A new biodemographic model to explain the trajectory of mortality

Since Buffon's time (1749), biologists and demographers have repeatedly sta ted that a man in good health will live to be 90, 100 or 110 years old but not longer. For demographers, mortality measures essentially the current co nditions: the quality of the ecological and social environment. For biologi sts, mortality measures mainly the ageing process. Can a biodemographic app roach measure the current conditions (i.e. the quality of the environment) and the ageing schedule together, taking into account that human beings spe nd the greater part of their time improving the quality of their physical a nd social environment, making it more and more favourable to the realisatio n of their potential longevity? I propose two measures of the quality of th is environment: first at the age when individuals (in average by cohort), i n the course of their development, are the most robust and the most resista nt to environmental hazards, indicated by the lowest mortality rate recorde d; second at the age when individuals (in average by cohort) become frail b ecause of the passage of time, with no or extremely little resistance to en vironmental hazards, indicated by a constant mortality rate among the oldes t old. Between these two measures of the quality of the environment, mortal ity measures the ageing process leading young vigorous individuals into fra il senile elders. (C) 2001 Elsevier Science Inc. All rights reserved.