We have not only twice as many years as our ancestors, but we have twice as many good years. The "circular causation chain" shows some of the more important elements which jointly brought about the fundamental change from an unpredictable to a relatively predictable lifespan: better housing conditions, better nourishment, better communication systems, better working conditions, improved economic situation, etc., etc.

This model was developed during a visit as guest lecturer in India and Bangladesh (which are following us at present in many respect and would like to avoid our historical mistakes). The graph in the middle shows the decrease in infant mortality and the corresponding increase in life expectancy at birth in Switzerland, 1880-1990.

Source: CD-ROM Historical Demography (1995), Fig. 22.