Common sense: folk wisdom that ethnobiological and ethnomedical research cannot afford to ignore

Common sense [CS], especially that of the non-scientist, can have predictive power to identify promising research avenues, as humans anywhere on Earth have always looked for causal links to understand, shape and control the world around them. CS is based on the experience of many individuals and is thus believed to hold some truths. Outcomes predicted by CS are compatible with observations made by whole populations and have survived tests conducted by a plethora of non-scientists. To explore our claim, we provide 4 examples of empirical insights (relevant to probably all ethnic groups on Earth) into causal phenomena predicted by CS: (i) "humans must have a sense of time", (ii) "at extreme latitudes, more people have the winter blues", (iii) "sleep is a cure for many ills" and (iv) "social networks affect health and disease". While CS is fallible, it should not be ignored by science - however improbable or self-evident the causal relationships predicted by CS may appear to be.