Based on the findings of previous studies carried out by our group, which will be briefly summarised, the present paper puts forward several hypotheses to account for the evolution of depressive symptoms and the possible increase observed in risk of depression subsequent to social changes. The particular mood disorders presented by Senegalese emigrants and several protective factors which appear to determine a low risk in these populations, such as a strong social support, will be examined. Based on a previous investigation carried out by our group, which seems to indicate the presence of depressive pictures among poorly westernised populations such as the Peul nomads or Dogon farmers from the Sub-Saharian regions, the hypothesis that “westernalisation” (considered as the loss at an individual level of traditional ways of life, working habits, cultural patterns and languages in favour of different attitudes influenced by western culture) may represent a risk factor for depressive illness, in its clinical expressions commonly observed in western contexts, has been considered. In these populations, with the exception of educated individuals, the albeit rare depressive symptoms appear to be secondary to serious somatic disorders. Research performed identified two well-defined means of clinical expression, which has been termed, respectively, “western style” or “guilty” and “traditional” or “dislocation from the group”. Further studies carried out in rapidly changing areas seem to indicate how environmental factors are able to influence the evolution of depressive symptoms from the first form to the latter and to modify the threshold of onset of emotive, behavioural and depressive patterns. It has been hypothesised that rapid changes in the social organisation tend to exacerbate attitudes of “compulsive hyper-responsibilisation”, a cognitive set of basic assumptions which may be considered at the same time both as a product of “westernalization” at an individual level and a risk factor for depression. Individuals who possess these basic characteristics, subsequent to the opportunities afforded by the social changes, tend to develop new complex systems of interpreting reality, causality, controlling of events and ways of expressing emotions. Accordingly, we herewith propose a reviewal of the entire threshold concept and provide a means of interpreting the transformation in depressive phenomena in view of the fact that, although the new levels of knowledge and learning better equip subjects to face the new situations, they also render them more vulnerable to depression.