenced, not just by actual risks, but also by strong forces of cultural learning that can drive and lock in arbitrary rules, even in the face of contrary evidence.

Never eat a Pigeon with a Pumpkin: a model for the emergence and fixation of unsupported beliefs

Abstract

A popular poster from Myanmar lists food pairings that should be avoided, sometimes at all costs. Coconut and honey taken together, for example, are believed to cause nausea, while pork and curdled milk will induce diarrhea. Worst of all, according to the poster, many seemingly innocuous combinations that include jelly and coffee, beef and star fruit, or pigeon and pumpkin, are likely to kill the unwary consumer. But why are these innocuous combinations considered dangerous, even fatal? The answer is relevant, not just to food beliefs, but to social beliefs of many kinds. Here we describe the prevalence of food combination superstitions, and an opinion formation model simulating their emergence and fixation. We find that such food norms are influenced, not just by actual risks, but also by strong forces of cultural learning that can drive and lock in arbitrary rules, even in the face of contrary evidence.

Paper Structure

This paper contains 19 sections, 7 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Background
  3. The Myanmar poster
  4. Risks of the food on the poster
  5. Structure of the poster pairings
  6. Taboo pairings
  7. Religious taboos
  8. Theory-based combination taboos
  9. Fruit and milk
  10. Dangerous drink
  11. Actually risky pairings
  12. Summary
  13. Pre-Conclusion
  14. Models
  15. Observational evidence
  16. ...and 4 more sections

Figures (3)

  • Figure 1: Graph of food interactions in the poster. Each line corresponds to a set of warnings, with width proportional to the number of cases. The left-hand graph represents claimed deadly interactions, the right-hand graph merely sickening ones.
  • Figure 2: 10 realizations of the lifelong opinion model. Starting with an even mix of safety views, random copying of views between members of a society leads fixation where everybody agrees it is safe or unsafe.
  • Figure 3: Full model of food risk estimation using observation and copying. The vertical axis shows the fraction of the population believing a given combination (marked by color) is unsafe as a function of time. At time 1500 a broadcast of opinion similar to the poster is introduced. $P_pickyness=2$, $c_{evidenceUpdateOK}=0.3$, $c_{evidenceUpdateBad}=0.95$, $c_{opinionUpdateOK}=0.3$, $c_{opinionUpdateBad}=0.95$, $c_{opinionUpdatePoster}=0.1$.